Lab Experiment 01

Electrical hazards and laboratory Safety

Object: To be familiar with the Electrical hazards and Laboratory Safety.

Theory:People’s dependence on electricity is undeniable. It is the main part and need of our modern world but it is very dangerous for us. Electricity can kill or severely injure people and cause damage to property. These hazards can be fortunately prevented or minimized through proper awareness and application of effective ways.

The main hazards of working with electricity are:

Electric shock and burns from contact with live parts. Injury from exposure to arcing, fire from faulty electrical equipment or

installations.

Explosion caused by unsuitable electrical apparatus.

Electrical hazards Safety:

To protect from electrical hazards, there are some rules which are to be followed:

Ensure that, workers know how to use the electrical equipment safely. Make sure enough sockets are available. Check that socket outlets are not overloaded by using unfused adaptors as this can cause fires.

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Ensure there are no trailing cables that can cause people to fall.

Switch off and unplug appliances before cleaning or adjusting them.

Make sure anyone working with electricity has sufficient skills, knowledge and experience to do so. Incorrectly wiring a plug can be dangerous and lead to fatal accidents or fires.

Stop using equipment immediately if it appears to be faulty–get it checked by a competent person.

Cables, plugs, sockets and fittings must be robust enough and adequately protected for the working environment. Ensure that machinery has an accessible switch or isolator to cut off the power quickly in an emergency.

In wet surroundings, unsuitable equipment can become live and make its surroundings live too. Fuses, circuit-breakers and other devices must be correctly rated for the circuit

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they protect.

Laboratory Safety:There are some laboratory safety rules to protect from any danger:

Read labels carefully. Never work alone in laboratory. Never do unauthorized experiments. Don’t take shortcut, always follow the rules. Use equipments in a right way. Don’t eat, drink or smoke while working in laboratory.

If any piece of equipment fails, immediately inform the lab assistant. Report any unsafe condition such as broken power cables to lab assistant.

Extra book, purse etc should be kept away from equipment to prevent it from overheat.

Don’t use any equipment unless you are trained.

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Review Question

Q.1. How to respond in the event of an electrical hazard?

______________________________________________________________________________________________________________________________________________________________________ ___________________________________________________________________________________

Q.2.What are the types of electrical injuries?

______________________________________________________________________________________________________________________________________________________________________ __________________________________________________________________________________

Q3. How safety rules protect us from danger?

_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Lab experiment 02

Electrical Measuring Instruments

Object: To be familiar with different electrical measuring instruments.

Equipments:

Ammeter Voltmeter Wattmeter Ohmmeter Multimeter Power Factor meter Frequency meter Clamp on meter

Theory:

Ammeter:

A device that measures current is called an ammeter. The current to be measured must pass directly through the ammeter. This means that the ammeter is connected in series in the circuit. If it is connected across the load so it will short out the load. It has a low resistance coil connected in parallel hence named shunt resistor.

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Voltmeter:

A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit. It is connected in parallel with a circuit to measure a voltage drop across it. It has a high resistance coil connected in series hence named multiplier.

Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of analog to digital converter. General purpose analog voltmeters may have an accuracy of a few percent of full scale, and are used with voltages from a fraction of a volt to several thousand volts. 

Wattmeter:

Electric power is measured by means of a wattmeter. This instrument is of the electro-dynamic type. It consists of a pair of fixed coils, known as current coils, and a movable coil known as the potential coil.

The fixed coils are made up of a few turns of a comparatively large conductor. The potential coil consists of many turns of fine wire. The current coil (stationary coil) of the wattmeter is connected in series with the circuit (load), and the potential coil (movable coil) is connected across the line.

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Ohmmeter:

Ohmmeter, instrument for measuring electrical resistance, which is expressed in ohms. In the simplest ohmmeters, the resistance to be measured may be connected to the instrument in parallel or in series. If in parallel (parallel ohmmeter), the instrument will draw more current as resistance increases. If in series (series ohmmeter), current will decrease as resistance rises. For high resistances, the scale is usually graduated in mega ohms (106 ohms), and the instrument is called a megohmmeter or “megger.”

