Short circuit rating of substation equiments

[ceekay1973]

How does a 31.5KA existing substation(AIS) interface with a new 40KA rated AIS of a power power generation plant. Short circuit study suggest that the new power plant equipment shall have 40KA rating .

 

[beyond86]

You have to limit short current to 31.5 kA for existing substation. How is old SS and new SS connect?
Install series reactors at interconnection lines will help to limit SC for old SS.

 

[ceekay1973]

The old plant is more than 20 years old. Is a bus sectionaliser will help?

 

[thermionic1]

Is a bus sectionaliser will help? - 100% as long as it's kept open.

 

[RRaghunath]

The interconnector is for providing standby supply to the power station switchgear in the event of power station shutdown, I suppose.
If yes, you can have Interconnector Normally Open at one end and have a scheme to close automatically when required.

 

[wcaseyharman]

What is the configuration? hV substation feeding a generator step up transformer? Adjusting the transformer impedance can reduce the generator contribution to the fault current, with a corresponding reduction in system stiffness which could impact stability and voltage support capability.

 

[Parchie]

@ceekay1973,
Did you mean to say that the 40 kA study is done at the substation terminals or was it done at the POCC? If the latter case, you might have to compute the kA available at the substation equipment point for good measure. Even with a service drop of about 100 feet, the available fault current could have dropped below your 31.5 kA equipment rating if the conductors are small (#6AWG Cu or #4AWG Aluminum)!

 

[bacon4life]

Much of the transmission level equipment now defaults to a 40 kA rating as the minimum AIC available. Thus we typically don't ever specify anything less than 40 kA for transmission equipment. For existing equipment, check the actual expected fault current rather than the recommended class for the new equipment.

 

[Parchie]

Agree. The North American practice defaults to 500MVA short-circuit MVA at the distribution voltages of 7.2kV - 24 kV.

 

[davidbeach]

MVA hasn't been the unit of measure for interrupting ratings for decades now. 40kA is a common rating across a wide range of voltages.

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