Phasing 1

[golruss]

Hi All,

I was just wondering whats the best way to ensure phasing is correct between two sources, one is the ultility and the other is a emergency generator. Source voltages are 4160v and has two sets of PTs connected Open Delta with B-phase grounded on each. I was thinking of doing a rotation check on both sources and compare them. I am also going to do a phase angle check with phase B- as reference, what angles should I be seeing?
Thanks any help would be appreaciated.

Golruss

 

[davidbeach]

A sync check relay (IEEE device 25) is the best was of verifying correct synchronization. You want the angular difference to be as small as possible, usually less than 10 degrees and smaller is better.

 

[ScottyUK]

Phase rotation is very important: European sync-checks usually only use one phase from each side, and assume that the phase rotation has been verified at commissioning. That obviously puts the responsibility on the commissioning engineer to test thoroughly.

Are you actually wanting to parallel the supplies, or just ensure that they have the same electrical rotation? Unless your generator has a good governor under the control of a synchronising relay (or synchroniser) - not a synch-check relay - then your generator will drift in and out of phase. Once the frequency difference exceeds one Hertz or so your instruments will become hard to read. The three light bulb method is an old but easily-rigged technique for proving synchronism. It is remarkably effective too. You could also use a synchroscope but unless you can borrow one or have frequent use for it I wouldn't suggest buying one just for this test.


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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[rbulsara]

This is an emergency generator,means that it will come only when utiltiy power is off.

So as ScottyUK said if you are not paralleling, all you need to do is verify the phase rotation. No synching is required.

If you are infact paralleling with the utility then sycn check or sychronizer is required.

In that case, relying just on PT wiring is dangerous, if PT leads are swapped. So during first commissioning you must have a qualified testing company (or contractor)check the phase rotation with "Hot Phasing".There are proper probes available for this at this voltage. Then you need to validate your PT wiring.

I do not understand your phase angle check with "B" as reference. For parallelling you need to check the phase angle between like phases of the two source (across the tie breaker ), that is A to a, B to b and C to c . This phase angle difference should be less than 10 degrees. Lesser the better.

 

[aolalde]

Hello golruss
BE1-25 Sync-Check Relay Checks for proper phase angle and voltage before closing a breaker.
See the following site,

http://www.basler.com/html/pcsdf-25.htm#BE125A

 

[golruss]

Thanks for all the responce, I went to the site today and found that there is indeed a synch check relay ABB 25S. The problem is after the passage of the hurricane the utility supply was lost (broken conductors and down poles). The utility supply is actually the emergency supply and is only used when there is a need for additional capacity. The customer was told by the utility that there is the posibillity of incorrect phase sequence so they were afraid to try and sync. without it being checked. I verified the phase sequence on both supplies and since they were using phase A & C, I just checked the angular difference A being the ref. and got a reading of C lagging A by 300deg, which is correct. I told them everything was ok and left.
Thanks to all again for you help.
Golruss

 

[rbulsara]

300 deg?? and why would you check between A and C?? It may only be for checking roation.

and even if you do, 3 phases are 120 deg apart from each other.. so the diff will be +/-120 or +/-240 degrees, why 300 deg is Ok?

 

[stevenal]

I told them everything was ok and left.

Well, given the first action I guess the second one would be advisable.

 

[eglaude]

No offence Golruss, but you better have an electrical testing firm familiar with parallel systems check out your problem. Sounds like your sources will be paralleled, thus hot phasing is a must and make sure that your alternate source, i.e. genset perhaps, is in sync too.

I have to agree with rbulsara. What kind of measurement techniques were you using and perhaps more importantly what did you sign off on? Wow!!

 

[ScottyUK]

If your check-synch relay is typical and only uses a single phase sensing circuit (line-neutral or line-line), then you should consider alternate means for proving phase rotation because a single relay of this type can not detect a reverse rotation condition. A second synch-check relay wired across a different phase pair used in conjuction with the existing one would achieve this. Most applications don't expect the utility to periodically reverse the phasing (or the generator to run backward ) so the single sensing circuit is usually perfectly acceptable.

Agree with previous three posts: something sounds very odd with a 300[°] phase shift. Is one feed from a delta and the other from a star winding? Get someone with experience to help you.


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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[bacon4life]

I heard about a crew needing to check phasing, but not having the right equipment. After a little brainstorming, they decided to use a small fuse they had on the truck, figuring if it was wrong, the fuse would simply open. Instead both feeders saw the fault and opened.

 

[HCBFlash]

Uh, It seems to me that using a simple phase rotation tool (at initial setup time/ system commisioning) will give you the rotation of both units. If A leads B on util, it needs to on your gen. Swap leads to accomplish this.

Sync for loaded transfer is important, obviously, assuming there are loads sensitive to "rapid" transfer. However... I have been in facilities with very few rotating loads that required transfer while rotating, no other loads needing instantaneous xfer, and were delayed or even "tripped" for manual restart. Yes that included HACR loads.

If you connect to util when your generator output falls outside of electrical parameters, you've obiously got some phase rot angle (relative to util) drift, even frequency droop/drift, so tight sync is almost randomized, and absolute 0v transfer would be achieved only by voodoo and a winning lotto number.

Were the original phasing controls ruined entirely? They're off-the-shelf repair parts for CAT units.

Please let us all know how this works out for you!

 

[ScottyUK]

Hi HCB,

... The customer was told by the utility that there is the possibillity of incorrect phase sequence...

A test at commissioning only tells you that it is right (or wrong) at that moment in time. Such a test is not much use if the utility reverses rotation after commissioning, which seems to be a risk under abnormal conditions when the utility service has been damaged and a temporary supply is rigged.


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Start each day with a smile. Get it over with.

 

[itsmoked]

OW! How could a utility ever allow a phase reversal?!?!? That's like having the Sun come up in the west! Think of the thousands of fans suddenly turning the wrong way and the drill presses... And all the down hole pumps that spontaneously disassemble.. ugh.