about diesel-generator voltage control

[turkoman]

hello, ? wanna ask you about the relation between diesel-generator automatic voltage control and compensation, for example we have a d.g and a mains and we feed the loads from mains and cos fi= 0,75 and we have no compensation system, at that point the mains is gone and we transfer the power onto the diselgenerator, so if we have a AVR on the dieselgen what will be our cos fi on the final situation?(I wonder if AVR makes a compensation??)

 

[dpc]

The power factor is a function of the load. The generator has to deliver the watts and vars when running isolated from the utility. So if the load power factor is 0.75 on the utility, it will be 0.75 when running on the generator. When not tied to the utility, the AVR will adjust the field to maintain the generator voltage at whatever the voltage setpoint is.




"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg

 

[turkoman]

yes you are right but what are the drawbacks when we use compensation system with isolated working diesel generator?
by the way excuse me i confused the this situation with the one in which a generator connected to the infinite bus can make compensation if works as motor (synchron machine)...

 

[dpc]

The term "compensation" is not one I normally use. I assume you are referring to what I would call power factor correction.

The isolated generator is not compensating or correcting. It must provide the reactive power requirements of the load. The loads draw current and the generator provides it. If some type of power factor correction is added, the generator will not have to provide as much reactive, which might allow it to provide more real power.

The generator can only provide up to its rated current, regardless of the power factor of the load. (Actually, it's a bit more complicated - it is based on the generator capability curve.)

"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg

 

[turkoman]

in theory a generator and capacitor banks for PFC can provide a compensation but in practice we dont operate both of them on the same time isnt it? i ask you why we dont use them together? i mean generator and capacitor banks for PFC

 

[dpc]

You can use them together. When you have a synchronous generator or motor, it is generally easier and cheaper to let the machine provide the vars if it has the capacity. But capacitors can still be used to help free up generator capacity.

"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg

 

[turkoman]

in here we call this PFC system as compensation what do you call it?

 

[dpc]

Just power factor correction or PFC.

"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg

 

[catserveng]

If you try to use the capacitors along with the generator make sure you don't end up in a large leading power factor. You can have problems with voltage control and if the power factor gets outside of the generators capability curve it could cause damage.