Degradation from Primary Injection

[fiberstress]

Hi Sparkies,

If you would, I need help finding a paper or book (or your experience) on the degradation effects of primary injection circuit breaker testing. Surely there must be something out there?

Thanks,
fiberstress (gearhead)

 

[rcw retired EE]

I have many stories of problems found by primary current injection that would not show up using secondary injection or solid state trip unit tests sets.

Most of the problems were on 600V switchgear breakers with some molded case circuit breakers.

Only detrimental effects were some slight arcing on the contacts for the instantaneous trip test. Other problems were broken parts caused by improper handling of the breakers or not putting the switchboard bus back together correctly.

 

[dpmac]

There are models of breakers out there that we have refused to perform trip tests on (primary or secondary) as the plastic charging mechanism parts always broke when we charged the breakers to trip them. Actually we no longer bid jobs that contain this type as the breakers get jammed and stuck during the racking in/out process.

As mentioned above, we have found many problems performing primary injection ranging from bad trip units, wrong wiring, defective or damaged wiring, open or wrong ct', etc.

We always recommend primary injection for commissioning and the next maintenance cycle. Depending on the facilities requirements and/or reliability factors secondary may be done every other one or two cycles.

Some secondary kits are a joke and don't do more then simply trip the breaker with out even talking to the programmer logic.

IMO primary injection testing will not degrade a well made breaker. Of course there is more risk of damage due to the removal, transprt and handling of the equipment.

 

[Zogzog]

I have seen a paper on this and it was covered at Powertest this year. ST and INST tests will cause some minor erosion to contacts during primary injection testing, but secondary injection testing only tests the trip unit functions and actuator is is not an accepted test per NETA/ANSI standards.

What some people are starting to buy into is Pirmary current injection with secorady injection verification. In other words you do the LT tests via primary injection to verify the entire system (Including CT's) works right on all 3 phases and then do secondary injection to test the ST and INST functions.

 

[rcw retired EE]

An example:

A new 480V, 3200A Main intermittently tripped on GF. No bus faults, no feeder breakers tripped and data loggers showed no neutral or ground current on the supply transformers. Troubleshooting with secondary tests sets found nothing wrong. Finally, primary injection testing at 5,000 Amps exposed a problem in the trip unit. The device was designed for 3-phase, 4-wire but supplied for 3-phase, 3-wire service with the neutral CT input not connected internally. At high currents the floating neutral CT input picked up noise and triggered a GF trip. A solder jumper cured the problem.

In the process of pulling the breakers and connecting to the test set, the technicians broke one high current stab finger assembly, a minor plastic barrier and one racking mechanism.

Primary current injection testing located the problem but the testing activities created more minor problems.

During initial commissioning these breakers were tested as Zog describes: primary current was injected to verify CT ratios and polarity and trip unit LT pickup, then secondary test sets verified the settings and functions. The primary injection currents were too low to expose the trip unit problem.

Full primary testing may have located the problem earlier. It would have cost more initially but been cheaper in the long run.

As a side note, the false trips during plant performance tests cost us about $200K in delay penalties. Troubleshooting cost about $75K with overtime and expediting the high current test sets to the site.

The switchgear factory manager knew these trip units had this problem, but he did not share that in early telephone conversations with us and his engineers. He let us spend money and time until we discovered it ourselves, just after warranty was up. He then wanted us to pay for rebuilt trip units on 48 similar breakers in four "copy-cat" plants that were in construction. (I believe the manager and his QA/QC lead was fired.)

Full primary injection testing would have found the problem before the end of warranty.

 

[edison123]

A great thread. Thanks everyone for interesting information.

Muthu

http://www.edison.co.in

 

[fiberstress]

I should've also mentioned that I'm working with low voltage (600V). Any change of opinions? Has anyone heard of a IEEE, ANSI, NETA, etc., formal report or paper? Thanks for your time.

 

[fiberstress]

I'm also looking for a source of information for reliability, failure rate, etc. info. If I look for this with the mfg., who/what should I ask for? Thanks for the help.