Question about LTC Transformers

[user1011]

I'm performing Reactive power study for a solar plant to determine compliance with FERC 827 and quantify if there is a need for additional reactive power compensation device. Should I include in the study the effect of LTC of the main transformer on the reactive power flow at the POI?

 

[waross]

It depends.
LTC adjusts the voltage.
Voltage adjustments tend to vary the reactive current.
Due diligence suggests considering the effect of LTC operation.
The effect may be significant or it may be negligible.
It depends on information not given.

 

[JJ_Roy]

Yes. Compliance with FERC 827 requires the reactive power capabilities to met at the high side of the station transformer. Some interconnections requirements say it's at the point of interconnection (POI).

As warross noted, the LTC could have a significant impact....

I'd check with the interconnecting utility (or system operator) as there is probably some sort of planning procedure that dictates how you determine the reactive capability.

 

[crshears]

The Technical Interface Requirements or equivalent of the Authority Having Jurisdiction [AHJ] will largely determine the answer to your question.

 

[wcaseyharman]

Biggest impact of LTCs I think of on IBRs is the loss of VAR capability at high voltage. If the taps aren’t set right the VAR capability can be severely limited. Right now for that reason I plan to set the LTC in our new wind farm to manual - I just don’t see much value in the LTC anymore with the turbines and plant controllers capable of controlling VARs, and it has the potential to mess with the VAR capability of the plant.

 

[user1011]

Yes. Compliance with FERC 827 requires the reactive power capabilities to met at the high side of the station transformer. Some interconnections requirements say it's at the point of interconnection (POI).

As warross noted, the LTC could have a significant impact....

I'd check with the interconnecting utility (or system operator) as there is probably some sort of planning procedure that dictates how you determine the reactive capability.

Thanks for the reply. I'm just wondering why it needs to be considered since LTC operation is slow and not dynamic compared to SVC/STATCOMs.

 

[waross]

The tap position may affect the power factor and may affect the ASCC. (Available Short Circuit Current)