Summary NrEvent DateReport IDFatSICEvent Description

4120108570107/14/200409506251731Employee'S Fingers Crushed By Jaws Of Crimper Head

4220105863304/19/200409506423711Employee Is Injured In Fall From Hydraulic Press

4320082245003/17/200405214003469Employee Injured When Operating A Hydraulic Press

4420116594103/17/200409506413492Employee'S Fingers Partially Amputated In Press

4520208660912/01/200305247003493Employee'S Arm Is Caught In Hydraulic Press

4620169103711/21/200309506623444Employee Thumb Is Amputated After Being Crushed

4720115788007/12/200309506333499Employee Amputates Fingers When Caught In Hydraulic Press

4820115780707/07/200309506337629Employee Injures Fingers While Operating Hydraulic Press

4920115768206/03/200309506333089Employee'S Hand Crushed In Hydraulic Press

5020208648404/25/200305247003714Employee Injured When Hand Lacerated By Hydraulic Press

5120169084902/20/200309506623443Employee'S Fingers Amputated While Setting Up A Press

5220233940411/22/200203524303544Employee Suffers Finger Amputation

5317113508009/09/200210553605521Employee'S Fingers Are Crushed In Hydraulic Press Brake

5420080071209/03/200205233003585Employee'S Fingers Are Amputated In Press Brake

5520077220008/20/200201340003499Employee'S Thumb Is Amputated In Press

5620082184107/08/200205214003363Employee Ampuataes Arm In Hydraulic Press Accident

5720179601806/07/200209506443398Employee'S Finger Amputated By Hydraulic Press

5820179561403/25/200209506443089Employee Struck In The Head By Flying Object

5920150327303/06/200209506143444Hand Crushed In Hydraulic Shearing Press

6020105627212/15/200109506423444Employee Injured When Right Fingertip Is Caught By Press

Safety regulators are investigating the death of a 38-year-old worker after a hydraulic press accident yesterday in Oakford, south of Perth.According to a WorkSafe, the man was working with a manual hydraulic press in the workshop when a metal cylinder shattered, striking him in the chest.Inspectors travelled to the site soon after the incident to interview witnesses and investigate the circumstances.A WorkSafe WA spokesperson toldSafe to Workthat the investigation will continue, and it still too early in the process to determine the exact circumstances of the incident.The hydraulic press will be examined thoroughly to find out what went wrong and what other factors may have contributed to the workers death.WorkSafe WA Commissioner Lex McCulloch said any work-related death was a tragedy, and relayed his sincere condolences to the mans family.In a statement, the safety regulator reiterated that its mission is to thoroughly investigate serious work-related injuries and deaths in WA with a view to preventing future incidents of a similar nature.ABC Radio Australia's news siteandABC News onlinealso ran stories about this incident.

ACCIDENT INVOLVING HYDRAULIC PILING MACHINEPhoto 1: Hydraulic Piling Machine at accident scene

An accident took place on 20th May 2008 at around 8:00pm when piling work was being carried out. The accident occurred AT a construction site which is situated next to the public parking area. The Hydraulic Pile Jacking Machine (model YZY 240) was equipped with a crane and a hydraulic piling press. Investigation revealed that the machine is located about 2 meters from the site hoarding which is adjacent to the public parking area. During the accident, one of the concrete piles which weigh about 2.8 tonnes with the dimensions of 12 meters (Length) x 300 mm (Width) X 300mm (Thickness) fell and crushed two vehicles in the parking area. The accident happened due to the failure of the lifting lug and sling which were used to tie the concrete pile.

Recommendations:

1.Hazard identification, risk assessment and risk control (HIRARC) shall be implemented before any piling activity.

2.Adequate lighting is crucial if the piling activity is carried out at night. Piling activity should only be done during broad daylight.

3.Safe lifting procedure should be updated. Use of spreader device is necessary to ensure the stability of the 12 meters length concrete pile during lifting. Use of spreader will ease the process and prevent the concrete pile from colliding with the crane boom section due to limited clearance between pile and crane boom.

4.Routine inspection of lifting gear should be carried out prior to any lifting activity to check for defects. Furthermore, all attachments involving sling or shackle with lifting lug must be done correctly to ensure safe lifting.

5.Good communication between crane operator and signalman is vital during such piling activity:a)Signalman appointed should be properly trained to provide clear two-way communication and correct information to the crane operator

b)Lifting and piling should be supervised and adequate number of workers should be provided.

References:

RIKEN OPTECHRIKEN OPTECH - Safety Light curtain sensor for Press machine, Area safety sensor for Press Machine, Safety of Stamping machine.The Safety and Automation Systems ofRIKEN OPTECHis involved in developing and marketing equipment for use in stamping operations, such as safety equipment for preventing accidents, malfunction detectors and load monitor for maintaining quality control.-www.tjsolution.comRIKEN Optech - Safety Device product lineup1. Riken Optech- SE2 Safety Light curtain sensor (Reflection Type)

Feature of SEII1. Reflection type, light can be adjusted easily.2. Special filter protects device from dirt and fog.3. Tolerant of ambient light.4. Built-in self-check circuit automatically checks the electronic circuit to monitor the safety of operation.5. It is designed to be vibration resistant so as to mitigate the influence from the action of the press machine.All Riken Optech SE2 model : SEII-24 (H.200 mm.), SEII-32 (H.280 mm.), SEII-40 (H.360 mm.), SEII-48 (H.480 mm.)

2. Riken Optech- RPH4 Safety Light curtain sensor (Direct Protection Type)

Spec. of Press machine that can apply this model(RPH4) to useType of the machine a press machine ---> having an emergency stop and nor-repeat mechanism.Emergency stop time ---> 300ms or lessSafety distance ---> (Response Time + emergency stop time of the press machine) x 1.6 or morePressure Capacity ---> (50,000kN or less)Scope of the die size ---> within the width of the bolster-www.tjsolution.comFeature of RPH41. It will turn off the output through the action of a self-diagnosis function. Fail-safe design is thoroughly pursued.2. When an abnormal incident occurs, the press machine will be stopped instantly! We have created a system that provides a high level of safety.3. The goal of creating a safety system supported by technology has been realized.4. This safety equipment is the result of using the highest level of safety design expertise and FMEA analysis.5. The system complies with global standards for safety sensors.6. The Type 4 Sensor conforms to the IEC Standards and EN Standards.7. Various safety functions are built in to the sensor.8. The introduction of an LED bar supports ease of use.-www.tjsolution.com9. The compact size is perfect for installation in dangerous areas.10. The detection width and the sensor length are identical thus keeping the space required to the minimum.All Riken Optech RPH4 model : (RPH425-n ; n=13~120 ), (RPH414-n ; n=21~125)

3. Riken Optech- RBS(PSDI) Presence Sensing Device Initiaion System.Photo-electric safety device withactivation function will improve production efficiency and reduce production fatigue.

Riken Optech - RBS(PSDI) Function- Optional functions for RBS type devices designed to elevate labor efficiency and safety also have acquired the official approval of the Ministry of Health, Labor and Welfare of Japan.1. Movable GuardsThe movable guard not only will reduce the time required to exchange dies, confirm the safety, and resume formal work but also will improve the overall safety of the press machine.2. Three-Optical-Axes Floating Blanking Function is available.This is an optional item for enhancing the function of the light curtain used for processing long strip work-pieces with pass the sensing field of the light curtain.Press machines will not be stopped even when up to three optical axes are interrupted. When four optical axes are interrupted, the press machine will be forcibly stopped.

Spec. of Press machine that can apply this model(RBS) to use-www.tjsolution.com- Press machines with an emergency stop mechanism and an anti-reactivation mechanism that can accept a safety light curtain.- Height of the bolster is 75mm or more.- Depth of the bolster is 1,000mm or less.- Length of the stroke is 600mm or less.- Set angle of overrun is within 15 degrees. (excluding hydraulic press machines)- Emergency stopping time is 300ms or less.- Pressure capacity is 5,000t or less.

4. Riken Optech- Safety Laser Scanner sensor for safety area (RS-4)

Riken Optech model RS-4 Laser scanner safety sensor,it performs continuous scanning over the wide range of 190 degrees covering the entire operating range and if an object or person happens to enter the protective area, it outputs a stop signal. The specifications of this equipment conform to the Type 3, IEC61496-3 Standards. Therefore, it is best suited for safety-related uses. The area sensor with high sensitivity and high resolution has wide-ranging applications. RS-4 is best suited for the protection of humans from mobile systems and static systems requiring safety measures up to the extent of the EN954-1 Type 3 Standards.- Four Protection Areas are ProgrammableAreas can randomly be set with the radius of 4 meters for the protection of humans or for an area with the radius of 15 meters for the detection of objects.

- Setting up the Protective Area. There are two ways to set the protective area.1. Directly inputting the data from a PCAs a rectangular area by using numerical data.2. Learning functionsMake an outline of a protective area out of cardboard and place it before this equipment. The read-in process starts when the learning function command is executed. The device will scan the outline of the cardboard. A new protective area will be decided based on the data acquired. It also has a function to store the parameters into the database.

