DC generator reverses polarity
DC generator reverses polarity
(OP)
Hello,
Has anyone seen or heard of this happening? I haven't gotten all the details but here is the main points. A motor driven dc generator is used to provide the excitation to 2 ac generators. Units are running fine until recent trip. Operator could not get unit back on line and calls an electrician to troubleshoot. Electrician tells me that the dc voltmeters are indicating reverse polarity.
Any thoughts on how this could happen or am I being yanked?
Has anyone seen or heard of this happening? I haven't gotten all the details but here is the main points. A motor driven dc generator is used to provide the excitation to 2 ac generators. Units are running fine until recent trip. Operator could not get unit back on line and calls an electrician to troubleshoot. Electrician tells me that the dc voltmeters are indicating reverse polarity.
Any thoughts on how this could happen or am I being yanked?





RE: DC generator reverses polarity
Just flash the field in positive direction and you should be fine again.
And.. Er.. Drive carefully!
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: DC generator reverses polarity
Could you explain or direct me to a more detailed explaination of what happens and why?
RE: DC generator reverses polarity
I'm just wandering why the electrician told you that a dc voltmeter indicates reverse polarity while the unit was never get back on-line..??
"Whenever you are asked if you can do a job, tell them, certainly I can! Then get busy and find out how to do it." Theodore Roosevelt.
RE: DC generator reverses polarity
This unit is seperate motor driven dc generator to provide dc to 2 hydroelectric generators, so we able to run it for testing. The dc voltmeters on the board were pegged in the wrong direction and reverse polarity confirmed with a voltmeter.
RE: DC generator reverses polarity
I would expect that a transient or reverse voltage must have enough energy to exceed the hysteresis of the magnetic circuit of the generator so as to be able to reverse the polarity.
respectfully
RE: DC generator reverses polarity
in the future -- but can you supply the data of the DC
generator?
Is it shunt field? Can you tell- or measure -- the field
current and VTG, too ? Perhaps a diode could do the trick.
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RE: DC generator reverses polarity
A diode would work as long as the transient did not exceed the voltage rating, (or current rating, if it was a transient in the opposite direction.) During the event you may have had a low frequency AC fed back to the exciter generator from loss of load and resulting speed variations. A pole slip would probably give a much more aggressive transient.
Rather than add diodes I would repair the brush holders and spend my energy on preventive maintenance.
That said, I would not say that diode protection is wrong.
My point of view.
Your choice.
respectfully