Multimeter:

A multimeter or a multitester, also known as a VOM (Volt-Ohm meter) is an electronic measuring instrument that combines several measurement functions in one unit. A typical multi-meter would include basic features such as the ability to measure voltage, current, and resistance. Analog multi-meters use a micro ammeter whose pointer moves over a scale calibrated for all the different measurements that can be made. Digital multi-meters (DMM, DVOM) display the measured value in numerals, and may also display a bar of a length proportional to the quantity being measured. Digital multi-meters are now far more common but analog multimeters are still preferable in some cases, for example when monitoring a rapidly varying value.

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Power factor meter:

AC power flow has three components: real power (also known as active power) (P), measured in watts (W); apparent power (S), measured in volt-amperes (VA); and reactive power (Q), measured in volt-ampere reactive (VAR).The power factor (COSӨ) is defined as: the ratio of the real power flowing to the load to the apparent power in the circuit. So this instrument is used to measure the power factor.

Frequency meter:

A frequency meter is an electronic instrument that displays the frequency of a periodic electrical signal.

It is a device for measuring the repetitions per unit of time (customarily, a second) of a complete electromagnetic waveform.

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Clamp-on-meter:

Clamp meters are very convenient testing instrument that permits current measurements on a live conductor without circuit interruption. When making current measurements with the ordinary multimeter, we need to cut wiring and connect the instrument to the circuit under test. Using the clamp meter, however, we can measure current by simply clamping on a conductor. One of the advantages of this method is that we can even measure a large current withoutshutting off the circuit being tested.

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Review Question

Q.1.Why ammeter can’t be connected in parallel?

_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q.2. In what manner, ohmmeters are connected to measure the resistance?

_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q. 3.How a clamp meter differs from a multimeter?

_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Lab Experiment 03

Earthing Concepts

Object: To be familiar with the concept of Earthing.

Theory:

Earthing:

In electrical engineering, ground or earth is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth.

Earthing a tower/equipment means connecting that tower /equipment to general mass of earth by means of an electrical conductor. Connection to earth is achieved by embedding a metal plate or rod or conductor in earth. This metal plate or rod or conductor is called as "Earth electrode".

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Objectives of earthing:

Main Objectives of Earthing systems are:

i. Provide an alternative path for the fault current to flow so that it will not endanger the user.

ii. Ensure that all exposed conductive parts do not reach a dangerous potential.iii. Maintain the voltage at any part of an electrical system at a known value so as to prevent

over current or excessive voltage on the appliances or equipment.

Types of Earthing:

System Earthing:

This is primarily concerned with the protection of electrical equipment by stabilizing voltages with respect to ground.

This is basically achieved by earthing the neutral of the supply system. just connecting the neutral point of transformer or generator to earth.

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Benefits of System Grounding:

System grounding is the intentional connection of the neutral points of transformers, generators and rotating machinery to earth ground to provide a reference point of zero volts, which offers many advantages over an ungrounded system including:

Reduced magnitude of transient over-voltages Simplified ground fault location Improved system and equipment fault protection Reduced maintenance time and expense Improved lightning protection Reduction in frequency of faults

Equipment Earthing:Equipment Earthing is the earthing associated with non-current carrying metal work & is essential for the security of human life and property.

Step Potential: Voltage between the feet of a personWhen current is flowing from the tower to the earth ground, the ground potential rises at the tower and a voltage gradient will occur based on the resistivity of the soil, resulting in a potential difference between two points on the ground. This is called a Step Potential as it can cause voltage between a person’s feet.

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Touch Potential: Voltage between energized object and feet of a personIf the ground connection between the tower and the soil is high resistance (common with some soil conditions), the tower itself (and any conductive item touching the tower) can be energized. Touch potential is the voltage between the energized object and the feet of a person in contact with the object.

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Review Question

Q.1.Why there is a need to increase the resistivity of soil?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q.2.What is the difference between step potential and touch potential?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q. 3.Which type of earthing is required for human safety?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Lab Experiment 04

Standard symbols on dial of measuring instruments

Object: To familiarize with standard symbols provided on the scale of various electrical measuring instruments.

