Bulk/Static correction and billing.

[Electrical guy]

Voltz
How long is the cable run from the starter to the motor? If it is short it would not make any difference if the caps were ahead of the starter. Utilities bill for the max KVA demand during the month at about $5.00 per kva. It does not take much to save a lot of money. The the I2R saving are usually small unless the motor is use for many hours. Most designers place the caps at the motor. You need to make sure you don't have any VFD on the motors. Capacitors and VFD do not play well together.

Bob,
To keep excessive current build up and other problems from arising, should not the caps be placed at least 50 feet away (conductor length) from the VFD.

 

[VoltzElectric]

[QUOTE=Electrical guy;1095905
For billing purposes, I was under the assumption Static control (caps at load) do not lower the customers bill at all, if a well installed PF correction switching bank (.95) was present at the main. The assumption was, static control as you stated reduces demand and increases efficiency internally only. Correct me if I am wrong.

If you already have a capacitor bank installed at the main, this only helps out the POCO, not you as a consumer, for all your loads are still drawing the higher current and not correcting until you get to the capacitor bank. IF you go to a CAL system, you are reducing your current demands right at the source, thus saving on the I2R losses back to the main:grin:

 

[Electrical guy]

Bob,

I can live with that, Thanks for the input. Always good to have other opinions.

 

[beanland]

Reduced Losses

Reduced Losses

There are too many variables to be specific on changes in losses. I dug into a large transformer quote to get an idea on losses. These losses were 0.09% of nameplate for iron/core loss and 0.33% for load/copper losses at full nameplate loading. There is no way to save more than 0.33% in reduced losses in this transformer. In reality, savings will be a small fraction of this because you are not running at full load and you are not reducing to no load. Remember that copper loss is proportional to the square of the current. Copper loss at 50% loading is 25% of that at full nameplate.

I would be amazed if any combination of power factor capacitors could even come close to saving 1%. More realistic is some number under 0.1% of load.

 

[Electrical guy]

Forgive me for my ignorance, I am not familiar with the term "CAL system" could you please elaborate. Are you refering to what I term "Static"

 

[mivey]

...6.Power factor correction introduced at the load only, lowers your KWH.T I?R loss is reduced
7.Power factor correction introduced anywhere, does not alter KW DEMAND T.

Bob, I agree with your responses except #7. If #6 is true, then #7 must be false. The kW demand will also be reduced by the I?R amount.

As I'm sure you know, it might be worth noting that without var penalties (or kVA charges), it rarely makes sense to correct much past the low 90's. It can make sense to correct to the upper 90's if the charges for vars are high enough. Over-correction can hurt you because it increases the demand as well but must be weighed against the number of hours and size of the load.

 

[bob]

Our peak Demand is $8.85/KW. What Im not sure on is exactly how they come up with that. THey would have to add the apparent power usage in there some how, they're not just gonna give it to me for free.

If you are being bill for KW, the added caps will not help reduce you billing. Are you sure its KW and not KVA? Here a customer is on a KW billing up to about 800 kw. Any higher and they are billed on KVA demand and billed about $5.00 per KVA so it helps to improve the power factor.

 

[VoltzElectric]

If you are being bill for KW, the added caps will not help reduce you billing. Are you sure its KW and not KVA? Here a customer is on a KW billing up to about 800 kw. Any higher and they are billed on KVA demand and billed about $5.00 per KVA so it helps to improve the power factor.

our peak KW demand is around 1170kw. Like I stated earlier, I am trying to get out of the POCO what exactly, or rather how exactly that gets broken down.

 

[bob]

Bob, I agree with your responses except #7. If #6 is true, then #7 must be false. The kW demand will also be reduced by the I?R amount.

As I'm sure you know, it might be worth noting that without var penalties (or kVA charges), it rarely makes sense to correct much past the low 90's. It can make sense to correct to the upper 90's if the charges for vars are high enough. Over-correction can hurt you because it increases the demand as well but must be weighed against the number of hours and size of the load.

I agree regarding #6 and #7. My thoughts were that the I?R would be small when compared with the KW demand and would not make much of a difference in the KW demand billing.
The utility I have dealt with charge $5.00 per KVA. There have been some cases that improving the power factor above 0.90 proved to be cost effective when installation of larger capacitors could be done for the same labor cost and the added cost was only the cost difference of the capacitors.
We were using a payback period of 2 years.

 

[VoltzElectric]

Forgive me for my ignorance, I am not familiar with the term "CAL system" could you please elaborate. Are you refering to what I term "Static"

CAL = Capacitor At Load
You get more bang for your buck, because you are reducing your amp draw from the cap back to the main, where when you have a bank at the main, you arent reducing any amp draw after the capicitor bank. It is more expensive initially, but has a better payout in the long run.

 

[Electrical guy]

CAL = Capacitor At Load
You get more bang for your buck, because you are reducing your amp draw from the cap back to the main, where when you have a bank at the main, you arent reducing any amp draw after the capicitor bank. It is more expensive initially, but has a better payout in the long run.

