Problems with a three phase generator

[petronila]

Dear All

We was rewound the main rotor of one low voltage synchronous generator (2160 kW-1500 rpm-400 v-50 Hz), we was test the generator and don´t generate.

We was change the AVR, and don´t generate too.

We was follow all troubleshutting procedures, we try with external excitation with battery and then the generator works but with the AVR ´connected don´t (AVR New)
The generator belongs to one cogenerative plant and works with otherone in parallel, so we don´t know if in the plant they have some device to make it work.

Could the magnetic remanence will loose?

How can I restart the remanence?

Thanks for the inputs

Carlos

 

[waross]

The first step is to reverse the connections from the AVR to the field. That may be all it takes. If that fails, the next step is to energize the field with a battery, and then reconnect the AVR with the same polarity.
If the AVR has separate sense and power terminals, power the AVR from an alternate source, run the generator up and then shut down and reconnect the power terminals to the generator.


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

 

[petronila]

Hello Bill

Thanks for the answer, we was start the generator and we have more problems, the permanet magnet stator of the exciter burn off, in normal conditions the no load exciter volage it´s 10 or 11 volts and raise once the load increases but now we have 50 Volts, is too high.

What do you think?

Thanks again

Carlos

 

[waross]

It sounds as if your AVR may be shot.
The Permanent Magnet Exciters that I am familiar with develop about 220 Volts, but the difference in voltage is not important as long as it is the design voltage. What is important is the method of operation.
An AVR must have power in before it is able to send power out to the generator exciter field.
The conventional method of powering the AVR is to use the residual voltage of the generator. This is only a few volts but as soon as the AVR rectifies this and sends it back to the exciter, it adds to the residual voltage and the output voltage starts to rise. This continues until the desired voltage is reached and the AVR then cuts back its output so as to control the voltage.
The newer method is to use a Permanent Magnet Generator (PMG) to supply power to the AVR.
It sounds as if your PMG is bad. This may have been caused by insulation failure or by a faulty AVR.
Note, there is no relation between the voltage output of the PMG and the DC output of the AVR. There is no protection on the PMG so a turn to turn short will develop heat from circulating currents and possible arcing. The heat developed will eventually cause the failure of adjacent windings and may progress to complete failure of all the PMG windings.

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