EXCITER FAULT REMEDY 3

[chimse]

i have a bit of a problem i would like to share.how do you resolve the excitation problem on a one megga volts diesel generator,the genset is unable to generate voltage due the non performance of the exciter,the exciters winding has been worked on but still cant perform

 

[edison123]

What sort of exciter, static, brushless, dc machine ? Post full details of the generator.

Muthu

http://www.edison.co.in

 

[waross]

Assuming that it is brushless;
Check the AVR.
Disconnect the rotating diodes and surge suppressor(s).
Do megger and continuity checks on the exciter stator winding, the exciter rotating winding, and the main field winding.
Change the rotating diodes and surge suppressor(s).
Check output using an automotive battery to supply excitation. You may wish to fit a discharge diode to the field to make disconnecting the battery safer
If this is a PMG machine, check the output of the PMG. Expect to find 200V to 300V, AC.

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

 

[chimse]

the exciter being a DC Machine,the Genset is a 1250kva,1500rpm,0.8pf disel engine with compressor engine start,the genset is able to run but no generated voltage due to non perfomance of the exciter which is also coupled to the prime mover on a seperat belt driven.i have tried to rewind the exciter wdgs but it has not responded

 

[chimse]

the genset being a 1250kva,the exciter is a dc machine

 

[edison123]

Many reasons why a dc generator excite

1. Wrong direction of rotation.

2. Loss of residual magnetism.

3. The field winding resistance (with regulating resistance in series) exceeding the critical resistance.

4. Underspeed.

Muthu

http://www.edison.co.in

 

[rbulsara]

You say the exciter has been worked on. What was done to it?

Verify that DC exciter itself is wired correctly, especially the polarities of field windings. Test actual leads and winding continuities, they could have been landed on wrong terminals.

Rafiq Bulsara

http://www.srengineersct.com

 

[chimse]

the exciter wdgs were rewired after problem was noticed.

 

[waross]

Energize the generator field with an automotive battery in place of the exciter. 12 volts. See what voltage the generator will produce. If the generator will not produce voltage the problem may be in the generator itself.
How is the voltage controlled?
Do you have an Automatic Voltage Regulator (AVR) or does the set use current transformers, diodes and resistors to control the exciter?
We should know this before giving more suggestions.

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

 

[chimse]

it uses current transmers diodes and resistors for voltage regulation,so with the automotive batery to be used how do i make the connections so to excite the generator field?

 

[waross]

Disconnect the regulator from the exciter and connect the battery. The polarity should be the same. You should get an output from the generator.
If not, disconnect the exciter from the generator and connect the battery to the main generator field.
It is good practice to connect a discharge diode across the fields before connecting the battery. The diode will provide a discharge path and avoid high voltage pulses which are dangerous to both people and machines.

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

 

[chimse]

actually it uses manual voltage control regulation

 

[chimse]

so you mean the output connection of the exciter after disconnection should the ones i connect to the battery then to the generator

 

[burnt2x]

Any diagrams? Pictures/drawings speak a thousand words, they say.

 

[rbulsara]

It should be easy enough to see if the exciter produces the voltage on its own, without connection to the generator.

Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

That is correct, Rafiq. My thinking is still influenced by checking brushless exciters.
However, regulator problems may be the cause of the exciter failing to produce. Hence the battery in place of the regulator.

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

 

[edison123]

chimse - Don't take this the wrong way. You need to bring in an generator expert. Trying to troubleshoot with the tips here is not a good idea unless you're a generator expert.

Muthu

http://www.edison.co.in