Measurement of the resistance of switchgear main circuit (High Voltage Circuit Breakers and Bus bars) in site.

1. Measurement of the resistance of Switchgear
main circuit (High Voltage Circuit Breakers
and Bus bars) in site:

2. How to
measure the
resistance?
For Circuit-Breaker, The resistance
measurements shall be made across
the terminals of each pole.
For Busbars, the FAT measured resistance across the
complete main circuit of an assembly of metal-enclosed
switchgear and controlgear is indicative of the proper
condition of the current path. FAT measured resistance
shall be reference for the main circuit. The measured
value of the type test can be used to determine the limit
of resistance value for the routine test.

3. What is the test current?
Usually, the test current is 100A d.c..
However, it is possible to perform the test by any
convenient value between 50A and the rated
current.

4. How to analyze the test result?
The measured test values shall be
compared against the FAT Type-
test report by considering the
general conditions (ambient
temperature, points of
measurement, current etc.).

5. What if measured values are
not matching with FAT?
Any discrepancy in test result shall
not be attributed to bad
connections.
In such case, test shall be repeated
with higher current, as close as
possible to thee normal rated
current.

6. Are there
any limits for
test result?
The site measurement shall
not exceed 1.2RU,
Where RU is the resistance
measured before the FAT
temperature-rise test.

7. What are
the test
standards?
IEC 60694
IEC 62271-200
Clause 7.3