Procedure for Distribution Circuit Paralleling and Load Transfer?
Procedure for Distribution Circuit Paralleling and Load Transfer?
(OP)
I'm looking for feedback on utility operating procedure for momentary paralleling of two distribution feeders fed from two different substations. This would typically involve closing a normally open group-operated air break switch that is at the end of two feeders. The purpose is to temporarily parallel the feeders then open one of substation breakers to put all the load on one feeder. And then the subsequent re-transfer back to the normal condition.
So my questions relate to standard procedures for attempting to match voltages at the tie point and operation of the substation load tap changer or regulators:
Prior to paralleling:
Place one or both LTCs or regulators in manual?
Run both to neutral or to the same tap?
Any attempt to measure/match actual voltages at the remote normally open switch prior to closing?
Same questions would apply to a re-transfer procedure.
I'm curious what procedures the various utilities represented here might be following and any issues that have come up.
Thanks in advance,
Dave
So my questions relate to standard procedures for attempting to match voltages at the tie point and operation of the substation load tap changer or regulators:
Prior to paralleling:
Place one or both LTCs or regulators in manual?
Run both to neutral or to the same tap?
Any attempt to measure/match actual voltages at the remote normally open switch prior to closing?
Same questions would apply to a re-transfer procedure.
I'm curious what procedures the various utilities represented here might be following and any issues that have come up.
Thanks in advance,
Dave






RE: Procedure for Distribution Circuit Paralleling and Load Transfer?
RE: Procedure for Distribution Circuit Paralleling and Load Transfer?
If it is possible and practical it never hurts to measure the voltage. It depends on what is available. A lot of the voltage hot sticks I have seen have an analog gauge and it is being read from quite a distance. One would expect ~Zero volts across the open tie.
RE: Procedure for Distribution Circuit Paralleling and Load Transfer?
The other obvious check is to make sure that the 2 circuits were "phased in" when the switch was installed. Generally they are.
I don't worry about disabling the 51G if we are doing 3 phase gang switching as opposed to single phase hookstick switches since it is generally faster to trip if there is a problem.
I always disable reclosing on both circuits while switching.
Alan
RE: Procedure for Distribution Circuit Paralleling and Load Transfer?
Alan
RE: Procedure for Distribution Circuit Paralleling and Load Transfer?
One concern is that the voltages at the open switch can be different even if the LTC taps are set the same. This can result in some large current flows that sometimes come as a surprise to the linemen.
Cheers,
Dave
RE: Procedure for Distribution Circuit Paralleling and Load Transfer?
Alan
RE: Procedure for Distribution Circuit Paralleling and Load Transfer?
This is especially true if the LTC's / Transformers do not share the exact same ratio. Different manufacturers, ages, specs, etc.
If you are writing a procedure for an existing utility, they generally have a feel for how their system works. If in doubt, or if there is a new piece of equipment coming into play, measuring the voltage across the open switch with a digital hot stick meter is your safest bet. Treat it as a commissioning test and document the results of the LTC positions at both ends. Adjust as necessary. This generally adds a comfort factor to the linemen.
RE: Procedure for Distribution Circuit Paralleling and Load Transfer?
RE: Procedure for Distribution Circuit Paralleling and Load Transfer?