machines lab 2 mnual

8/11/2019 machines lab 2 mnual

1/19

Cut Section of DC Machine

NV7038

Learning Material

Ver 1.2

Designed & Manufactured by:

141-B, Electronic Complex, Pardesipura, Indore- 452 010 India, Tel.: 91-731- 4211500,

Telefax: 91-731-4202959, Toll free: 1800-103-5050, E-mail: [email protected]

Website: www.nvistech.com
mailto:[email protected]:[email protected]


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Nvis Technologies Pvt. Ltd. 2
http://www.nvistech.com/


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Cut Section of Machine

NV7038

Table of Contents

1. Introduction 4

2. Features 5

3. Technical Specifications 6

4. Theory 7

5. Warranty 18

6. List of Service Center 19

7. List of Accessories 20


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Introduction

NV7038 Cut Section of Machine is an important part for all Electrical laboratories

considering the wide spread use of Electric Machines, study of these machines

becomes integral part of any educational course in electrical engineering and to let

students have basic knowledge of operation of these machines, this trainer plays a

vital role.

A comprehensive cut section of all type of machines is designed to explain theworking principal behind the major machines parts. With this, students are able to see

clearly the major component of the machines and how they are interconnected; both

electrically and mechanically this helps them in enhancing their knowledge.


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Features

Quality designed motor

Stand alone operation

Provided with terminal box for ease of connection

Self-contained

Easy to operate

Learning Material

2 Year Warranty


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Technical Specifications

Model No. Rating Type of Machines Rated Voltage

NV7038 1HP DC Shunt 200V

NV7038A 1HP DC Compound 200V

NV7038B 3HP 3-Phase AC Synchronous 415V

NV7038C 1HP 3-Phase AC Squirrel cage induction 415V

NV7038D 1HP 3-Phase AC Slip Ring induction 415V

NV7038E 1HP DC Series 200V

NV7038F 1HP 1-Phase Capacitor start Capacitor

run induction

230V


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Theory

DC Motor Basic

DC motor is a machine which converts electrical energy in to mechanical energy. So

motor is consuming power whereas generator is generating power. DC motors consist

of rotor-mounted windings (armature) and stationary windings (field poles). In all DC

motors, except permanent magnet motors, current must be conducted to the armature

windings by passing current through carbon brushes that slide over a set of copper

surfaces called a commutator, which is mounted on the rotor. The commutator bars

are soldered to armature coils. The brush/commutator combination makes a sliding

switch that energizes particular portions of the armature, based on the position of the

rotor. This process creates north and south magnetic poles on the rotor that are

attracted to or repelled by north and south poles on the stator, which are formed by

passing direct current through the field windings. It's this magnetic attraction and

repulsion that causes the rotor to rotate.

Figure 1

Direct-current (DC) motors are often used in variable speed applications. The DC

motor can be designed to run at any speed within the limits imposed by centrifugal

forces and commutation considerations. Many machine tools also use DC motors

because of the ease with which speed can be adjusted.

Various Parts of DC Machine

Stator:

The stator is the part of a motor or generator that is stationary. In DC machines, the

purpose of the stator is to provide the magnetic field. The stator is provided by apermanent magnet.

Stator with Yoke Stator with Winding Figure 2


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Rotor:

The purpose of the rotor is to provide the rotating element in a DC machine. In a DC

generator, the rotor is the component that is rotated by an external force. In a DC motor, the

rotor is the component that turns a piece of equipment. In both types of DC machines,

the rotor is the armature.

Rotor of DC motor Figure 3

Armature:

The purpose of the armature is to provide the energy conversion in a DC machine. In a

DC generator, the armature is rotated by an external mechanical force, such as a steam

turbine. This rotation induces a voltage and current flow in the armature. Thus, the

armature converts mechanical energy to electrical energy. In a DC motor, the

armature receives voltage from an outside electrical source and converts electrical

energy into mechanical energy in the form of torque.

The armature is the part of a DC motor that rotates and provides energy at the end of

the shaft. It is basically an electromagnet, since it is a coil of wire that has to be

specially designed to fit around core material on the shaft. The core of the armature is

made of laminated steel and provides slots for the coils of wire to be pressed onto.

The armature core is made of laminated steel to prevent the circulation of eddy

currents. If the core were solid, magnetic currents would be produced that would

circulate in the core material near the surface and cause the core metal to heat up.

