# EEE Department Power systems lab manual

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EEE Department

Power systems lab manual

Experiment no:1 Characteristics of IDMT over current relay Aim: To study the Operation of a Non- Directional (I D M T relay) and plot the inverse time current characteristics.

Apparatus:

Non-Directional Over current relay --1 no

Time Totalizer

--1 no

Fault creation Panel

--1 no

Digital Ammeter

--1 no

Theory:

IDMT relay is inverse definite minimum time relay. It is one in which Time of operation is inversely proportional to magnitude of fault current near pickup value and becomes substantially constant slightly above the pickup value of the Relay. Fault current and measure relay operation time is used to conduct the experiment. Values recorded for various TSMs and PSMs. Characteristics studied with the help of a graph and correlated with theory.

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EEE Department
Circuit Diagram:

Power systems lab manual

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EEE Department

Power systems lab manual

Procedure:-
1. Switch ON the MCB. 2. Initially rotor switch should be in OFF position. 3. Now set the described fault current by using the current source. For that switch
ON the rotor switch and move the current till the described fault current is indicated in the ammeter. 4. Now move the rotor switch is OFF position and press the green button. Note down the time in seconds after relay operated. 5. Repeat the same procedure for various T.S.M and P.S.M 6. Plot the graph between time take for relay to operate Vs P.S.M for various T.S.M.
Precautions:-
1. Disc must be stationary before applying fault current. 2. TSM setting must be changed with due care.

PSM =

TSM =

SNO.

Fault Current

.

Time of operation

Expected graphs:

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EEE Department

Power systems lab manual

Result:
Conclusion:
Discussion questions: 1. Why CT is required in this experiment? 2. Can we design the experiment without Current Injection Unit? 3. What is TSM & PSM and why different TSM & PSM? 4. Identify different terminals of the relay and explain their use. Write them in your record.

Anurag college of Engineering, Aushapur

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EEE Department

Power systems lab manual

Experiment no:2
Differential Protection on Single Phase Transformer Aim: To study the differential protection scheme for a single phase transformer with unequal turn’s ratio
Apparatus:
Single phase transformer, Current transformer, Single phase variac, Suitable ammeters and over current relay.
Theory: A Differential relay responds to vector difference between two or more similar electrical quantities. From this definition the Differential relay has at least two actuating quantities say 1-1 and 2-1. The two or more actuating quantities should be same.
Ex: Current/Current.
The Relay responds to vector difference between 1-1 &2-1which includes magnitude and /or phase angle difference. Differential protection is generally unit protection. The protection zone is exactly determined by location of CTs. The vector difference is actuated by suitable connection of CTs or PTs secondaries. Most differential relays are current differential relays in which vector difference between current entering the winding & current leaving the winding is used for relay operation. Differential protection is used for protection of Generators, Transformers etc. Internal fault is created using switch and relay operation observed for various TSMs. Relay operations for external faults can also be studied.

Anurag college of Engineering, Aushapur

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EEE Department
Circuit Diagram:

Power systems lab manual

Procedure:
1. Make the connections as shown in fig.1 2. Select the transformation ratio 2:1 and the C.T. ratios of 2:1 and 4:1 Set PSM of the relay equal to 0.5. 3. Apply rated voltage 230V to primary by varying the variac. 4. Without applying fault, note down different meter readings. 5. By applying load observe whether the relay is operating of not . 6. Now close the switch so as to create an internal fault. 7. Note the various ammeter readings when relay operates. 8. Create internal fault at different loads and note the various meter readings. 9. Now create an external fault and observe whether the relay operates or not, note the various meter readings.

Anurag college of Engineering, Aushapur

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EEE Department

Power systems lab manual

Observation:- For Internal Fault

S.No

I Primary

I Secondary

I relay

I fault

Relay operates/doesn’t operate

For External Fault

S.No

I Primary

I Secondary

I relay

I fault

Relay operates/doesn’t operate

Result:
Conclusion:
Discussion Questions: 1. Why identical CTs are required in this scheme. 2. How would you take into account CT imbalances? 3. What do you understand by internal fault?
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EEE Department

Power systems lab manual

Experiment no:3 Characteristics of Microprocessor Based Over Voltage and Under Voltage Relay Aim:
Apparatus:
Theory:
Panel Layout

CIRCUIT DIAGRAM
MV12
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EEE Department

Power systems lab manual

Procedure: (1) Switch on the MCB.

(2) Initially Rotary switch should be in OFF Position.

3) Now to set the desired fault voltage we will be using voltage source. For that switch ON the Rotary switch marked as voltage set and move the voltage source till the desired fault voltage is indicated on the voltmeter, it is quit possible that while adjusting the fault voltage the trip LED will start blinking at a frequency of one second and will continue till relay trips It will stop blinking and will remain permanently ON as soon as relay trips. Then you have to reset the relay by pressing reset button. The Rotary switch must be brought in OFF position.

(4) Now the desire Fault voltage is SET. Now move the Rotary Switch on OFF position and press the green push button and timer counting will start and counting will STOP once the relay is operated. Note down the time in seconds.

(5) Now for various T.M.S. (Time Multiplier Setting) and P.S.M. (Plug Setting Multiplier) the time taken by the relay to operate at various fault voltage may be note down.

(6) Now plot the graph between time take for the relay to operate Vs Plug Setting Multiplier at various T.M.S.

Tabular Column

Plug

Setting = Voltage

TMS= 1.0

0.8 TMS=

S NO

Applied Voltage Volts

Operating Time Sec

Applied Voltage volts

Operating Time Sec.

1

2

3

4

121V TMS= 0.6

Applied Voltage volts

Operating Time Sec.

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5

Power systems lab manual

Graph: A graph of operation time v/s applied voltage for any one plug setting.

Result:

Conclusion:

Discussion questions:

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