Equipments:

Ammeter Voltmeter

Theory:

Before using any measuring instrument it is necessary to be familiarized with the symbols provided on the scale of the measuring instrument. The manufacturer provides various symbols on the scale of measuring instruments, The symbols that are provided on the scale of measuring instruments give an idea about the manufacturer’s logo ,Accuracy class (0,05,0,5,1,2,5) of instrument, Measured units [A(ampere),V(voltage) and W(watts)],Type of measurement (AC/DC),Test Voltage and Measuring system. The most common type of symbols seen on the scale of measuring instruments are:

1.Manufacturer’s Name or Logo: This symbol simply indicates the name or logo of the company that has manufactured the instrument.

2. Serial No : This symbol simply indicates the serial No of a particular instrument.

3.Measured Unit: This symbol indicates that what kind of electrical quantity can the instrument measure either voltage,current or power etc.

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4.Type of Measuring quantity: This symbol simply indicates that what type of electrical quantity can the insrtument measure either AC or DC:

5.Accuracy class: This symbol indicates that how much precisely or accurately a measuring instrument can measure the electrical quantities:

6. Test Voltage: This symbol defines the isolation of a measuring instrument between it’s casing and measuring system:

test voltage of 500v test voltage of 3Kv

7. Type of Measuring system: This symbol indicates what type of Measuring system is present within the Instrument (Moving iron type, Electrodynamometer type, Electrostatic type etc):

Moving iron type.

PMMC Type.

Electrodynamic type.

Electrostatic type.

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Rest of the important symbols are shown in the following fig:

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The following figs show the ammeter and voltmeter bearing the standard symbols:

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Review Questions:

Q.1.What does the symbol on dial of meters specify?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q.2.What is difference between instruments having vertical dial and horizontal dial?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q. 3.Which symbols should be given by the manufacturer so that we use the instrument with complete command?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Lab Experiment 05

Power Measurement

Object: Measurement of AC Power by wattmeter.

Equipments:

Power Supply Watt Meter. Resistive Load Connecting Wires.

Theory:

Wattmeter:

The wattmeter is a measuring instrument use to measure electric power. The wattmeter consists of a Pressure Coil and Current Coil. The current coil of the Instrument carries the load current, while the pressure coil carries the current proportional to, and in phase with the voltage. The deflection of the wattmeter depends upon the current in these two coils and upon the power factor. Inductance in the pressure coil circuit should be divided as far as possible, since it causes the pressure coil current to lag behind the applied voltage. A high non-inductive resistance is connected in series with the pressure coil in order that the resultant of the coil itself shall be small in comparison with the resistance of the whole pressure coil circuit taken by the pressure coil shall be small.

Connections:

Load

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~ v

Watt meter

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Procedure:

Connect the voltmeter in parallelwith the source. Connect the wattmeter in parallel with the load. Now vary the load & measure the Power in watts.

Observation:

I V P

Review Question

Q.1. How many coils are used in Wattmeter to calculate Power?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q.2. On what parameters the deflection of wattmeter depends?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Lab Experiment 06

Power Factor Measurement

Object: Measurement of Power Factor

Equipments:

Power Supply Voltmeter. Ammeter. Watt Meter. Resistive Load Inductive Load.

Theory:

In AC circuits, the power factor is the ratio of the real power that is used to do work and the apparent power that is supplied to the circuit. The power factor can get values in the range from 0 to 1.When all the power is reactive power with no real power (usually inductive load) - the power factor is 0.When all the power is real power with no reactive power (resistive load) - the power factor is 1

Connections:

Load

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~ VVVv

Watt meterA

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Procedure:

First connect the ammeter in series with the source Connect the voltmeter in parallel with the source. Now connect the wattmeter with the load. Now vary the load and measure the Power factor.

Observation:

FOR RESISTIVE LOAD

I V S P COSɵ

FOR INDUCTIVE LOAD

I V S P COSɵ

Review Question

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Q.1.Why it is necessary to calculate the power factor?

_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q.2.What happens to power factor meter when a capacitive load is connected to it?

_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q. 3. Where the wattmeter is connected to system in order to calculate power factor?

_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Lab Experiment 07

Phase sequence indication by two bulb method

Object: To determine the phase sequence of 3 phase supply using two bulb method.

Equipments:

3 phase supply module. Two bulbs of 1200 ohms. One capacitor of 1200 ohms. Connecting wires.

