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bharath boss
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Rotor Current

06/14/2020 11:32 AM

Hi all,

An Hydro Generator, Pelton wheel type turbine,vertical, under shutdown condition voltage is experienced in rotor winding (Note: Under operating condition, the rotor winding will be fed with DC current via slip ring)

Checked with multimeter and it shows +ve to Ground 4 Volt AC and -ve to Ground 4 Volt AC. Stator has been earthed properly. But I am confused how does the AC voltage comes in rotor,that too under shutdown condition. No other AC circuit is linked with the rotor. Please clarify.

Thanks.

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SolarEagle
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#1

Re: Rotor current!

06/14/2020 11:42 AM

Your exciter is still on?

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bharath boss
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#8
In reply to #1

Re: Rotor current!

06/14/2020 11:40 PM

No... Everything is in OFF condition.

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#2

Re: Rotor current!

06/14/2020 1:44 PM

Induction, perhaps. Are there other generators in the vicinity that are running? Some more specifics about the readings you took might help.

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SolarEagle
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#4
In reply to #2

Re: Rotor current!

06/14/2020 2:27 PM

Ghost voltage, put a load on it to see if it disappears...an led or two...

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bharath boss
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#11
In reply to #4

Re: Rotor current!

06/14/2020 11:54 PM

I discharged it... But again it builds up...

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PWSlack
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#16
In reply to #11

Re: Rotor current!

06/15/2020 8:11 AM

Does it light a 4-6V tungsten light bulb? If not then it is just stray voltage picked up by a high input impedance voltmeter.

If it proves worrisome then simply short-out the output terminals when the equipment is in <...shutdown condition...>, and it will go away.

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bharath boss
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#9
In reply to #2

Re: Rotor current!

06/14/2020 11:45 PM

Yes sir.. Other units are in running condition .. Paralleled.

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SolarEagle
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#15
In reply to #9

Re: Rotor current!

06/15/2020 8:07 AM

Well why didn't you say so, then the coil is sitting in a moving electrical field generated by the other generators, and you are seeing some induction voltage manifesting in the rotor windings....

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bharath boss
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#18
In reply to #15

Re: Rotor current!

06/15/2020 12:10 PM

If so... The same should be with other units.. But I checked with another unit in shutdown condition, no voltage was found in rotor.. Only this specific unit is getting AC voltage in rotor winding..

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PWSlack
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#20
In reply to #18

Re: Rotor current!

06/15/2020 12:12 PM

Why is this any trouble or any cause for concern?

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#21
In reply to #18

Re: Rotor current!

06/15/2020 12:21 PM

Well then I would check the em fields with your handy em field tester to locate the field effecting that coil...

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PWSlack
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#22
In reply to #21

Re: Rotor current!

06/16/2020 3:26 AM

These can come in handy too:

.

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#23
In reply to #22

Re: Rotor current!

06/16/2020 7:32 AM

True, they do a great job of identifying presence and polarity but they are difficult to use to measure field strength.

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bharath boss
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#25
In reply to #15

Re: Rotor current!

06/18/2020 8:55 AM

If so... The same should be with other units.. But I checked with another unit in shutdown condition, no voltage was found in rotor.. Only this specific unit is getting AC voltage in rotor winding..

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SolarEagle
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#3

Re: Rotor current!

06/14/2020 2:21 PM

Your meter is out of calibration...?

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bharath boss
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#10
In reply to #3

Re: Rotor current!

06/14/2020 11:53 PM

No sir... I checked in different multimeters.. Same value..

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#5

Re: Rotor current!

06/14/2020 5:12 PM

Well, it's actually rotor voltage, not current. My guess is that there are stray magnetic fields in the vicinity and the coils in the rotor are acting as the secondary coil of a transformer. A voltmeter provides very little load to a circuit. There is voltage but almost no current, so there is probably not much power there.
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redfred
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#6

Re: Rotor current!

06/14/2020 6:06 PM

Congratulations. You have now rediscovered the magnetic core antenna.

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SolarEagle
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#7

Re: Rotor current!

06/14/2020 10:55 PM

Maybe it's some of that free energy they talk about...

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PWSlack
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#14
In reply to #7

Re: Rotor current!

06/15/2020 6:28 AM

Is that related to dark matter?

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PWSlack
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#12

Re: Rotor current!

06/15/2020 3:08 AM

Is the thing spinning at all?

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#24
In reply to #12

Re: Rotor current!

06/16/2020 12:50 PM

Is the thing spinning at all?

That's a very good question. Even without any exciter current, residual magnetization (remanence) of the core will generate a voltage.

This voltage is actually essential for self-excited machines, to boot-strap themselves and generate their own exciter current. If a machine has sat idle for a long time, this residual field disappears and it is sometimes necessary to flash the field to reestablish it so the generator can start up properly.
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SolarEagle
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#26
In reply to #24

Re: Rotor current!

06/19/2020 6:58 AM

It would be interesting to see if the voltage drops a bit everyday...or stays the same..

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PWSlack
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#13

Re: Rotor current!

06/15/2020 3:15 AM

Please describe <...shutdown condition...>?

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bharath boss
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#17
In reply to #13

Re: Rotor current!

06/15/2020 11:36 AM

Means generator is in standby. Generator field breaker is in open condition.

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PWSlack
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#19
In reply to #17

Re: Rotor current!

06/15/2020 12:12 PM

What is being seen is the rotor spinning in Earth's magnetic field and other stray fields, then: a few volts as seen by a high impedance measuring device and nothing much in the way of current.

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