Generator Voltage Problem

I'm not an expert, but maybe you have an automatic voltage regulator (avr) as a controller and the avr is over responding to the electrical loading of the alternator, the avr is designed to maintain the rpm of the machine thus frequency and output voltage is kept constant.

one way of checking is to ensure that the speed is not suddenly increasing as you load up the machine.

best of luck

Hello Ally,

Just a correction..Avr controls the voltage and does not control the rpm of the machine.

Check the droop setting in the AVR of the generator.

What is the Pf reading on load ?

I suggest calling the supplier tech representative to deal with this if the machine is still under warranty.

The rpm of machine is controlled by governor which is a different animal.

Cheers.

Perfect answer. I gave you a GA for that.

Droop characteristic is the problem. In fact the droop is a rise for some reason!!! The AVR should then be lowering the excitation to achieve a steady and correct voltage.

It is possible to design an alternator to have a rising characteristic instead of a droop, its not usual, but completely possible.

How much of a load are you placing on the genset when its output goes high?

If you have a no load run, what does the voltage regulator regulate (you said that it works OK) ?

Usually, the voltage regulator has a reference voltage with whom it compares the output voltage and, if the voltage is lower, it increases the excitation voltage to bring it back to the prescribed value ( with a +/- 2.5% usually). This voltage drop occurs when you apply load. How much is tends to go down depends on how much and what type of load you apply ( more for inductive load, less for resistive load and the least for capacitors (in this case you may even see an increase in the output voltage with increased load)). If the speed of the driving motor goes down (and it usually tends to go down when you apply a load to it), the speed (rpm) regulator tends to bring the speed up to the set value ( corresponding to 60 Hz). If the speed regulator does not work, the voltage regulator has to take care of this drop in voltage too and correct the difference in voltage. However it does not take care of the frequency difference (Hz). The described symptoms tend to point out to either a defective voltage regulator or a capacitive load, that the existing regulator cannot handle. Check also the frequency (it should be stable at 60 Hz)

I totally agree with views expressed by the guest.

Its a long time since I had anything to do with this, but an AVR should be controlled by a PID unit. Proportional, Integral and Derivative control.

Proportional responding to the difference in set point, Integral the rate that a set point is varying, Derivative the time it is away from set point.

Integral and derivative normally cause large hunting swings, so if the voltage is steady at a larger reading, then it may suggest a proportional band setting? droop I think would accept a drop before reacting?

Like I said its been a long time, others may need to fill in.

Regards JD.

The problem is most likely swapped phases on voltage sensing and/or wrong current direction from CTs to load controller/AVR, as the droop on the machine is working in the opposite direction.

What if the AVR does not have a pot to adjust the droop setting.On this 20kVA leroy sommer alternator I was working on the AVR had pots for adjusting volts and stability only no droop.

What's the stability adjustment for?