Capacitor Banks on a paralleled header

[aelectricalman]

This industrial building is several years old and has an original 2500A service (underground). In the last 5 years an additional service was added to the building. The service is overhead and is 2500A as well. The services are both fed onto the property as a single customer owned 12.47kV system. Customer is metered at 12.47kV on the pole before the two services are paralleled in the building, therefore there is only one meter to satisfy. We are installing a 2000KVAr bank that is fed primary 12.47kV. Our original intention was to place the bank on the immediate pole after the meter so it will catch the lines before they split into two parallel lines (old and new). We have decided there is too much on the pole and it would be too cluttering to do so. There is plenty of room to place the bank on one of the paralleled lines going into the building. Since the bank is only on 1 header entering the building, the customer is concerned there may be issues with installing the full KVAr on half of the capacity. I assured the customer that the VAR will flow where they are needed to satisfy the meter. Also, I assured him that there will be no over voltage issues. Furthermore, each paralleled section is fused appropriately. Am I over looking any possible issues that can arise due to the bank not being immediately after the meter? Any thoughts.

 

[Haji]

aelectricalman:

The setup you are proposing is wrong.

Here is why.

One parallel feeder to which you propose to connect the fully rated capacitor bank would, most probably, be carrying more or less half the full load current only and so the net current with the capacitor bank in that feeder would be leading. This condition would cause over voltage transient.

 

[hurk27]

I have never heard of PF correction at a service except some of the snake oil fixes being sold out on the Internet, in most all PF correction systems I have seen the caps were installed at the loads and sized for correcting the PF of that load, and would be disconnected if that load was turned off, this way there is no chance of over correcting the PF of the whole building, and the owner gets the benefit of lower I?R losses in the feeders to the loads as well as lower voltage drop.

I can understand that lower PF will save on the utilities penalties they charge for bad PF, but I think some also charge for over PF also???

I do know the Iwire also has stores he service that also use PF correction at the service point but I cant see this as saving as much as it would with the PF correction located at the loads?

Maybe I'm wrong?

 

[bob]

Chris
Install another clean pole inline for the caps. Done it a hundred times. Works great.

 

[Haji]

Maybe I'm wrong?

You are not wrong unless you mean considerable energy saving by load side capacitors can also be effected in electrical installations spread over small areas.

 

[iwire]

I have never heard of PF correction at a service except some of the snake oil fixes being sold out on the Internet,

I have worked at industrial sites where PF correction was handled at the service, in one case actually ahead of the service switch.

However, these units had multiple banks of capacitors that the control system would bring on as needed to keep the PF within the desired range.

Obviously at the load would be better but much more costly to retrofit after the fact.

 

[aelectricalman]

aelectricalman:

The setup you are proposing is wrong.

Here is why.

One parallel feeder to which you propose to connect the fully rated capacitor bank would, most probably, be carrying more or less half the full load current only and so the net current with the capacitor bank in that feeder would be leading. This condition would cause over voltage transient.

You are correct except this is 12.47 V. The resulting current increase is minuscule. These banks output at 165 A primary.

 

[mivey]

You are correct except this is 12.47 V. The resulting current increase is minuscule. These banks output at 165 A primary.

165A? Not 93 A?

 

[aelectricalman]

I have never heard of PF correction at a service except some of the snake oil fixes being sold out on the Internet, in most all PF correction systems I have seen the caps were installed at the loads and sized for correcting the PF of that load, and would be disconnected if that load was turned off, this way there is no chance of over correcting the PF of the whole building, and the owner gets the benefit of lower I?R losses in the feeders to the loads as well as lower voltage drop.

I can understand that lower PF will save on the utilities penalties they charge for bad PF, but I think some also charge for over PF also???

I do know the Iwire also has stores he service that also use PF correction at the service point but I cant see this as saving as much as it would with the PF correction located at the loads?

Maybe I'm wrong?

