Power factor correction and synchronous generators fuel consumption

[stulea]

Situation:

Investigating the benefits of placing power factor correction capacitors close to the generator upon an offshore platform.

Offshore platform has a system load with a 0.8 pf

Benefit for placing the correction capacitor close to the generator is to reduce the MVAr the generator produces.

Due to safety considerations it is not possible to retrofit PF correction at the load points on the system.

Offshore, the power source is gas turbine driven generators and the platform load is normally met by two main generation units.

I understand that fuel input (KW input) is directly related to load.

I also understand that the efficiency of the generator increases with the pf of the load.

If therefore should you increase the pf of the load you increase the efficiency of the generator and should therefore reduce the input required to drive the generator.

I am interested if you can comment on if power factor correction can reduce the mechanical drive required for a synchronous generator given a fixed MW load?

If there is a reduced drive requirement by the generator and can this translate to a reduced fuel input to the gas turbine and therefore reduced emissions from the turbine?

any comments welcome

 

[dede61]

Power factor correction will reduce the load demand of the turbine and therefore also the fuel consumption.

regards,

Danny

 

[stulea]

I am looking to justify the cost of installing power factor correction.

are you able to suggest a method of quantifying the reduction in mechanical input power to the generator with the drop in MVA output given a constant MW load?

regards,

Stuart

 

[jlazucena]

Stulea after reading your statements, here you have my comments
You know that the generators have the ability of working at leading power factor (Producing reactive power) where
*The power input to the turbine regulates the most of the real power that the generator generates.
*The generator voltage behind the synchronous reactance regulates the most of the reactive power that the generator generates.

Electrical Machines (Fitzgerald 5th edition Page 253) gives a good sample of the real power as a function of the voltage and saliency.
When we take in consideration generator saliency we can write equations to describe the real power and reactive power in function of the generator voltage and see that the “turbine input power” regulates about 95% of the generator real power output and the “Voltage Regulator” regulates about 95% of the generator reactive power output…

Do you have efficiency versus power factor curves?
Can you calculate the fuel reduction?
You can use a "capacitor bank life of 15 years" to evaluate the inversion versus saving…

My opinion: the application of capacitor banks for power factor correction will improve efficiency and reduced emissions from the turbine but the effect in fuel consumption is minimum.

 

[dede61]

I can only find the formula for calculating PF compensating capacitors in my books here, maybe someone else has some more information/expierience in this field. I know of one company that is using power monitors with integrated THD metering for fuel input regulation and the active power factor compensation contributes to the efficiency of the system.

regards,

Danny.

 

[dpc]

Addition of pf correction capacitors will have minimal impact on fuel consumption.

For an isolated system such as an oil platform, the main benefits would be:

Release of additional generator capacity for production of kW instead of kVARS. This is only a benefit if you actually need the kW.

Improvement of voltage regulation.

If the generator has adequate capacity to produce the kVARS and the kW required by the system, the addition of capacitors would be hard to justify on purely economic basis.

 

[jlazucena]

Dede61:
You are right, I do agree that a capacitor bank will improve the efficiency of the generators.
Do you know the PF of that company before applying Caps?
Has this company poor power factor and a lot of harmonics?
That company may be solving more than one problem with the Caps.

Stulea, to justify the caps in your application you may model (Load Flow) the gen with and without the caps.
Then you know the real power (Turbine input) and the reactive power (AVR input) that the gens require.
Next, from manufacturer tables find the expected fuel consumption and get the fuel consumption savings per week/month/year and compare it with the inversion for a cap bank with an expected life of 15 years.
Note: the caps may last longer than 15 years but this number takes in consideration caps maintenance and it is better than nothing.

 

[stulea]

Thanks for your input. I am looking to prove it one way or another.

I understand that with pf correction, the capacity of the generator will increase.

jlazucena to answer your questions.

i have a efficiency versus apparent power plot for a 15000KVA generator. There is an increase in efficiency noted with the increase in system power factor.

how would you calculate the reduction in fuel input?

regards stuart

 

[jlazucena]

Find manufacturer's tables
You may have to dig for “Bid Evaluations” or some other Bid generator-turbine documents.
The manufacturer has to have given tables about fuel consumption.
Fuel consumption is paramount to define the winning offer.

 

[rbulsara]

As dpc indicated power factor correction do not signinficantly affect fuel consumption.

Prime movers (turbies or engines) only supply real (kW) power. Since prime mover do not supply reactive or 'imaginary'(kvAR) power, reduction in kVAR do not affect fuel consuption.

Only effieciecny improvement is in the I^2*R losses upstream of the capacitors. Placing PFC near turbines do nothing to the system downstream.

 

[edison123]

stulea,

For a given MW, improved pf reduces the MVA and the generator copper losses, which reduce as square of MVA. Since all generator losses are supplied by the prime mover, you can say that with improved pf, energy requirement from turbine is reduced. To quantify the energy / fuel savings at turbine end, one needs to study turbine characteristics and performance parameters.

Another major plus point is that with improved pf and resultant lower copper loss, the generator winding temp comes down, which aids in prolonging the usable life of the insulation.

However, due to bulk pf correction you are proposing, care must be taken not to over-compensate and land the system in leading pf operation at any stage of load. Also, to avoid the deleterious effects of resonance, a lag pf of about 0.95 at all loads may be ideal.

 

[stulea]

Thanks for you input.

I very much appreciated it.

Stuart