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Do you mean that I don't need to change the setting pickup value? Here's what I calculate and my assumption (please CMIIW) Currently, the setting pickup value (I_Pickup_Percentage Differential) is 0.1 Ie (Ie = 5 A) The ratio turns of CT are 300:1 (HV side) and 3000:1 (LV side) The primary...

So... is it impossible to do what I proposed in the beginning?

We use 0.3 Ie for now. But, how to make sure that it won't trip if the generator stand-still and SST takes power from the grid? I still don't get it, sorry. I already calculated the nominal current, rated current, and CT secondary current for MTR and SST. Can you tell me what I must calculate...

Okay, thank you for the advice guys! After doing my calculation, I got 26 A for the nominal current of Station Service Tr and the CT secondary current is 0.0874773 For the Main Tr, I got 0.69 and 0.94 (CT secondary current). Can I safely say that if the CT secondary current for SST is lower...

I already calculate the primary fault current which is approx. 18 kA and that's really high from the "current" setting pickup value (0.23 Ie) I think I'm doing something wrong

Thank you stevenal and wcaseyharman. Yeah, I do definitely need the training since this is my first time learning the protection, so I'm truly sorry if sometimes my question seems too dumb. I already do my own research on this topic but am still clueless in many ways. Is there any way to...

What if the current drawn by station service tr is far higher than the fault current? Is it okay?

So, I need to set the differential pickup by considering 2 conditions, when the generator is running and stand-still. What if the current drawn by auxiliary tr from the grid (condition 2) is higher than the setting value from condition 1?

I'm sorry, David. I can't understand what winding s, u, w, and x refer to. Can you please enlighten me by telling me the references? Thanks

Would it make it to the same configuration with the same problem too? With CT3 - CT4 protected by 50/51 and 27, it needs more than 1.36 s to tackle the short circuit incident. Thus, the fire incident occurred. I want to reduce the time needed (by installing the 87T on CT2 and CT6).

Thanks to you all, especially Raghunath, for answering my question. However, I still have further questions. As you said, I need to set the differential pickup. But, it doesn't change the fact that if the station service takes power from the grid, the 87T will always read it as a fault right...

Thanks for the answers. I'll give the diagram here: So, I want to add 87T between CT2 and CT6 so the 11 kV line will be protected by 87T. The status quo is: The 11kV network is only protected by 50/51G and 27 relay (between CT3 and CT4). Last time, there was an incident when a 3-phase short...

Is 87T able to change the setting value automatically according to generator status so 87T won't activate for tripping while the generator is in stand-still status?

I'm trying to understand this single line diagram (HEPP) by doing it on ETAP. However, I find it difficult to translate this file into ETAP. For example, I can't find NGR, DS, GCB, SA, the diode rectifier thingy on exciter, and so on. Do you have any tips for me? TIA