Generator, Power Factor Correction and Fuel Usage

The answer pivots on the efficiency of the device you use for power factor correction. Capacitor banks are relatively efficient but they do suffer from the switching problem you mentioned along with the inability to "tune" to any desired reactance. The synchronous condenser approach will be tuneable but includes its own set of IR power losses in order to excite the DC field.

However one improves the power factor it can usually reduce the mechanical power needed to make electric power, but every added device has its power cost.

Thank you for your reply

Thermal loss of a good quality SVG is around 3%, so will still be less than the power required to generate the required KVAR for the load, so the net gain will still be positive.

I think you hit it on the head: with PF correction, you reduce the amount of current necessary to deliver a given amount of power to the load. The power to heat the copper in the generator (and transmission lines) has to come from the generator, i.e. fuel for the engine.

Thats what I have been trying to find out, but no one else seems to agree, it seems to defy logic.....so I am not insane by making these assumptions

I really appreciate all the replies gentlemen.

Well, the logic most people apply is the Law of Conservation of Energy.

So, yes, any excess current due to the reactive loads will result in additional IR losses in the whole system. So if you can show the delta between PF=1 and whatever PF, then you could calculate the energy losses that the generator is going to take from the engine or turbine or whatever power source is being used.

Then it becomes a question of ROI. Complexity has it's costs too. And you can almost always count on the Laws of Unintended Consequences.

There are only two real situations in which PF correction saves you money;

1) when the Power Company assesses a PENALTY for having poor PF, and

2) When you use a fuel based generator. That's because fuel is consumed for providing kVA, not kW. So if you have a low PF, that means your load kW is going to be low, but your kVA is still going to be high and therefore your fuel consumption will be commensurate with that kVA. But if you use PFC, the kVA per kW as seen by the generator is lower, ergo the fuel consumption is lower. So the operative issue then, as was mentioned earlier, is just the efficiency of how you correct the PF. Mechanically Switched Capacitors (MSC) are the most efficient, but are going to have to act in steps that may or may not be accurate to the dynamics of the load. Synchronous Condensors (SC) are an analog response solution, but are slow to change and consume more energy because there are always mechanical losses (friction, wind) as well as electrical losses (I²R in the windings, eddy current losses in the steel). Static VAR Compensators (SVC) are a good compromise because they react faster than SCs, but have internal losses closer to those of MSC.

BUT, you should check with your generator supplier because of possible resonance and AVR issues.

Thank you, The compensation will be only via SVG, so 20ms response time, no real capacitance as it is a current amplifier, so that negates the risk of resonance and AVR issues completely.

But the KW of the Prime mover is a unit of mechanical power, not electrical power, it is converted into electrical power (KVA) by the Alternator, and KVA is the sum of your reactive and active power.

As mentioned as well, we will not be using capacitors but static var generators, that do not have any of the same electrical properties of capacitors, they work by using current amplifiers to be a source of lagging or when required, leading reactive power as well.

Stability is not a problem and you can run the PF at 0.99 all day due to the response time, the AVR wont see any fluctuations besides the need to provide more or less active power as the load change.

Remember, we are not aiming to reduce I2R losses, that happens as a consequence of this, we are aiming to reduce the amount of current the alternator has to put out by reducing KVAR demand as close to zero as possible.

CR4 is not really set up to sustain argument.

That's right, kW² + KVA_r² = KVA²

So where does the current come from to supply the reactive power that the load requires?

The excitation is the 'source' of the current, in so far that if you have no internal excitation, then the magnetizing current for the generator comes from the power system, other generators, capacitors.

There is no fuel penalty for the reactive power, except for the power (not amperes but kW) required to excite the field. The concept of your idea is valid, it is just an order of magnitude lower in opportunity than you imagine. Plus, regardless of your opinion to the contrary, mechanical power system stability is significantly improved by having a good strong coupling between the rotor and the stator.

The I2R losses of the field and stator windings are what you can save by reducing stator current. Unless the machine is a hopelessly inefficient design, if you calculate the power dissipation difference between the two conditions, using the only real and ignoring the reactive component of the amperes, you should find that your fuel measurement instrument will not be sensitive enough to measure the difference between generator leading 65% power factor and leading 95% power factor.

You have to ask yourself where the energy goes. Energy In = Energy Out.

Ultimately, it all ends up as heat at the end of the line. I2R losses are heat. The work that the loads do eventually ends up as heat. So where is the wasted energy when you have leading or lagging PF?

Your load will required Reactive energy whether you like it or not, the SVG will provide the reactive energy, and it will not have to come from the Generator.

Got to dig those unrestrained TLAs.