- Protection by PasswordInput process can be restricted to specific passwords so that it runs only when the specified passwords are inputted. Passwords corresponding to the levels of importance and safety can be set to the equipment.-www.tjsolution.com

1. Small BodyDimensions 140 x 155 x 135 (W x H x D) in mm4. Number of detection zones: 4 (changeover via switch inputs)

2. High Speed Scanning / High resolution- Scanning rate: 25 scans/s or 40 ms/scan- Angle range: 190 degrees(Max.)- Angle resolution: 0.36 degrees5. The protection area is set by a personal computer.

3. With 2 different protection areas are programmable at the same time.- Caution Area: 4m- Warning Area: 15m6. EN regulation- IEC 61496-1 type 3- IEC 61496-3 type 3

For more information about"RIKEN Optech"please contact our sale engineer.

Machine pressFrom Wikipedia, the free encyclopediaThis article'stoneor style may not reflect the encyclopedic tone used on Wikipedia.See Wikipedia'sguide to writing better articlesfor suggestions.(February 2013)

Manualgoldsmithpress

Power press with a fixed barrier guardThis articleneeds additional citations forverification.Please helpimprove this articlebyadding citations to reliable sources. Unsourced material may be challenged and removed.(November 2009)

Aforming press, commonly shortened topress, is amachine toolthat changes the shape of a workpiece by the application of pressure.[1]Presses can be classified according to their mechanism:hydraulic,mechanical,pneumatic; their function:forging presses,stamping presses,press brakes,punch press, etc. their structure, e.g.Knuckle-joint press,screw press their controllability: conventional vs.servo-presses

Contents[hide] 1An example of peculiar press structure: shop press 2Some examples of presses by application 3An example of peculiar press control: servo-press 4A table of comparison among presses 5History 6Safety 7References 8External linksAn example of peculiar press structure: shop press[edit]A simple frame,fabricatedfrom steel, containing a bottle jack or simple hydraulic cylinder. Good for general-purpose work in the auto mechanic shop, machine shop, garage or basement shops, etc. Typically 1 to 30 tons of pressure, depending on size and expense. Classed withengine hoistsandengine standsin many tool catalogs.Some examples of presses by application[edit] Apress brakeis a special type of machine press that bends sheet metal into shape. A good example of the type of work a press brake can do is the backplate of a computer case. Other examples include brackets, frame pieces and electronic enclosures just to name a few. Some press brakes haveCNCcontrols and can form parts with accuracy to a fraction of a millimetre. Bending forces can exceed 4,000 kilonewtons (900,000lbf).[citation needed] Apunch pressis used to form holes. A screw press is also known as a fly press. Astamping pressis a machine press used to shape or cut metal bydeformingit with adie. It generally consists of a press frame, a bolster plate, and a ram. Capping presses form caps from rolls ofaluminiumfoil at up to 660 per minute.An example of peculiar press control: servo-press[edit]Aservomechanismpress, also known as aservo pressor a 'electro press, is a press driven by anACservo motor. Thetorqueproduced is converted to a linearforcevia aball screw. Pressure and position are controlled through aload celland anencoder. The main advantage of a servo press is its low energy consumption; its only 10-20% of other press machines. Another advantage is a quiet and clean work environment.A table of comparison among presses[edit]Comparison of various machine presses

Type of pressType of framePosition of frameActionMethod of actuationType of driveSuspensionRamBed

Open-backGapStraight-sideArchPillerSolidTie rodVerticalHorizontalInclinableInclinedSingleDoubleTripleCrankFront-to-back crankEccentricToggleScrewCamRack& pinionPistonOver directGeared, overdriveUnder directGeared, underdriveOne-pointTwo-pointFour-pointSingleMultipleSolidOpenAdjustable

BenchXXXXXXXXXXXXXXXXX

Open-back inclinableXXXXXXXXXXXXXXXXXX

Gap-frameXXXXXXXXXXXXXXXXXXXXXXXX

Adjustable-bed hornXXXXXXXXXXXXXXX

End-wheelXXXXXXXXXXXX

Arch-frameXXXXXXXXXXXX

Straight-sideXXXXXXXXXXXXXXXXXXXXXXXXXX

ReducingXXXXXXXXXXXXXXX

Knuckle-leverXXXXXXXXXXXXXXXX

Toggle-drawXXXXXXXXXXXXXXXX

Cam-drawingXXXXXXXXXXXXXXX

Two-point single-actionXXXXXXXXXXXXXXX

High-productionXXXXXXXXXXXXXX

Dyeing machineXXXXXXXXXX

TransferXXXXXXXXXXXXXXX

Flat-edge trimmingXXXXXXXX

HydraulicXXXXXXXXXXXXXXXXXX

Press brakeXXXXXXXXXXXX

History[edit]Historically, metal was shaped by hand using ahammer. Later, larger hammers were constructed to press more metal at once, or to press thicker materials. Often a smith would employ a helper or apprentice to swing thesledgehammerwhile the smith concentrated on positioning the workpiece. Addingwindmillorsteampower yielded still larger hammers such assteam hammers. Most modern machine presses use a combination of electric motors andhydraulicsto achieve the necessary pressure. Along with the evolution of presses came the evolution of thediesused within them.Safety[edit]Machine presses can be hazardous, so safety measures must always be taken. Bi-manual controls (controls the use of which requires both hands to be on the buttons to operate) are a very good way to prevent accidents, as are light sensors that keep the machine from working if the operator is in range of the

DC motorFrom Wikipedia, the free encyclopedia

Workings of a brushed electric motor with a two-pole rotor (armature) and permanent magnet stator. "N" and "S" designate polarities on the inside faces of themagnets; the outside faces have opposite polarities. The+and-signs show where the DC current is applied to thecommutatorwhich supplies current to thearmaturecoilsElectromagnetism

Electricity Magnetism

Electrostatics[show]

Magnetostatics[show]

Electrodynamics[show]

Electrical network[show]

Covariant formulation[show]

Scientists[show]

v t e

ThePennsylvania Railroad's class DD1 locomotive running gear was a semi-permanently coupled pair of third rail direct current electric locomotive motors built for the railroad's initial New York-area electrification when steam locomotives were banned in the city (locomotive cab removed here).ADC motorrelies on the fact that like magnet poles repel and unlike magnetic poles attract each other. A coil of wire with a current running through it generates aelectromagneticfield aligned with the center of the coil. By switching the current on or off in a coil its magnet field can be switched on or off or by switching the direction of the current in the coil the direction of the generated magnetic field can be switched 180. A simpleDC motortypically has a stationary set of magnets in thestatorand anarmaturewith a series of two or more windings of wire wrapped in insulated stack slots around iron pole pieces (called stack teeth) with the ends of the wires terminating on acommutator. The armature includes the mounting bearings that keep it in the center of the motor and the power shaft of the motor and the commutator connections. The winding in the armature continues to loop all the way around the armature and uses either single or parallel conductors (wires), and can circle several times around the stack teeth. The total amount of current sent to the coil, the coil's size and what it's wrapped around dictate the strength of the electromagnetic field created. The sequence of turning a particular coil on or off dictates what direction the effective electromagnetic fields are pointed. By turning on and off coils in sequence a rotating magnetic field can be created. These rotating magnetic fields interact with the magnetic fields of the magnets (permanent orelectromagnets) in the stationary part of the motor (stator) to create a force on the armature which causes it to rotate. In some DC motor designs the stator fields use electromagnets to create their magnetic fields which allow greater control over the motor. At high power levels, DC motors are almost always cooled using forced air.Thecommutatorallows each armature coil to be activated in turn. The current in the coil is typically supplied via two brushes that make moving contact with the commutator. Now, some brushless DC motors have electronics that switch the DC current to each coil on and off and have no brushes to wear out or create sparks.Different number of stator and armature fields as well as how they are connected provide different inherent speed/torque regulation characteristics. The speed of a DC motor can be controlled by changing the voltage applied to the armature. The introduction of variable resistance in the armature circuit or field circuit allowed speed control. Modern DC motors are often controlled bypower electronicssystems which adjust the voltage by "chopping" the DC current into on and off cycles which have an effective lower voltage.Since the series-wound DC motor develops its highest torque at low speed, it is often used in traction applications such aselectric locomotives, and trams. The DC motor was the mainstay of electrictraction driveson both electric anddiesel-electric locomotives, street-cars/trams and diesel electric drilling rigs for many years. The introduction of DC motors and anelectrical gridsystem to run machinery starting in the 1870s started a newsecond Industrial Revolution. DC motors can operate directly from rechargeable batteries, providing the motive power for the first electric vehicles and today'shybrid carsandelectric carsas well as driving a host ofcordlesstools. Today DC motors are still found in applications as small as toys and disk drives, or in large sizes to operate steel rolling mills and paper machines.If external power is applied to a DC motor it acts as a DC generator, adynamo. This feature is used to slow down and recharge batteries onhybrid carand electric cars or to return electricity back to the electric grid used on a street car or electric powered train line when they slow down. This process is calledregenerative brakingon hybrid and electric cars. In diesel electric locomotives they also use their DC motors as generators to slow down but dissipate the energy in resistor stacks. Newer designs are adding large battery packs to recapture some of this energy.Contents[hide] 1Brush 2Brushless 3Uncommutated 4Permanent magnet stators 5Wound stators 5.1Series connection 5.2Shunt connection 5.3Compound connection 6See also 7External links 8ReferencesBrush[edit]Main article:Brushed DC electric motor

