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LTC Transformers on Reactive Power Study

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.

I saw several studies where they consider LTC tap movement to increase reactive power capability at the POI but I'm wondering why it was done so because LTC movement is not even on the dynamic range. If somebody has some insights on this, I appreciate your comments.

lmcqueen's avatar
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lmcqueen
asked 2025-04-02 12:05:35 -0500
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I believe it is up to interpretation whether LTC operation can be considered fast enough to be considered "dynamic." It is my opinion that it is nowhere near fast enough. You can make an assumption that the taps do move after the unit MW output is in the steady state which allows the transformer to choose the tap that makes sense before a voltage disturbance happens

transmissionplanning's avatar
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transmissionplanning
answered 2026-07-15 20:45:00 -0500
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This is not so much a PSSPY question, but I will say that, at higher voltages, passive reactive devices (switched caps for example) will contribute more reactive power. A transformer LTC might be set to maximize capacitor voltage and thus get higher reactive performance. In many cases LTC tap position will be different for leading and lagging cases. For reactive capability validation, it is better to set transformer taps where aggregate plant reactive output meets criteria over the entire range of operating voltages. Apart from transformer taps, one must also consider allowable range at PV inverter terminals and collector equipment.

What did you mean by "LTC movement is not even on the dynamic range"?

MarkG's avatar
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MarkG
answered 2025-04-04 10:49:14 -0500
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