Generator Sequence Impedances

[veritas]

If I know what the Xd", Xd' and Xd are for a generator how can I estimate the negative phase sequence and zero sequence impedances for the generator? Are there any rules of thumb? No manufacturer's data available.

Do the rules of thumb vary with the size of the generator?

Thanks in advance.

Veritas

 

[alehman]

One rule-of-thumb is the negative sequence subtransient reactance is close to the average of the positive sequence direct axis and the positive sequence quadrature axis subtransient reactances. Zero sequence cannot be estimated.

 

[davidbeach]

The zero sequence reactance will be more than ra (ra is the resistive component) but less than Xd''. If the generator is impedance grounded the generator zero sequence can be assumed to be zero as it will be very small compared to the grounding impedance. If solidly grounded you need to be concerned if you can't get good data.