> Rutjoe... Fuses or Protective Relay? If the latter, then Phase-Current unbalance is the simplest!
sorry for the late replay...
using protective relay..my understanding is that to detect unbalance in single ungrounded Wye banks is to measure the bank neutral or zero sequence voltage. If the capacitor bank is balanced and the system voltage is balance the neutral voltage will be zero. A change in any phase of the bank will result in a neutral or zero sequence voltage. my concern is how do i rate my VT(phase to ground)ratio to measure the neutral voltage. if am to use unbalance currents how do i go about implementing that?
Rutjoe... I apologize for not asking the following question earlier:
Are you talking about a single-bank used for Power Factor Correction (PFC) for an industrial plant, or one associated with a Transmission & Distribution system provider?
Rutjoe... my question regarding application had to do with the fact that Utility Companies tend toward redundant systems. That said, I will address only your basic request for information.
a) Voltage-Based.
The most basic protection method is measurement of the bank’s neutral-to-ground voltage. And, even though some will disagree, I recommend the PT, if you prefer VT, should have a rating equal to the system’s ph-ph voltage!
b) Current-Based.
The second most used method is phase-current measurement, that is, using CT’s to compare line-currents.
c) Caveat.
I have not included any discussion on how selection is affected by a number of other factors: non-fusing, internal-fusing or external fusing; number of elements per phase; transients such as Ferro-resonance and switching; excitation inrush-current; 3rd harmonics; surge-arrestor application; and special functions provided by Numeric Protection Relay vendors.