These magnetic currents are called eddy currents. When laminated steel sections are

pressed together to make the core, the eddy currents cannot flow from one laminated

segment to another, so they are effectively canceled out. The laminated core also

prevents other magnetic losses called flux losses. These losses tend to make the

magnetic field weaker so that more core material is required to obtain the same

magnetic field strengths. The flux losses and eddy current losses are grouped togetherby designers and called core losses. The laminated core is designed to allow the

armature's magnetic field to be as strong as possible since the laminations prevent

core losses.

Figure 4


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Notice that one end of the core has commutator segments. There is one commutator

segment for each end of each coil. This means that an armature with four coils will

have eight commutator segments. The commutator segments are used as a contact

point between the stationary brushes and the rotating armature. When each coil of

wire is pressed onto the armature, the end of the coil is soldered to a specific

commutator segment. This makes an electrical terminal point for the current that will

flow from the brushes onto the commutator segment and finally through the coil of

wire. Figure 5 shows the coil of wire before it is mounted in the armature slot, andFig. 5 shows the coil mounted in the armature slot and soldered to the commutator

segment.

The shaft is designed so that the laminated armature segments can be pressed onto it

easily. It is also machined to provide a surface for a main bearing to be pressed on at

each end. The bearing will ride in the end plates and support the armature when it

begins to rotate. One end of the shaft is also longer than the other, since it will provide

the mounting shaft for the motor's load to be attached. Some shafts have a key way orflat spot machined into them so that the load that is mounted on it can be secured. You

must be careful when handling a motor that you do not damage the shaft, since it must

be smooth to accept the coupling mechanism. It is also possible to bend the shaft or

cause damage to the bearings so that the motor will vibrate when it is operating athigh speed. The commutator is made of copper. A thin section of insulation is placed

between each commutator segment. This effectively isolates each commutator

segment from all others.

Field:The purpose of the field in a DC machine is to provide a magnetic field for producing

either a voltage (generator) or a torque (motor). The field in a DC machine is

produced by either a permanent magnet or an electromagnet. Normally,

electromagnets are used because they have an increased magnetic strength, and the

magnetic strength is more easily varied using external devices. In Figure 7 the field is

provided by the stator.

CollectorThe collector is a characteristic member of the d.c. machines allowing to convert the

alternating voltages and currents of the armature conductors in the direct currents and

voltages present at the power terminals of the machine. It is made up of copper bars

occupying the different azimuthal positions, isolated with mica or plastic reinforced

by fiber glass from 0.5 to 1.5 mm thick and connected to the windings of the armature

winding. The bars are also connected to the two power terminals of the machine

through creeping contacts with the fixed brushes as to the stator. These are present in

pairs, symmetrically set along the azimuthal, development of the collector. Rather

than using brushes of big section we prefer using more than one brush set in rows, to

obtain a better contact with the bars.

Motor Frame

Simply put, the interaction of two magnetic fields causes the rotation in a DC motor.

The DC motor has field poles that are stationary and an armature that turns on

bearings in the space between the field poles. A simple DC motor has two field poles:

a north pole and a south pole. The magnetic lines of force extend across the opening

between the poles from north to south. For larger or more complex motors there are

one or more electromagnets. These electromagnets receive electricity from an outside

power source and serve as the field structure.

The armature is placed inside the frame of the motor where the field coils are

mounted. When the field coils and the armature coils become magnetized, the


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armature will begin to rotate. The field winding is made by coiling up a long piece of

wire. The wire is mounted on laminated pole pieces called field poles. Similar to an

armature, these poles are made of laminated steel or cast iron to prevent eddy current

and other flux losses. Figure 9 shows the location of the pole pieces inside a DC

motor frame.

Figure 5

Figure 6 (a) this diagram shows the location of the pole pieces in the frame of a DC

motor. (b) This diagram shows an individual pole piece. You can see that it is made of

laminated sections. The field coils are wound around the pole pieces.

The amount of wire that is used to make the field winding will depend on the type ofmotor that is being manufactured. A series motor uses heavy-gauge wire for its field

winding so that it can handle very large field currents. Since the wire is a large gauge,

the number of turns of wire in the coil will be limited. If the field winding is designed

for a shunt motor, it will be made of small-gauge wire and many turns can be used.

