Circuit breaker - primary injection testing

[nkn5]

Hello,

Could you please share your experiences on primary injection tests for circuit breaker of high current ratings (say 1600 to 5000 Amps) with integral trip units. I can't see many commercially available test equipment capable of supplying the level of currents. Needless to say, true testing of short time or instantaneous settings is near to impossible.

I can understand the difficulty in generating such high currents (~2000 to 20000 Amps). I would like to understand what is the common practice of testing circuit breakers - especially the ones with high current ratings.

Thanks,

 

[DTR2011]

There are several manufacturers of primary injection test sets for the exact purpose you have.

Megger, Phoenix and Programma come to mind. In the old days of dash pot or thermal magnetic trip units this was a must.

Some will say (including NETA specifications) that primary injection is still required. There is a value to proving the entire CT>>Trip UNit> trip coil.

On the other hand there are also secondary test sets available for specific trip units, generally from the manufacturer.

There are methods, such as testing the unit at a much reduced current level (few hundred amps), with primary current, which proved the CT's, wiring and trip circuit, then testing the trip unit itself with a secondary test set, which can accomplish the same. It is how protection systems are tested for MV/HV systems all of the time (separate testing of the devices and perhaps a lower current primary test to prove the system 100%).

The primary test sets that are capable of 100-200 kA, are big monsters and generally require a connection to ~480 V to get that kind of output current (100kA+). In a shop situation, that can be set up quite efficiently, with various custom breaker stab sets to facilitate efficient testing. Doing this in the field is also possible, but it requires more logistics, transportation and manpower ($$$).

 

[unclebob]

We have one custom built at the shop. Not easy to transport. 3 pieces , one transformer, one 5000:5 CT w auto-transformer and the injection module.
Max current is about 20000 A with good connections. Testing molded case breakers is easy, but one has to remove them from the panel first. Testing power circuit breakers is ok providing you have adapters to fit the stabs/clusters. Short and Instantaneous are tested at minimal setting. Only way to 100% test a newly retrofitted breaker w electronic trip unit.

Needless to say that at 20000 A, strange sounds keep people away from the area.

 

[oldfieldguy]

I fall out strongly in favor of primary injection testing.

Some manufacturers have secondary test sets that do some testing of the sensors, but most do not. The primary injection test makes the entire breaker do its job, including breaker opening, the trip unit, its sensors, etc. Not testing the sensors is a pretty serious omission.

This points out many common issues such as failed trip units, failed or incorrectly scaled sensors, and sticky mechanisms.

All of these assume that the technician performing the test knows how to properly test the breaker.

In some cases in the past, we did an initial test of circuit breakers using primary injection to prove out the system, then, after receiving the proper settings (much later in the project) we validated the settings using secondary injection.

old field guy