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Thanks for your explanation. So, if there is no tertiary winding and neutral terminal isolated to ground, then zero sequence current can't pass through H to L terminal?

Thanks all for the answer, I have one more question: What If I remove neutral-ground connection of a single winding autotransformer, can it transform zero sequence current? or it's zero sequence circuit will be open circuit like Yy transformer?

I checked the winding connection, it was delta connected. What is tertiary winding connection in autotransformer actually used for? And what will be the effect if the delta circuit is changed or modified into broken delta?

Thanks David & Bill, I had always thought that this transformer have no tertiary winding. All study always model this transformer as Yyn transformer with no tertiary winding. I've checked the old drawing and I found that actually the T1-T6 terminals are delta connected. But I'll check to the...

@bholas Bus F is quite far from Bus B (30000 ft), so it is needed to boost the voltage. @davidbeach TR3 connection is like this, I thinks there is no tertiary winding in TR3

Yes, I'm sure.

Yes, there are Dy and Dd transformers (delta on 13.8 kV side)

Only some of of them are VFD driven, but the main the reason is that they have small inertia with large impedance (cables) between the motor and connected bus.

@KS227 Yes, but it should be not that significant because they are ESP motors. @wroggent I model the transformer as Ynyn

answer: Yes, load under TR3 are mostly motors.

I got your point, three leg core transformer will create additional ground path due to Zm. So, there will be current contribution from this feeder to the fault. If I want to omit current contribution from this feeder, what should I do? Remove neutral to ground connection of this transformer...

Hi all, Recently there was single line to ground fault in my plant, below is the current based on the actual record on related relays: * TR1 and TR2 LV winding are connected to ground with low resistance NGR (1000A * Neutral point of generators are connected to ground with high resistance...

@bacon4life before load disconnected → V = 33.7 kV, I= 21 A , P= 37 kW. after load disconnected → V = 34 kV, I= 21 A , P= 76 kW. @lionelHutz Originally this feeder was a spare feeder, the MRCT was already installed before.

To HamburgerHelper, This feeder supply power to another company plant, and KWh measurement at this feeder being calculated for the billing. PF reading changes then KWh reading changes as well but there is no load changes at the other plant. Note: we are an oil company, so we are not used to...

Hello, In my plant there is a 34.5 kV feeder that supply very far but light load (current parameters at supply feeder: V = 34 kV, I= 21 A , PF= 0.06). The feeder use C100 CT's ( multi-tap CT 100/5) and ION 7300 to measure the load. I found out that whenever the load was disconnected, PF reading...

Stevenal, thanks for noticing the mistake. The correct one is 3 line diagram. The terminals at 4.16 kV switchgear are not fully insulated. I have checked the terminal but no sign of fault/arcing. The only area that's not checked yet is CT area, wich located between 4.16 kV swg terminal with...

Yes, the CTs are located in 13.8 kV and 4.16 kV switchgear. Transformer HV and LV terminals are connected to switchgear through CLX cable - XLPE insulation (cable length approximately 100m each). The cables installed on cable tray. Yes, I think the fault could have occurred on the cable. I have...

Stevenal, looking at the phasor, is it safe to say that the fault should be located inside the protection zone?

This Transformer is paralleled with another 5 MVA transformer, IB2 from 4.16 kV should be supplied from another transformer. Attached below the illustration. *Note: I tried upload the picture in this post (using upload image feature) but always failed...

Well noted to ground CT star point at 4.16 kV side. This transformer and the protection relay has been in service for many years, and I've observed the differential current at full load condition. So I think there is nothing wrong with the wiring except the neutral poit of 4.16 kV side CT...