I2R Losses and Power Factor Correction

[aelectricalman]

Recently I decided to put together a spreadsheet that tracks CO^2 emissions reduction from the implementation of Power Factor Correction equipment. After I spent countless hours doing the math, expecting one result, coming up with another, it finally hit me....On the user end (not the power company end), there is no signicicant benefit from a Carbon Dioxide reduction standpoint. What is being delivered to the facility is theoretically 100%. The facility, through capacitors and inductors are the reason for the reactive loads on the system that create the inefficencies to start with (theoretically- assuming PoCo gives you 100 PF). So, through my research Im finding that even thought the KVA reductions total roughly 20%-30%, the REAL reductions in CO^2 gases comes from the reduction of I^R losses in a facility from correcting the PF. These seem to be in the low teens for 480 V systems and less than 1% at 12.470kV. That is not much at all for a 12.470kV system but it seems to be considerable at lower voltages (480V). Maybe its a mix up in my formulas but here is my question......Should I expect a greater percentage of KW reduction when looking at terminal voltages of 480 versus that of 4160 or 12.470kV? If this is correct what it tells me is that I can safely state that customers who have 480V systems will have a larger percentage of CO^2 reductions. This does not seem accurate but the data supports it. if that is the case, maybe customers who are subject to future cap and trade(assuming it comes) should then start to consider whether it is optimal to purchase primary sevice versus 480 V from the PoCo. Any thoughts.

 

[GoldDigger]

Recently I decided to put together a spreadsheet that tracks CO^2 emissions reduction from the implementation of Power Factor Correction equipment. After I spent countless hours doing the math, expecting one result, coming up with another, it finally hit me....On the user end (not the power company end), there is no signicicant benefit from a Carbon Dioxide reduction standpoint. What is being delivered to the facility is theoretically 100%. The facility, through capacitors and inductors are the reason for the reactive loads on the system that create the inefficencies to start with (theoretically- assuming PoCo gives you 100 PF). So, through my research Im finding that even thought the KVA reductions total roughly 20%-30%, the REAL reductions in CO^2 gases comes from the reduction of I^R losses in a facility from correcting the PF. These seem to be in the low teens for 480 V systems and less than 1% at 12.470kV. That is not much at all for a 12.470kV system but it seems to be considerable at lower voltages (480V). Maybe its a mix up in my formulas but here is my question......Should I expect a greater percentage of KW reduction when looking at terminal voltages of 480 versus that of 4160 or 12.470kV? If this is correct what it tells me is that I can safely state that customers who have 480V systems will have a larger percentage of CO^2 reductions. This does not seem accurate but the data supports it. if that is the case, maybe customers who are subject to future cap and trade(assuming it comes) should then start to consider whether it is optimal to purchase primary sevice versus 480 V from the PoCo. Any thoughts.

I think that your calculations are probably correct. The reason that HV transmission is used is to minimize I²R loss without requiring excessively large wires. The result is that overall I²R losses, as a percentage of the power actually transmitted, will be lower for HV systems.

In PV solar, the benefit of increasing system DC voltage surprises some people because in addition to reducing the absolute voltage drop in proportion to the voltage factor, you also reduce the percentage VD by the same factor again.

I would say that your study just confirms the fact that the benefits to society at large of PF reduction are small compared to the expense that goes into it.
POCO benefits by being able to use smaller equipment for the same real power load, and that is about it.
Of course that reduction in equipment required corresponds to a lower carbon footprint for building the power infrastructure. It sounds like your analysis is not taking that into account, so you might raise that idea too! At least in a footnote.

As far as the cap-and-trade consequences, I will have to think about that some more. I suspect that the benefits there will also be small compared to the expense, but it is worth running the numbers. Certainly using MV motors can be a factor, but the tradeoffs in cost, safety and maintenance come into play there.
For service delivery voltage, there will be transformers in almost the same place either way, it will just be a question of who owns them. PF correction is more easily done at higher voltages. (Throwing in random thoughts.)

 

[aelectricalman]

Of course that reduction in equipment required corresponds to a lower carbon footprint for building the power infrastructure. It sounds like your analysis is not taking that into account, so you might raise that idea too! At least in a footnote.

Thanks for the insight into HV power and confirming my suspictions! Very helpful. My main reason for this work is to show the customer that in addition to the roughly 30% savings in their utility bill from reducing the demand there is also a benefit in saving CO^2 gases. It really does not look like there is much of a benefit except for the I^2R losses.

And good call on the infrastructure point out! That is a good sell point too.

 

[aelectricalman]

For service delivery voltage, there will be transformers in almost the same place either way, it will just be a question of who owns them. PF correction is more easily done at higher voltages. (Throwing in random thoughts.)

Right. Thats exactly right. Its just a matter of whether or not the savings belong to the customer or the utility. I guess, however, in a MV situation, I can site the savings even though technically they belong to the utility. if the customer cares anything about CO^2 then semantics shouldnt matter, i suppose!

 

[GoldDigger]

Right. Thats exactly right. Its just a matter of whether or not the savings belong to the customer or the utility. I guess, however, in a MV situation, I can site the savings even though technically they belong to the utility. if the customer cares anything about CO^2 then semantics shouldnt matter, i suppose!

