Phasing vs. Rotation

[Oldbull]

I am working on a project that requires installing a manual transfer switch to a UPS so it can operate on normal or emergancy power.

My question is does the rotation of the feeds and the phasing need be the same for the two powers coming into the switch?. The rotation is clock wise for both but the phasing is CBA for the normal power and ABC for the Emergency power. The Emergency power feed is the original feed for the system.

My major concern is that the difference between the phases may cause problems in the unit it is attached to.

 

[qcroanoke]

I am working on a project that requires installing a manual transfer switch to a UPS so it can operate on normal or emergancy power.

My question is does the rotation of the feeds and the phasing need be the same for the two powers coming into the switch?. The rotation is clock wise for both but the phasing is CBA for the normal power and ABC for the Emergency power. The Emergency power feed is the original feed for the system.

My major concern is that the difference between the phases may cause problems in the unit it is attached to.

If they are both in the same rotation (clockwise) it should be fine.
A lot of UPS units will not operate if the incoming power is out of rotation.

 

[kwired]

rotation is most important, only time actual phasing is important is when you have two sources that operate in parallel - then you need to have equipment to control phasing. Utility phasing is usually going to be pretty solid and consistent, some other smaller local source is what would need to be matched to the utility if paralleling to the utility.

Other case not involving paralleled sources would be something like a high leg delta system - you may need to make sure the high leg is in same position when either source is applied depending on the load(s) supplied.

 

[xformer]

I am working on a project that requires installing a manual transfer switch to a UPS so it can operate on normal or emergancy power.

My question is does the rotation of the feeds and the phasing need be the same for the two powers coming into the switch?. The rotation is clock wise for both but the phasing is CBA for the normal power and ABC for the Emergency power. The Emergency power feed is the original feed for the system.

My major concern is that the difference between the phases may cause problems in the unit it is attached to.

IMHO... The Phasing needs to be the same. Since all the equipment connected to the the system is phased for normal power, a phase reversal in the emergency power can cause adverse side effects in equipment.

 

[GoldDigger]

If the UPS is of the dual conversion (constantly supplying inverter power to load) type, then the input switchover should not have any effect on either the UPS or the loads.
But if normally operates in bypass mode, then flipping the transfer switch can suddenly apply out of phase voltage to single phase or three phase motors and transformers. This could cause a current surge comparable in magnitude to the starting or turn on surge on that equipment. The result could be noisy and might even trip a breaker in the UPS or power source, yes?

Tapatalk!

 

[Oldbull]

Thanks to ALL

Thanks to ALL

Thanks to everyone that replied to my question!

I think you have cleared up any questions I had with any possible problems with the unit.


Have a Good Day and be SAFE!

 

[kwired]

IMHO... The Phasing needs to be the same. Since all the equipment connected to the the system is phased for normal power, a phase reversal in the emergency power can cause adverse side effects in equipment.

You are absolutely correct, OP may or may not be going deeper then just phase "rotation" though. There is a difference between just having same rotation and being truly "in phase". In phase becomes much more important when you have two separate sources either connected together or when making a rapid transfer between them.

If you have wind, PV or other on site power production and are connecting it on line with the utility, you must have your on site production "in phase" (even with single phase sources) with the utility, or the two sources will not play well together.

 

[ATSman]

Phasing

Phasing

If the two sources are fed from the same transformer then a simple voltage check will determine if the phasing is the same. Voltage between phase A1 to A2, B1 to B2, and C1 to C2 should all be zero. If one or more readings read phase to phase voltage then the phases are rolled and have to be swapped.
If the sources are fed from separate transformers then the readings should be close to zero (by several volts) due to the phase shift of the windings.
In both cases if the phasing is the same then the phase rotation is automatically the same between the 2 utility sources.