power factor correction, help?

Smudge · Mar 21, 2013

I am after a little help if anyone can, on a problem i've been given at the factory i work in...

We have a limit on our supply capacity we are allowed to use (950kVA) before we get hit with extra charges. Using our own energy monitors, our usage (max) is approximately 880kVA over the last couple of days, and that seems to be the normal sort of load over recent weeks too.

Our problem now is that we want to install a new bit of plant that has a potential demand of around 150kW, pushing us way over our capacity allowance. Upon some quick readings we have taken from the energy meters, they are saying we are achieving a p.f. of around 0.904. After some research, i have come across a general view that the p.f. should be greater than 0.95. We have capacitors on our incoming already, however, these would have been sized at a time before some rapid growth of our plant, and haven't been given any attention since they were put in >10years ago.

How can i check if they are the correct size? Are they easily maintained? And how can i explain to the boss's above that improving p.f. can help achieve greater capacity and lower costs?!?

thanks for reading

plugsandsparks · Mar 21, 2013

Even though they are 10years old, if it were me i would contact the manufacturer of what you have and ask them.

Knobhead · Mar 21, 2013

Look in to automatic PF correction units. Trying to achive 0.95 is a pointless exercise, 0.9 is the usual threshold for PF surcharges. You won't get within you're MD with the new drive fitted and a bit of tweaking of the PF.

Marvo · Mar 21, 2013

If your pf is over 9 even after considerable expansion then your existing correction units might already be automatic. Achieving 9.5 or better is going to be a tall order without large capital expenditure.

desigo · Mar 21, 2013

Whats your voltage like too high no good too low not good

MarkieSparkie · Mar 22, 2013

Trying achieve power factor greater than 0.9 is a pointless, but costly, exercise in diminishing returns ie. the cost of the correction equipment escalates rapidly for every fractional energy saving achieved. Unless the energy usage is large >10 MW, the annual potential savings rarely justify such action.

malcoa · Mar 22, 2013

You need to talk to you DNO and make out an application for a greater authorised supply really, they may have extra capacity on the local network/transformer that they can sell you, obiously your main switch and supply cables may need a look at. you never know until you apply.

Smudge · Mar 23, 2013

thanks for the response. I'm not sure i agree with it being a pointless exercise? Don't take that the wrong way, but we are getting monthly electricity bills of 20-25grand. Even a very slight improvement would save thousands per year. I appreciate that won't help our max capacity, and will get on to Scottish power first thing on Monday.

malcoa · Mar 23, 2013

They may be 20-25K but what is the charge for the reactive element of the supply, it will show on the bills?

Smudge · Mar 23, 2013

thats in a little bit of dispute just now?!? we are waiting on a breakdown of the bill from e-on, as it isn't clear from our statement. It just says £43.87 reactive charge on our latest bill. I'll get back to you on their response, as the person on the phone wasn't sure at all and said they would get back to me.

Knobhead · Mar 23, 2013

So you propose to spend £XXXX to save £43-87? You need you're bumps feeling.

Gage · Mar 23, 2013

Get a new tariff or deal with the charges, if you're still making substantial profit (which I assume you will be) from the new additions + extra charges just leave it. Take the advice given to you here.

Engineer54 · Mar 23, 2013

You've been given good advice, your corrected PF of .90 is about as good as your going to get without throwing some serious money at it!!

Now, is the DNO supply coming into your company at MV and an on-site DNO 1 MVA transformer?? If so, it would be worth looking at the cost of providing your own 1200 KVA or larger transformer and any associated switchgear etc, (depending on available DNO power available at MV). It all depends on the viability and profitability of your company at the end of the day, as to whether this is a time, to make a substantial plant investment. As it stands, your dammed if you don't, and dammed if you do. Down to the bosses as to what is the medium and long term plan for the company!! lol!!

Then again, if were only talking of £45 a bill as it stands at the moment...... lol!!

Sparks1962 · Mar 23, 2013

Maybe look at calling in a firm who specialise in PF correction gear, I often do this on Industrial and Agricultural installations with significant motor and discharge lighting loads. It'll be easier on you as they will do the necessary calculations, take reading at the intake/metering point and quote you fot a complete package or supply of equipment only. We use a local (ish ) manufacturer and install it ourselves, with them taking care of the maintenance side. Most manufacturers are happy to provide brochures or presentation brochures for your manager/customer with case studies of previous installations.

Hope this helps!

Chr!s · Mar 26, 2013

Smudge said:
I am after a little help if anyone can, on a problem i've been given at the factory i work in...

We have a limit on our supply capacity we are allowed to use (950kVA) before we get hit with extra charges. Using our own energy monitors, our usage (max) is approximately 880kVA over the last couple of days, and that seems to be the normal sort of load over recent weeks too.

Our problem now is that we want to install a new bit of plant that has a potential demand of around 150kW, pushing us way over our capacity allowance. Upon some quick readings we have taken from the energy meters, they are saying we are achieving a p.f. of around 0.904. After some research, i have come across a general view that the p.f. should be greater than 0.95. We have capacitors on our incoming already, however, these would have been sized at a time before some rapid growth of our plant, and haven't been given any attention since they were put in >10years ago.

How can i check if they are the correct size? Are they easily maintained? And how can i explain to the boss's above that improving p.f. can help achieve greater capacity and lower costs?!?

thanks for reading