Grounding Cable Type
Grounding Cable Type
(OP)
A 6.6kV system is fed by 6.6kV generators, the generator neutrals are ungrounded. However, the 6.6kV bus is grounded by a grounding transfomer. The grounding transformer is primary star and secondary open delta with a resistor connected at the open delta to limit the gound fault current to 30A. To get the ground fault current flowing obviously the star primary has to be grounded. My question is whether the neutral cable from grounding transformer primary star point to ground should be a normal gounding cable or it has to be a power cable with insulation suitable for primary voltage ie. 6.6kV.






RE: Grounding Cable Type
RE: Grounding Cable Type
If true (to be verified through calculation as per IEEE), then the neutral potential could rise close to phase potential during single phase-to-ground fault.
It means that the grounding cable needs to be 6.6kV insulated cable (may be same specification as the phase cable).
RE: Grounding Cable Type
There is also no information in the post to indicate what voltage the delta is wound for, so it isn't possible to answer a question regarding the cable connecting the resistor to the broken delta (NOT open delta).
RE: Grounding Cable Type
By the way, the secondary voltage is 120V.
RE: Grounding Cable Type
Also, with this grounding method, during a ground fault on the high side, you will be seeing as much as full phase-to-phase voltage from the unfaulted phases to ground.