It is very common and much more effective to correct 12.47kV at the pole. Saving customers $5000-$10000 per month satisfying the meter, is not snake oil. Also, correcting at a voltage source is predominately good for line loss which is a very small part of the overall savings. Where I live, correcting PF is much more economical when you are approaching it from a reduction in KVAr standpoint. When you are charged $14.00 per KVA demand and you have 5000 kW, it is very beneficial to take a 75% PF and make it 99%. Also, we never install capacitors without over voltage regulators. Fixed or automatic. With voltage regulators installed, we are protected, because our PoCo's do not charge for leading KVAr. Now of course we size our fixed banks for a lower PF but our autobanks have controllers that limit the PF to 99%. With steps and all the other safety measures, I think we are covered. Thanks for the feedback.

 

[aelectricalman]

165A? Not 93 A?

Different KVAr banks are going to output different current ratings. But really, I was just making a reference to fuse sizing. So yes you could be right I suppose. The point of my conversation was to say that current is hardly a factor!

 

[aelectricalman]

I have worked at industrial sites where PF correction was handled at the service, in one case actually ahead of the service switch.

However, these units had multiple banks of capacitors that the control system would bring on as needed to keep the PF within the desired range.

Obviously at the load would be better but much more costly to retrofit after the fact.

Agreed!

 

[mivey]

Different KVAr banks are going to output different current ratings.

But 2000 kvar at 12.47 is 93 A. 165 amps sounds more like the load current you probably have on each of the paralleled lines.

 

[mivey]

But really, I was just making a reference to fuse sizing.

That sounds more reasonable.

 

[aelectricalman]

Chris
Install another clean pole inline for the caps. Done it a hundred times. Works great.

I agree. We had a very clustered group of poles, so we ended up dropping a new one half way down one of the 12.47kV parallel lines on the load side of the meter. I agree, it looks much better. What part of the world are you in?

 

[aelectricalman]

That sounds more reasonable.

Actually the fuse sizes on that bank is really 125A or maybe slightly larger, I don't remember. We ended up installing a 3MVAr, 3.6 MVAr, 2 MVAr and a 1.107MVar.

 

[mivey]

Actually the fuse sizes on that bank is really 125A or maybe slightly larger, I don't remember. We ended up installing a 3MVAr, 3.6 MVAr, 2 MVAr and a 1.107MVar.

Normal would be 135% of load current or 92.6 * 1.35 = 125 A for a 100% rated fuse (and you would divide by 1.5 for a 150% rated fuse, etc.).

For the 2000 kvar case.

 

[mivey]

Am I over looking any possible issues that can arise due to the bank not being immediately after the meter? Any thoughts.

If the feeders are the same size, and the loads are about the same, and the location is close to where you were going to put them anyway, I don't really see a problem.

For very unbalanced feeders, if you put all the correction on the smaller feeder you may overload it.

 

[aelectricalman]

I have worked at industrial sites where PF correction was handled at the service, in one case actually ahead of the service switch.

However, these units had multiple banks of capacitors that the control system would bring on as needed to keep the PF within the desired range.

Obviously at the load would be better but much more costly to retrofit after the fact.

There's another school of thought to consider. If your goal is to satisfy the meter, don't you want to be as close to the meter as possible? That is, if your intention is to reduce KVA? Keep in mind I'm talking about medium voltage. Otherwise you are also correcting at 480 V at the utilization equipment and you also have to size the banks for the 89% PF of the 12.47kV/480V XFMR as well as whats in the building. Plus equipment cost is outrageous when you have to add a mechanical disconnect for over-current protection. And to top it off, you are very far from the meter you are trying to satisfy. The research I've done shows that line losses are a very small piece of the pie. Please correct me if I'm wrong because I want to learn more about Caps. This could also be a result in how each of our PoCo's bill. We could both be exactly right.

 

[aelectricalman]

Normal would be 135% of load current or 92.6 * 1.35 = 125 A for a 100% rated fuse (and you would divide by 1.5 for a 150% rated fuse, etc.).

For the 2000 kvar case.

thanks,

 

[mivey]

The research I've done shows that line losses are a very small piece of the pie. Please correct me if I'm wrong because I want to learn more about Caps. This could also be a result in how each of our PoCo's bill. We could both be exactly right.

We have had this discussion before. For very large var loads, located a long way from the meter, with a lot of run time, the line loss savings are significant, as well as the savings in feeder and equipment sizing (assuming you get in on the front end).