A brushed DC electric motor generating torque from DC power supply by using an internal mechanical commutation. Stationary permanent magnets form the stator field. Torque is produced by the principle that any current-carrying conductor placed within an external magnetic field experiences a force, known as Lorentz force. In a motor, the magnitude of this Lorentz force (a vector represented by the green arrow), and thus the output torque,is a function for rotor angle, leading to a phenomenon known as torque ripple) Since this is a single phase two-pole motor, the commutator consists of a split ring, so that the current reverses each half turn ( 180 degrees).Thebrushed DC electric motorgenerates torque directly from DC power supplied to the motor by using internal commutation, stationary magnets (permanentorelectromagnets), and rotating electrical magnets.Advantages of a brushed DC motor include low initial cost, high reliability, and simple control of motor speed. Disadvantages are high maintenance and low life-span for high intensity uses. Maintenance involves regularly replacing the carbon brushes and springs which carry the electric current, as well as cleaning or replacing thecommutator. These components are necessary for transferring electrical power from outside the motor to the spinning wire windings of the rotor inside the motor. Brushes consist of conductors.Brushless[edit]Main articles:Brushless DC electric motorandSwitched reluctance motorTypical brushless DC motors use a rotating permanent magnet in the rotor, and stationary electrical current/coil magnets on the motor housing for the stator, but the symmetrical opposite is also possible. A motor controller converts DC toAC. This design is simpler than that of brushed motors because it eliminates the complication of transferring power from outside the motor to the spinning rotor. Advantages of brushless motors include long life span, little or no maintenance, and high efficiency. Disadvantages include high initial cost, and more complicated motor speed controllers. Some such brushless motors are sometimes referred to as "synchronous motors" although they have no external power supply to be synchronized with, as would be the case with normal AC synchronous motors.Uncommutated[edit]Other types of DC motors require no commutation. Homopolar motor A homopolar motor has a magnetic field along the axis of rotation and an electric current that at some point is not parallel to the magnetic field. The name homopolar refers to the absence of polarity change.Homopolar motors necessarily have a single-turn coil, which limits them to very low voltages. This has restricted the practical application of this type of motor. Ball bearing motor A ball bearing motor is an unusual electric motor that consists of twoball bearing-type bearings, with the inner races mounted on a common conductive shaft, and the outer races connected to a high current, low voltage power supply. An alternative construction fits the outer races inside a metal tube, while the inner races are mounted on a shaft with a non-conductive section (e.g. two sleeves on an insulating rod). This method has the advantage that the tube will act as a flywheel. The direction of rotation is determined by the initial spin which is usually required to get it going.Permanent magnet stators[edit]Main article:Permanent-magnet electric motorA PM motor does not have a field winding on the stator frame, instead relying on PMs to provide the magnetic field against which the rotor field interacts to produce torque. Compensating windings in series with the armature may be used on large motors to improve commutation under load. Because this field is fixed, it cannot be adjusted for speed control. PM fields (stators) are convenient in miniature motors to eliminate the power consumption of the field winding. Most larger DC motors are of the "dynamo" type, which have stator windings. Historically, PMs could not be made to retain high flux if they were disassembled; field windings were more practical to obtain the needed amount of flux. However, large PMs are costly, as well as dangerous and difficult to assemble; this favors wound fields for large machines.To minimize overall weight and size, miniature PM motors may use high energy magnets made withneodymiumor other strategic elements; most such are neodymium-iron-boron alloy. With their higher flux density, electric machines with high-energy PMs are at least competitive with all optimally designedsingly fedsynchronous and induction electric machines. Miniature motors resemble the structure in the illustration, except that they have at least three rotor poles (to ensure starting, regardless of rotor position) and their outer housing is a steel tube that magnetically links the exteriors of the curved field magnets.

Wound stators[edit]

A field coil may be connected in shunt, in series, or in compound with the armature of a DC machine (motor or generator)Main article:universal motorSee also:Excitation (magnetic)There are three types of electrical connections between the stator and rotor possible for DC electric motors: series, shunt/parallel and compound ( various blends of series and shunt/parallel) and each has unique speed/torque characteristics appropriate for diffent loading torque profiles/signatures.[1]Series connection[edit]A series DC motor connects thearmatureandfield windingsinserieswith acommonD.C. power source. The motor speed varies as a non-linear function of load torque and armature current; current is common to both the stator and rotor yielding current squared (I^2) behavior[citation needed]. A series motor has very high starting torque and is commonly used for starting high inertia loads, such as trains, elevators or hoists.[2]This speed/torque characteristic is useful in applications such asdragline excavators, where the digging tool moves rapidly when unloaded but slowly when carrying a heavy load.With no mechanical load on the series motor, the current is low, the counter-EMF produced by the field winding is weak, and so the armature must turn faster to produce sufficient counter-EMF to balance the supply voltage. The motor can be damaged by over speed. This is called a runaway condition.Series motors called "universal motors" can be used on alternating current. Since the armature voltage and the field direction reverse at (substantially) the same time, torque continues to be produced in the same direction. Since the speed is not related to the line frequency, universal motors can develop higher-than-synchronous speeds, making them lighter than induction motors of the same rated mechanical output. This is a valuable characteristic for hand-held power tools. Universal motors for commercialpower frequencyare usually small, not more than about 1kW output. However, much larger universal motors were used for electric locomotives, fed by special low-frequencytraction power networksto avoid problems with commutation under heavy and varying loads.Shunt connection[edit]A shunt DC motor connects the armature and field windings in parallel or shunt with a common D.C. power source. This type of motor has good speed regulation even as the load varies, but does not have the starting torque of a series DC motor.[3]It is typically used for industrial, adjustable speed applications, such as machine tools, winding/unwinding machines and tensioners.Compound connection[edit]A compound DC motor connects the armature and fields windings in a shunt and a series combination to give it characteristics of both a shunt and a series DC motor.[4]This motor is used when both a high starting torque and good speed regulation is needed. The motor can be connected in two arrangements: cumulatively or differentially. Cumulative compound motors connect the series field to aid the shunt field, which provides higher starting torque but less speed regulation. Differential compound DC motors have good speed regulation and are typically operated at constant speed.

TransformerFrom Wikipedia, the free encyclopediaThis article is about the electrical device. For the media and toy franchise, seeTransformers. For other uses, seeTransformer (disambiguation).

Pole-mounteddistribution transformerwithcenter-tappedsecondary winding used to provide 'split-phase' power for residential and light commercial service, which in North America is typically rated 120/240 volt.[1][2]Atransformeris an electrical device that transfers energy between two circuits throughelectromagnetic induction. A transformer may be used as a safe and efficientvoltage converterto change the AC voltage at its input to a higher or lower voltage at its output. Other uses include current conversion, isolation with or without changing voltage andimpedance conversion.A transformer most commonly consists of two windings of wire that are wound around a common core to provide tight electromagneticcouplingbetween the windings. The core material is often a laminatediron core. The coil that receives the electrical input energy is referred to as the primary winding, while the output coil is called the secondary winding.An alternatingelectric currentflowing through the primary winding (coil) of a transformer generates a varying electromagnetic field in its surroundings which causes a varyingmagnetic fluxin the core of the transformer. The varying electromagnetic field in the vicinity of the secondary winding induces anelectromotive forcein the secondary winding, which appears avoltageacross the output terminals. If a load impedance is connected across the secondary winding, a current flows through the secondary winding drawing power from the primary winding and its power source.A transformer cannot operate with direct current; although, when it is connected to a DC source, a transformer typically produces a short output pulse as the current rises.Contents[hide] 1Invention 2Applications 3Basic principles 4Basic transformer parameters and construction 5Construction 6Classification parameters 7Types 8Applications 9History 10See also 11Notes 12References 13Bibliography 14External linksInvention[edit]The invention of transformers during the late 1800s allowed for longer-distance, cheaper, and more energy efficienttransmission,distribution, and utilization ofelectrical energy. In the early days of commercial electric power, the main energy source was direct current (DC), which operates at low-voltage high-current. According toJoule's Law, energy losses are directly proportional to the square of current. This law revealed that even a tiny decrease in current or rise in voltage can cause a substantial lowering in energy losses and costs. Thus, the historical pursuit for a high-voltage low-current electricity transmission system took shape. Although high voltage transmission systems offered many benefits, the future fate of high-voltage alternating current still remained unclear for several reasons: high-voltage sources had a much higher risk of causing severe electrical injuries; many essential appliances could only function at low voltage. Regarded as one of the most influential electrical innovations of all time, the introduction of transformers had successfully reduced the safety concerns associated with alternating current and had the ability to lower voltage to a value that was required by most essential appliances.[3]Applications[edit]Transformers performvoltage conversion;isolation protection; andimpedance matching. In terms of voltage conversion, transformers can step-up voltage/step-down current from generators to high-voltage transmission lines, and step-down voltage/step-up current to local distribution circuits or industrial customers. The step-up transformer is used to increase the secondary voltage relative to the primary voltage, whereas the step-down transformer is used to decrease the secondary voltage relative to the primary voltage. Transformers range in size from thumbnail-sized used in microphones to units weighing hundreds of tons interconnecting thepower grid. A broad range oftransformer designsare used in electronic and electric power applications, including miniature, audio, isolation, high-frequency, power conversion transformers, etc.Basic principles[edit]The functioning of a transformer is based on two principles of the laws of electromagnetic induction: An electric current through a conductor, such as a wire, produces amagnetic fieldsurrounding the wire, and a changing magnetic field in the vicinity of a wire induces a voltage across the ends of that wire.The magnetic field excited in the primary coil gives rise to self-induction as well as mutual induction between coils. This self-induction counters the excited field to such a degree that the resulting current through the primary winding is very small when no load draws power from the secondary winding.The physical principles of the inductive behavior of the transformer are most readily understood and formalized when making some assumptions to construct a simple model which is called theideal transformer. This model differs fromreal transformersby assuming that the transformer is perfectly constructed and by neglecting that electrical or magnetic losses occur in the materials used to construct the device.Ideal transformer[edit]