"It's not just a question of semantics, it is also about the words we use."
---Steven Colbert

 

[gar]

130823-2214 EDT

aelectricalman:

First, forget about CO2, that is simply a function of how much you reduce the source power required to get a certain amount of output power. If you know the change in input power at the generator for your change from power factor correction, then you can determine the CO2 effect afterward.

Suppose total transmission power loss is 10%. How much of this can you affect by whatever you do? Suppose 5% is after your meter point. Then what part of that 5% can you change by power factor correction? Suppose 1%, and further suppose that your change reflects to a 1% change on the power company side, then under these assumptions a maximum of 2% change in input energy, or 2% change in CO2. But you alone probably don't produce a 1% change in your power component on the power company side. Note: all of your load won't be from poor power factor components.

Second, assume there is no power factor correction penalty, then how much energy loss reduction can be achieved by power factor correction? To maximize the value of PF correction the means of correction must be part of the switched load. Suppose you can reduce the X% loss to X/2% loss for the low power factor circuits, then what is the cost of the power factor correction components in relationship to the energy saving?

I believe there are sales people that claim quick payback on this power loss saving when there is no PF penalty, but is it really true?

.

 

[mivey]

Thanks for the insight into HV power and confirming my suspictions! Very helpful. My main reason for this work is to show the customer that in addition to the roughly 30% savings in their utility bill from reducing the demand there is also a benefit in saving CO^2 gases.

How do you arrive at a 30% savings? That could be possible for some fringe scenarios with some unusually high var charges but I would call it the exception, not the norm.

It really does not look like there is much of a benefit except for the I^2R losses.

Which is better at the load inside the plant rather than at the service point for some loads.

 

[mivey]

...KVA...KW

The correct cases are:
kVA
kvar
kW
kWh
kvarh
kVAh

 

[GoldDigger]

The correct cases are:
kVA
kvar
kW
kWh
kvarh
kVAh

The correct case is bb+/bb=?

(FYI, my barber (British) had the California vanity plate "BBOR0BB")
naught

 

[aelectricalman]

How do you arrive at a 30% savings? That could be possible for some fringe scenarios with some unusually high var charges but I would call it the exception, not the norm.

Which is better at the load inside the plant rather than at the service point for some loads.

hum....

 

[GoldDigger]

Which is better at the load inside the plant rather than at the service point for some loads.

To avoid overcompensation, with the associated VAR penalties anyway as well as potential regulation instability, it is best to have the compensating capacitors switched on and off along with large individual loads. This removes the need to sense the PF at the service point and control the compensation separately.
How close, physically and electrically, that compensation should be to the load itself may be influenced by resonance and harmonic issues as well as just I²R losses.

 

[JoeStillman]

The correlation between energy savings and power factor correction is affected as much by physical distances as by voltage levels. Large facilities that distibute 480V power for long distances stand to gain the most by correcting power factor as close to the load as possible. Correcting power factor at the load reduces current and, consequently, I?R losses, in the feeders. The higher the currents (typical of the lower voltages), the more opportunity for loss reduction. Correction at the load end also reduces transformer losses upstream.

I worked on a large industrial campus that distributed power at 2400V, 480V and 240V. We calculated I?R losses due to low power factor of around 35 kW or 120 MWH-per-year for a plant with 5.5 MW demand.

Some utilities penalize customers who have low power factor. The higher your demand, the higher your required power factor. For small facilities with concentrated low-power-factor loads, eliminating the penalty is the only attractive cost savings. In these facilities, you'll see a bank of capacitors fed right off of the service gear. The utility company gets all the energy-loss reduction. The only thing the customer gets is no penalty.

Some facility owners have a policy of installing capacitors at the ATL starters for all motors 10 HP and larger. These owners get the maximum benefit of PF reduction for low first cost. Here is a table of capacitor sizes for standard induction motors. You need a separate contactor for the capacitors if the starter is solid state. You don't need capacitors at all if its a VFD. Thes run with very high power factor.

 

[mivey]

To avoid overcompensation, with the associated VAR penalties anyway as well as potential regulation instability, it is best to have the compensating capacitors switched on and off along with large individual loads. This removes the need to sense the PF at the service point and control the compensation separately.
How close, physically and electrically, that compensation should be to the load itself may be influenced by resonance and harmonic issues as well as just I²R losses.

Correct. I often scratch my head at why motors get installed without correction and then someone wants to go back later to fix it. The cheapest time to install correction is when the motor is being installed.

The reason the motors have such a low power factor is because it is a trade off between efficiency and better power factor. The norm is to make a more efficient motor and correct for low power factor externally. For some reason, the second part often gets ignored. It could be because there are no pf penalties or the motor is close to the service.

To justify pf correction on losses alone, you need a large motor (or group of motors) located a long way from the meter, that also has a lot of run time.

 

[Besoeker]

Correct. I often scratch my head at why motors get installed without correction and then someone wants to go back later to fix it. The cheapest time to install correction is when the motor is being installed.

It also means that you can get by with installing a smaller supply cable.