Power Factor Improvement - Diesel Generator

At which pf, it can deliver 60KW (it may be there in name plate) or you have to give the KVA rating.

Its 62.5KVA / 50 KW generator & not 60 kw as mentioned earlier.

Use 3 x 5KVAR capacitor panel and connect it as star or delta according to generator output winding connection.

For such a small machine is it worth the expence?

He may not needed full load at all time....

No problem if it is a 3 x 3 KVAR capacitor bank.

What is your suggestion?

Dear Justin,Thank you for immediate response. We have loaded the generator to 40 KW(80% of gen capacity).Hence after starting it, within half an hour its stops due to Alternator overloading / overheating.when checked ,we found the overall PF of factory load is 0.65/0.68.We need to improve this to 0.8 ,for which alternator is designed.

1) Whether your system is using varying power? (It was not mentioned in the question). If the power consumption is varying you can not use a fixed pf compensator. Real time compensator is available now. (With PWM technology)

OR

2) Try to find out which machines are working with low pf and how much VAR it needs, and give compensation with that machine. (Ignore machines with small ratings)

Also don't start your generator when capacitor is connected. Start capacitor only after DG is started.

If your need is 40KW you have to supply around 6KVAR only. KVAR requirement will vary with power requirement.

I agree with above comments from others about installing a Capacitor Bank is not a Cost effective solution when compared to the load. "If your need is 40KW you have to supply around 6KVAR only. KVAR requirement will vary with power requirement." as stated above How did you arrive at 6KVAr for a 40KW load i believe you would require nearly 13~17KVAr capacitor bank.

Sorry, typing error.....

I meant 16 KVAR.

50kW at 0.8 pf needs 62.5kVA and kVAr = 37.5

AT 0.65 pf the kVAr = 47.5

To rectify to 0.8, you need to produce (47.5-37.5) = 10kVAr in 3 phase supply. Which means that each phase will need 10/√3 = 5.8 ~ 6kVAR

YOU WERE CORRECT!

it was calculated for 40KW we are getting nearly 16.76 KVAR. normally KVAR is mentioned for a 3 PHase, i dont know how single phase KVAR is mentioned for a 3 phase load.

If we calculate:

KVAR = KW(Tan(P.f present) - tan (P.f to be achieved))

= 40 (tan(cos-1(0.65) - tan (cos -1 (0.8)))

= 40 (1.169- 0.75) = 40 * 0.419 = 16.76 KVAR required to increase the PF from 0.65 to 0.8 for a 40KW load.

Sorry, you are correct!

I kept the same KVA in my calc...

This is the solution I would go along with. The correction only comes in as required. Automatic correction is far to expensive for such a small installation.

Thinking about it, it would be cheaper to purchase a new generator than automatic PF correction.

I agree with TS. The cost will easily outweigh the benefits.

However for a factory 50KW looks to be very small (are you sure about it?)

For the compensator, if you insist, find out the culprit (the low pf equipment) and put the bank near it.

Most likely it is a motor running at much lower than the rated load.

UD15

What is your load which has 0.65 PF. Buy equipments/motors which has better power factor.

I agree with above comments from others about installing a Capacitor Bank is not a Cost effective solution when compared to the load.

"If your need is 40KW you have to supply around 6KVAR only. KVAR requirement will vary with power requirement." as stated above

How did you arrive at 6KVAr for a 40KW load i believe you would require nearly 13~17KVAr capacitor bank.

Sorry, typing error.....

I meant 16 KVAR.

If you add to each load a small cap bank sized for that load, that is switched in and out as the load is switched in and out, there is no big deal. Also, nobody can make a mistake!!!

SIMPLE!

that is also the way I would try to fix it, so GA andy

Dear Ram Das,

Proposing of capcitor bank with power factor controller( for varying load ) is not economically viable for small size DG set.. Since in any factory/ industry about 70% of load is inductive; i.e; motors, gas dischrarge lamps, welding set, etc; it is better to installed capacitor across each inductive load for lagging VAR compensation. Also you may please check proper functioning of cooling system of DG set.

Regards,

Manindra

As suggested earlier, putting capcitor bank of 16 kvar & manually switching on after the generator start by placing the cap bank in switch gear control panel(main distribution board ) should solve the problem.Do everybody agree?

No, that was not the gist of it. You are supposed to ascertain where your "problem" machines/motors are. then, as ANDY pointed out again use caps only sized for that load, at the load. These caps will switch in everytime the load comes on, and they will be only big enough to take care of the reactive component on that particular macine. The way you are proposing is a totally manual system where you supply KVAr for your full load. Manually switching that bank is calling for overcompensating problems.

How many motors are there in your factory, and what size?

As jvrj said you're going to cause yourself more problems with over compensation if you switch the capacitors on after starting the generator. If you are determined to go down the road of a single capacitor bank then switch them in at about 60% of total load. If the load varies during the day you're going to get fed up of switching them on and off.

Go for single drive correction on say just 5 drives, you'll have to decide which. You know the machines.

Well said and thanks Tonys, now if only the OP will heed this.

What are your connected loads ? How many motors and what is their HP ?