Page 338 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

Note: Now the fault current set value is 2 Amp and the relay should trip in the time as per the dial
indication.

7 Switch ‘ON’ the current injection and note down the tripping indicated by the timer fitted on the current injection
unit.

8 Reduce the time by setting TMS by 0.5
Note: Since the short circuit current cannot be generated practically the tripping time is reduced by
taking the short circuit current is present now.
9 Ensure the rotating aluminium disc returns to its original position.

10 Switch ON the injection unit and note down the tripping time in seconds.
Note: This time will be half time of the first reading.
11 Change the tap setting at 2 amps slot in the relay and repeat the steps 4 to 9.

12 Record the readings in the Table and get it approved by your instructor.
Table 1
Test tripping of circuit breaker definite time charts

Sl. No Tap setting TMS value Time Multiplier Total fault Actual Error in %
current current tripping
current
1

2

3

4

TASK 2 : Tripping circuit breaker in extreme inverse characteristic condition

1 Repeat the step 1 to 3 in Task 1.
2 Set the TMS at 0.2 position.
3 Set the tap setting plug into maximum current input on the dial.
4 Select the maximum multiplier value in the dial record the fault current (plug set value ‘X’ multiplier) and the
tripping time in Table 2.
5 Check the pickup current for the tap set value.
6 Set the fault current in the current injector unit
7 Switch ‘ON’ and note down the actual tripping time in Table 2.

8 Try to some higher value of fault current and repeat the step 5 to 7. Record the values in Table 2.
Table 2
Sl. No Tap setting TMS value Time Multiplier Total fault Actual Error in %
current current tripping
current
1
2

3
4

321

CITS : Power - Electrician & Wireman - Exercise 115