# Low Hertz/high voltage



## Rjbmed (Nov 19, 2017)

I have a 25kva 60 Hz diesel generator, 1800 RPM, I can now only get 57 Htz, with 260 VAC, if I raise the RPM the voltage increases with no change in the Htz, ????


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## Osviur (Sep 7, 2015)

Hi Rjbmed,

In a synchronous generator, as yours, the frequency (Hz) is tied to the RPM.
In a 3600 RPM generator (2 poles), each revolution per second is a cycle per second (Hz). in a 1800 RPM generator (four poles), each revolution per second generates 2 cycles per second.

1800 RPM means 30 RPS and in a 4 poles generator, 60 Hz. 57 Hz means 1710 RPM.
You can increase the engine speed up to 1800 RPM, then you will obtain 60 Hz.

The voltage generated (between certain limits) is not affected by this little increase in speed, because it is AVR (Automatic Voltage Regulator) dependent and will remain in 260 Volts and can be adjusted in the control panel to the rated value.

Regards


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## KRE (Nov 29, 2011)

Rjbmed said:


> I have a 25kva 60 Hz diesel generator, 1800 RPM, I can now only get 57 Htz, with 260 VAC, if I raise the RPM the voltage increases with no change in the Htz, ????


First, is the engine governor a mechanical, hydraulic, or electronic? If you don't know post photo's of the complete gen set, an engine from all angles. Then one of the engine speed control, its linkage (if any) or the device that moves the fuel control.

You have the Voltage adjusted to high so back it back down if you know how, if not post photos of the A/C alternator as well and I'll point out where if any the adjustment is,


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## Rjbmed (Nov 19, 2017)

If I increase RPM, the voltage increases, even @ 270 VAC, which I verified with 2 multimeters, I have only 57+ Htz, my multimeters do not measure Htz either, I have no tachometer, so not sure of exact RPM's, so I am kind of flying blind. On the panel there is potentiometer, marked AVR, this made no change, so I replaced it, and still no change.


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## Rjbmed (Nov 19, 2017)

If I decrease the voltage, the htz drop accordingly, it appears to be completely manual, governor, throttle, and I see nothing on the alternator, at least externally, that can be adjusted.


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## Rjbmed (Nov 19, 2017)

I do have a potentiometer, on the panel, which had no impact, on anything, so I replaced it and still no impact


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## KRE (Nov 29, 2011)

Who out seeing what you have I can not help you at all. There are 100's of different kind's of gensets made, w/o knowing what you have, trying to help you is pointless.


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## Osviur (Sep 7, 2015)

Hi,

If you increase the engine RPMs, the output voltage increases too and the Hz stay the same, then:

The AVR is not working properly, it must maintain a fixed voltage even with engine speed variations or load changes.

The Frequency meter (Hz meter) must change with the engine RPMs so it not working properly and its reading is not valid.

Do not connect any load until be sure that the voltage supplied is correct and the frequency is really 60 Hz and then, when the generator is connected to its load, it must maintain both values very near. 

Regards


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## KRE (Nov 29, 2011)

My guess is the hertz meter is reading incorrectly. 
It's way cheaper to test than guess an hertz meters are cheap.


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