Ideal transformer with a source and a load. NPand NSare the number of turns in the primary and secondary windings respectively.The assumptions to characterize the ideal transformer are: The windings of the transformer have no resistance. Thus, there is nocopper lossin the winding, and hence no voltage drop. Flux is confined within themagnetic core. Therefore, it is the samefluxthat links the input and output windings. Permeability of the core is infinitely high which implies that net mmf (amp-turns) must be zero (otherwise there would be infinite flux) hence IPNP- ISNS= 0. The transformer core does not suffermagnetic hysteresisoreddy currents, which cause inductive loss.If the secondary winding of an ideal transformer has no load, no current flows in the primary winding.The circuit diagram (right) shows the conventions used for an ideal, i.e. lossless and perfectly-coupled transformer having primary and secondary windings with NPand NSturns, respectively.The ideal transformer induces secondary voltageVSas a proportion of the primary voltageVPand respective winding turns as given by the equation,where,a is the windingturns ratio, the value of these ratios being respectively higher and lower than unity for step-down and step-up transformers,[4][5][a][b]VPdesignates source impressed voltage,VSdesignates output voltage, and,According to this formalism, when the number of turns in the primary coil is greater than the number of turns in the secondary coil, the secondary voltage is smaller than the primary voltage. On the other hand, when the number of turns in the primary coil is less than the number of turns in the secondary, the secondary voltage is greater than the primary voltage.Anyload impedanceZLconnected to the ideal transformer's secondary winding allows energy to flow without loss from primary to secondary circuits. The resulting input and outputapparent powerare equal as given by the equation.Combining the two equations yields the following ideal transformer identity.This formula is a reasonable approximation for the typical commercial transformer, with voltage ratio and winding turns ratio both being inversely proportional to the corresponding current ratio.The load impedance ZLand secondary voltage VSdetermine the secondary current ISas follows.The apparent impedance ZL' of this secondary circuit loadreferredto the primary winding circuit is governed by a squared turns ratio multiplication factor relationship derived as follows[7][8].For an ideal transformer, the power supplied to the primary and the power dissipated by the load are equal. If ZL= RLwhere RLis a pure resistance then the power is given by:[9][10]

The primary current is given by the following equation:[9][10]

Induction law[edit]A varying electrical current passing through the primary coil creates a varying magnetic field around the coil which induces a voltage in the secondary winding. The primary and secondary windings are wrapped around a core of very highmagnetic permeability, usuallyiron,[c]so that most of the magnetic flux passes through both the primary and secondary coils. The current through a load connected to the secondary winding and the voltage across it are in the directions indicated in the figure.

Ideal transformer and induction lawThe voltage induced across the secondary coil may be calculated from Faraday's law of induction, which states that:

whereVsis the instantaneous voltage,Nsis the number of turns in the secondary coil, and d/dt is thederivative[d]of the magnetic flux through one turn of the coil. If the turns of the coil are oriented perpendicularly to the magnetic field lines, the flux is the product of themagnetic flux densityBand the areaAthrough which it cuts. The area is constant, being equal to the cross-sectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary. Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer,[7]the instantaneous voltage across the primary winding equals

Taking the ratio of the above two equations gives the same voltage ratio and turns ratio relationship shown above, that is,.The changing magnetic field induces an emf across each winding.[11]The primary emf, acting as it does in opposition to the primary voltage, is sometimes termed thecounter emf.[12]This is in accordance withLenz's law, which states that induction of emf always opposes development of any such change in magnetic field.As still lossless and perfectly-coupled, the transformer still behaves as described above inthe ideal transformer.Polarity[edit]

Instrument transformer, with polarity dot and X1 markings on LV side terminalThe relationships of theinstantaneous polarityat each of the terminals of the windings of a transformer depend on the direction the windings are wound around the core. Identically wound windings produce the same polarity of voltage at the corresponding terminals. This relationship is usually denoted by thedot conventionin transformer circuit diagrams, nameplates, and on terminal markings, which marks the terminals having an in-phase relationship.[13][14][15][e][f]Real transformer[edit]The ideal transformer model neglects the following basic linear aspects in real transformers.Core losses, collectively called magnetizing current losses, consist of[18] Hysteresislosses due to nonlinear application of the voltage applied in the transformer core, and Eddy currentlosses due to joule heating in the core that are proportional to the square of the transformer's applied voltage.Whereas windings in the ideal model have no impedance, the windings in a real transformer have finite non-zero impedances in the form of: Joule losses due to resistance in the primary and secondary windings[18] Leakage flux that escapes from the core and passes through one winding only resulting in primary and secondary reactive impedance.If a voltage is applied across the primary terminals of a real transformer while the secondary winding is open without load, the real transformer must be viewed as a simple inductor with an impedance Z:

.Leakage flux[edit]Main article:Leakage inductance

Leakage flux of a transformerThe ideal transformer model assumes that all flux generated by the primary winding links all the turns of every winding, including itself. In practice, some flux traverses paths that take it outside the windings.[19]Such flux is termedleakage flux, and results inleakage inductanceinserieswith the mutually coupled transformer windings.[12]Leakage flux results in energy being alternately stored in and discharged from the magnetic fields with each cycle of the power supply. It is not directly a power loss, but results in inferiorvoltage regulation, causing the secondary voltage not to be directly proportional to the primary voltage, particularly under heavy load.[19]Transformers are therefore normally designed to have very low leakage inductance. Nevertheless, it is impossible to eliminate all leakage flux because it plays an essential part in the operation of the transformer. The combined effect of the leakage flux and the electric field around the windings is what transfers energy from the primary to the secondary.[20]In some applications increased leakage is desired, and long magnetic paths, air gaps, or magnetic bypass shunts may deliberately be introduced in a transformer design to limit theshort-circuitcurrent it will supply.[12]Leaky transformers may be used to supply loads that exhibitnegative resistance, such aselectric arcs,mercury vapor lamps, andneon signsor for safely handling loads that become periodically short-circuited such aselectric arc welders.[21]Air gaps are also used to keep a transformer from saturating, especially audio-frequency transformers in circuits that have a DC component flowing in the windings.[22]Knowledge of leakage inductance is also useful when transformers are operated in parallel. It can be shown that if the percent impedance (Z) and associated winding leakage reactance-to-resistance (X/R) ratio of two transformers were hypothetically exactly the same, the transformers would share power in proportion to their respective volt-ampere ratings (e.g. 500kVAunit in parallel with 1,000 kVA unit, the larger unit would carry twice the current). However, the impedance tolerances of commercial transformers are significant. Also, the Z impedance and X/R ratio of different capacity transformers tends to vary, corresponding 1,000 kVA and 500 kVA units' values being, to illustrate, respectively, Z ~ 5.75%, X/R ~ 3.75 and Z ~ 5%, X/R ~ 4.75.[23][24]Equivalent circuit[edit]See also:Steinmetz equivalent circuitReferring to the diagram, a practical transformer's physical behavior may be represented by anequivalent circuitmodel, which can incorporate an ideal transformer.[25]Winding joule losses and leakage reactances are represented by the following series loop impedances of the model: Primary winding:RP,XP Secondary winding:RS,XS.In normal course of circuit equivalence transformation,RSandXSare in practice usually referred to the primary side by multiplying these impedances by the turns ratio squared, (NP/NS)2=a2.

