Transfer Switch Phase Differential

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steve066 said:
I'm not really sure what you mean by a time delay neutral. I've heard of solid neutral, a switched neutral, and overlapping neutrals.

Steve
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Time Delay Neutral is with the transfer switch not connected to either source. The transfer switch would have 3 positions, source 1, neutral, & source 2. After a preset delay not connected to either source it would transfer to the good source or back to the preferred source.

Load Decay may be an option. The transfer switch monitors the load bus and transfers when the voltage on it decays to a preset level.
 
I know I am late to the party and have not read all posts this late but have you checked simple 3 phase rotation?? I would think that this may lock out a transfer for obvious reasons. The phase delay I have never run across a problem and have put in countless asco xfer switches as long as voltage was within range and rotation was right. Second guess would be a 15 min call to the transfer switch company tech reps they will be able to troubleshoot quickly and acurately. Night Night . Be back tomorrow earlier.
 
One more thing .. I cant sleep, on this one .... The phase angle is determined when the start command hits the generator. Unless there is synching electronics in the generator it should not matter as long as both normal and emergency power ROTATION is the same. I think a hospital is supposed to start/transfer /and carry the full load within 10 seconds from memory. There is no synchronization that I have seen other than in a power plant where the Genny had a Woodhull I think they called it device which synchronized it with the grid.
 
I have verified that phase rotation is correct. So that's not the problem. I will take more voltage measurements today and post the results. As far as the neutral time delay goes, there are no critical loads associated with the 208Y120v transfer switch, so a temporary loss of load would not be a problem.
 
SG-1 said:
Time Delay Neutral is with the transfer switch not connected to either source. The transfer switch would have 3 positions, source 1, neutral, & source 2. After a preset delay not connected to either source it would transfer to the good source or back to the preferred source.

Load Decay may be an option. The transfer switch monitors the load bus and transfers when the voltage on it decays to a preset level.
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I've always heard that refered to as a "delayed transition" transfer switch. A "time delay neutral" sounded like you are delaying the connection of the neutral wire. I guess they are probably refering to a "neutral" position on the switch that isn't connected to either source.

Must be a different manufacturer than I am used to dealing with.
 
Many ASCO transfer switches had an in-phase monitor. The primary purpose is to transfer loads back to the normal supply from the generator when the sources are in phase. This "Return-To-Normal" transfer always occurs between two live sources.

The ASCO switch transfers fast enough to keep most loads from dropping out. That fast operation creates an issue if the transfer back to normal occurs out of phase because the inrush current to the motors trips the breakers and can stress the motors. Inrush can be several times normal starting inrush.

The in-phase monitor has to see an out-of-phase condition before it will start looking for an in-phase event. That's to prevent transferring to a dead source and to make sure the monitor is seeing good voltages. (If it just gave an OK when voltage = 0 it would signal a transfer between two dead feeds.) A generator will very seldom run at exactly 60 Hz, so the two sources will be out of synch and the monitored voltages will swing in and out of synch, triggering the transfer.

But trying to transfer between two utility sources, the two voltages are never out of phase, so the in-phase monitor never starts it monitoring and never gives the transfer command.

In this case, you probably have two sources that are out-of-phase due to transformer connections. It will work when the generator feeds it but not the utility.

Verify the phasing first. Then give the transfer switch supplier a call.
 
Phasing is all correct. I think the phase differential is 30 degrees. I was just guessing at 20-25 degrees based on the graph on the 'scope. It now makes sense to me that the transformers involved would cause that differential. This is, indeed, an ASCO switch. The problem I have is that even when the generator comes on after a loss of utility power, the ASCO switch doesn't transfer. The indicator light on the in-phase monitor shows that's it's ready to transfer, but for some reason won't make the transfer. :mad:
 
A-1Sparky said:
The problem I have is that even when the generator comes on after a loss of utility power, the ASCO switch doesn't transfer. The indicator light on the in-phase monitor shows that's it's ready to transfer, but for some reason won't make the transfer. :mad:
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I did suggest this might be an underlying problem in post #15, it seems like days ago; all this stuff about phase differences is just static in the airwaves, and not relevant to the situation when you only have one working source.
 
