sinhchoo
Electrical
- Nov 21, 2009
- 23
We have a 14MVA, 6.6kV generator generating power to the 33kV network through a 14MVA 6.6kV/33kV Transformer. This 14MVA Generator is grounded through a 762ohm grounding resistor to limit the fault current to 5A. Now we are going to add one unit of 2MVA generator to the 6.6kV system to run parallel with the 14MVA Generator.
My first question is how should we ground the neutral of the 2MVA Generator? If Neutral Grounding Resistor is required how should I size it?
In previous thread, xxjohnh posted a reply as follow:
"Most low voltage generators are soldly earthed and small, up to 2500 kVA.Trip on earth fault.
Most medium voltage generators 2 TO 10 Mva are low resistance grounded, 100 to 400amps, 10 secs, to limit damage to expensive machinery.Trip on earth fault.
Larger units 10 to 1000 Mva tend to be unit connected so they are high restistance grounded, 10 amps or so continous through a distribution transfomer or resistor. Sometimes just alarm and don't trip on ground fault."
My second question is why should we limit the fault current to so low current for large generator?
My first question is how should we ground the neutral of the 2MVA Generator? If Neutral Grounding Resistor is required how should I size it?
In previous thread, xxjohnh posted a reply as follow:
"Most low voltage generators are soldly earthed and small, up to 2500 kVA.Trip on earth fault.
Most medium voltage generators 2 TO 10 Mva are low resistance grounded, 100 to 400amps, 10 secs, to limit damage to expensive machinery.Trip on earth fault.
Larger units 10 to 1000 Mva tend to be unit connected so they are high restistance grounded, 10 amps or so continous through a distribution transfomer or resistor. Sometimes just alarm and don't trip on ground fault."
My second question is why should we limit the fault current to so low current for large generator?