Testing of Switchgear - Part 3 (Breaker operating timing test )

In previous blog, I discussed for Breaker Contact Resistance Measurement (CRM test) for switchgear. We will discuss further test in this post.

The next test we will discuss is as below.

Breaker Operating Timing Test

Purpose of the test :  

Circuit breaker is a part in electrical system which separates faulty part in event of fault. The separation time of the faulty part must be minimum and circuit breaker should do this quickly. This timing is called breaker operating time in which it removes the faulty part from system. Inside the breaker, it operates through mechanical operation. If this mechanism has any abnormality, then it will not operate smoothly and the breaker operating time will be more. When there is fault in the system, there will be high currents in the power circuit. Every equipment is designed to sustain for large current for very short time considering that circuit breaker will operate and will remove the fault from the system. If the circuit breaker will not operate within its desired time during the fault, there will be heavy damage to electrical equipment due to high currents. So we are checking the breaker closing and opening time through this test to ensure normal breaker timings.

Breaker Operating Time: Breaker operation time is total time of breaker closing time and opening time.

Breaker Opening Time: Breaker opening time is time between charging of tripping coil to separation of fixed and moving contact of breaker.

Breaker Closing Time: Breaker closing time is time between charging of closing coil to joining of fixed and moving contact of breaker.

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.