Thanks, for clarification.

 

[bob]

CAL = Capacitor At Load
You get more bang for your buck, because you are reducing your amp draw from the cap back to the main, where when you have a bank at the main, you arent reducing any amp draw after the capicitor bank. It is more expensive initially, but has a better payout in the long run.

how did you arrive at the size of the caps for the motor?

 

[VoltzElectric]

I am using a power analyzer to determine my apparent power, my true power, and my KVAR, then size cap to bring it up to .93ish or there about. If you size it too close to 1.0 you can end up with issues there as well.
If you search "power factor correction" in the search window, it will come up with some good info for you. I have learned alot from the guys on here in the last month!!!!

 

[mivey]

...we can reduce our KVA, but obvously not our true power. Our machines are pretty bad at around .5 - .6 PF. So, By reducing the KVA, we will see less current used at the meter, and make our savings on the I2R losses...

Heat loss is true power. But it will be small compared to the usage.

Using some rough calcs, I calculated correcting from a 50-60% pf to 95% can reduce the real power from losses by around 0.5-1% of the total load for a 200 ft run, depending on how the wire is sized.

While 1% is real money, the big money is probably in the kvar or kVA charges.

 

[bob]

I am using a power analyzer to determine my apparent power, my true power, and my KVAR, then size cap to bring it up to .93ish or there about. If you size it too close to 1.0 you can end up with issues there as well.
If you search "power factor correction" in the search window, it will come up with some good info for you. I have learned alot from the guys on here in the last month!!!!

Mfg will usually have a capacitor to match their motor. I understand what you are saying but your calculated cap may not match the mfg. Don't limit the pf to 0.93. Standard sizes may improve it to 0.95. Nothing wrong with that.

 

[Electrical guy]

Mfg will usually have a capacitor to match their motor. I understand what you are saying but your calculated cap may not match the mfg. Don't limit the pf to 0.93. Standard sizes may improve it to 0.95. Nothing wrong with that.

Is it not better to use emperical data as opposed to manufacturer specs, I found in the past motor loading and age of equip plays a large factor, data recorded and data from the manufacturer could be way out. Would it not be better to correct PF to about .93 if there is a chance unity could be obtained if there are slight variances and load fluctuations.

 

[bob]

Is it not better to use emperical data as opposed to manufacturer specs, I found in the past motor loading and age of equip plays a large factor, data recorded and data from the manufacturer could be way out. Would it not be better to correct PF to about .93 if there is a chance unity could be obtained if there are slight variances and load fluctuations.

That sounds like a good plan.

 

[Electrical guy]

I was just talking with a Rep. from MERIT (who sells CAL's) yesterday, and he was looking at our molding machines for helping us with poor PF. By installing the CAL after the motor starter, we can reduce our KVA, but obvously not our true power. Our machines are pretty bad at around .5 - .6 PF. So, By reducing the KVA, we will see less current used at the meter, and make our savings on the I2R losses. We can hope to gain aprox. 3 -6% off our electric bill. I still havent gotten in touch with the POCO to figure exactly how they are charging us on our Peak Demand, and how that plays in yet, but we could end up saving more than that in the long run. I beleive that with A CAL type system, you as the consumer will see the cost benefits vs. using a large auto switching bank at the transformer, that only helps the POCO out.

Need clarification on this,
When you speak of True Power not being reduced but will reduce I2R losses

1.Are not I2R losses (heat) True Power?
2 If I2R is True Power, would not these savings be minimal unless you have a large load and even then only show a small % reduction?
3. Would not I2R losses saved be proportional to conductor length and size, so would not distance play a role?
3. You say you will reduce KVA and see less current at the meter, and make your savings on I2R losses. Could you please elborate on how this will save you money.
4. Do not caps at main reduce your KVA demand therfore reducing your bill if you are billed for KVA, and not just help out the POCO?

Thanks,

 

[VoltzElectric]

Need clarification on this,
When you speak of True Power not being reduced but will reduce I2R losses

1.Are not I2R losses (heat) True Power?
2 If I2R is True Power, would not these savings be minimal unless you have a large load and even then only show a small % reduction?
3. Would not I2R losses saved be proportional to conductor length and size, so would not distance play a role?
3. You say you will reduce KVA and see less current at the meter, and make your savings on I2R losses. Could you please elborate on how this will save you money.
4. Do not caps at main reduce your KVA demand therfore reducing your bill if you are billed for KVA, and not just help out the POCO?

Yes all this plays into it.
1. correct
2. plan on a 2-3% reduction
3. If I reduce the amp draw right at the machine prior to going all the way back through the buss, switchgear, and back to transformer....then meter, I am saving in the I2R loss. The machines I run are running around 130 kva, or 70kw/hr. The 2-3% will pay itself off in a short amount of time
4. I sat down with my POCO, and they DO NOT charge me on my KVA (apparent power), they eat it. I was surprised to hear this. They dont add it in anywhere else either. We get a PF penalty of 2% if we are below .8.
So, having CAPS at the main only helps the POCO, and not us.