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I appreciate for your help. I summarized below step. 1. In fact, OCR can trip circuit breaker in high level ground fault. ('Ground fault current of a sufficient magnitude may be detected by phase-overcurrent devices.' - IEEE 242) 2. We need to calculate ground fault current in TN-S system. We...

Thanks for your help. I appreciate. I'm aware of that just 1 ohm make low level ground fault current. But in our TN-S system, ground fault loop consist of conductor and PE (Protective Conductor). So neutal resistance earthing to ground will be removed in ground fault circuit. (This is our...

Thanks for your help. Our client believes that only high ground fault occurs in TN-S system. And also there is no circumstance to not be protected by OC relay. It sounds like good plan. But I wonder that ZCT burden when OC relay fails to open circuit breaker as well as cable short time...

This is choi from Korea. I’m electrical engineer. Our client want to eliminate ground fault function in low voltage zone. TR : 6.6/0.38kV TR 2nd 3 phase short circuit current : 52kA TR 2nd Line to ground fault current : 51kA calculated by etap. Grounding system : TN-S —— ACB and MCCB have trip...

Dear 3DDave. Thanks for your reply. I understood that the reason why named by color is because it is important! and now, I know that it is not by important!

Dear TugboatEng. Thanks for you reply. Are you work in IEEE? If it's true, 'color' means not 'important' but 'only represent'?

I heard that 'special color book' in IEEE For example, IEEE 242 is buffer book, IEEE Std 142 is Green book. I don't know why this book is named by color. Because of 'Important'...?

I simulate 6.6kV generator's short circuit calculation in ETAP. Generator capacity is 3,900kW and rated voltage is 6.6kV. When I simulate SC, SC is just 2.7kA. I know that Short circuit calculation use the X''d If generator has small X''d, is that right generator's SC is small like this?