Genset 1

[2000Kvar]

Is there any draw back on adding capacitors to the terminal genset with a pf of .8 to raise it to 1.

why does most manufactures use a base of .8 and not a value closer to unity

 

[Skogsgurra]

The reason is, as I have always thought, that most loads are around 0.8 P.F. loads.

Gunnar Englund

http://www.gke.org

 

[davidbeach]

When the generator is only connected to the load (no utility in parallel) the generator will produce what ever power factor is required to by the load. If the generator is running in parallel with the utility, you can set the power factor to what ever you want (within reason). The .8 pf rating of the generator is to allow you to get rated kW out of the generator into a .8 pf load without exceeding exceeding the current (and therefore kVA) rating of the generator. If the generator had a 1 pf rating, its kVA and kW ratings would be the same and it would be nigh unto impossible to ever get the full rated kW out of the machine.

 

[rotman]

I think it's a kind of misunderstanding: if we're talking about genset with synchronous generator (am I right?), rated p.f. of 0.8 is lagging p.f., ie. generator delivers reactive power to the system. Change of generator p.f. is possible by regulation of excitation current: to increase p.f. to 1.0, exc.current is to be reduced. At pf. 1.0 the generator can still deliver its rated kW output (in fact, stator and rotor thermal loads are lower in this case).
Value of rated p.f. of 0.8(lag.) is standard for most generators. Generator with the same kW and higher p.f. (eg.0.9-1.0) could be smaller machine, but of course 'smaller' source of reactive power to the system.

 

[TheBlacksmith]

Generators kind of live in a box; defined by lagging power factor (excitation limits), kw (prime mover HP limits) and leading power factor (rotor heating). Since leading power factor are less likely and HP limts is kind of obvious (engine stalls), the power factor is usually published, but it's actual value is dependant on the load. (Fourth side of the box is no output side)

 

[aolalde]

A generator with PF=1.0 is not providing any reactive power (kVAR). That will be a generator capable to supply only resistive loads.
Your generator has PF=0.8 or capacity to provide real life resistive and inductive loads like electric motors. The lower the PF the more reactive power it can supply to feed reactive loads. As it was mentioned above, the load defines the PF, not the generator.

 

[davidbeach]

aolalde, not strictly true. A generator with a 1.0 pf could supply a 0.8 pf load, but only at 80% of its nameplate power rating.

 

[waross]

I am assuming that you are using a single, stand-alone generator.
The power factor is a characteristic of the load.
The manufacturers rating of 0.8 indicates the lowest power factor load that can be used on the set without derating the set.
You may add capacitors to the generator to improve the power factor of the load seen by the generator. You will reduce the generator current slightly.
As has been pointed out by TheBlacksmith, the kw rating is dependant on the size of the motor. Even if you correct the power factor you usually cannot get more kw out of the set because the engine slows down. If you have a load with a low power factor you may use capacitors to correct the power factor.
respectfully

 

[davidbeach]

If you put capacitors on, make absolutely certain, for sure, that the capacitors are switched with the load and not left connected to the generator when the load is removed. A highly capacitive load will cause significant trouble, even to the point of letting the smoke out of something.

 

[aolalde]

Davidbeach.

I mean a generator with operating PF=1.0, I do not mean the PF in the nameplate.

 

[waross]

davidbeach, aolalde, and others.
I was involved with a short experiment that illustrated this point.
Case; A small power plant, 2 x 600 kw gensets,plus 3 x 350 kw gensets.
The load is slightly over 600 kw and two generators are running. This is a common occurance.
The 600 kw set was rated 0.8 PF and was running close to 0.8 PF.
We think that if we correct the power factor with capacitors, we can run up to 750 kw and avoid the need for the second set.
We feel that we can safely overload the 600 kw set for a few minutes to test our theory. By adjusting the governors we start to overload the 600 kw set. At about 608 kw, the engine starts to lose speed and the frequency starts dropping.
Conclusions;
The maximum kw is determined by the power of the engine.
The engine in question was capable of producing 600 kw and no more.
A second illustration is the application of single phase generators in size ranges above about 20 kw.
At least one major gen-set manufacturer does not use single phase alternators above about 20 kw., nor do they assemble single phase sets above that size. They supply the single phase market by reconnecting and rerating three phase sets.
For example, a set may be rated at 50 KVA, 40 KW, 0.8 PF, three phase. If a single phase set is required this set may be reconnected in either zig-zag, or double delta.
The new kva rating is 2/3 of the original rating, or 33 KVA.
The same engine is used so there is enough power for 40 KW.
The new rating will be, 33 KVA, 33 KW, 1.0 PF.
respectfully