Real transformer equivalent circuitCore loss and reactance is represented by the following shunt leg impedances of the model: Core or iron losses:RC Magnetizing reactance:XM.RCandXMare collectively termed themagnetizing branchof the model.Core losses are caused mostly by hysteresis and eddy current effects in the core and are proportional to the square of the core flux for operation at a given frequency.[26]The finite permeability core requires a magnetizing currentIMto maintain mutual flux in the core. Magnetizing current is in phase with the flux, the relationship between the two being non-linear due to saturation effects. However, all impedances of the equivalent circuit shown are by definition linear and such non-linearity effects are not typically reflected in transformer equivalent circuits.[26]Withsinusoidalsupply, core flux lags the induced emf by90. With open-circuited secondary winding, magnetizing branch currentI0equals transformer no-load current.[25]The resulting model, though sometimes termed 'exact' equivalent circuit based onlinearityassumptions, retains a number of approximations.[25]Analysis may be simplified by assuming that magnetizing branch impedance is relatively high and relocating the branch to the left of the primary impedances. This introduces error but allows combination of primary and referred secondary resistances and reactances by simple summation as two series impedances.Transformer equivalent circuit impedance and transformer ratio parameters can be derived from the following tests:open-circuit test,[g]short-circuit test, winding resistance test, and transformer ratio test.Basic transformer parameters and construction[edit]Effect of frequency[edit]Transformer universal emf equationIf the flux in the core is purelysinusoidal, the relationship for either winding between itsrmsvoltageErmsof the winding, and the supply frequencyf, number of turnsN, core cross-sectional areaain m2and peak magnetic flux densityBpeakin Wb/m2or T (tesla) is given by the universal emf equation:[18]

If the flux does not contain evenharmonicsthe following equation can be used forhalf-cycle average voltageEavgof any waveshape:

The time-derivative term in Faraday's Law shows that the flux in the core is theintegralwith respect to time of the applied voltage.[28]Hypothetically an ideal transformer would work with direct-current excitation, with the core flux increasing linearly with time.[29]In practice, the flux rises to the point wheremagnetic saturationof the core occurs, causing a large increase in the magnetizing current and overheating the transformer. All practical transformers must therefore operate with alternating (or pulsed direct) current.[29]The emf of a transformer at a given flux density increases with frequency.[18]By operating at higher frequencies, transformers can be physically more compact because a given core is able to transfer more power without reaching saturation and fewer turns are needed to achieve the same impedance. However, properties such as core loss and conductorskin effectalso increase with frequency. Aircraft and military equipment employ 400Hz power supplies which reduce core and winding weight.[30]Conversely, frequencies used for somerailway electrification systemswere much lower (e.g. 16.7Hz and 25Hz) than normal utility frequencies (50 60Hz) for historical reasons concerned mainly with the limitations of earlyelectric traction motors. As such, the transformers used to step-down the high over-head line voltages (e.g. 15 kV) were much heavier for the same power rating than those designed only for the higher frequencies.

Power transformer over-excitation condition caused by decreased frequency; flux (green), iron core's magnetic characteristics (red) and magnetizing current (blue).Operation of a transformer at its designed voltage but at a higher frequency than intended will lead to reduced magnetizing current. At a lower frequency, the magnetizing current will increase. Operation of a transformer at other than its design frequency may require assessment of voltages, losses, and cooling to establish if safe operation is practical. For example, transformers may need to be equipped with 'volts per hertz' over-excitationrelaysto protect the transformer from overvoltage at higher than rated frequency.One example of state-of-the-art design is traction transformers used forelectric multiple unitandhigh-speedtrain service operating across the country border and using different electrical standards, such transformers' being restricted to be positioned below the passenger compartment. The power supply to, and converter equipment being supply by, such traction transformers have to accommodate different input frequencies and voltage (ranging from as high as 50Hz down to 16.7Hz and rated up to 25 kV) while being suitable for multiple AC asynchronous motor and DC converters & motors with varying harmonics mitigation filtering requirements.Large power transformers are vulnerable to insulation failure due to transient voltages with high-frequency components, such as caused in switching or by lightning.[31]Energy losses[edit]A theoretical (ideal) transformer does not experience energy losses, i.e. it is 100% efficient. The power dissipated by its load would be equal to the power supplied by its primary source. In contrast, a real transformer is typically 95 to 99% efficient, due to several loss mechanisms, including winding resistance, winding capacitance, leakage flux, core losses, andhysteresis loss. Larger transformers are generally more efficient than small units, and those rated for electricity distribution usually perform better than 98%.[32]Experimental transformers usingsuperconductingwindings achieve efficiencies of 99.85%.[33]The increase in efficiency can save considerable energy in a large heavily loaded transformer; the trade-off is in the additional initial and running cost of the superconducting design.As transformer losses vary with load, it is often useful to express these losses in terms of no-load loss, full-load loss, half-load loss, and so on.HysteresisandEddy currentlosses are constant at all load levels and dominate overwhelmingly without load, while variable windingjoule lossesdominating increasingly as load increases. The no-load loss can be significant, so that even an idle transformer constitutes a drain on the electrical supply. Designingenergy efficient transformersfor lower loss requires a larger core, good-qualitysilicon steel, or evenamorphous steelfor the core and thicker wire, increasing initial cost. The choice of construction represents atrade-offbetween initial cost and operating cost.[34]Transformer losses arise from:Winding joule lossesCurrent flowing through winding conductors causesjoule heating. As frequency increases, skin effect andproximity effectcauses winding resistance and, hence, losses to increase.Core lossesHysteresis lossesEach time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core. According to Steinmetz's formula, the heat energy due to hysteresis is given by, and,hysteresis loss is thus given by

where, f is the frequency, is the hysteresis coefficient and maxis the maximum flux density, the empirical exponent of which varies from about 1.4 to 1 .8 but is often given as 1.6 for iron.[34][35][36]Eddy current lossesFerromagneticmaterials are also goodconductorsand a core made from such a material also constitutes a single short-circuited turn throughout its entire length.Eddy currentstherefore circulate within the core in a plane normal to the flux, and are responsible forresistive heatingof the core material. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness.[34]Eddy current losses can be reduced by making the core of a stack of plates electrically insulated from each other, rather than a solid block; all transformers operating at low frequencies use laminated or similar cores.Magnetostriction related transformer humMagnetic flux in a ferromagnetic material, such as the core, causes it to physically expand and contract slightly with each cycle of the magnetic field, an effect known asmagnetostriction, the frictional energy of which produces an audible noise known asmains humortransformer hum.[4][37]This transformer hum is especially objectionable in transformers supplied atpower frequencies[h]and inhigh-frequencyflyback transformersassociated with PAL systemCRTs.Stray lossesLeakage inductance is by itself largely lossless, since energy supplied to its magnetic fields is returned to the supply with the next half-cycle. However, any leakage flux that intercepts nearby conductive materials such as the transformer's support structure will give rise to eddy currents and be converted to heat.[38]There are also radiative losses due to the oscillating magnetic field but these are usually small.Mechanical vibration and audible noise transmissionIn addition to magnetostriction, the alternating magnetic field causes fluctuating forces between the primary and secondary windings. This energy incites vibration transmission in interconnected metalwork, thus amplifying audibletransformer hum.[39]Core form and shell form transformers[edit]

Core form = core type; shell form = shell typeClosed-core transformers are constructed in 'core form' or 'shell form'. When windings surround the core, the transformer is core form; when windings are surrounded by the core, the transformer is shell form. Shell form design may be more prevalent than core form design for distribution transformer applications due to the relative ease in stacking the core around winding coils.[40]Core form design tends to, as a general rule, be more economical, and therefore more prevalent, than shell form design for high voltage power transformer applications at the lower end of their voltage and power rating ranges (less than or equal to, nominally, 230 kV or 75 MVA). At higher voltage and power ratings, shell form transformers tend to be more prevalent.[40][41][42][43]Shell form design tends to be preferred for extra high voltage and higher MVA applications because, though more labor-intensive to manufacture, shell form transformers are characterized as having inherently better kVA-to-weight ratio, better short-circuit strength characteristics and higher immunity to transit damage.[43]Construction[edit]Cores[edit]Laminated steel cores[edit]

Laminated core transformer showing edge of laminations at top of photo

Power transformer inrush current caused by residual flux at switching instant; flux (green), iron core's magnetic characteristics (red) and magnetizing current (blue).Transformers for use at power or audio frequencies typically have cores made of high permeabilitysilicon steel.[44]The steel has a permeability many times that offree spaceand the core thus serves to greatly reduce the magnetizing current and confine the flux to a path which closely couples the windings.[45]Early transformer developers soon realized that cores constructed from solid iron resulted in prohibitive eddy current losses, and their designs mitigated this effect with cores consisting of bundles of insulated iron wires.[46]Later designs constructed the core by stacking layers of thin steel laminations, a principle that has remained in use. Each lamination is insulated from its neighbors by a thin non-conducting layer of insulation.[47]The universal transformer equation indicates a minimum cross-sectional area for the core to avoid saturation.The effect of laminations is to confine eddy currents to highly elliptical paths that enclose little flux, and so reduce their magnitude. Thinner laminations reduce losses,[48]but are more laborious and expensive to construct.[49]Thin laminations are generally used on high-frequency transformers, with some of very thin steel laminations able to operate up to 10kHz.

