@wcaseyharman Thanks a lot for your help. I will check with the PT manufacturer for the overvoltage capability. I believe, in this case, its better to go for line-to-line rated PT 4160/120 since then I wont have to worry about PT saturation during fault and it will also give 120V L-L in Wye-Wye...
@wcaseyharman This is a dumb question but I just want to be sure: If there are two VTs (single phase) 4.16/sqrt(3) // 120/sqrt(3) and 4.16//120 VT, will we get the same output, that is 120 L-L and 120/sqrt(3) L-N for a 4.16kV system voltage, since the ratio of both VT is same? The only...
@wcaseyharman You are right, I get it now. I was wrong about the second point VLN is not the rated voltage of the VT. It is the VT secondary voltage under normal(un-faulted) condition. So if we choose 4160 // 120/sqrt(3) = 4160 / 69 VT then under normal operation VLN = 69/sqrt(3) and under fault...
@wcaseyharman I kinda get what you're saying, but its a bit confusing, so below is my step by step approach. Let me know where I am going wrong.
- The Broken Delta output is 3V0.
- VLN is the rated secondary voltage of the single phase VT.
- For a resistively grounded system during ground fault...
@wcaseyharman The resistance of the NER is 24 Ohms. Also, even if I am rating the VT for line-to-line, it should be 4160/120V, since during fault 3V0= 3VLN. So I need the secondary line-to-neutral output (VLN) of each VT to be 120V.
@wcaseyharman My system is also resistively grounded Wye. It's resistively grounded via a Neutral Earthing Resistor. Does it change anything, whether the system is solidly grounded or resistively grounded?
There are conflicting answers here on whether the VT should be line-to-line rated or...
@waross You're right. The VTs are rated line-to-neutral and connected in Wye Grounded on the primary side. I went for line to neutral since the system is Wye grounded. I suppose if it was Delta ungrounded then i would have to choose line to line rated VTs, correct me if i'm wrong. Also, let me...
I'm working on a 4.16kV, 40kA-3sec, 4000A Switchboard. We need Directional Earth Fault (67N) protection on the Generators. The relay manual (Siemens 7SR2..) mentions that the polarizing quantity for the directional protection can be "calculated from the 3 phase voltage inputs or the 3Vo input"...
In all 4-pole ABB MCCBs, above a certain range, it is mentioned that that there is an option to choose 50% or 100% Neutral protection. Specifically, it says "The four-pole circuit-breakers are always supplied with the neutral protected by the trip unit and with protection of the neutral at 100%...
