Page 337 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

EXERCISE 115 : Test tripping characteristic of circuit

breaker for over current and short circuit
current

Objectives

At the end of this exercise you shall be able to
• connect relay and circuit breaker for test tripping
• set the current injection unit for tripping current
• set the tripping current for definite time lag (over current)
• set the current for extreme inverse characteristic (short circuit current).
Requirements

Tools/Equipments/Instruments
• Trainees tool kit - 1 No.
• Air circuit breaker 400 KA 415V
with manual - 1 No.
• Over current relay with manual - 1 No.
• Current injection unit with manual - 1 No.

Procedure

TASK 1 : Tripping of circuit breaker for definite time with set fault current
This exercise is prepared to set the relay in definite time tripping in over current conditions and
extreme inverse tripping in short circuit situations. This model relay is not having the facility of
various tripping characteristics.
However short circuit current situation can be provided to trip the relay in short time by setting time
Multiplier Setting (TMS) to trip the relay instantly at high fault current situation.
1 Connect the relay, circuit breaker with the current injection unit by referring in block diagram. (Fig 1)

2 Check all the connections as per the instruction manual.
3 Set the tap setting current in 1 amp and note down the multiplier, time in seconds in Table 1.

4 Set the TMS at position 1 marked in the dial.
5 Check the pick up current of the set value of tap setting current and note down values in Table 1.
6 Set the fault current by selecting multiplier from the dial and note corresponding time in seconds and note the
values in Table 1.

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