Transfer Switch Phase Differential

[ATSman]

PF

PF

The incoming power probably has a better power factor than the generator. First thing that comes to mind is a capacitor bank.

Just to clarify, the phase angle between the load current and voltage has nothing to do with ATS transfer.

Tony

 

[donblackman]

Transfer Switches with in phase monitors need to see the sine waves cross each other. They measure the speed of crossing and then signal the ATS to transfer so that transfer is achieved within a certain window (usually 60 degrees max). With two utilities the sine waves never cross so the ats will sit there. The inphase monitor should be turned off.

 

[ssquared]

Transformers and phase shift

Transformers and phase shift

There is a 30 phase shift thru a transformer. If the ATS has a delayed transfer and/or the motor loads are not large, you can pull the phase differential. If the ATS is closed transiton, you have to fix the phase angle issue. An isolation transformer will give you a 30 degree phase shift on the 208. Then they may match. Then it would depend on the phasing/rotation.

 

[gar]

100304-2332 EST

A normal transformer can not be described as having a 30 degree phase shift thru it.

With no load on a normal transformer there is virtually no phase shift of the output voltage from the input voltage. Load the transformer and now you use the transformer internal impedance in combination with the output load to determine the phase angle of the voltage across the load relative to the transformer input voltage.

ssquared:

Find a book on the theory of transformers and study it. Get some small transformers and an oscilloscope and experiment with no load and loads.

.

 

[steve66]

100304-2332 EST

A normal transformer can not be described as having a 30 degree phase shift thru it.

With no load on a normal transformer there is virtually no phase shift of the output voltage from the input voltage. Load the transformer and now you use the transformer internal impedance in combination with the output load to determine the phase angle of the voltage across the load relative to the transformer input voltage.

ssquared:

Find a book on the theory of transformers and study it. Get some small transformers and an oscilloscope and experiment with no load and loads.

.

Gar:

In three phase systems, a delta-wye transformer has a 30 degree phase shift between input and output. In simple terms (because I don't remember the exact relationship), its because the output voltage of one winding is a combination of the input voltage on two other windings.

 

[gar]

100305-0913 EST

steve66:

The word transformer is singular. A normal usage of the word transformer would imply a primary coil and a secondary coil wound on a common magnetic core. In the case of a radio frequency transformer the core might be air.

There seems to be a loose use of the word transformer in the terminology three "phase transformer" where there are actually 3 single phase transformers. There may be some validity to the use of the singular here. It is also true that you can build a complex magnetic circuit with multiple primaries and secondaries to form a "three phase transformer".

When you have three single phase transformers where multiple input phases are summed in some fashion to produce a single output phase is seems more appropriate to call this a transformer network, than a transformer. Even in a real "three phase transformer" when you consider a specific primary and its associated secondary there is no phase shift from the primary to its secondary.

But in any event it is the external connections and what is used for phase reference of the multiple transformers that is producing the phase shift and not the primary to secondary transformer element.

Consider a delta-wye transformer network. If you compare the phase of the applied voltage to a primary with that of its secondary, then there is no phase shift. If you have a wye source feeding a delta primary and compare a wye voltage from line to neutral with a line to neutral output of the delta-wye transformer, then you have a phase shift.

.

 

[mivey]

...Even in a real "three phase transformer" when you consider a specific primary and its associated secondary there is no phase shift from the primary to its secondary.

But in any event it is the external connections and what is used for phase reference of the multiple transformers that is producing the phase shift and not the primary to secondary transformer element.

Consider a delta-wye transformer network. If you compare the phase of the applied voltage to a primary with that of its secondary, then there is no phase shift...

Just a slight shift due to the load current flowing through. Probably less than one or two degrees.

 

[A-1Sparky]

After much consideration, I'm thinking that I can eliminate the 208Y120v transfer switch and just use its cabinet as a junction box. The 480Y277v transfer switch is operating as it should, and it feeds, via a transformer, the 208Y120v loads anyway. The whole design seems amiss to me. Why would there be the 2nd (208Y120v) transfer switch to begin with?

 

[steve66]

100305-0913 EST

The word transformer is singular.
.

Wow, I hate to be the bearer of bad news, but the whole world isn't going to change to suit what you think should be called a transformer.

100305-0913 EST

Consider a delta-wye transformer network. If you compare the phase of the applied voltage to a primary with that of its secondary, then there is no phase shift.

As ssquared stated, yes there is. Nobody said it was the result of the "transformer". The Line-Line input voltage is across one primary winding, and the line-line output voltage is across two secondary windings, There is a 30 degree phase shift between these two voltages.

It is quite common, and even per the American Standards for notation (at least according to one text I have), to state there is a 30 degree phase difference between values on the low side and their corresponding values on the high side.

 

[Skokian]

Phase Difference Between 208 & 480 Four Wire Wye Sources

Phase Difference Between 208 & 480 Four Wire Wye Sources

If these two sources are from a utility, they may be derived in different combinations of Wye and Delta transformation, including Oepn Delta or Open Wye.

In some parts of the country two different utilities run on the same utility poles. I know of a plant where the fire pump is supplied by one utility in a "Wye-Wye Bonded Thru" fashion and the plant was fed by the other utility. Lightning storms always caused interesting scenarios.

I'd need more info. to speculate further.

Hope this helps.

Regards . . .

 

[wasasparky]

Between transformer pri/sec the term "phase difference" is probably more appropriate than "phase shift"...

...but I still say "light fixture", so who am I to judge....:grin:

 

[rcwilson]

Why would there be the 2nd (208Y120v) transfer switch to begin with?

A design with maximum reliability would have a transfer switch at every load so any failure in the upstream power system would not affect the load. Of course, this is not practical for most systems, even in hospitals. Look at your system to see if the 208V ATS was put in to mitigate a failure in a 480 V transformer, or other upstream device.

I worked on old medical center system that had a 208V ATS. When the building service went to 480V, the 480V ATS fed the old 208 ATS.

 

[ATSman]

Transfer Switches with in phase monitors need to see the sine waves cross each other. They measure the speed of crossing and then signal the ATS to transfer so that transfer is achieved within a certain window (usually 60 degrees max). With two utilities the sine waves never cross so the ats will sit there. The inphase monitor should be turned off.

Don,
You are correct when describing an emer generator synching to a utility. In this case the two ATS sources are coming from the same utility source so by definition the sine waves are always exactly in synch, there is is no "hunting" (crossing of the sine waves) involved.
I have worked on many utility to utility ATSs with inphase monitors and they transfer just fine. I will bet you if he turns the IF monitor off it still would not transfer. I am convinced that this ATS has other problems preventing it from transferring.

Tony

 

[A-1Sparky]

A design with maximum reliability would have a transfer switch at every load so any failure in the upstream power system would not affect the load. Of course, this is not practical for most systems, even in hospitals. Look at your system to see if the 208V ATS was put in to mitigate a failure in a 480 V transformer, or other upstream device.

I worked on old medical center system that had a 208V ATS. When the building service went to 480V, the 480V ATS fed the old 208 ATS.

The way this system is designed, if the 480V transfer switch doesn't transfer, then the 208Y120V loads will not be powered. That is why I am proposing possibly eliminating the 208V transfer switch altogether. I just need to make sure that the 480V transfer switch is rated to carry the entire load.

 

[A-1Sparky]

I did some more testing on the switch this morning, and determined that the in-phase monitor is no good. I'm going to eliminate the 208Y120v switch and just use its cabinet as a junction box. The 480Y277v switch is 225 amp-rated, and the associated loads are well below 100 amps. Just wanted to let you all know what I found out.