After the coils are wound, they are coated for protection against moisture and other

environmental elements. After they have been pressed onto the field poles, they must

be secured with shims or bolts so that they are held rigidly in place. Remember: When

current is passed through the coil, it will become strongly magnetized and attract or

repel the armature magnetic poles. If the field poles are not rigidly secured, they will

be pulled loose when they are attracted to the armature's magnetic field and then

pressed back into place when they become repelled. This action will cause the field tovibrate and damage the outer protective insulation and cause a short circuit or a

ground condition between the winding and the frame of the motor.

The ends of the frame are machined so that the end plates will mount firmly into

place. An access hole is also provided in the side of the frame or in the end plates so

that the field wires can be brought to the outside of the motor, where DC voltage can

be connected.

The bottom of the frame has the mounting bracket attached. The bracket has a set of

holes or slots provided so that the motor can be bolted down and securely mounted on


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the machine it is driving. The mounting holes will be designed to specifications by

frame size.

The dimensions for the frame sizes are provided in tables printed by motor

manufacturers. Since these holes and slots are designed to a standard, you can predrill

the mounting holes in the machinery before the motor is put in place. The slots are

used to provide minor adjustments to the mounting alignment when the motor is used

in belt-driven or chain-driven applications. It is also important to have a small amount

of mounting adjustment when the motor is used in direct-drive applications. It is very

important that the motor be mounted so that the armature shaft can turn freely and not

bind with the load.

Induction Motor Basic

The Induction motor is a single phase and three phase AC motor and is the most

widely used machine. These motors are probably the simplest and most rugged of all

electric motors. The supply is connected to the stator and the rotor power is received

by induction caused by the stator rotating flux, hence the motor obtains its name

induction motor. Its characteristic features are:

a) Simple and rugged construction.

b) Low cost and minimum maintenance.

c) High reliability and sufficiently high efficiency.

d) Needs no extra starting motor and need not be synchronized.

Open view of Three Phases Induction Motor Figure 6

Name Plate Parameters

A typical nameplate of an induction motor lists the following parameters:

Rated terminal supply voltage in Volts.

Rated frequency of the supply in Hz.(Hertz)

Rated current in Amps. (Amperes)

Speed in RPM. (Rotation Per Minute)

Power rating in Watts or Horsepower (HP).

Rated torque in Newton meters or Pound-inches.

Winding insulation type - Class A, B, F or H.

Type of stator connection (for 3-phase only), star (Y) or delta ().


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When the rated voltage and frequency are applied to the terminals of an induction

motor, it draws the rated current (or corresponding power) and runs at base speed and

can deliver the rated torque.

Construction:

Construction View of Three Phase Induction Motor gure 7

An Induction Motor has basically two parts:

Stator

Rotor

The Stator and the Rotor are electrical circuits that perform as electromagnets. In the

three phase induction motor, the windings of the rotor are not connected to a powersupply, but are essentially short circuits.

Figure 8

The Stator is the stationary electrical part of the motor. The Stator is made up of a

number of stampings with slots to carry three phase windings. It is wound for a

definite number of poles. The windings are geometrically spaced 120 apart. The


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stator consists of a cylindrical laminated and slotted core placed in a frame of rolled

or cast steel. The frame provides mechanical protection and carries the terminal box

and the end covers with bearings.

There are two general types of Rotors:

The Squirrel-Cage Rotor,

The Wound (or slip ring) Rotor.

The Squirrel-Cage Rotors:

In the squirrel-cage rotor, the rotor winding consists of single copper or aluminum

bars placed in the slots and short-circuited by end-rings on both sides of the rotor. In

the wound rotor, an insulated 3-phase winding similar to the stator winding and for

the same number of poles is placed in the rotor slots. The ends of the star-connected

rotor winding are brought to three slip rings on the shaft so the connection can be

made to it for starting or speed control.

Figure 9

Figure 10


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Wound Rotor:

An alternate design, called the wound rotor, is used when variable speed is required.

In this case, the rotor has the same number of poles as the stator and the windings are

made of wire, connected to slip rings on the shaft. Carbon brushes connect the slip

rings to an external controller such as a variable resistor that allows changing the

motor's slip rate. In certain high-power variable speed wound-rotor drives, the slip-

frequency energy is captured, rectified and returned to the power supply through an

inverter

Wound Rotor Induction Motor

Figure 11

Compared to squirrel cage rotors, wound rotor motors are expensive and require

maintenance of the slip rings and brushes, but they were the standard form for

variable speed control before the advent of compact power electronic devices.