Theory:

The pattern in which a phase voltage of the 3 phase supply follows the previous phase is called phase sequence. The phase sequence is determined at the generating station by the alternator’s direction of rotation. It is important to determine the phase sequence of the 3 phase supply for many reasons; the important reason is that it determines the rotation of 3 phase motors. In this practical we will determine the phase sequence of 3 phase supply by two bulb method:

Two Bulb Method:

Consider a 3 phase load consisting of two lamps of (1200 ohms) and a capacitor of 1200 ohms connected with 3 phase supply in star connection as shown in the fig:

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As shown in the above fig 2 lamps of 1200ohms are connected with phase a and b whereas the capacitor of 1200ohms is connected with phase c, we have assumed a balanced 3 phase supply having voltage vectors Vab=Vα0ᵒ, Vbc=Vα-120ᵒ ,Vca=Vα120ᵒ than by ohms law:

Ia = Vac /R-jXc+Vab /2R = Vα300ᵒ/1697α-45ᵒ +Vα/2400= Vα345/α1697 +Vα/2400

Ia= V/1200(1.414α345ᵒ+0.5α)=V/1200(1.866-j0.365)=1.901Vα-11.06/1200 A

Ib= Vbc/R-iXc + Vba/2R =Vα-120ᵒ/1697α-45ᵒ + Vα180ᵒ/2400= Vα-75ᵒ/1697 –Va/2400

Ib= V/1200(1.414α-75 – 0.5α)= 1.3716V-95.64ᵒ/1200 A

Ic= Vca/R-jXc +Vcb/R-jXc= Vα120ᵒ/1697α-45ᵒ + Vα60ᵒ/1697α-45ᵒ

Ic=Vα165ᵒ/1697+Vα105ᵒ/1697=V/1200(1.414α165ᵒ+1.414105ᵒ)

Ic= V/1200(-1.732+j1.732)=2.449V135ᵒ/1200 A

So as indicated by above mathematics that current flowing through lamp at phase a is greater therefore lamp at phase a will glow brighter and current flowing through lamp at phase b is small therefore the lamp at b will glow dim, the phase sequence according to above results is given by Bright dim and capacitor or ABC and if the phase lamp at phase b was bright and lamp at phase a was dim than the phase sequence would be ACB.

Procedure:

Take a 3 phase load 2 lamps of 1200 ohms and a capacitor of 1200 ohms. Connect the 3 phase load with 3 phase supply module in star connection as shown above. Do not connect the neutral conductor of loads with the supply leave it floating. Now check if lamp at Phase A is bright and Lamp at phase B is dim than the phase

sequence will be ABC which is proved above.

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Review Question

Q.1.What is Phase sequence?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q.2. Why Phase sequence is essential to determine?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q3. Phase Sequence measurement by two bulb method are star connected or delta connected?

_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Lab Experiment 08

Energy Meter Calibration

Object: Calibration of single phase ENERGY METER.

Equipments:

Circuit board. Energy meter. Stop watch. Resistive Load.

Theory:

Single Phase Watt-Hour Meter

Induction type meters are the most common form of AC meters. These meters measureElectrical energy in kilowatt-hour. The principle of these meters is practically the same asthat of the induction watt meters. In these meters magnet and spindle is used.The watt-hour meter consists of two main coils:(i) Pressure coil.(ii) Current coil.The pressure coil is attached to the source while the current coil is attached to the load. InKilowatt-hour meter the breaking magnet is provided to control the speed of the disc. TheBreaking magnet decreases the breaking torque.

Features:

They are induction type of instruments. They are light in weight. Torque to weight ratio is very small. Temperature change has very small effect on the instrument.

Calibration:

Comparison of an instrument which has error with some standard instrument is called calibration of an instrument.

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Accuracy Class:It is limiting error, means how much percentage of error is tolerable for full scale deflection. .

Measured Energy:The readings of the energy meter are measured energy.

Calculated Energy:Active power consumed by some load in particular interval of time is called Electrical Energy (Calculated energy).

