phase angle between two transformers

[psk101]

I have two light and power transformers TR1 & TR2. TR1 is 33kV/208V and TR2 is 13.8kV/208V, but their high voltage source is different source generation. TR1 is a delta-wye 33kV/208V. The 33kV supplied to this transformer is from another delta-wye transformer 138/33kV transformer.

TR2 is a delta wye transformer also 13.8kV/208V. but the 13.8kV of this transformer is supplied from a tertiary of an autotransformer (345/138/13.8). The autotransformer is wye-wye-delta configuration. The tertiary is delta winding. Note the generation source for this autotransformer is different than the for above TR1.

Both of these Light and power transformer are connected to a common ATS(automatic throwover switch) and then feed the load. One source is normal while other is emergency.
When I measure the voltage and phase angle across the ATS, the phase angle difference is very large and the voltage readings are not in line.
Ideal reading would be A-A approx 1-2 Volts, but I read 100volts with large phase angle difference. Why would that be? is it because of the high side transformer configurations?
Is it because there are 2 delta-wye conversion (138/33kV & 33/208V) through TR1, but wye-wye-delta to delta-wye conversion (345/138/13.8 & 13.8/208V) through TR2 causing this issue?

 

[kingpb]

It is because the systems are out of phase with each other. A phasing diagram including transformer connections would need to be done to see where the differences come from. As long as an open transition is done, it doesn't matter if they are out of phase. The issue would be if you wanted to do a closed transition.

Depending on what the phase diagram shows, an intermediate transformer may be necessary with a 1:1 voltage ratio to simply shift the phases to align with each other, or other options would be to replace one of the transformers with a different phase shift, and finally untank the windings and internally reconnect them to get the desired shift. Don't overlook the rolling of phases is also an option in some cases.

Keep in mind, depending on the phase shift needed (degrees), a single change of a transformer or connections may not be possible to fix the problem because the choices are not all inclusive. There are some degree shifts not possible with a transformer, i.e. 90 and 270.

 

[ATSman]

I have two light and power transformers TR1 & TR2. TR1 is 33kV/208V and TR2 is 13.8kV/208V, but their high voltage source is different source generation. TR1 is a delta-wye 33kV/208V. The 33kV supplied to this transformer is from another delta-wye transformer 138/33kV transformer.

TR2 is a delta wye transformer also 13.8kV/208V. but the 13.8kV of this transformer is supplied from a tertiary of an autotransformer (345/138/13.8). The autotransformer is wye-wye-delta configuration. The tertiary is delta winding. Note the generation source for this autotransformer is different than the for above TR1.

Both of these Light and power transformer are connected to a common ATS(automatic throwover switch) and then feed the load. One source is normal while other is emergency.
When I measure the voltage and phase angle across the ATS, the phase angle difference is very large and the voltage readings are not in line.
Ideal reading would be A-A approx 1-2 Volts, but I read 100volts with large phase angle difference. Why would that be? is it because of the high side transformer configurations?
Is it because there are 2 delta-wye conversion (138/33kV & 33/208V) through TR1, but wye-wye-delta to delta-wye conversion (345/138/13.8 & 13.8/208V) through TR2 causing this issue?

My first question to you is what happens when a test is performed from the ATS test switch (hot bus-hot bus) ? Do any breakers trip, fuses blow or does the load operate properly?
If it all works fine then we can only assume that the ATS is equipped with an In-phase Monitor and only allows transfer to emergency when the 2 sources are within a certain threshold (usually < 10 elec degrees.) In this case you can think of the emergency source (you claim comes from a different generation station from source 1) as an in-house generator that is going in and out of phase with source 1. If this is true then when you measure V across A - A at the ATS then you should see a voltage swing from 0 to (2 x 208V) as you would with a utility - generator setup.
If the 100V you measured on A - A does not change over time then both sources are fed from the same utility station and the voltage difference must be caused by the difference in winding configurations of TR1 and TR2.
Is this a new installation?

 

[SG-1]

If the voltage is a stable 100VAC then the phase shift is about 30 degrees between sources.