Tertiary Winding Current Calculation
Tertiary Winding Current Calculation
(OP)
I have a transformer with the following data:
50MVA, 115kV-34.5kV-13.8KV, groundWYE/groundWYE/Delta
Using Aspen software, I apply a single line to ground fault at 34.5kV side.(Note: there is no low side or other fault contributions).
Zero sequence fault current at 34.5kV side is 5850Amp.
Zero sequence fault current at 115kV side is 217Amp.
I wish to get the teriary fault current to do the settings of a relay used at the teriary. I need your wisdom and smartness to confirm if I did right.
Zero Sequence Short Circuit MVAsc at 34.5kV side = 1.732*34.5kV*5.850kA=349.56MVA
Zero Sequence Short Circuit MVAsc at 115kV side =
1.732*115kV*0.217kA=43.22MVA.
The difference is 349.56MVA-43.22MVA=306.34MVA and it must come from tertiary. So, the tertiary current is
306.34MVA/(1.732*13.8kV)=12,817Amp.
Thank you for your help.
Bing
50MVA, 115kV-34.5kV-13.8KV, groundWYE/groundWYE/Delta
Using Aspen software, I apply a single line to ground fault at 34.5kV side.(Note: there is no low side or other fault contributions).
Zero sequence fault current at 34.5kV side is 5850Amp.
Zero sequence fault current at 115kV side is 217Amp.
I wish to get the teriary fault current to do the settings of a relay used at the teriary. I need your wisdom and smartness to confirm if I did right.
Zero Sequence Short Circuit MVAsc at 34.5kV side = 1.732*34.5kV*5.850kA=349.56MVA
Zero Sequence Short Circuit MVAsc at 115kV side =
1.732*115kV*0.217kA=43.22MVA.
The difference is 349.56MVA-43.22MVA=306.34MVA and it must come from tertiary. So, the tertiary current is
306.34MVA/(1.732*13.8kV)=12,817Amp.
Thank you for your help.
Bing






RE: Tertiary Winding Current Calculation
RE: Tertiary Winding Current Calculation
RE: Tertiary Winding Current Calculation
Yes, only source is on the 115kV.
Although Aspen could model three winding transformers, but it could not give us tertiary current. We have need set the relay at tertiary winding.
Thanks,
Bing
Jghrist,
There is portion of 34.5kV fault currents from the circulating current in tertiary winding. Therefore, ratio inverse does not apply here.
Thanks,
Bing
RE: Tertiary Winding Current Calculation
RE: Tertiary Winding Current Calculation
I got the current. I seldom use tertiary and "return" the knowledge back to trainer. :)
Thank you for your help.
Best Regards,
Bing