Testing of Switchgear - Part 2 (Breaker Contact Resistance Measurement test)

In previous blog, I discussed for insulation resistance test for switchgear. We will discuss further test in this post.

The next test we will discuss is as below.

Breaker Contact Resistance Measurement (CRM test)

• Why we are carrying this test?

We are conducting this test to find the resistance of breaker contact where moving contact and fixed contact meet each other. This contact resistance should be low because the circuit breaker is carrying high current. So if the resistance of contact will be high, there will be more energy loss (more I²R) losses and it can’t pass high currents. By carrying this test, we come to know about looseness in contact, corrosion present at contact surface or any other contamination in the contact. This test shows healthiness of the contact.

• How to measure contact resistance of breaker ?

We are using one kit called CRM 100 for the test. This test works upon method of 4 wire Kelvin DC voltage drop test. In this method 4 wires are used for resistance measurement. Two wires are used for current injection and two wires are used for voltage measurement. In this method the current amount is set to high like 100 Amps. Higher the current we inject, more accurate resistance we get. Two current leads and two voltage leads are connected across each breaker pole. The resistance here we will get in terms of 20 micro ohms. All three breakers pole resistance should be same. Here the resistance value we obtain, depends upon capacity/ voltage rating of the breaker.

We will discuss further test in next blog for Breaker Operating Timing Test.