Generator exitation 1

[jncza]

I need help please.I am stuck with a 3,3MW Hydro generator that wont exite when exitation is selected after the machine reached operating speed,I tested the rotating diodes,exiter and auxilary exiter windings .Even external exitation with a 6v battery didnt help.When I test the exitation voltage it measures 1.4 Volt,is this enough to exite the machine?

 

[davidbeach]

I would expect that a 3.3MW machine would require considerably more than 1.4 volts on the field. What does the machine nameplate say? How many amps is the field pulling?

 

[jncza]

Hi ,I need to check on that.thanks

 

[waross]

Hello davidbeach
I have a suggestion, but i'd rather have your comments on it before suggesting that jncza try it on his machine.
With the machine stationary, If a moderate AC voltage was applied to the exciter field, would jncza be able to induce enough voltage and current to see if current is getting through the exciter and to the rotating diodes? It would also be a way to get current flowing in the main field. I would expect one phase of the exiter output to the rotating diodes to be higher than the others.
respectfully

 

[davidbeach]

waross, I really don't know.

 

[edison123]

jncza,

I assume you have a brushless exciter. How did you measure the excitation voltage as 1.4 V ?

Check your diodes for correct polarity and if they are working.


* The shin is the device to find your furnitures in the dark *

 

[jncza]

Hi.

It is brushless.The battery voltage is 6V.I measured the voltage across the exiter coil(4,1V) and then at the terminals where the exiter voltage goes into the AVR(1,4V)

 

[edison123]

What is the rated voltage of the field of the brushless exciter ?


* The shin is the device to find your furnitures in the dark *

 

[patrick7]

Are there any protective relays in the system that may have a contact stuck thus preventing the excitation system from operating?

 

[waross]

I'm not sure how you tested with the battery. Here's how.
Connect the battery in place of the voltage generator. It's a good idea to reverse connect a diode across the exiter windings to avoid the inductive kick when you disconnect. Properly applied, the diode must have a voltage rating greater than the battery voltage and a current rating equal to or greater than the current that will flow in the winding. When you disconnect the battery the current and voltage will both decay to zero as the energy of the field is disipated in the field winding.
With the set running you should get voltage out of the generator. If yes, then check your voltage regulator. If no voltage, check for problems inside the machine. It could be a winding shorted or open. It could be the diodes or suppresors. The 1.4 volts out put sounds like the residual voltage that you get with no field applied. This residual varies from machine to machine but is generally enough to "Bootstrap" the exitation system. If a generator looses its residual and won't pick up, usually the battery procedure wil induce enough residual to put it back in operation. (Sometimes it takes more).
However if you have connected a battery in place of the voltage regulator with no results it's time to start checking internally.
yours

First check the voltage regulator. Use the manufacturers recommended test procedure.
The

 

[waross]

Sorry I must be losing it.
"Connect the battery in place of the voltage generator."
Should read;
"Connect the battery in place of the voltage regulator."
Do you have a PMG (Pemanent Magnet Generator) exitation system?

 

[ScottyUK]

Start at the beginning: is your excitation power source present? What type of source is it: PMG, or field flashing battery?

Is the AVR able to drive current around the exciter field circuit?

Waross' idea with the 12V battery is reasonable since the machine is fairly small, but be careful not to over-excite the machine. Rated excitation current is usually based on the machine exporting reactive power: under no-load conditions the field current required to maintain rated terminal voltage will be substantially lower than under full load conditions. You will need a fairly large AH rated battery - an automotive battery would be a reasonable guess.

It would help if you would post some data on the excitation system.


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I don't suffer from insanity. I enjoy it...

 

[waross]

Hello ScottyUK
Yes, I was thinking 12 volt automotive battery for testing without the Automatic Voltage Regulator. For field flashind when there is some residual but not enough to bootstrap, My plan "A" is a "D" size flash light battery in series with the voltage regulator. It usually works (20 to 350 KW range). If that fails, I go for a heavier battery and use backfeed protection diodes so I don't blow the Automatic Voltage Regulator.
respectfully

 

[amps21]

I am not very familiar with generator excitation systems but JUst a thought. Is it not possible to check the field winding resistance and check with manufacturers tested value to see if the winding is shorted or open etc.

 

[waross]

hello amps21
Good suggestion. That will probably be our next suggestion.
In a machine with PMG (Permanent Magnet Generator) excitation you have a stationary winding in the PMG. This feed power to the AVR (Automatic Voltage Regulator). The AVR feeds the stationary windings of the brushless exciter. The (AC) power induced in the rotating winding of the exciter is fed to the rotating diodes and supressors. The DC from the diodes is then fed into the main rotating field.
What ScottyUK and I are discussing is basically breaking the system into two parts. If we get a good result with the battery we will assume that the fields are servicable and concentrate our efforts on the AVR and PMG.
If the results with the car battery are disapointing we will probably follow your suggestion and recommend to jncza that he start breaking connections and checking resistances and meggering. On the practical side, the connecting wires are probably tied down to the shaft so that centrifugal force doesn't throw then out. The connections are often heavily coated with glyptol. I don't like to touch the rotating parts and connections until I have proven by external tests that I must.
I hope this answers your question amps21.
yours

 

[amps21]

10-4,

Thanks

 

[tbwil1]

If you have "flashed the field" with a battery and you saw no increase at all in output voltage at the main stator then you have pretty well ruled out the regulator or PMG (assuming your battery voltage didn't drop to near zero when you connected it). Even at 6 volts you would see a rise in output voltage at the stator. Polarity of the diodes comes to mind if you have had them out of the machine. If those check OK you are down to main rotor and stator resistance checks as suggested above. Good luck.
regards

 

[tbwil1]

One other thing, you should see F1 and F2 designations on the wires that you are applying the battery voltage to. They will be connected at the voltage regulator as the output.Your earlier post mentioned you were measuring input to the avr, this test is temporarily replacing the avr. Be sure you are applying the battery voltage to the right components with the right polarity.
regards