Phase Sequence problem.

There is no way to easily change the phase sequence without recreating the phase voltages using complicated (& expensive - 20kVA) electronics.

The easiest way is as you described - shut down the problem supply & physically change the phase sequence on the incoming side.

How did this happen? Make sure that a phase sequence meter is used. If you can't use this kind of meter (synchroscope), 3 incandescent lamps can be arranged to indicate correct phase sequence between the 2 supplies.

If I was in charge of the hospital, I'd be getting the generator fixed.

Can you plese explain how 2 incandescent lamps canbe arranged to indicate phase sequence betewen th 2 suplies

Mohammad-

Whether you are syncing two generators, a UPS or any two power sources, here is the procedure.

You can use a volt meter or lamp rated for the voltage of your two power sources. The procedure to "phase" the sources is as follows:

Using meter:

1. Place one meter lead on Phase One, Source One and the other meter lead on Phase One , Source Two.

2. The Phases will be in "sync" if the meter reads "0" volts. Any other voltage reading will be 120 or 240 electrical degrees out of phase on a 3-phase system.

3.Determine the existing power plant's phasing order. The power supply that feeds all existing motors, UPS, computer plants, etc. Match the new power source phasing to the existing plant phasing using the procedure in #1 & #2. Most power plants in the US follow a color code. Blue-Red-Black, etc. New power sources or motor loads are wired as per the existing code. If a motor runs backwards, the wires are rotated at the motor, not the breaker, etc.

Using a Lamp:

1. Like using a meter, place one lead of the lamp socket on Phase One, Source One and the other lamp lead on Phase One , Source Two.

2. The Phases will be in "sync" if the lamp does not light. The lamp will glow in luminent stages of brightness depending on how far "out of phase" you are to Source One, Phase One.

3. Rotate the Phases of Source Two until all reading from Source One to Source Two produce NO lamp and follow #3 above in "Using Meter" above.

Please remember that if the speed of a generator is not synchronized with the existing power source or another generator on a parallel bus, your readings will not be in phase no matter how many times you try and the result will be a Gen Set or UPS trip upon connection.

Please obtain and read the literature of the units you are trying to connect together. I can send you copies of generic instructions that give greater detail. Just ask!