Phasing
Phasing
(OP)
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
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





RE: Phasing
RE: Phasing
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.
----------------------------------
One day my ship will come in.
But with my luck, I'll be at the airport!
RE: Phasing
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.
RE: Phasing
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
RE: Phasing
Thanks to all again for you help.
Golruss
RE: Phasing
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?
RE: Phasing
RE: Phasing
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!!
RE: Phasing
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.
----------------------------------
One day my ship will come in.
But with my luck, I'll be at the airport!
RE: Phasing
RE: Phasing
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!
RE: Phasing
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.
----------------------------------
Start each day with a smile. Get it over with.
RE: Phasing