E = P x t

OBSERVATIONS:

Measured energy(Em)

Power (P) Time (t) Calculated Energy (Ec)

Calculated Energy (Ec) = P x t

% Error = Em−EcEm

∗100

Note: -ve Sign shows speed of a meter is very small. +ve Sign shows that speed of a meter is very fast

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Review Questions:

Q.1.How many coils are used in Induction Type Energy Meters?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q.2. What do you mean by calibration of Energy meter?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q. 3.How creeping error occurs in Energy meter?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Lab Experiment 09

Three phase power measurement by two wattmeter Method

Object:  To measure the power of 3 phase load by two wattmeter method

Equipment:

Three phase power supply Three phase load Connecting wire Three watt meters (voltmeter-ammeter set)

Theory:

In this method of power measurement we measure the power of load by two watt meter not by single watt meter this is because we have three phase supply and three phase load. First of all we energize three voltmeters by individual three single phase supply then connect three ammeters in series with the load. Finally we will have line voltage at load in order to maintain and balance there should be line voltage in voltmeter too so we will connect voltmeters in delta connection. for the measurement purpose we will consider two watt meter .in 3 of wattmeter two are giving very close readings and only one that is slightly different so well consider only two closed reading meters

Fig#01

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Fig#02

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Review Questions:

Q1. Why we use two watt meter to measure 3phase load power?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q2. What readings does three watt meter gives?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q3. Can we use single watt meter to measure 3phase load power?

_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Lab Experiment 10Instrumentation Transformers

Object: To familiarize with Instrumentation Transformers

Equipment:

Current Transformer Potential Transformer

Theory:

Instrumentation transformers are special type of transformers use for measurement of the voltage, current, power and energy. These transformers are used in conjunction with relevant instruments such as: Ammeters, Wattmeter, Voltmeters and Energy meters.

It is used for the following two reasons as:

1. To insulate the high voltage circuit from the measuring circuit in order to protect the measuring instruments from burning

2. To make it possible to measure the high voltage with low range voltmeter and high current with low range ammeter.

These instrument transformers are also used in controlling and protecting circuits, to operate relays, circuit breakers etc. The workings of these transformers are similar as that of ordinary transformers.

Such transformers are of two types:

1. Current Transformer (or Series Transformer)

2. Potential Transformer (or Parallel Transformer)

CURRENT TRANSFORMER:

A current transformer is an instrument transformer which is used to measure alternating current of large magnitude by stepping down by transformer action. The primary winding of CT is connected in series with the line in which current is to be measured and the secondary is connected to the ammeter.

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The secondary winding has very small load impedance which is the current coil of ammeter. The primary side has a few number of turns and the secondary side has large number of turns. The primary winding carries a full load current and this current is stepped down to a suitable value which is within the range of ammeter.

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POTENTIAL TRANSFORMER:

These are used to measure alternating high voltage by means of low range voltmeters or for energizing the potential coils of wattmeter and energy meters. These types of transformers are also used in relays and protection schemes.

The high voltage which is to be measured is fed to the primary of PT, which is stepped down and is measured by a low range voltmeter on the secondary. The turns of primary side are more than secondary side. The turn ratio of transformer is so designed which keep secondary voltage 110 V when full rated voltage is applied to the primary side.

The principle of operation of potential transformer is same as that of power transformer.

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Review Question

Q.1.What is the purpose of Instrument Transformer?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q.2.Why Current Transformer is called Series Transformer?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q. 3.Why Current is greater at secondary side of the Potential Transformer?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Lab Experiment 11

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Introduction to Tachogenerator

Object: To be familiar with the use of Tachogenerator

Equipments:

Tachogenerator Motor(different types) Power supply

Theory:

Tachogenerator is originally DC generator but with very less power range. i.e it cannot be loaded, only it’s output is used for metering. The output of tachogenerator is multiplied by the manufacturer standard voltage to rpm ratio. In the final rpm of the machine to be measured is achieved.

Procedure:

We use two tachogenerator of each different type and we see different reading of revolution or speed.

Techogenerator No#1

Dynamo Tachometeric plus dc shunt motor We use this tachogenerator to find the speed (rpm) of dc shunt motor. We have given variable dc supply to dc shunt motor. The shaft of dc shunt motor is coupled with tachogenerator. As motor starts to rotate, tachogenerator will give the output on the terminals. But this output is not actual rpms of the motor. This output (volts) is multiplied by the standard ratio then after calculation there will be actual rpm. In Dynamo Tachometeric tachogenerator we get two outputs; viz. 6volt/rev and 2mv/rev. as we increase dc supply voltage, speed of the motor increases and output of the tachogenerator also increases, increasing the final result.

