Capacitor Installations

[iwire]

Does anyone have any info about capacitor installations?

Is there a length limit for the conductors connecting a capacitor bank to the electrical system?

Any info will be appreciated, Thanks Bob

 

[bphgravity]

Is this a DYI question?

I wish I could help, but to be honest, I don't think I have ever read Article 460...

 

[iwire]

Is this a DYI question?

LOL....alright you got me.

I am not doing the work, I am asking for a friend.

I wish I could help, but to be honest, I don't think I have ever read Article 460...

I think we are set on the code issues, this is more of a design issue.

 

[BAHTAH]

Capacitor Installation

Capacitor Installation

Typically if this is going at a MCC for example, the GEM units that are made by GE have mounting brackets so they can be installed either on the wall or on top of the MCC or even on the floor. You need overcurrent protection for the conductors supplying the cap unit unless its connected to the load side of the motor OL if its for a single motor application. The GEM type unit has the discharge resistors build-in and reduce the voltage to 50 volts or less within about one minute after the unit is denergized. I am not sure what you mean by long leads. I try and keep the leads as short as possible and the unit as close as possible to where I am using it. There are other larger Cap units that are automatic and fast-switching for power factor correction on a larger scale. These come in free standing enclosures. Not sure just what your looking for, hope this info is of some help.

GAR

 

[don_resqcapt19]

The one I worked on is 4.16kV and there is about 85' of parallel 350kcmil copper between the capacitors and the main switch gear.
Don

 

[iwire]

I don't have a lot of info from my friend, I will tell you what I know.

This capacitor bank is being connected to the main service switch board of a super market.

The service is either 480Y/277 or 208Y/120.

Apparently there is an issue of space and my friend wants (or needs) to place the capacitor bank far from the gear. He has been getting conflicting info from the engineer and the vendor if this will be OK.

Thanks, Bob

 

[ghostbuster]

I don't have a lot of info from my friend, I will tell you what I know.

This capacitor bank is being connected to the main service switch board of a super market.


Thanks, Bob

The problem with the main board area is there should be a spare disconnect or breaker to feed the cap bank. Then the bank can be physically placed where ever you want.(I have never seen a cap cable length restriction)
Some code areas allow you to tap directly onto the main busbar (switchboard has been turned off and has been pre-approved by code prior to install) to feed this cap bank if there are no spares in the board. This is where it gets tricky and highly subjective. The bank c/w disconnect has to be installed within this switchboard room to be approved.(note:the cabling to the cap bank now is only protected by the main switchboard breaker).I would strongly recommend to check with your local code officials prior to proceeding with this latter approach.

 

[iwire]

Overcurrent protection is being provided. :smile:

 

[robbietan]

I have seen capacitor banks placed far from the main entrance. the owners wanted the capacitors to be placed well near the manager's office so that he can monitor the operation. beats me why...

 

[ptonsparky]

I have been researching this for customer with possible harmonics problems in conjunction with PF capacitors.

I found this on the www.eatonelectrical.com. Might be something to consider. Document SA02607001E

1. If the plant?s total 3-phase non-linear load
(in kVA, 1 hp = 1 kVA) is more than 25% of the
main transformer capacity, harmonic filters will
almost always be required for power factor
correction.
2. If the plant?s total 3-phase non-linear load is less
than 15% of the main transformer capacity, capacitors
can usually be applied without problems.
3. If the plant?s total non-linear load is between
15 and 25%, other factors should be considered.​

 

[bob]

Is there a length limit for the conductors connecting a capacitor bank to the electrical system? Thanks Bob

If your friend is asking about the conductor length effecting the correction of power factor by the capacitors, then he should not be concerned. You do get a voltage rise when the conductors are long.

 

[steve66]

Why are the capacitors being installed? For PF correction to reduce the demand or to reduce the amount of energy being wasted?

If that's the case, then there will still be some energy wasted on the conductors between the capacitor and the service. The longer the conductors, the more wasted.

 

[peter d]

I've been personally involved with one of the installations. I was told that it's for energy savings.

It's been a while since I took electrical theory. How does adding a cap. bank save energy? I thought the poco charged and metered true power, not apparent power? Reactive power is not actually consumed, is it? So how would canceling it out save energy? I'm confused, obviously.

Don't the poco's charge a penalty for customers with bad PF? So the savings would be from eliminating the penalty?

 

[steve66]

I've been personally involved with one of the installations. I was told that it's for energy savings.

It's been a while since I took electrical theory. How does adding a cap. bank save energy? I thought the poco charged and metered true power, not apparent power? Reactive power is not actually consumed, is it? So how would canceling it out save energy? I'm confused, obviously.

Don't the poco's charge a penalty for customers with bad PF? So the savings would be from eliminating the penalty?

Here is how I understand it without getting too complicated. VAR's flow to the motor on part of the cycle, and are returned to the source on another part of the cycle. There is a real current flow associated with this, and the real power losses are this current flow times the resistance of the wire. The longer and smaller the wire, the more the losses.

Add a capacitor, and the VAR's flow between the capacitor and motor (instead of all the way back to the source). Put too much resistance between the motors and capacitors, and again you are loosing real power.

With the capacitor, it seems like a lot more of the losses would be on the customers side of the meter. Without the capacitor, it seems like the POCO would be footing the bill for most of the losses.

Steve

 

[bob]

How does adding a cap. bank save energy? I thought the poco charged and metered true power, not apparent power? Reactive power is not actually consumed, is it? So how would canceling it out save energy? I'm confused, obviously. Don't the poco's charge a penalty for customers with bad PF? So the savings would be from eliminating the penalty?

Some POCO customers are billed on KVA demand rather than KW demand.
The savings would occur due to a reduction in the KVA demand with the addition of the capacitors.

 

[jcormack]

I actually spec at minimum of ten ft of wire in metallic conduit between a capacitor and its motor-starter if switched on with the starter@ 480 vac. This Small amount of imp. might seem trivial, but it actually helps in reducing inrush to the caps and nuciance fuse blowing. Extremely long leads (100's of feet in conduit) could lead to a "ring" situation in which you have created a resonance problem (Bad!).
Don't install caps close to Voltage regulators with tap changers !
As long as you are not talking more than 60 to 70 ft, I would not worry, if longer, just have an engineer look at system X/R to see if any issues exist.

 

[robbietan]

Don't the poco's charge a penalty for customers with bad PF? So the savings would be from eliminating the penalty?

That is the main selling point of capacitor vendors here in my neck of the woods. Trouble is, since deregulation and an 'unbundled bill', the discount became smaller. Instead of a payback of 2 years, now you have to wait 5 years.

 

[ghostbuster]

I actually spec at minimum of ten ft of wire in metallic conduit between a capacitor and its motor-starter if switched on with the starter@ 480 vac. This Small amount of imp. might seem trivial, but it actually helps in reducing inrush to the caps and nuciance fuse blowing. .

In the "old days" the contractor would coil the wire around a broom stick (10-15 turns) before connecting to the starter.In my country,there is actually a standard dealing with this cap. current inrush problem (I helped write this standard).