Page 332 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

EXERCISE 113 : Practice setting of pick up current and

time setting multiplier for relay operation

Objectives
At the end of this exercise you shall be able to
• calculate the fault current in different percentage
• set up current in injector unit for different fault current
• set the pick up current of a 50% fault current
• set the time multiplier for time setting under various fault condition.

Requirements

Tools/Equipments/Instruments
• Trainees tool kit - 1 No.
• Over current relay with manual - 1 No.
• Current injection unit with manual - 1 No.

Procedure

TASK 1 : Identify of pickup current and trip the relay for different fault current
1 Identify the supply voltage required for operating over current relay to its tripping coil.

2 Identify the current input terminals of relay.
3 Identify the shorting pins of NC/NO relay contacts.

Note: The current Injector unit is required to provide different fault current levels. The fault current
settings is done in tap setting provided in the relay along with percentage of fault current with time.

4 Connect the tripping coil voltage and fault current connections from current injector to relay as per the manual
instruction. Keep all the controls at zero position in current injector unit.

Note: Some coils requires DC supply that can be taken from current injector unit.
5 Set the tap on relay for one amp. Calculate the multiplier from the dial and set the current in current injector
unit. Record the values in Table 1.
Note : A sample reading is recorded in Table 1 on the tap setting at 1A; and multiplies value-2. Trip
time displayed in dial an 10 seconds
Select multiplier 2, so that the total fault current is 2 amp. ensure the time multiplier disc kept at
position 1.
6 Note down the corresponding time displayed on the dial for multiplier 2.

Note: The current injection unit have different makes and specifications . Energise the relay using
manual supplied along with current injection unit.

7 Switch on the current injector unit ensure that relay is energised.
8 Increase slowly the current which is the input of relay to pickup.

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