Synchronous generator cannot produce enough voltage
Synchronous generator cannot produce enough voltage
(OP)
Hello,
I can use some advice on a generator problem. I have a synchronous generator 10MW, 13.8kV. About a month ago, the plant had a shutdown, and afterwards they couldn't get on line because the generator couldn't build enough voltage. We got to about 9.4kV. The rotor was pulled out and checked out. No problems have been found in the rotor. The field current used run at 117A to get the stator voltage to 13.8kV. Now we need 150A to get to 9.4kV. Has anyone encountered such a problem, and can you give me a head start on what to look for?
thanks
I can use some advice on a generator problem. I have a synchronous generator 10MW, 13.8kV. About a month ago, the plant had a shutdown, and afterwards they couldn't get on line because the generator couldn't build enough voltage. We got to about 9.4kV. The rotor was pulled out and checked out. No problems have been found in the rotor. The field current used run at 117A to get the stator voltage to 13.8kV. Now we need 150A to get to 9.4kV. Has anyone encountered such a problem, and can you give me a head start on what to look for?
thanks






RE: Synchronous generator cannot produce enough voltage
If this is a static exciter do you have a blown diode?
Bill
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"Why not the best?"
Jimmy Carter
RE: Synchronous generator cannot produce enough voltage
RE: Synchronous generator cannot produce enough voltage
If there is a double ground on the rotor, he cannot run the machine at all. It would short part of the rotor winding leading to severe magnetic unbalance and vibrations. I agree with your turn shorts though (ac pole drop test should confirm that) along with Bill's speed, diodes and measurement issues.
eeprom
How do you measure the rotor current ? Do you have sliprings on the rotor (DC exciter or static excitation ?) What checks did you run on the rotor ?
RE: Synchronous generator cannot produce enough voltage
RE: Synchronous generator cannot produce enough voltage
Rafiq Bulsara
http://www.srengineersct.com
RE: Synchronous generator cannot produce enough voltage
The location of the double grounds can be within the same pole, just a few turns apart, so only a few turns are shorted out. I agree, if grounds involve large portions of the same pole winding or more than one pole winding, there will be significant vibration.
RE: Synchronous generator cannot produce enough voltage
I like the idea of checking out the voltage measuring device. I don't think that has been looked into.
RE: Synchronous generator cannot produce enough voltage
RE: Synchronous generator cannot produce enough voltage
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Synchronous generator cannot produce enough voltage
RE: Synchronous generator cannot produce enough voltage
RE: Synchronous generator cannot produce enough voltage
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Synchronous generator cannot produce enough voltage
RE: Synchronous generator cannot produce enough voltage
rmw
RE: Synchronous generator cannot produce enough voltage
RE: Synchronous generator cannot produce enough voltage
rmw
RE: Synchronous generator cannot produce enough voltage
RE: Synchronous generator cannot produce enough voltage
rmw
RE: Synchronous generator cannot produce enough voltage
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If we learn from our mistakes I'm getting a great education!
RE: Synchronous generator cannot produce enough voltage
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Synchronous generator cannot produce enough voltage
correctly.
1.You may want to check the output from the Permanent
Magnet Generator supplying your AVR.
2.Check if the AVR is reading the same voltage as the
busbar. If they are the same then the AVR is fine.
If not the same replace the AVR.
RE: Synchronous generator cannot produce enough voltage
Don't get too wrapped up in this. Think of one winding consisting of two pieces of wire, connected in parallel. The stator is a two pole synchronous. Under normal operating conditions, the field current is around 120A and the stator voltage is 13.8kV.
The AVR?? It's not that complicated. The AVR could be in another state, it doesn't matter. While the rotor voltage/current were measured at 243V/146A, the stator voltage got to a little over 10kV. So, unless the rotor's two winding were wired with opposing fields, then the rotor was producing a field. The rotor speed was verified at 3600 rpm. So, knowing this much, what would cause the stator voltage to be so low?
RE: Synchronous generator cannot produce enough voltage
Rafiq Bulsara
http://www.srengineersct.com
RE: Synchronous generator cannot produce enough voltage
The AVR design matters if it is a rotating rectifier type because a failed diode or diodes on the shaft effectively reduces the gain of the system, so a given excitation current produces a smaller output. If it's a slipring machine then that's something which can be discounted. That's why people are trying to establish what the machine configuration is.
If this is a slipring machine then I'd be looking (and praying) for an instrumentation fault, then shorted turns on the rotor. If there's a rotating rectifier then add that between the previous two guesses in the order of likelihood and desirability.
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If we learn from our mistakes I'm getting a great education!
RE: Synchronous generator cannot produce enough voltage
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Synchronous generator cannot produce enough voltage
RE: Synchronous generator cannot produce enough voltage
RE: Synchronous generator cannot produce enough voltage
rmw
RE: Synchronous generator cannot produce enough voltage
How do you know that there are two sets of coils ? This is a cylindrical rotor, in which you cannot physically see the rotor coils. And in a two pole machine, they cannot be connected in parallel since that that would require a lot of complicated connection arrangement not warranted for this capacity of generator.
You have misunderstood how the windings are connected and if they are connected in opposite,as you claim, you'll get zero voltage from the stator.
You're yet to post the generator and exciter details despite many prompts here. If you want proper answers, you should post full details instead of telling us "don't get too wrapped up in this".
RE: Synchronous generator cannot produce enough voltage
eeprom:
The two pole rotor has two sets of coils. Both sets of coils are connected in series but the first coil is wound in opposite direction to the other in order to get one north pole and one south pole.
Seems you mix-up the phase voltage with the terminal voltage (rated terminal voltage is 13800 volts, the phase voltage is 7967 volts). You better check the P.T. arrangement (check this for all three phases). The other possibility is a mix-up between series and parallel connection of the stator winding in case there are two separate circuits. The last possibility I can think of is that the calibrated shunt in the excitation circuit is defect. If the cross section is reduced (broken connection within the shunt) the respective voltage drop increases and simulates a higher excitation current.
It would help the forum to know what kind of work was performed on the generator and excitation equipment between plant shutdown and re-commissioning. We also would be interested to hear from you in case the problems were solved.
Regards
Wolf
WWW.HYDROPOWER-CONSULT.COM
RE: Synchronous generator cannot produce enough voltage
I checked the panel switch to see if it had a big voltage drop. It was okay. Then I traced out the circuit as shown on the three line. I had already checked all the fuses, so I started looking for breaks in the circuit. After some time, I found a wire pulled out of terminal block. And that was it. I re-connected it and all voltages were normal again. Someone had recently installed a new metering device on that circuit, and in doing so put too may wires into a terminal block and one of those wires didn't stay connected.
RE: Synchronous generator cannot produce enough voltage
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Synchronous generator cannot produce enough voltage
rmw
RE: Synchronous generator cannot produce enough voltage
Bill got it right in his 30th July post.