Laminating the core greatly reduces eddy-current lossesOne common design of laminated core is made from interleaved stacks ofE-shapedsteel sheets capped withI-shapedpieces, leading to its name of 'E-I transformer'.[49]Such a design tends to exhibit more losses, but is very economical to manufacture. The cut-core or C-core type is made by winding a steel strip around a rectangular form and then bonding the layers together. It is then cut in two, forming two C shapes, and the core assembled by binding the two C halves together with a steel strap.[49]They have the advantage that the flux is always oriented parallel to the metal grains, reducing reluctance.A steel core'sremanencemeans that it retains a static magnetic field when power is removed. When power is then reapplied, the residual field will cause a highinrush currentuntil the effect of the remaining magnetism is reduced, usually after a few cycles of the applied AC waveform.[50]Overcurrent protection devices such asfusesmust be selected to allow this harmless inrush to pass. On transformers connected to long, overhead power transmission lines, induced currents due togeomagnetic disturbancesduringsolar stormscan cause saturation of the core and operation of transformer protection devices.[51]Distribution transformers can achieve low no-load losses by using cores made with low-loss high-permeability silicon steel oramorphous (non-crystalline) metal alloy. The higher initial cost of the core material is offset over the life of the transformer by its lower losses at light load.[52]Solid cores[edit]Powdered iron cores are used in circuits such as switch-mode power supplies that operate above mains frequencies and up to a few tens of kilohertz. These materials combine high magnetic permeability with high bulk electricalresistivity. For frequencies extending beyond theVHF band, cores made from non-conductive magneticceramicmaterials calledferritesare common.[49]Some radio-frequency transformers also have movable cores (sometimes called 'slugs') which allow adjustment of thecoupling coefficient(andbandwidth) of tuned radio-frequency circuits.Toroidal cores[edit]

Small toroidal core transformerToroidal transformers are built around a ring-shaped core, which, depending on operating frequency, is made from a long strip ofsilicon steelorpermalloywound into a coil, powdered iron, orferrite.[53]A strip construction ensures that thegrain boundariesare optimally aligned, improving the transformer's efficiency by reducing the core'sreluctance. The closed ring shape eliminates air gaps inherent in the construction of an E-I core.[21]The cross-section of the ring is usually square or rectangular, but more expensive cores with circular cross-sections are also available. The primary and secondary coils are often wound concentrically to cover the entire surface of the core. This minimizes the length of wire needed, and also provides screening to minimize the core's magnetic field from generatingelectromagnetic interference.Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level. Other advantages compared to E-I types, include smaller size (about half), lower weight (about half), less mechanical hum (making them superior in audio amplifiers), lower exterior magnetic field (about one tenth), low off-load losses (making them more efficient in standby circuits), single-bolt mounting, and greater choice of shapes. The main disadvantages are higher cost and limited power capacity (seeClassification parametersbelow). Because of the lack of a residual gap in the magnetic path, toroidal transformers also tend to exhibit higher inrush current, compared to laminated E-I types.Ferrite toroidal cores are used at higher frequencies, typically between a few tens of kilohertz to hundreds of megahertz, to reduce losses, physical size, and weight of inductive components. A drawback of toroidal transformer construction is the higher labor cost of winding. This is because it is necessary to pass the entire length of a coil winding through the core aperture each time a single turn is added to the coil. As a consequence, toroidal transformers rated more than a few kVA are uncommon. Small distribution transformers may achieve some of the benefits of a toroidal core by splitting it and forcing it open, then inserting a bobbin containing primary and secondary windings.Air cores[edit]A physical core is not an absolute requisite and a functioning transformer can be produced simply by placing the windings near each other, an arrangement termed an 'air-core' transformer. The air which comprises the magnetic circuit is essentially lossless, and so an air-core transformer eliminates loss due to hysteresis in the core material.[12]The leakage inductance is inevitably high, resulting in very poor regulation, and so such designs are unsuitable for use in power distribution.[12]They have however very highbandwidth, and are frequently employed in radio-frequency applications,[54]for which a satisfactory coupling coefficient is maintained by carefully overlapping the primary and secondary windings. They're also used forresonant transformerssuch as Tesla coils where they can achieve reasonably low loss in spite of the high leakage inductance.Windings[edit]

Windings are usually arranged concentrically to minimize flux leakage.It has been suggested thatCompensation windingbemergedinto this article. (Discuss)Proposed since March 2014.

Theconducting materialused for the windings depends upon the application, but in all cases the individual turns must be electrically insulated from each other to ensure that the current travels throughout every turn.[55]For small power and signal transformers, in which currents are low and the potential difference between adjacent turns is small, the coils are often wound fromenamelled magnet wire, such as Formvar wire. Larger power transformers operating at high voltages may be wound with copper rectangular strip conductors insulated by oil-impregnated paper and blocks ofpressboard.[56]

Cut view through transformer windings. White: insulator. Green spiral:Grain oriented silicon steel. Black: Primary winding made ofoxygen-free copper. Red: Secondary winding. Top left: Toroidal transformer. Right: C-core, but E-core would be similar. The black windings are made of film. Top: Equally low capacitance between all ends of both windings. Since most cores are at least moderately conductive they also need insulation. Bottom: Lowest capacitance for one end of the secondary winding needed for low-power high-voltage transformers. Bottom left: Reduction ofleakage inductancewould lead to increase of capacitance.High-frequency transformers operating in the tens to hundreds of kilohertz often have windings made of braidedLitz wireto minimize the skin-effect and proximity effect losses.[28]Large power transformers use multiple-stranded conductors as well, since even at low power frequencies non-uniform distribution of current would otherwise exist in high-current windings.[56]Each strand is individually insulated, and the strands are arranged so that at certain points in the winding, or throughout the whole winding, each portion occupies different relative positions in the complete conductor. The transposition equalizes the current flowing in each strand of the conductor, and reduces eddy current losses in the winding itself. The stranded conductor is also more flexible than a solid conductor of similar size, aiding manufacture.[56]The windings of signal transformers minimize leakage inductance and stray capacitance to improve high-frequency response. Coils are split into sections, and those sections interleaved between the sections of the other winding.Power-frequency transformers may havetapsat intermediate points on the winding, usually on the higher voltage winding side, for voltage adjustment. Taps may be manually reconnected, or a manual or automatic switch may be provided for changing taps. Automatic on-loadtap changersare used in electric power transmission or distribution, on equipment such asarc furnacetransformers, or for automatic voltage regulators for sensitive loads. Audio-frequency transformers, used for the distribution of audio to public address loudspeakers, have taps to allow adjustment of impedance to each speaker. Acenter-tapped transformeris often used in the output stage of an audio poweramplifierin apush-pull circuit. Modulation transformers inAMtransmitters are very similar.Dry-type transformer winding insulation systems can be either of standard open-wound 'dip-and-bake' construction or of higher quality designs that includevacuum pressure impregnation(VPI),vacuum pressure encapsulation(VPE), andcast coil encapsulationprocesses.[57]In the VPI process, a combination of heat, vacuum and pressure is used to thoroughly seal, bind, and eliminate entrained air voids in the winding polyester resin insulation coat layer, thus increasing resistance to corona. VPE windings are similar to VPI windings but provide more protection against environmental effects, such as from water, dirt or corrosive ambients, by multiple dips including typically in terms of final epoxy coat.[58]Cooling[edit]