Readings:

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S.No. Dc supply(V)

Techogenerator (output)

Ratio Calculations Actual RPMs

Fig: Dynamo Tachometeric plus DC Shunt Motor

Tachogenerator No#2

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Edibon Tachogenerator with Single phase Induction Motor:

Here Edibon tachogenerator is use to find the speed (rpm) of single phase capacitor start capacitor run A.C motor (single phase induction motor).We have taken following different readings at different applied voltage to the motor.

Readings:

S.No. AC supply(V)

Tachogenerator (output)

Ratio Calculations Actual RPMs

Fig no:2 Edibon tachogenerator with single phase induction motor

Review Questions:

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Q.1.What is tachogenerator?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q.2 What is the difference b/w tachogenerator and hand held tachometer?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Q. 3. What is the working principle of tachogenerator?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Lab Experiment 12Control Room of Grid

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Object: To familiarize the control room of 132KV grid station

Equipment:

Protection Relays Bus Bar Panel Circuit Breaker Control Panel Tape Changer Control Panel

Theory:

Control Room:

Control room of 132KV grid distribution system is consist of feeders belong to different areas or regions of a city. Each distribution feeder consists of the circuit breakers, switchgears and electrical measuring instruments which aware us about the rating of power system at every instant. From the instrumentation and measurement point of view we’ll concerned with the meters installed in each distribution box of a feeder.

Protection Relays:

A relay is devices that detect the faults and direct the circuit breaker to isolate the faulty part/equipment from the system. A relay perform three functions

Sensing Comparing Tripping

1. Sensing: Relay first sense the fault and respond to change if any in the currents passing through it

2. Comparing: It compares the current value passing through it to the predefined value which is assigned to relay. It only reacts at the instant when current passing through it is higher than the pre-defined value.

3. Tripping: If current passing through it will be greater than the pre-defined range of relay then it sends information to circuit breaker to be tripped.

Bus bar Panel:

Bus Bar voltage is constant supplier conductor. These are the nerve centers of power system where various circuits are connected together. This is simplest system to connect various

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generators, transformers together. All the generators and transformers are connected to bus bars with the help of circuit breakers and isolators. Bus bars are important element which requires the immediate attention of protection and inspection staff for safeguard against any possible faults. It can’t be maintained or cleaned without switching off the whole system. If fault occur at bus bar whole the arrangement is to be switched off.

Circuit Breaker Control Panel:

An electrical circuit breaker panel is the main distribution point for electrical circuits in your

home. It usually provides between 100 and 200 amps of power to your home, depending on your

home’s load demand. Power comes in to your home from the utility company, through a service

entrance. It flows through an electrical meter, through an electrical disconnect and then to the

main breaker in your electrical panel.

Electrical Service Panel

Residential Electrical

Breaker Panel

Circuit Breaker

Electrical House Wiring

The main breaker is located at the top or bottom of two rows of breakers, depending which way

the panel is mounted. The main breaker is marked with the value of protection (like 100 amps)

on the breaker handle. This breaker is either factory mounted or can be added by either bolting it

in or snapping it into place

A 100-amp service is the minimum size service required for a new home. In older homes, many

were equipped with 60-amp services and some, believe it or not, only had “A” phase feeding the

entire house.

Other Parts of a Circuit Breaker Panel:

The breaker panel also comes equipped with a neutral buss and a grounding bar. The enclosure is

sealed off for protection by a panel cover and is usually mounted with screws. It features a panel

access door that allows you to access the breakers without removing the cover.

Inside the door is a panel index. This is where you will write down what the circuits are feeding

for easy reference. The entire breaker panel is usually gray in color and is made of metal. It can

either be surface mounted or installed within a wall for a neater, more hidden look.

