1-phase voltage regulators and distribution switching 1

[ePOWEReng]

Does anybody know whether or not voltage regulators will "hunt" (that is due to circulating current which increasing with the tap change, one goes to max boost and the other to max buck) when paralleled (parallel connections are on in the 13kV distribution system and one in the 115kV system), if they are connected to different distribution transformers (that are tapped the same) to the same 115kV system? Also, do you know of any good references for distribution switching especially concerning voltage regulators and what state they should be in during the switching? Thanks in advance.

 

[dpc]

Step-type voltage regulators are auto-transformers and if put in parallel, need to be on the same tap, or they will experience high current. These are not normally operated in parallel.

For switching operations to bypass a regulator, the regulator should be stepped to the "neutral" position prior to bypassing.

Other switching operations are more problematic, and depend on the exact situation. If you are closing a tie switch on two feeders with a regulator on each feeder, it gets complicated. Alot of people just run both regulators to neutral and hope for the best when they close the tie. The amount of current flow will depend on voltage difference and the current phase angle. If the tie switch is several miles from each regulator, it is difficult to predict, without knowing voltage and phase angle across the tie switch.

 

[busbar]

If there is not an interconnection between two load-tapchanger controls to accommodate load sharing, then circulating reactive current can make attempts to regulate voltage very difficult on the distribution bus served by two regulators. Because the circulating current is purely reactive, it does not register on wattmeters, but only manifests itself as additional {non-load-based} current.

The same situation could exist whether, for instance, LTCs are on two [115/12kV] paralleled power transformers, a [115/12kV] transformer and a [12kV] poletop regulator, or two [12kV] poletop regulators.

http://www.beckwithelectric.com/infoctr/appnotes/App11.pdf

describes the situation with examples. The note also suggests that if the loadsharing feature is enabled and one LTC is taken out of service, the loadsharing feature must be disabled for the in-service LTC to work correctly in a non-paralleled mode.