Phasing an induction generator
Phasing an induction generator
(OP)
I am to commission an old 11kV 1000kVA induction generator. How can you reliably and easily check that the phase rotation of the rotating generator is the same as the grid?
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Phasing an induction generator
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Phasing an induction generatorPhasing an induction generator(OP)
I am to commission an old 11kV 1000kVA induction generator. How can you reliably and easily check that the phase rotation of the rotating generator is the same as the grid?
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RE: Phasing an induction generator
You can use this fact to determine phase rotation. Connect an oscilloscope or a recorder to the terminals and rotate the machine by hand or using a power tool. Observe the induced voltage and see if A comes before B and B comes before C - then the rotation is positive. If not, it is negative.
See attached recording. In this recording, the machine was given a little nudge to start rotating. The rotation slows down during the recording, which can be seen in the waning amplitudes.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Phasing an induction generator
Keith Cress
kcress - http://www.flaminsystems.com
RE: Phasing an induction generator
You can also use a phase rotation meter on the secondary of the PT's, though be careful because some rotation meters don't work well if you have delta PT's. What I have done is use the phase rotation meter and then reverse the connection and check it again, checking to get a reversed phase reading with the leads reversed.
I have used both, when using the PT's I like to use the same set of PT's both times to double check the PT connections.
Good luck and be careful, David
RE: Phasing an induction generator
Has to determine direction by other means.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Phasing an induction generator
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Phasing an induction generator
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Phasing an induction generator
RE: Phasing an induction generator
I would disengage the prime-mover, start the induction generator as an induction motor, direct-on-line and note that direction of rotation. If it matches the rated direction of rotation, then you are done. Else, you switch any two phases.
Does anyone see any problem with this ?
RE: Phasing an induction generator
Keith Cress
kcress - http://www.flaminsystems.com
RE: Phasing an induction generator
A)residual magnatism may be in a new machine from the workshop testing, but can be problematic in an old machine
B) This is a hydo machine(s) on the end of a long rural feeder. Starting DOL would take out the line, but at least I would only do it once!
C) However, what if the generator is in the region of 4MW(one was commissioned here the other week with a huge inertia, they are not unusual)
D) Often with hydo turbines the turbine is overhung on the generator shaft, so a bigger job disconnected to check direct on line
E) I have heard that there is a technigue for running the generator up to speed and closing in only two phases, measuring the third. I can't make this work in my head, any comments?
RE: Phasing an induction generator
If it's a hydro unit I would think you can spin it with the breaker open. Between the PT's om the primary, and a high voltage probe on the unit you should have enough voltage to verify the phase connection. Although the rotating frequency means you have to look at more than one phase at a time.
Connecting two phases makes the unit a single phase machine in essence, which means sending or recieving power will make the machine unbalanced.
Interesting enough closeing two phases of some capacitor banks, and phasing in the third is something that's being done now.
RE: Phasing an induction generator
If it is an old machine, how were they synchronizing before ?
And, residual magnetism doesn't die down with age.
BTW, I don't think synchronizing by generator residual magnetism is fool-proof. The 11 KV PT could have been wrongly wired leading to a misleading assumption that the phases are matched.
I have always perfered a single PT being fed individually from the line or the generator at anyone time and checking with the sequence meter. But, in your case, I am stumped.
RE: Phasing an induction generator
RE: Phasing an induction generator
RE: Phasing an induction generator
Edison123...I do not know, they where uplifted from a decommissoned plant and are being relocated. However, we are seeing more and more small plants that are using second hand motors. I have just redone the automatic controls system on a 2 x 1000kW pelton system with old 3.3kV mining motors. Been running for 6 years.
RE: Phasing an induction generator
With what facts are you backing this?
I have used it so many times that I can guarantee it will work on every machine, from FHP to MW. Even if there are only a few volts, the sequence will always be true.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Phasing an induction generator
Your question "E) I have heard that there is a technigue for running the generator up to speed and closing in only two phases, measuring the third. I can't make this work in my head, any comments?"
The answer is: YES!
That is how many small workshops produce three-phase systems out of two phases. I did not have any recordings, so I set up a small machine (.55 kW/400 V/50 Hz) to get one. See attached file.
As you can see, there are three very distinct phases. Because the machine is small and run off 230 V instead of 400, the resulting three-phase system is not perfect. But there is no doubt as to phase sequemce.
If you can run the generator up to speed and if you can connect to two phases, which I think should be rather easy and also possible. Then hot sticks can be used to check rotation. You must be very close to synchronous speed to be sucessful, though.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Phasing an induction generator
Keith Cress
kcress - http://www.flaminsystems.com
RE: Phasing an induction generator
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Phasing an induction generator
This is not a check for synchronizing but that's not what the OP asked.
RE: Phasing an induction generator
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Phasing an induction generator
Never thought about using analogue meters. I am a 'scope-and-recorder' guy, myself. But three 260's would be quite an impressing sight. I haven't go but one
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Phasing an induction generator
Many thanks Gunnar.
RE: Phasing an induction generator
A Simpson is a North American analogue meter similar to an AVO 8.
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If we learn from our mistakes I'm getting a great education!
RE: Phasing an induction generator
However, would modern safety standards prohibit this method?
Also, there was the problem of finding volunteers to hold the hot-sticks - they're the type of people that volunteer for bomb disposal, or finding the source of major radiation leaks!
RE: Phasing an induction generator
Re. volunteers:
I'm totally uncompromising if I'm not happy with someone's attitude toward live HV testing: I won't work with anyone who has a gung-ho attitude or treats working on live plant as some kind of rite-of-passage. A substation ain't the place for adrenaline junkies. Most times direct interaction with live HV can be avoided: sometimes it takes a little longer to do it safely, but you are dead for a real long time if the short cut goes wrong.
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If we learn from our mistakes I'm getting a great education!
RE: Phasing an induction generator
RE: Phasing an induction generator
I even saw this with a SEL relay, because of a setting (Really confused the tech.).
RE: Phasing an induction generator
I wasn't really meaning to go as far as the sync check relay, just the VTs. I'm quite happy with a meter at the VTs to prove that the phasing is ok, but valid point about the relay. Thanks.
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If we learn from our mistakes I'm getting a great education!
RE: Phasing an induction generator
RE: Phasing an induction generator