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People,
Many years ago, when I was Engineering manager of a very large Auto parts maker, where we had over 3000 machine tools, we had a relatively low power factor, about 0.92 to 0.95, aminly due to the large no. of induction motors and induction furnaces. We added a number of power factor correction capacitors with auto cut-in cut-outs to keep the power factor between 0.96 and 0.98. This reduced copper losses, plus we paid less as the Utility charged us for KVAR as well.

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Vee,
Many moons ago, in my previous life I did exactly the same. We were penalized if the power factor dropped below 0.93 and also penalized if it became positive! I mean the β€œpushed” reactive power to the grid. We had both fixed and variable capacitors. The system worked well.

Terry,
Yes, it is applicable everywhere. As a matter of fact if you size the capacitors correctly in many cases you can go with smaller transformer. And of course losses are smaller.

In the USA many utilities do not charge for the power factor. So the gains are purely due to lower losses which are difficult to calculate. So plants really do not care about this that much. This may change in the near future though as utilities are trying to defer investment in new generators….
RM
Kris,

Thanks for sharing your experience.

Terry, as Kris stated, if the Utility does not charge for KVAR, consumers save only the losses they incur as copper losses. this can still be substantial, up to 1 or 2% of energy costs. Taking Howard's data on auto plants, where he told us that 55% of prodn. costs are for energy, 2% of that can still be quite impressive.
However consider, if all the consumers got their power factor up to say 0.96 or 0.97, transmission losses would save the Utility 1-2% on their copper loss account. That means less greenhouse gases. All the losses result in heat, so that is that much of reduced direct global warming inputs.
RM
Vee,

I do agree with your statement. And yes the savings can be substantial. If my memory serves me well the transmission losses are close to 8% - 12%. So reducing it even by 2% would be equivalent of a major power station! If not more.

As a matter of fact we have been working with a major Utility for last couple of years on helping their industrial customer reduce electricity usage. Why with the utility? They are close to the limit of their generating capacity so in order to defer investment in a new Power Station they decided to help their industrial customers. That way everybody benefits – utility, customers, environment.

What customers get out of it? Free energy audits and help with financing energy improvement projects. Power factor correction systems are past of energy solutions as many utilities started looking into the KVAR issues and losses caused by it – increased current.

Let’s hope this is not just another program of the month but a trend.

Global warming or not we all need to conserve energy. We need to educate general public, engineers, financial people……
RM
Jack,

As you know, with AC (we will discuss single phase AC, for simplicity), the voltage and current vextors are out of phase. Usually, the current vector lags by a few degrees. So it has two components, the cosine component in phase with the voltage (just like with DC powere), the sine component is at 90 degrees to the voltage vector. Useful power is the product of the voltage and the current component in phase with it or VIcosPgase angle. The sine component is reactive power, so no real energy is involved as far as the motor or other load is concerned. Pure resistance takes zer reactive power, pure inductance takes 100% lagging reactive power, pure capacitance takes 100% leading reactive power.

However, the result of the reactive component of current is to increase the total current required. All of this flows through the transmission and distribution system. These have resistance due to the materials used, usuyally copper or aluminum. The wjo;le of the current, active+ reactive flows through them. Power lost in e.g. transmission is the proiduct of I squared and R, where I is the total current and R the resistance of the cables. This I2R is called copper loss.
RM
Vee,
Induction motor manufacturers claim increased efficiency today. Basically increased efficiency is achieved by reducing the losses. How do they reduce losses? Not much can be done to reduce copper losses and iron losses for a given power to weight ratio. Mechanical losses are minimal as cooling air power and bearing friction are optimised. So there is not much to win here.
The major leap forward is made by reducing the β€˜extra losses’. These losses are related to magnetic field harmonics in the airgap region. To reduce these extra losses induction motor manufacturers have increased the airgap.
As a result total sum of kW losses reduce significantly. However reactive current increases. Therefore kW losses in the network increase. KW losses do not disappear but are removed from motor and dumped into the network! This trick makes a high efficiency induction motor less green then it looks like Red Face.

Arie Mol
RM
Arie,
Thanks, that is an excellent explanation.
It only shows that utilities MUST charge heavy penalties for KVAR to keep these transfers in check.

Years ago, I helped a friend in the US replace what we thought was a water pump in his car, a US model/make. When we took it out, I found it was a small fan, blowing into the exhaust manifold. This was puzzling initially, till I figured out that the way the Big 3 automakers 'beat' the pollution laws (clean air act) by diluting the exhaust gases with a healthy dose of fresh air! More green design!
RM
The move to power factor improvement is also taking hold at the generation level. There are an increasing number of aeroderivative gas turbines being coupled to generators with disconnect type clutches, typically SSS Clutch from the UK. When demand tapers off the gas turbine is secured but the generator is left synchronized to the line, thus operating as a synchronous condenser and improving power factor. Another bonus is when the demand for power starts to climb, the turbine is lit off and brought to speed, thus producing power to the grid. This is somewhat of an over simplification but the system as a whole works very well.

John from PA
RM
Mr. Vee,
You have a rare quality of asking the right questions! Wink

Seriously, I am glad to see this discussion. It shows that there are many people who do care and have a lot of knowledge. Moreover, they are implementing the solutions!

John,
This is an interesting solution on the generation side. It remains me of β€œgood old days” when synchronous motors were widely used as primary movers for large load. Often they were kept running just to correct the power factor….unfortunately this knowledge is slowly eroding….
RM
On the subject of power factor correction, I have a question on a problem with our power system. We have two cogenerators rated 450 KW each. They are used primarily for heatand power and operate at 480 volt with a power factor set at .90. When on line with PG & E, they maintain the power factor but with our system set up we back feed thru a 1500 KW transformer into our system grid of 21 KV to distribute through the rest of the system. However the power factor on the system is any where from .2 to .5. The question is whether or not the correction is transferred through the transformer or not. It seems in our case Not. Is there a solution to this situation?

Del H
Electrician
DSRSD
California
RM
It's tough to say whether power factor is transferred through a transformer.

Power factor describes the relationship between reactive power (vars) and real power (watts). The system obeys a var balance and a real power watt balance. All of the vars and watts consumed on the load side of the transformer are transferred through the transformer, assuming there are no other var or watt sources on the load side of the transformer. Additionally, the transformer itself consumes of vars: There is a constant no-load vars consumed by the transformer due to its magnetizing reactance. There is also a load-dependent vars consumed by the transformer due to the leakage impedance. There is also a small amount of watts consumed by the transformer, but much less than the vars consumed. So the input of a transformer typically has a lower power factor than the output (assuming the loads are lagging).

0.2 to 0.5 is a very low power factor. One guess is that you are drawing a very light watts load in the plant and so the no-load vars associated with the transformer creates a low power factor as sensed at the generator (not necessarily that you are consuming high vars, but the low watts is dragging power factor down). To get a better guess, we need more details. Power factor measured at generator. Power factor measured on load side of transformer. Watts and vars at both location. Clarification of leading or lagging for vars and power factor. Description of loads, capacitors, voltage magnitudes, trasnformer tap settings, voltage control methods could also give clues.
RM
Last edited by Registered Member

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