Power Factor Correction and Gen Sets

ECONOMICS. AND DON'T SHOUT ABOUT IT!

Economics, probably. Many generators are rated for both KVA and KW, a common PF assumption being 0.8. Most motors, if well loaded, will achieve that, and so will not overload a properly matched genset. If the motors are lightly loaded, the PF will typically decline, but even so, the lesser load will still be within the genset's ratings. PF correction on the motors may save a bit on fuel costs, but the payback (ROI) is likely to be low/long.

On a power grid, however, you may be charged penalties for low PF that are considerably larger than those fuel inefficiencies. In this case, PF correction can pay for itself fairly quickly.

Either scenario can be analyzed economically, leading to a suitable decision.

And yes, please turn off the all-caps font.

pf correction on generator is usually not practiced since the pf (the bad guy) is from load.

The generator supplies what it is asked for even at the cost of burdening itself with unwanted things.

That's why the power utilities ask the consumers to control their pf and put penalty on them.

The Golden Rule for DG Set loading is:

"LOAD THE ALTERNATOR IN AMPERES

LOAD THE ENGINE IN KILOWATTS or HP"

Usually when a DG Set manufacturer quotes for a set, he assumes the load PF to be 0.8 lag and arrives at the kW or HP rating of the Engine. Supposing you want a 300 kVA DG Set, he will supply a 300kVA alternator coupled to a 400HP Diesel Engie,say, duly taking into account the engine efficiency, and assuming that the kW loading on the alternator would be 240kW. Now, if you improve the power factor to say unity and try to load the alternator to 300kW (300kVA x UPF), this kW loading will be thrown on to the diesel engine and it will be overloaded.

Assuming that you have an engine capable of delivering 300kW, then you can very well improve the PF of the DG set. But, that would make the DG Set costlier and you wouldn't buy the set from him.

Dear Friend,

You seem to be new to this site. Here use of capitals for your thread is considered shouting and that is not considered good manner and members get irritated with such use. So please remember this point.

Power factor of your load has to be maintained as nearer to unity to avoid energy loss due to kVAR . Weather the source is a local generator or power supply from Electrical supply agency the pf has to be maintained at optimum value considering the economic considerations to install and operate power factor correction units. The PF correction is to be made considering the type of load and not the source. The most appropriate method is PF correction along with each load , but it is not practicable in industry and hence power factor corrector units are installed in LT distribution substations along with switching panels to ensure that the system PF remains at least above the minimum contracted value by the supplier to avoid Low PF penalty by the energy provider.

Question . . . if you are standing in the control room of a medium to large electrical power generation station . . . that is full base load operation . . . paralleled to a grid (very large total load - maybe like the entire countries generating capacity) . . . what control do you manipulate to adjust pf?

your generator engine is designed to work based on 0.8PF and if you want to operate your generator with unity power you will kill the engine god knows who selected .8PF for generator engine But its as per Relevant ISO the engine manufacturers stick to world over

crm

guest; pf affects the generator, not the engine,a 10 kw unit is rated 12.5 kva. perry

Furthermore, if you read the documentation provided by the manufacturer, you will see a note that states something to the effect that one must derate the power rating of the generator as the power factor is increased from 0.8 to 1.0...Read the manufacturer's recommendations FIRST. Since they are the ones responsible for the warranty, they are going to be fairly conservative in their recommendations. My experience teaches me that in a typical diesel-powered generator system, there is very little difference in fuel consumption between operating at 0.8 and 0.9...

All the comments made basically comes down to one thing:

If a pure resistive load is connected to the set the power factor from the load will be 1 or very close, in this case fitting pf correction is a waste (you cannot better the power factor) If inductive loads are fitted and the power factor is at 0.8 or lower you may want to fit power factor correction to improfe the pf.

Not everybody has the same requirements and why pay for something you do not need?

I know that this question is addressed perhaps at a small capacity engine driven generator . . . But in my humble opinion to understand the true significance of pf an understanding of when it is most important needs to be the foundation knowledge for pf in a small scale situation. This can be a lengthy discussion, or I can just shut up and go away. The feedback on my posts will help me make tha decision.

From my experience I am going to try and explain why pf must be controlled but first we must look at multiple generators, transmission systems, substations, distribution system and load. From this understanding, comes the basis for understanding a single generator operating on limited load . . . that can be a large generating station that finds its self in an "Isolated grid" or a small engine driven system that is a standalone power source to a load.

In a large electrical power system . . . it consists of essentially four major components . . . a step-up transformer/switchyard . . . a high voltage transmission system . . . 220kv, 345 kv, 700kv . . .a substation that drops this voltage down to 22kv, 16.8, 8.4 kv . . . a distribution system that delivers the power to a consumer base and finally the consumer loads. This large system has multiple electrical generators connected to it in parallel.

Since all these generators are in parallel they are essentially locked in synchronization. No single generator is sufficiently large to control the frequency on the gird. Thus as any attempt is made to raise the speed of an on comming machine or an attempt is made to raise the speed of any machine on the grid the machine being adjusted picks up electrical load. So what is happening on the grid, if frequency is locked and even though the load of the grid my be hundreds or tens of thousands of megawatts? Some relationship between the grid and the on-coming machine must happen . . . or be controllable such that no major pertubation occurs on the gird . . . what is the parameter that is changing? Voltage

As voltage is influenced what is happening on the gird?

The power sharing between the generator is re-adjusted.

As you know the current by a generator

I_x = (E_x- V_grid)/Z_x

The Ex, the EMF of the generator is controlled by the system (depending on the requirements, field controls, governers et allcome into picture)

Z_x is the equivalent internal impedence of the generator.

It is exactly like putting a number of 1.6V cells in parallel. As you add another cell, you will see that the output voltage will fractionally increase as will be the current sharing.

And the ratios will not be same as earlier due to another source with a different impedance in system.

Easiest way is to make the power circuit, load circuit and see the interaction.

IF POWER FACTOR CORRECTION CAN IMPROVE LOADING CAPACITY OF GEN SET WHY IS IT NOT PRACTISED.

Power factor deviation can be best described as "Watt less energy". this has been a known and accepted fact since the early years of power generation.

I am aware of at least two units in New England from the mid 1920's that were installed as a set, Both units had a separable jaw coupling between the turbine and generator. The intent of the coupling was that you could either run both units up as generators and output power. The other option was to disconnect one unit from it's turbine, tie it to the other unit electrically on turning gear and then drive the separated generator to line speed with the coupled unit. After the unit was synchronized (both units tied to the system eclectically). the coupled unit would provide power, the free wheeling unit would have it's excitation varied to improve power factor (synchronous condenser operation) of the system.

To illustrate the significance of these units and the concern about the power factor losses one only has to realize that these units were rated at about 45 Meg-Watt, this was at that time at the least significant sized units. This was also about 8 years before the TVA project.

I personally don't think you can "IMPROVE LOADING CAPACITY OF GEN SET" per se, I do think the power companies can do a better job of identifying whose load is causing the problem and put the charges where they belong.