Out of Phase voltages? 1

[RelayDesignMan]

This question is mainly in regards to consequences. I have a station service throw-over scheme to put in service; and I'm wondering what happens if it's connected wrong. I'm talking phase A station service tx on the normal and accidentally using phase C station service tx on the emergency. What's the worst consequences assuming no sync check relay and no time delay?

 

[rockman7892]

What if the phase rotation was correct and when closing the same phases were closed together however they were slightly out of phase due to different circuit paramaters on each network.

In other words, instead of closing in phases A to C (Big Bang!) we closed in both A phases (A to A) however these A phases were out of phase by some amount due to paramaters (Network Reactances) on their two respective networks. Would we still have a big bang?

 

[davidbeach]

Depends on what the magnitude and phase angles on both sides were just prior to closing. Less than 15[°] close to generators or less than 30[°]further away and you probably won't have any particular problems. Every case is somewhat different and your mileage will vary.

 

[waross]

I've mentioned before the little power plant with a connection issue to the synchroscope. This was a mix of 350 kW and 600 kW diesel generators. As the load changed, there were generators going online several times a day. Some days 6 or more synchronizations.
The synchroscope was 30 degrees out. This was generators in the same plant and real power,not a reactive phase shift. Most times the installation would survive closing at 30 degrees of displacement. Once or twice a month, when the boys closed a little early and at a greater angle, a breaker would trip.
Once or twice a year they would come in a lot early and blow a coupling.
This was real power and the generator would have to make an abrupt angular shift to line the poles up with the rotating field. The equipment would survive closing at 30 degrees of displacement.
Your question is a little different. If the phase displacement is the result of reactive voltages, that implies that the lines are at differing power factors.
Closing on this would result in enough reactive current flowing through the breaker to give a weighted average to the power factor. Probably no big deal.
HOWEVER
If your 30 degree displacement is the result of an odd number of delta/wye conversions, it becomes more serious. Close in expect heavy currents possibly in excess of full load current. With a lot of miles of line expect a lot of energy to be lost heating transmission lines.
By the way, I agree completely with davidbeach. His system is many times larger than mine and not as forgiving as the small generators.

Bill
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"Why not the best?"
Jimmy Carter