Grounded vs ungrounded capacitor banks
Grounded vs ungrounded capacitor banks
(OP)
We are under the gun to conform with the new NERC power Factor requirements of 97%. This will involve the installation a many new cap banks.
My problem is that we use the Cannon Technologies AMR system and have blocking units in the neutral of each bank to prevent the signal from being shunted to ground. The blocking units are expensive.
Is there any disadvantage to not grounding the cap bank and letting it float so that I can forego the blocking unit?
My problem is that we use the Cannon Technologies AMR system and have blocking units in the neutral of each bank to prevent the signal from being shunted to ground. The blocking units are expensive.
Is there any disadvantage to not grounding the cap bank and letting it float so that I can forego the blocking unit?






RE: Grounded vs ungrounded capacitor banks
Also, if there are single phase fuses or switches on the source side of an ungrounded wye bank, they can get phase-to-phase voltage across the open contacts and must be rated appropriately.
RE: Grounded vs ungrounded capacitor banks
http://www.sandc.com/webzine/101804_1.asp
By the way, I am curious, what is the NERC PF requirement of 97%, could you refer me to the standard or explain it in a little more detail?
RE: Grounded vs ungrounded capacitor banks
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RE: Grounded vs ungrounded capacitor banks
On the negative side, we use single-bushing capacitor cans on the line and our safety work practices requires us to ground the cans. With a single bushing arrangement, we can simply ground the rack. If we lift the neutral to ground connection, the cans will be at some elevated potential.
An alternative is to use 2-bushing cans. This way the can can be grounded and it doesn't tie it to the neutral. Maybe you're already using 2 bushing cans for your system, but for us that would be a big obstacle to overcome.
The problem isn't really related to Cannon Technology, but rather to the use of power line carrier as the communication means. I believe Cannon's equipment will work with other communications choices.
RE: Grounded vs ungrounded capacitor banks
As magoo2 states, the 97% PF is aimed at the transmission lines. In the ERCOT Deregulated market, this responsibility has been dumped onto the distribution utilities. The cap banks I was referring to are on 12.5Kv and 24.9 Kv grounded wye distribution systems and are typically two bushing units.
As far as Cannons' Technology, it is simply a case of their 12.5 Khz signal being shunted to ground due to the low impedance of the caps at that frequency (which is the reason for the blocking units).
Not being an engineer (and having a ton of cap banks to install) we were hoping to save some money on the installation by foregoing the blocking units and using the ungrounded banks.
Does supermaccs' expanation of a higher recovery voltage still apply?
RE: Grounded vs ungrounded capacitor banks
With 2 bushing units, you should have no difficulty installing the traps (filters) between the bank neutral and the system neutral or simply ungrounding the bank - which is a lot cheaper.
RE: Grounded vs ungrounded capacitor banks
RE: Grounded vs ungrounded capacitor banks