Transistorized inverters with variable-frequency drive can now be used for speed

control, and wound rotor motors are becoming less common. (Transistorized inverter

drives also allow the more-efficient three-phase motors to be used when only single-

phase mains current is available, but this is never used in household appliances,

because it can cause electrical interference and because of high power requirements).

Synchronous machine basic

A Synchronous machine is an ac machine in which the rotor moves at a speed which

bears a constant relation ship to the frequency of currents in the armature winding. A

synchronous machine is one of the important types of electric machines. Large ac

network operating at constant frequency of 50 Hz or 60 Hz rely almost exclusively on

synchronous generators also called the alternators, for the supply of electrical energy

and may have synchronous compensators at key points for control of reactive power.

Synchronous motors provide constant speed industrial drives with the possibility of

power factor correction

Synchronous machine is fundamentally the same as that of a dc machine but unlike

the latter in the synchronous machine there is no need to rectify the time varying e.m.f

which is induced in the armature winding. Consequently a synchronous machine does

not require a commutator. It is in fact quite possible to use a dc generator as analternator by placing a set of collector rings on the shaft and connecting these rings to

the proper points on the armature winding brushes riding on the rings can then be

connected to the load. But unlike dc generator they are to be driven at a very definite

constant speed as the frequency of generated e.m.f is determined by that speed. The

latter is usually referred to as the synchronous speed for which reason these machines

are frequently called the synchronous generators.

Synchronous generators because of absence of commutator are comparatively simple

and possess several important advantages over the dc generators.


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Construction of Synchronous Machines:

Synchronous machine consists essentially of two parts namely the armature (or stator)

and the field magnet system.

Armature (or stator):

The armature is an iron ring, formed of laminations of special magnetic iron or steel

alloy having slots on its periphery to accommodate armature conductors and is knownas stator. The whole structure is held in a frame which may be of cast iron or welded

steel plate.

Figure 12

The open slots are more commonly used because the coils can be form-wound and

insulated prior to being placed in the slots giving least expenditure and most

satisfactory winding method this type of slots also facilitate in removal and

replacement of defective coils but this type of slots have disadvantage of distributing

the air gap flux in to branches or tufts which tends to produce ripples in the e.m.f

wave. The semi-closed type slots are better in this respect but do not permit the use of

formwound coils. Totally closed slots are rarely used.

Number of slots per pole per phase should be large to give sinusoidal generated e.m.f

in general the number of slots per pole per phase should be large to give sinusoidal

generated e.m.f. In general the no of slots per pole per phase is 3 to 4 for small

machines and more than 5 for large machines small machines may have integral slotwinding with enough chording. For large machines fractional slot winding is used and

so the number of slots per pole per phase may not be an integer.

The minimum tooth width should be such that the maximum flux density in it does

not exceed the limit of flux density in it does not exceed the limit of flux density in it

does not exceed the limit of flux density in teeth permissible to avoid saturation. The

depth of the slots and shape is such as to accommodate the required number of

conductors per slots for the rated voltage to be produced at the rated speed. Generally

depth is 4 to 6 times the width. If the depth is increased synchronous reactance in slot

increases core losses in teeth are larger and more excitation will be required for the

machine.

Field magnet system or Rotor:

The magnetic field required for the generation of alternating voltage is provided by

field magnets similar to those of a dc machine and these need to be supplied with

direct current this may be had from some external source, but so as to make the

alternator self contained and independent of other source of supply it is more usual to

install a small dc generator for this purpose. The generator is called the exciter and is

coupled to the engine or turbine driving the alternator.


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Figure 13

The exciter armature is connected directly to the alternator field winding, usually

without any kind of controlling resistance so that except for variations due to

temperature changes the resistance of the exciter load is constant. For the successful

operation of alternator it is necessary to be able to vary the exciting current over a

wide range from practically zero to the full output of the exciter, and this is achieved

by varying the resistance in exciter field circuit. For making the field current entirely

independent of the armature terminal voltage a small pilot exciter is designed to be

saturated at its terminal voltage, by reason of which its terminal voltage remains

sensibly constant at all loads. It is usually coupled mechanically to the main exciterand the two are often enclosed together in the same housing.

The field system of the alternator is rotated within the armature ring and is known as

rotor. The exciting current is supplied to the rotor through two slip-ring and brushes.