Cutaway view of liquid-immersed construction transformer. The conservator (reservoir) at top provides liquid-to-atmosphere isolation as coolant level and temperature changes. The walls and fins provide required heat dissipation balance.See also:Arrhenius equationTo place the cooling problem in perspective, the accepted rule of thumb is that the life expectancy of insulation in allelectric machinesincluding all transformers is halved for about every 7C to 10C increase inoperating temperature, this life expectancy halving rule holding more narrowly when the increase is between about 7C to 8C in the case of transformer winding cellulose insulation.[59][60][61]Small dry-type and liquid-immersed transformers are often self-cooled by natural convection andradiationheat dissipation. As power ratings increase, transformers are often cooled by forced-air cooling, forced-oil cooling, water-cooling, or combinations of these.[62]Large transformers are filled withtransformer oilthat both cools and insulates the windings.[63]Transformer oil is a highly refinedmineral oilthat cools the windings and insulation by circulating within the transformer tank. The mineral oil andpaperinsulation system has been extensively studied and used for more than 100 years. It is estimated that 50% of power transformers will survive 50 years of use, that the average age of failure of power transformers is about 10 to 15 years, and that about 30% of power transformer failures are due to insulation and overloading failures.[64][65]Prolonged operation at elevated temperature degrades insulating properties of winding insulation and dielectric coolant, which not only shortens transformer life but can ultimately lead to catastrophic transformer failure.[59]With a great body of empirical study as a guide,transformer oil testingincludingdissolved gas analysisprovides valuable maintenance information. This underlines the need to monitor, model, forecast and manage oil and winding conductor insulation temperature conditions under varying, possibly difficult, power loading conditions.[66][67]Building regulations in many jurisdictions require indoor liquid-filled transformers to either use dielectric fluids that are less flammable than oil, or be installed in fire-resistant rooms.[68]Air-cooled dry transformers can be more economical where they eliminate the cost of a fire-resistant transformer room.The tank of liquid filled transformers often has radiators through which the liquid coolant circulates by natural convection or fins. Some large transformers employ electric fans for forced-air cooling, pumps for forced-liquid cooling, or haveheat exchangersfor water-cooling.[63]An oil-immersed transformer may be equipped with aBuchholz relay, which, depending on severity of gas accumulation due to internal arcing, is used to either alarm or de-energize the transformer.[50]Oil-immersed transformer installations usually include fire protection measures such as walls, oil containment, and fire-suppression sprinkler systems. Another protection means consists infast depressurization systemswhich are activated by the first dynamic pressure peak of the shock wave, avoiding transformer explosion before static pressure increases. Many explosions are reported to have been avoided thanks to this technology.[69]Polychlorinated biphenylshave properties that once favored their use as adielectric coolant, though concerns over theirenvironmental persistenceled to a widespread ban on their use.[70]Today, non-toxic, stablesilicone-based oils, orfluorinated hydrocarbonsmay be used where the expense of a fire-resistant liquid offsets additional building cost for a transformer vault.[68][71]PCBs for new equipment was banned in 1981 and in 2000 for use in existing equipment in United Kingdom[72]Legislation enacted in Canada between 1977 and 1985 essentially bans PCB use in transformers manufactured in or imported into the country after 1980, the maximum allowable level of PCB contamination in existing mineral oil transformers being 50 ppm.[73]Some transformers, instead of being liquid-filled, have their windings enclosed in sealed, pressurized tanks and cooled bynitrogenorsulfur hexafluoridegas.[71]Experimental power transformers in the 500-to-1,000 kVA range have been built withliquid nitrogenorheliumcooledsuperconductingwindings, which eliminates winding losses without affecting core losses.[74][75]Insulation drying[edit]Construction of oil-filled transformers requires that the insulation covering the windings be thoroughly dried of residual moisture before the oil is introduced. Drying is carried out at the factory, and may also be required as a field service. Drying may be done by circulating hot air around the core, or by vapor-phase drying (VPD) where an evaporated solvent transfers heat by condensation on the coil and core.For small transformers, resistance heating by injection of current into the windings is used. The heating can be controlled very well, and it is energy efficient. The method is called low-frequency heating (LFH) since the current used is at a much lower frequency than that of the power grid, which is normally 50 or 60Hz. A lower frequency reduces the effect of inductance, so the voltage required can be reduced.[76]The LFH drying method is also used for service of older transformers.[77]Bushings[edit]Larger transformers are provided with high-voltage insulatedbushingsmade of polymers or porcelain. A large bushing can be a complex structure since it must provide careful control of theelectric field gradientwithout letting the transformer leak oil.[78]Classification parameters[edit]Transformers can be classified in many ways, such as the following: Power capacity: From a fraction of a volt-ampere (VA) to over a thousand MVA. Duty of a transformer: Continuous, short-time, intermittent, periodic, varying. Frequency range:Power-frequency,audio-frequency, orradio-frequency. Voltage class: From a few volts to hundreds of kilovolts. Cooling type: Dry and liquid-immersed - self-cooled, forced air-cooled; liquid-immersed - forced oil-cooled, water-cooled. Circuit application: Such as power supply, impedance matching, output voltage and current stabilizer or circuit isolation. Utilization:Pulse,power, distribution,rectifier,arc furnace, amplifier output, etc.. Basic magnetic form: Core form, shell form. Constant-potential transformer descriptor: Step-up, step-down,isolation. General winding configuration: ByEIC vector group- various possible two-winding combinations of the phase designations delta, wye or star, andzigzag or interconnected star;[i]other -autotransformer,Scott-T,zigzag grounding transformer winding.[79][80][81][82] Rectifier phase-shift winding configuration: 2-winding, 6-pulse; 3-winding, 12-pulse; . . . n-winding, [n-1]*6-pulse; polygon; etc..Types[edit]Various specific electrical application designs require a variety oftransformer types. Although they all share the basic characteristic transformer principles, they are customize in construction or electrical properties for certain installation requirements or circuit conditions. Autotransformer: Transformer in which part of the winding is common to both primary and secondary circuits.[83] Capacitor voltage transformer: Transformer in which capacitor divider is used to reduce high voltage before application to the primary winding. Distribution transformer, power transformer: International standards make a distinction in terms of distribution transformers being used to distribute energy from transmission lines and networks for local consumption and power transformers being used to transfer electric energy between the generator and distribution primary circuits.[83][84][j] Phase angle regulating transformer: A specialised transformer used to control the flow of real power on three-phase electricity transmission networks. Scott-T transformer: Transformer used for phase transformation from three-phase totwo-phaseand vice versa.[83] Polyphase transformer: Any transformer with more than one phase. Grounding transformer: Transformer used for grounding three-phase circuits to create a neutral in a three wire system, using a wye-delta transformer,[80][85]or more commonly, azigzag grounding winding.[80][82][83] Leakage transformer: Transformer that has loosely coupled windings. Resonant transformer: Transformer that uses resonance to generate a high secondary voltage. Audio transformer: Transformer used in audio equipment. Output transformer: Transformer used to match the output of a valve amplifier to its load. Instrument transformer: Potential orcurrent transformerused to accurately and safely represent voltage, current or phase position of high voltage or high power circuits.[83]Applications[edit]

Anelectrical substationinMelbourne,Australiashowing three of five 220kV 66kV transformers, each with a capacity of 150MVA[86]

Transformer at theLimestone Generating StationinManitoba,CanadaTransformers are used to increase voltage before transmitting electrical energy over long distances throughwires. Wires haveresistancewhich loses energy through joule heating at a rate corresponding to square of the current. By transforming power to a higher voltage transformers enable economical transmission of power and distribution. Consequently, transformers have shaped theelectricity supply industry, permitting generation to be located remotely from points ofdemand.[87]All but a tiny fraction of the world's electrical power has passed through a series of transformers by the time it reaches the consumer.[38]Transformers are also used extensively inelectronic productsto step-down the supply voltage to a level suitable for the low voltage circuits they contain. The transformer also electrically isolates the end user from contact with the supply voltage.Signal and audio transformers are used to couple stages ofamplifiersand to match devices such asmicrophonesandrecord playersto the input of amplifiers. Audio transformers allowedtelephonecircuits to carry on atwo-way conversationover a single pair of wires. Abaluntransformer converts a signal that is referenced to ground to a signal that hasbalanced voltages to ground, such as between external cables and internal circuits.History[edit]Discovery of induction[edit]

Faraday's experiment with induction between coils of wire[88]Electromagnetic induction, the principle of the operation of the transformer, was discovered independently and almost simultaneously byJoseph HenryandMichael Faradayin 1831. Although Henry's work likely having preceded Faraday's work by a few months, Faraday was the first to publish the results of his experiments and thus receive credit for the discovery.[89]The relationship between emf and magnetic flux is an equation now known asFaraday's law of induction:.whereis the magnitude of the emf in volts and Bis the magnetic flux through the circuit inwebers.[90]Faraday performed the first experiments on induction between coils of wire, including winding a pair of coils around an iron ring, thus creating the firsttoroidalclosed-core transformer.[91]However he only applied individual pulses of current to his transformer, and never discovered the relation between the turns ratio and emf in the windings.Induction coils[edit]

Faraday's ring transformer

Induction coil, 1900, Bremerhavn, GermanyThe first type of transformer to see wide use was theinduction coil, invented by Rev.Nicholas CallanofMaynooth College, Ireland in 1836. He was one of the first researchers to realize the more turns the secondary winding has in relation to the primary winding, the larger the induced secondary emf will be. Induction coils evolved from scientists' and inventors' efforts to get higher voltages from batteries. Since batteries producedirect current (DC)rather than AC, induction coils relied upon vibratingelectrical contactsthat regularly interrupted the current in the primary to create the flux changes necessary for induction. Between the 1830s and the 1870s, efforts to build better induction coils, mostly by trial and error, slowly revealed the basic principles of transformers.First alternating current transformers[edit]By the 1870s, efficientgeneratorsproducingalternating current (AC)were available, and it was found AC could power an induction coil directly, without aninterrupter.In 1876, Russian engineerPavel Yablochkovinvented a lighting system based on a set of induction coils where the primary windings were connected to a source of AC. The secondary windings could be connected to several'electric candles'(arc lamps) of his own design.[92][93]The coils Yablochkov employed functioned essentially as transformers.[92]In 1878, theGanz factory, Budapest, Hungary, began manufacturing equipment for electric lighting and, by 1883, had installed over fifty systems in Austria-Hungary. Their AC systems used arc and incandescent lamps, generators, and other equipment.[94]Lucien Gaulardand John Dixon Gibbs first exhibited a device with an open iron core called a 'secondary generator' in London in 1882, then sold the idea to theWestinghousecompany in the United States.[46]They also exhibited the invention in Turin, Italy in 1884, where it was adopted for an electric lighting system.[95]However, the efficiency of their open-core bipolar apparatus remained very low.[95]Early series circuit transformer distribution[edit]Induction coils with open magnetic circuits are inefficient at transferring power toloads. Until about 1880, the paradigm for AC power transmission from a high voltage supply to a low voltage load was a series circuit. Open-core transformers with a ratio near 1:1 were connected with their primaries in series to allow use of a high voltage for transmission while presenting a low voltage to the lamps. The inherent flaw in this method was that turning off a single lamp (or other electric device) affected the voltage supplied to all others on the same circuit. Many adjustable transformer designs were introduced to compensate for this problematic characteristic of the series circuit, including those employing methods of adjusting the core or bypassing the magnetic flux around part of a coil.[95]Efficient, practical transformer designs did not appear until the 1880s, but within a decade, the transformer would be instrumental in theWar of Currents, and in seeing AC distribution systems triumph over their DC counterparts, a position in which they have remained dominant ever since.[96]

Shell form transformer. Sketch used by Uppenborn to describe ZBD engineers' 1885 patents and earliest articles.[95]

Core form, front; shell form, back. Earliest specimens of ZBD-designed high-efficiency constant-potential transformers manufactured at the Ganz factory in 1885.

