Power Factor

Simon, you are correct that under normal load conditions, as long as the power factor is above 0.85-0.9, there is not much benefits to add compensation even with high electricity cost.

But, when the load vary wildly, the voltage swings can become problematic. In this case, the fast capacitor banks switchers using SCR and a fast controller can make all the difference in the world for the power quality.

We manufacture a line of these fast controllers similar to the product described above. The difference is that we specialize in difficult applications that require above industrial quality like the marine and mining environment.

Here is an example of the power on an oil platform before and after installation of our fast capacitor controller.

The scales were lost in the graphic translation. They are line volt in red at 250V/div and the line current in blue at 2500A/div.

As you can see, this is not a small installation. They needed two diesel generators on before installing our controller, now they operate from one. That is a considerable savings just in fuel and maintenance.

There power quality is much better with less computer crashes and light flickering.

We have pamphlets and presentations but I cannot figure out how to add them here. Drop me an email by clicking on my name if you want details and distributor info.

Note that these controllers protect against transient lagging and leading power factor within one line cycle. They also have negligible transient switching. See what happens when a capacitor bank is turned on.

Finally, if you already have the capacitor banks, our controller and switches can be used to replace your slow system to increase the performances with a minimum of investment.

As these loads are intermittent, is it worth doing economically? While PFC can yield economies for continuous loads, doing the same for intermittent loads may not be worth all the trouble. Which is sort-of-why it isn't usually done.

Quote Marcot "Simon, you are correct that under normal load conditions, as long as the power factor is above 0.85-0.9, there is not much benefits to add compensation even with high electricity cost."

I would disagree with that statement. Lets assume you have a demand of 1200 KVA with a PF of 0.85. We decide to improve the PF to 0.95. That would reduce the demand to 1073 kva or a reduction of 127 kva. In the US the KVA billing is about $5.00 per kva per month. 127 kva x $5 x 12 mo = $7620. Even starting with 0.90. the reduction saves about $3780 per year. That not bad for an installation of about 600 kvar. The ROI is about 1 year.

Wareeagle, you are confusing KVA and KW. Most (if not all) electrical meters accumulate the KWh (energy) and that is what you pay for. There are penalties if the power factor decrease below a certain limit but in general you only pay for the KWh you consume. This means that as long as your power factor is above the penalty limits, you don't save anything.

The main saving seen at high PF is the reduction of the electrical feeder needed for your plant which could be about 10%-20% smaller.

The real energy saving is for the losses on the electrical utility network and their equipment size. This is why they are the one imposing a penalty if your PF is too low.

The "green" answer is that we want to reduces all the power losses produced in the distribution. Since the efficiency of the distribution network should be least 95% (to be verified by people with real data), your 127 KVA saving reduces the distribution losses by approximately 6KW. This is approximately 0.5% of your plant energy consumption (1200KVA at PF 0.9).

If you really want to save energy, use efficient production equipment and look at heat losses in the building. You will quickly exceed this 0.5% saving and it will come off your electricity bill!

There are condition where power factor improvement is needed:

1-When you need a larger electrical feed, you might avoid large expenses by improving the power factor.

2-When the PF gets lower than 0.85 and or it varies widely and rapidly, the collateral damages caused by poor power quality can pay for a power factor regulator.

3-When the harmonics voltage distortion is higher than ~5%. The power quality can also cause collateral damages.

4-I am sure that somebody will find another good reason to add to this list.

One must realize that there are problems with capacitor banks and they can cause damages to other equipment. This is not something you add to your plant supply and all your problems will be filtered out. The side effects must be considered, especially when you try to reach a PF of 0.9 and above.

I'm not confused. There are large commercial and industrial customers in the US that are billed on KWH's and KVA demand. The KWH's are not affected but the Demand Charges are. You can reduce the Demand Charge but the KWH's remain the same. This may not be the case where you are. I would agree with you if the only reduction was only the system losses. But here the meter records the KVA demand and the KWH's.

Marcot

Are we discussing the sale thing?

Quote Wareagle "

Marcot

Are we discussing the sale thing?"

That should be Are we discussing the same thing.

Sorry.

Wareagle,

It looks like we are not comparing the same type of systems. I agree that if a customer is billed for the KVA, the economics are totally different. I have not been asked to look at such system yet but based on what you say they do exist.

Regards,

Marco

can you try to select the reqd capacitor bank by trial and error method for eot crane so that when you switch on the crane the appropriate bank of capacitors is selected only when you operate the crane.pl try this

You should not do that unless there are no other ways and that you know what you are doing. You need at least the motor(s) / drive(s) specifications and if possible a power monitor report including usage and worst case numbers and waveforms at major feeders through the plant. A complete plant electrical distribution diagram is also very useful.

From this, a competent engineer can evaluate your needs and avoid parallel resonances that can turn your filters into nightmares.

Marcot

I am surprised. I thought this billing was fairly standard among utilities. In the US a large customer is billed for KWH's and either a KW or KVA demand. This is part of the billing structure. At some point in the demand amount, the customer is either KW or KVA. I have seen several question on this forum about KW demand billing along with KWH's.

Why do you want to maintain pf during load swings? Does your utility company penalize you for pf during such swings?

As far as I know, utilities compute your pf in per month basis. They use your total kVARhr reading in one month. Even if your pf for one day is only lets say 70%, but for the whole month your pf is still 95% for example, then there is really no point in pursuing a high pf during load swings.

Concentrate more on your kVARhr consumption not on your pf. Coz at the end of the month, its the kVARhr reading that the utility will be using to compute your pf and decide whether to penalize or discount you.

Some utilities use the peak (low) PF value but the main reason is for power quality.

You will have to contact Cummins Power Generation Business Unit, Power Electronics Department for the Power Quality Analysis.

Regards

Pravin