The polarities of the field produced is alternately north (N) and south (S).the power

rating of exciter is ordinarily 0.5 to 1% of power rating of the synchronous generator.

The voltage rating of the exciter is usually between 125 and 250 volt.

Recently brushless excitation system has been developed in which a 3-phase ac

exciter and a group of rectifiers supply to the alternator. Hence brushes, slip-rings and

commutator are eliminated.


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Warranty

1) We warranty the product against all manufacturing defects for 24 months from the

date of sale by us or through our dealers. Consumables like dry cell etc. are not

covered under warranty.

2) The warranty will become void, if

e) The product is not operated as per the instruction given in the learning material.

f) The agreed payment terms and other conditions of sale are not followed.

g) The customer resells the instrument to another party.

h) Any attempt is made to service and modify the instrument.

3) The non-working of the product is to be communicated to us immediately giving

full details of the complaints and defects noticed specifically mentioning the type,

serial number of the product and date of purchase etc.

4) The repair work will be carried out, provided the product is dispatched securely

packed and insured. The transportation charges shall be borne by the customer.


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List of Service Centers

Baroda

Flat No.A/1, Mudra Complex,

Behind Sudha Hotel, Ellora

Park, Baroda-390023 (Gujarat)

Tel: +91-0265-3089505

Fax : +91- 0265-3089506email : [email protected]

Guwahati

Avijit Roy Building, A.K. Dev

Road, Fatashil Ambari, Near

alaram Mandir,

Guwahati-25 Assam

Mobile: 09435144068email: [email protected]

Indore

94, Electronic Complex,

Pardesipura, Indore-452 010

Tel: 91-731-2570301/02,

4211100,

Fax: 91-731-2555643E-mail: [email protected]

New Delhi

First Floor, C-19, F.I.E.,

Patparganj Industrial Area,

Delhi-110092 (INDIA)

Ph: 011- 22157370, 22157371,

Fax: +91-011-22157369

email: [email protected]

Bangalore

202/19, 4th Main Street,

Ganganagar,

Bangalore - 560032

Ph.: +91-080-41285011

T.Fax: +91-080-41285022


Kolkata

AC-101, Prafullla Kanan, Near

Kestopur Bus Stop, Krishnapur,

Kolkata- 700059 (West Bengal)

Tel: +91 33-65266800

Mob: 9433029888


Mumbai

E Type, Bldg No. 5/1/3, Sector1,Vashi, Navi Mumbai-400703

Ph: +91-022-27826616,

65266616


Jaipur

Flat No. G-2, S-101, BhagatVatika North, Civil Lines,

Jaipur - 302006 (Raj.)

Mobile: 097998-10236

email:[email protected]

Lucknow

First Floor, 279/54/20/A,Chuhar Singh Colony, Pan

Dariba, Lucknow (U.P.)

Mobile: 09918670737


Hyderabad

Plot No. 24, Flat no. 203,

Laxmi Residency, Chandragiri

Housing Society, Trimulgherry

Secunderabad- 500015.

Ph:040-27740147,9247712763


Cochin/Kochi

C/o Pragalbha Valsan,Poriyama-

dathil house, ABMS Lane,

Asoka Road,Near Mathrubhumi,

Kaloor, Kochi - 682 017

Ph: 0484-2409441


Chandigarh

201, 2nd floor KMB Hospitality

Services, SCO 19, Near Kabir

Petrol Pump, Ambala-Zirakpur

Highway Zirakpur, Mohali-140603

Ph.: 0172-6530329

email:[email protected]

Pune

105/106, 1st floor, Ajinkyatara,

GaneshMala, Sinhgad Road,

Pune - 411030

Ph.: +91-020-24254244/55

Fax: +91-020-24254244


Chennai

Flat C, 1st Floor, Old No. 49

New No. 64, Bajanai Koil

Street, Sriram Nagar Extention,

Pallipattu, Chennai-600113

Tel: 044-43514212, 43514213


Orissa

Plot No-67 (1st Floor)

Aerodrom Area,Vimpur mouza

Near Vimpur Primary School

Bhubaneswar- 751020

Mobile: 09238307873

mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:email:[email protected]:email:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:email:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


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List of Accessories

1. Patch Cords.6 Nos.

2. Learning Material CD1 No.

machines lab 2 mnual

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