If you know you only have 30 deg. of phase difference, I don't know why you would need the in-phase monitoring. I would be tempted to turn it off.

I'm assuming the rotation of both sources has been checked.

Steve
 
Yes, rotation has been checked and is correct. I'd like to eliminate the in-phase monitor all together and use a neutral time-delay relay for transfer.
 
A-1Sparky said:
...in-phase monitor in the transfer switch is not allowing a full transfer upon loss of utility voltage.
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Are you expecting a seamless transfer of load if the normal source is lost?

If that is the case you would need a static transfer switch.
If that is not the case, you only have the alternate source left...so nothing to sync to...

Is the real problem transferring back to the normal source? (both sources available but out of phase...)
 
A-1Sparky said:
Yes, rotation has been checked and is correct. I'd like to eliminate the in-phase monitor all together and use a neutral time-delay relay for transfer.
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I'm not sure why you want to use a neutral time delay (or delayed transition) switch either. I'm assuming that will require you to replace the entire transfer switch.

30 degrees of phase shift should be less of a bump than letting the motor stop, and restarting it.

Steve
 
A-1Sparky said:
If I could just bypass the in-phase monitor, that would be fine with me.
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If you have a newer ASCO switch with the group 5 controller (probably so if the switch is less than 5 years old), then turning off the in-phase monitor is just a programming setting that can be turned off in the blink of an eye. If its an older switch, I'm not sure. There might be jumpers or dip switches that turn off this feature. ( I think you mentioned somewhere it was an ASCO switch.)

This is where I've heard that switching between phases with less than 60 degrees doesn't cause a surge larger than the starting motor:

http://www.ascoapu.com/

If you register, they have videos that talk about the different types of transfer switches, and switching motor loads.

If your ATS also drives VFD's or soft starters, that might be another consideration. I'm not sure how they would react to a fast 30 deg. phase change.

Steve
 
Yeah, it's an ASCO switch, and is about 15 years old. It's got a bunch of the dip switches in it. Looks like I'll have to give Kohler a call and see if their tech department can walk me through it. Thanks again for all the responses.
 
A-1Sparky said:
Phasing is all correct. I think the phase differential is 30 degrees. I was just guessing at 20-25 degrees based on the graph on the 'scope. It now makes sense to me that the transformers involved would cause that differential. This is, indeed, an ASCO switch. The problem I have is that even when the generator comes on after a loss of utility power, the ASCO switch doesn't transfer. The indicator light on the in-phase monitor shows that's it's ready to transfer, but for some reason won't make the transfer. :mad:
Click to expand...

I am jumping in here after breezing thru all the posts so bear with me.
How are you testing the ASCO? If you are using the test switch then it is a hot-bus, hot bus transfer and the inphase monitor (synch check relay) is active. You will need a difference of 0.1 to 0.2 HZ between the gen and utility to get a timely transfer. If the F of the gen is dead on 60.00HZ then it may or may not transfer at all because the sweep time between voltages is too slow. I get a lot of calls because of this because the gen techs insist on exactly 60.0000000HZ!! As you increase the speed (HZ) of the gen then the sweep time increases and once the phase angle between the voltages becomes less than around 10 degrees is should transfer.
Now, if you are doing the test by opening the normal source breaker (dead-bus, hot-bus) then the synch check is not active and defaults to allow transfer because like other posts indicated, you are not comparing sources. In this case the phase angle argument goes out the window.
You said the light on the inphase monitor stays on then it sounds like you
are testing by opening the breaker. If this is the case the problem is elsewhere. A 15yr old ASCO without the proper maintenance is prone to failure. The factory grease dries up and the transfer mech becomes sluggish
preventing transfer. Manually transfer it and if it feels tight, clean & relube.
Check the solenoid coil resistance, it may be open. Good luck.
one more thing, shut the switch down, manually transfer it to emergency, and then close the normal breaker. If it transfers to normal then the coil is good.;)
 
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