Professional Electrical Engineer
In the MVA Method Short Circuit Calculation tutorial, we have discussed how to calculate the three (3) phase and phase to ground fault currents.
The faults currents for three (3) phase unbalance faults are as follows:
1. Three (3) Phase Fault
2. Phase to Ground Fault
3. Phase to Phase Fault
4. Phase to Phase to Ground Fault
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A Registered Professional Engineer of Queensland (RPEQ) – Australia and Professional Electrical Engineer (PEE) – Philippines with extensive experience in concept definition, front-end engineering, detail design, construction and commissioning of Hazardous and Non-Hazardous Area electrical installations.
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In the calculation of the Line to Ground Fault at the 400V bus above, the MVAsc0 = 33.33 which is the equivalent MVA of the 2MVA Transformer only. Why is it that the contributions of the 300kVA and 596kVA motors are not considered? They are not blocked by the transformer. MVAsc0 must be 41.43. May be a case of oversight?…
The contribution of the 400V motors are already considered on the MVAsc1 = 28.28 & MVAsc2 = 28.28. Motors do not contribute to the zero sequence fault current as these are commonly delta connected or if wye connected, motors are ungrounded thus not contributing to the zero sequence current. It is only the transformer therefore which contributes to the zero sequence current.
How to determine the MVA sc1 & sc2 which is 28.28 in this case.
I try to apply the formula of Phase to grount fault at 400 bus but i cant get it.
Sir,
How about the single line to ground fault currents on 33kV and 11kV bus?
Is there any changes in computing the short circuit MVA since utility have given their fault duty that is different on three phase fault duty?
Hi Glenn,
If you calculate the single line to ground fault based on the 3 phase MVA, it will be the same as what the utility have given you.
Good day Mr.Ver
Tried to contact you through the Contact Form.
Anyway, may I request for your email as I have few enquiries with regards to protection.
@adam,
There was a glitch on the contact form. I have already fixed it. Please use it to contact me. Thank you.