The ZBD team consisted ofKroly Zipernowsky,Ott BlthyandMiksa Dri

Stanley's 1886 design for adjustable gap open-core induction coils[97]Closed-core transformers and parallel power distribution[edit]In the autumn of 1884,Kroly Zipernowsky,Ott BlthyandMiksa Dri(ZBD), three engineers associated with the Ganz factory, had determined that open-core devices were impracticable, as they were incapable of reliably regulating voltage.[98]In their joint 1885 patent applications for novel transformers (later called ZBD transformers), they described two designs with closed magnetic circuits where copper windings were either a) wound around iron wire ring core or b)surrounded by iron wire core.[95]The two designs were the first application of the two basic transformer constructions in common use to this day, which can as a class all be termed as either core form or shell form (or alternatively, core type or shell type), as in a) or b), respectively (see images).[40][41][99][100]The Ganz factory had also in the autumn of 1884 made delivery of the world's first five high-efficiency AC transformers, the first of these units having been shipped on September 16, 1884.[101]This first unit had been manufactured to the following specifications: 1,400 W, 40Hz, 120:72 V, 11.6:19.4 A, ratio 1.67:1, one-phase, shell form.[101]In both designs, the magnetic flux linking the primary and secondary windings traveled almost entirely within the confines of the iron core, with no intentional path through air (seeToroidal coresbelow). The new transformers were 3.4 times more efficient than the open-core bipolar devices of Gaulard and Gibbs.[102]The ZBD patents included two other major interrelated innovations: one concerning the use of parallel connected, instead of series connected, utilization loads, the other concerning the ability to have high turns ratio transformers such that the supply network voltage could be much higher (initially 1,400 to 2,000 V) than the voltage of utilization loads (100 V initially preferred).[103][104]When employed in parallel connected electric distribution systems, closed-core transformers finally made it technically and economically feasible to provide electric power for lighting in homes, businesses and public spaces.[105][106]Blthy had suggested the use of closed cores, Zipernowsky had suggested the use ofparallel shunt connections, and Dri had performed the experiments;[107]Transformers today are designed on the principles discovered by the three engineers. They also popularized the word 'transformer' to describe a device for altering the emf of an electric current,[105][108]although the term had already been in use by 1882.[109][110]In 1886, the ZBD engineers designed, and the Ganz factory supplied electrical equipment for, the world's firstpower stationthat used AC generators to power a parallel connected common electrical network, the steam-powered Rome-Cerchipower plant.[111]AlthoughGeorge Westinghousehad bought Gaulard and Gibbs' patents in 1885, theEdison Electric Light Companyheld an option on the US rights for the ZBD transformers, requiring Westinghouse to pursue alternative designs on the same principles. He assigned toWilliam Stanleythe task of developing a device for commercial use in United States.[112]Stanley's first patented design was for induction coils with single cores of soft iron and adjustable gaps to regulate the emf present in the secondary winding (see image).[97]This design[113]was first used commercially in the US in 1886[96]but Westinghouse was intent on improving the Stanley design to make it (unlike the ZBD type) easy and cheap to produce.[113]Westinghouse, Stanley and associates soon developed an easier to manufacture core, consisting of a stack of thin 'Eshaped' iron plates, insulated by thin sheets of paper or other insulating material. Prewound copper coils could then be slid into place, and straight iron plates laid in to create a closed magnetic circuit. Westinghouse applied for a patent for the new low-cost design in December 1886; it was granted in July 1887.[107][114]Other early transformers[edit]In 1889, Russian-born engineerMikhail Dolivo-Dobrovolskydeveloped the firstthree-phasetransformer at theAllgemeine Elektricitts-Gesellschaft('General Electricity Company') in Germany.[115]In 1891,Nikola Teslainvented theTesla coil, an air-cored, dual-tuned resonant transformer for generating veryhigh voltagesat high frequency.[116][117]

See also[edit]

Step Down TransformerPosted byP. MarianinPower supply,Theorywith37 commentsTagged with:transformers What is a step down transformer: is one whose secondary voltage is less than its primary voltage. It is designed to reduce the voltage from the primary winding to the secondary winding. This kind of transformer steps down the voltage applied to it.As a step-down unit, the transformer converts high-voltage, low-current power into low-voltage, high-current power. The larger-gauge wire used in the secondary winding is necessary due to the increase in current. The primary winding, which doesnt have to conduct as much current, may be made of smaller-gauge wire.

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Model: GPC-1005220V primary to 110V secondaryPower Rating: 500VAPrice: $69.95more detailsJump to chapter Step Down Tranformer Considerations how to wire a step down transformer how to check a step down transformerStep-Down Tranformer ConsiderationsIt is possible to operate either of these transformer types backwards (powering the secondary winding with an AC source and letting the primary winding power a load) to perform the opposite function: a step-up can function as a step-down and visa-versa. One convention used in the electric power industry is the use of H designations for the higher-voltage winding (the primary winding in a step-down unit; the secondary winding in a step-up) and X designations for the lower-voltage winding.you can buy transformers at very low prices fromhereOne of the most important considerations to increase transformer efficiency and reduce heat is choosing the metal type of the windings. Copper windings are much more efficient than aluminum and many other winding metal choices, but it also costs more. Transformers with copper windings cost more to purchase initially, but save on electrical cost over time as the efficiency more than makes up for the initial cost.Step-down transformers are commonly used to convert the 220 volt electricity found in most parts of the world to the 110 volts required by North American equipment.How to Wire a Step Down Transformer1. Observe and identify the schematic and rating of the step down transformer to be installed. Remove the terminal connection box cover placed at the lower side of the transformer. Only the high amperage types will have this enclosure, while lower powered transformers will have an exposed screw terminal.2. Know termination identification follows for all step down transformers: H1, H2, H3 and H4 signify the high voltage side or power feed end of the transformer. This holds true regardless of the size of the transformer. Interconnection of the transformer will vary depending on the manufacturer and voltage used for feeding the transformer.3. Terminate the feed power wires first by cutting the wires to length. If you are using large wire lugs be sure to take into consideration the length of the lug and the amount of wire that can be inserted into the female crimp area.4. Strip back the outer insulating of the wires with the pocketknife or wire strippers. Insert the eye ring or wire lug over the bare copper wire and crimp the connection device, using the appropriate-size crimper, permanently to the wire.5. Terminate the high side, high voltage of the step down transformer. If the high side terminals are bolts, be sure to follow any torque requirements that are listed by the manufacturer.6. Terminate the low side, low voltage of the transformer. Note these terminals will be identified by X1, X2, X3 and X4. Again follow the manufacturers individual schematics for that particular type of transformer. Note that on small control transformers there will only be an X1 and X2. X1 is the power or hot side and X2 is generally the grounding and neutral portion of the low voltage.7. Terminate the small control transformer for X1 and X2. X1 will go directly to the control circuit after passing through a small fuse that is rated for the circuit. X2 will be terminated not only to the neutral side of the control circuit, but the grounding safety as well. In other words, the X2 side of the small control transformer must be tied to the grounding system of the electrical circuit.8. Replace all covers on the transformer and any enclosures that protect you from electricity. Apply the high voltage to the transformer by switching on the feeder power circuit. Turn on the low side safety circuit control.9. Use a volt meter to test for proper voltage on the step down side of the transformer. It should be the same that is listed on the specs tag provided by the manufacturer.How to Check a Step Down Transformer1. Remove all wires from the transformer terminals using the screwdriver. Identify the wires if they are not already identified. Use a clear tape and pen. Write the terminal that the wires are attached to and place the identified tape on the wires end.2. Turn the volt ohmmeter to the Ohms position and place the red lead into the connector identified as Ohms. Touch the black lead to the metal frame of the transformer.3. Touch the red lead to the transformers terminals in the following order: H1, H2, X1 and then X2. The meter should read infinite ohms or wide open. Infinite ohms on a digital meter will be identified as a blank screen or a wide open will have the word Open displayed. If the meter registers any form of resistance, there is an internal problem with the windings. The copper coils may be shorted