Tap Changer Control Panel:

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A tap changer is a connection point selection mechanism along a power transformer winding that allows a variable number of turns to be selected in discrete steps. A transformer with a variable turns ratio is produced, enabling stepped voltage regulation of the output. The tap selection may be made via an automatic or manual tap changer mechanism. If only one tap changer is required, manually operated tap points are usually made on the high voltage (primary) or lower current winding of the transformer to minimize the current handling requirements of the contacts. However, a transformer may include a tap changer on each winding if there are advantages to do so. For example, in power distribution networks, a large step-down transformer may have an off-load tap changer on the primary winding and an on-load automatic tap changer on the secondary winding or windings. The high voltage tap is set to match long term system profile on the high voltage network (typically supply voltage averages) and is rarely changed. The low voltage tap may be requested to change positions multiple times each day, without interrupting the power delivery, to follow loading conditions on the low-voltage (secondary winding) network. To minimize the number of winding taps and thus reduce the physical size of a tap changing transformer, a 'reversing' tap changer winding may be used, which is a portion of the main winding able to be connected in its opposite direction (buck) and thus oppose the voltage. Insulation cost reduction requirements place the tap points at the low voltage end of the winding. This is near the star point in a star connected winding. In delta connected windings, the tappings are usually at the center of the winding. In an autotransformer, the taps are usually made between the series and common windings, or as a series 'buck-boost' section of the common winding. Some designs utilize an internal series voltage step-up transformer to reduce currents on the tap changer contacts.

Off-circuit designs (NLTC or DETC)

In low power, low voltage transformers, the tap point can take the form of a connection terminal, requiring a power lead to be disconnected by hand and connected to the new terminal. Alternatively, the process may be assisted by means of a rotary or slider switch.

Since the different tap points are at different voltages, the two connections cannot made simultaneously, as this would short-circuit a number of turns in the winding and produce excessive circulating current. Consequently, the power to the device must be interrupted during the switchover event. Off-circuit or de-energized tap changing (DETC) is sometimes employed in high voltage transformer designs, although for regular use, it is only applicable to installations in which the loss of supply can be tolerated. In power distribution networks, transformers commonly include an off-circuit tap changer on the primary winding to accommodate system variations within a narrow band around the nominal rating. The tap changer will often be set just once, at the time of installation, although it may be changed later during a scheduled outage to accommodate a long-term change in the system voltage profile.

On-load designs (OLTC)

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Also called on circuit tap changer or On Load Tap Changer (OLTC)

For many power transformer applications, a supply interruption during a tap change is unacceptable, and the transformer is often fitted with a more expensive and complex on-load tap-changing (OLTC, sometimes LTC) mechanism. On-load tap changers may be generally classified as mechanical, electronically assisted, or fully electronic.

Review Questions:

Q.1. What do you mean by control room of grid station?

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Q.2.What is the purpose to install the battery room in the grid station?

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Q. 3. Why Protection relays are used in Grid station?

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Lab Experiment 13

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Oscilloscope

Object: Introduction to oscilloscope

Equipments:

Oscilloscope

Introduction:

An oscilloscope is a device that converts electrical signals (voltage, current) into visual one. This device consists of controlling parts, screen and channels (two). Its screen is of two dimensional X and Y graph plotted where x represents the time while y is considered as any quantity to be measured. Screen consist of equally spaced divisions for analyzing and varying quantities ( volts) with respect to divisions.

Theory:

The purpose of an oscilloscope is to measure a voltage that changes with time and show it in a graphical format

This is two dimensional plane where horizontal axis is function of time and vertical axis is function of voltage and we can say oscilloscope visualize time varying signals.

Oscilloscope: Screen

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Signature of Lab Engr. Score: Date:

A sine wave is shown in the oscilloscope screen. Notice that the screen has ruled divisions both

horizontally and vertically. The axes can be scaled.

For example: one horizontal division is of 5 volts and vertical division is of 2 seconds.

Oscilloscope: Control Panel

• The section to the right of the screen contains the controls necessary to adjust how the waveform is displayed on the screen.

• The controls allow you to alter the sweep time, amplitude, and triggering method.

Oscilloscope: Input Channels

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• • This area is broken into two parts

– Left Half for Channel 1 (X)

– Right Half for Channel 2 (Y)

• In the center is a switch that determines which channel will serve as the input to the scope: 1, 2, Dual or Add.

Equipment: Function Generator

• Purpose: Produces waves of different

Shapes (sinusoidal, square.)

Amplitude Frequency

The Setup

In this section, we will power on the oscilloscope and set it up to display a signal connected to the CH1 input.

Turning on the Oscilloscope:

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• Press the POWER button located below the bottom right corner of the Oscilloscope’s screen.

