Load tap changer on Primary 1

[samy81]

Hello Everyone,
Does the controller on the on load tap changer of a power transformer always monitors the voltage on the secondary side no matter if the tap changer is on the primary or secondary side?
Thank you and best regards,

 

[davidbeach]

The controller has to monitor the voltage that is to be regulated. In the general case you're looking at stepping down from a higher transmission voltage to a lower voltage closer to the load. In that case you don't particularly care what the voltage is on the transmission side, but you do care what the voltage is on the load side. If the tap changer doesn't affect the voltage on the transmission side, you won't know what step it should be on, but it will always impact the load side voltage and you can tell what it needs to do.

 

[Mbrooke]

My understanding is yes. You are trying to maintain a fixed voltage (usually 1.05PU) on the distribution bus. If the voltage goes above or bellow for exceeding a period of time, tap changers will advance up or down to move that voltage back to its desired value.

 

[bacon4life]

David nailed it. Some newer LTC controllers have options for PT inputs from both sides as well as schemes to track tap position. With the proliferation of distributed generation, LTC control strategies may be becoming more complex.

Distribution voltage regulators work a bit differently than LTCs since the source side may change during distribution switching. Many regulators have the capability to regulate the voltage on either side of the regulator. The controller can be programmed to recognized which way power is flowing and adjust the control scheme accordingly. Some controllers can even automatically determine which side has the "fixed" voltage my moving a couple of taps and then looking at the resulting voltages. Some vendors sell the same controller for both LTCs and regulators, so there may be more options available than should actually be used for any specific situation.

I assume you were asking for just distribution substation transformers. For LTCs on transmission banks, the control scheme may be based on both primary and secondary voltages as well as voltage and reactive flows at adjacent substations.