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Phasing an induction generator
5

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?

RE: Phasing an induction generator

3
There's always some remanence in the rotor. In an 11 kV motor, there is enough to kill someone touching the terminals while the machine is rotating.

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

Hot sticks across the breaker a to a, b to b, c to c, when the syncroscope is at zero is very reliable.  If you have PT's and relays that detect phase rotation also can be used.

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

There is not enough voltage on the induction machine before it has been connected to 10 kV. Remanent field usually does not produce more than a few hundred volts at nominal speed. Enough to kill a man, but not enough for hot sticks.

Has to determine direction by other means.  

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Phasing an induction generator

You can try energising with a low voltage and see which way it turns. Rotation should be the same either as a motor or as a generator.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Phasing an induction generator

Of course! Starting an 11 kV motor on LV is trivial. That's a good one, Bill!

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Phasing an induction generator

oops, didn't pay attention to the induction generator part.

RE: Phasing an induction generator

Is this a wind turbine 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

Just the shaft job!  Er.. I mean the hassle of decoupling that large a motor from a load.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Phasing an induction generator

(OP)
Thank you, however, some comments.
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

Interesting question, as we may have one like that soon. Except not so big, and at a lower voltage.

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

Rodmcm

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

(OP)
I have done several induction generators from 11kV to 400V, all were new and of course we had faith in the 'standards' for phase rotation wrt to the drive end. I have never had a failure, however, these are old machines being reused and I cannot necessay trust the rotation and phase markings on the windings. Hence I have been thinking about a full proof method. It also needs to be practical in that the local service supplies for a 2 MW hydro can be less than 50kVA, there is little in the way of a local service supply on the site to run up a 1000kW motor. I know of and have used the methods of Gunnar Englund, but I am also wary about residual magnetism in induction motors/generators.



 

RE: Phasing an induction generator

Rent a 2MW gen set at 480V. Take to site and set up, verifying phase rotation of generators matches phase rotation of utility connection.  Connect to "generator" in question and motor it.  With the wicket gates closed you should get some motion out of it.  Verify proper shaft direction, if not swap leads from the "generator" and try again.

RE: Phasing an induction generator

(OP)
Yes Davisbeach, perhaps that is the only way... expensive though.....

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

"A)residual magnatism may be in a new machine from  the workshop testing, but can be problematic in an old machine"

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
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Phasing an induction generator

Rodmcm,

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

So those two are in popper sequence with the network?  What happens if they aren't, what would be the trace picture?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Phasing an induction generator

Blue and red change place. You get A-C-B instead of A-B-C.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Phasing an induction generator

I agree with Skogs method.  I've done this many times.  It doesn't matter how slow you rotate the rotor.  I use 3 simpsons so you can see the deflection easily. Connect them directly to the output bus and rotate the generator a few RPM

This is not a check for synchronizing but that's not what the OP asked.

 

RE: Phasing an induction generator

That's nice Gunnar. Thank you.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Phasing an induction generator

GT,

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 sad

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Phasing an induction generator

(OP)
Thank you all, looks like I can safely go ahead. What are '3 simpsons' GT?

Many thanks Gunnar.

 

RE: Phasing an induction generator

Rod,

A Simpson is a North American analogue meter similar to an AVO 8.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Phasing an induction generator

Maybe getting off-track a bit, but with regards to "pwrengrds" suggestion of using hot-sticks and synchroscope, this is the method that I used to use (not with induction generators though).

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

Phasing across a breaker equipped for synchronising is fairly easy if the load can be disconnected and the breaker closed. From that state it is easy to verify the VT secondary phasing matches by closing the breaker. Obviously there is no possibility of incorrect primary phasing with the breaker closed. The less direct interaction with the HV plant the better.

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.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Phasing an induction generator

Well technically you only need two analog meters but then you have to think a little :)

RE: Phasing an induction generator

From the perspective of testing with the breaker closed, even if the disconnect's are open, the 52b contact is in a position the disconnects many older sync-check relays. This might interfear with some other testing that might be going on (just a note).

I even saw this with a SEL relay, because of a setting (Really confused the tech.).

RE: Phasing an induction generator

Hi cranky,

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.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Phasing an induction generator

edison123 already posted a simple way: i.e. starting the generator as induction motor from the grid (11kV) with the hydro intake valves closed. If the rotation of the generator is the same as direction when you run the hydro-generator off-grid (intake valves open but generator breakers off), then you know you're phase-in with the grid.

RE: Phasing an induction generator

(OP)
On synch gens we always disconnect the cabes at the generator and close in the 52G breaker, everythimg then gets energised in phase so the VTs ( bus ad gen),synch check, protection synch, gen metering et al can be checked. By closing the 52G under test mode from an autosynch the breaker timing can also be checked. Simple, easy, effective

 

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