• Set the Channel Mode to CH1.

• Set the Trigger Mode to AUTO.

• A green line or dot should appear on the screen.

If not, try adjusting the Intensity or Position dials

Channel Mode Switch:

• The oscilloscope is capable of measuring voltages from two different sources.

• The channel mode switch is used to alternate between these sources.

• For this lab, we will be using Channel 1, so set the switch to the CH1 position.

Cables:

• We will use three types of connecters in this lab.

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Set Trigger ToAuto

Set Mode to CH1Press Power

– BNC

– Banana

– Mini-Grabber

Making First Connection:

• Obtain a BNC cable, Mini-Grabber attachment and connection them together.

• Connect the free end of the BNC cable to CH1 on the oscilloscope

Time Per Division Dial:

• Find the Time/Div dial on the oscilloscope. This dial controls the amount of time per centimeter division.

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• Adjust to dial to 2 milliseconds per centimeter.

Horizontal Position:

Adjust the Position dial for Channel 1 to center the horizontal line

Adjusting the Display:

• If the display is difficult or out of focus, the Intensity and Focus dials can be used to adjust it.

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• The INTEN dial controls the brightness of the line.

• The FOCUS dial controls the sharpness of the line.

• Take a moment to adjust each one and notice the difference.

At this point:

• The channel mode should be set to 1.

• The TIME/DIV should be set to 2mS per centimeter.

• A BNC cable should be connected to the channel 1 input. The other end should have a free Mini-Grabber connection.

• The Trigger Mode should be set to AUTO.

• The Oscilloscope should be ON.

• The intensity and focus should be adjusted so the line is clear to see.

• The channel 1 position dial should be adjusted so that the green line is centered on the screen.

Measuring an AC signal

In this section, we will use the built-in FUNCTION GENERATOR to create an AC signal to measure with the oscilloscope

Measuring a Time Varying (A.C.) Voltage:

• Look at the function generator built into your Oscilloscope.

• This device produces a voltage that varies over time.

• In the upcoming slides we will exam each of the controls that allow us to shape the output.

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Built In FunctionGenerator

Function Generator Controls: Wave Shape:

• An important part of a function generator is the shape of the wave it creates.

• This function generator can produce a

– Square Wave

– Triangle Wave

– Sine Wave

• Press the FUNC key to change until the light below the Sine wave is lit.

• (Note: The Oscilloscope must be on in order to change the this option.)

Function Generator Controls: Frequency Range:

• This generator allows you to change the frequency (Cycles per Second) of the output wave.

• There are two main settings:

– Range/Order of Magnitude

– Scaling Factor

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• First, set the range to 1K (1 kilohertz) by pressing the RANGE button until the light below 1K is on.

• Then, turn the frequency dial (Scaling Factor) so it points straight up. This represents a Scaling Factor of 1.

• Turning the dial to the left will reduce the output frequency and to the right will increase it.

Function Generator Controls: Amplitude Dial:

• Another 2 Parameter Control

– DC-Offset (Inner Dial)

– Amplitude (Outer Dial)

• Adjusting the outer dial

– Clockwise will increase the amplitude.

– Counterclockwise will decrease the amplitude.

• Turn the inner dial until it points straight up.

• Turn the outer until it points straight up.

Making the Connection:

• Locate the Function Generator’s Output.

• Using a B.N.C. Cable, Connect the Function Generator’s Output to the CH1 Input.

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• Set the Volts/Division dial to 2. The inner dial should be turned fully clockwise.

• Change the AC-GND-DC switch to AC.

• Use the Position dial to raise or lower the image until it is centered on the screen.

• The Time/Division dial corresponds to the amount of time in each division along the X-direction.

• Set this dial to 0.5ms.

• If it isn’t already, turn the SWP. VAR. dial to CAL

Triggering:

• Now we need to tell the scope when to display the signal.

• Electric signals change much faster than we can observe, so we must tell the Oscilloscope when to refresh the display.

• We accomplish this by setting a Triggering Level.

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Review Question

Q.1.How many channels are there in oscilloscope?

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Q.2. What is the use of Function Control Generator of Oscilloscope?

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Q. 3. What type of cables are used to provide input to Oscilloscope?

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