mgtrp
Electrical
- May 4, 2008
- 326
I am relatively new to North America, but have noticed a difference in approach to the importance of protection systems as compared to my home country - highlighted recently, when during commissioning of a generator, on-site staff decided to get rid of those pesky differential trips by turning off the step-up transformer protection... not as big a deal as you might think, as they'd never applied proper settings to it anyway!
Regardless, one specific item that I would like to know about is "to what extent is primary injection testing carried out on new and existing installations?"
I am used to seeing primary injection testing on all new installations to prove the ratio, polarity and wiring (although secondary injection to prove operation or the relays etc). On differential and REF elements, stability and operation would also be tested.
At the North American utility I am working with now, however, primary injection testing does not seem to be used at all. In fact, CT installations seem almost designed to inhibit primary injection, as they are often inaccessible bushing CT's in oil-filled transformers - a big no-no where I come from, due in part to the need to primary inject, but the feature seems to be ubiquitous in North America.
In the past year, I have seen situations where primary injection testing would likely have prevented several trips: the aforementioned transformer trips I suspect will turn out to be mis-wired CT's (trip occurs when the generator goes on load), and a case of a neutral CT being wired back-to-front causing several instantaneous operations of a transmission step-down transformer LV REF element for earth faults on the any of the connected MV distribution feeders.
Thoughts?
Thanks,
mgtrp
Regardless, one specific item that I would like to know about is "to what extent is primary injection testing carried out on new and existing installations?"
I am used to seeing primary injection testing on all new installations to prove the ratio, polarity and wiring (although secondary injection to prove operation or the relays etc). On differential and REF elements, stability and operation would also be tested.
At the North American utility I am working with now, however, primary injection testing does not seem to be used at all. In fact, CT installations seem almost designed to inhibit primary injection, as they are often inaccessible bushing CT's in oil-filled transformers - a big no-no where I come from, due in part to the need to primary inject, but the feature seems to be ubiquitous in North America.
In the past year, I have seen situations where primary injection testing would likely have prevented several trips: the aforementioned transformer trips I suspect will turn out to be mis-wired CT's (trip occurs when the generator goes on load), and a case of a neutral CT being wired back-to-front causing several instantaneous operations of a transmission step-down transformer LV REF element for earth faults on the any of the connected MV distribution feeders.
Thoughts?
Thanks,
mgtrp