ABB REC670 Applications Manual page 224

Section 8
Current protection
218
1. Capacitor units should be capable of continuous operation including
harmonics, but excluding transients, to 110% of rated IED root-mean-square
(RMS) voltage and a crest voltage not exceeding of rated RMS voltage. The
capacitor should also be able to carry 135% of nominal current. The voltage
capability of any series element of a capacitor unit shall be considered to be its
share of the total capacitor unit voltage capability.
2. Capacitor units should not give less than 100% nor more than 110% of rated
reactive power at rated sinusoidal voltage and frequency, measured at a
uniform case and internal temperature of 25°C.
3. Capacitor units mounted in multiple rows and tiers should be designed for
continuous operation for a 24h average temperature of 40 °C during the hottest
day, or −40 °C during the coldest day expected at the location.
4. Capacitor units should be suitable for continuous operation at up to 135% of
rated reactive power caused by the combined effects of:
• Voltage in excess of the nameplate rating at fundamental frequency, but
not over 110% of rated RMS voltage
• Harmonic voltages superimposed on the fundamental frequency
• Reactive power manufacturing tolerance of up to 115% of rated reactive
power
5. Capacitor units rated above 600 V shall have an internal discharge device to
reduce the residual voltage to 50 V or less in 5 or 10 minutes (depending on
national standard).
Note that capacitor units designed for special applications can exceed these ratings.
Thus, as a general rule, the minimum number of capacitor units connected in
parallel within a SCB is such that isolation of one capacitor unit in a group should
not cause a voltage unbalance sufficient to place more than 110% of rated voltage
on the remaining capacitors of that parallel group. Equally, the minimum number
of series connected groups within a SCB is such that complete bypass of one group
should not pause voltage higher than 110% of the rated voltage on the remaining
capacitors of that serial group. The value of 110% is the maximum continuous
overvoltage capability of capacitor units as per IEEE Std 18-1992.
The SCB typically requires the following types of IED protection:
1. Short circuit protection for SCB and connecting leads (can be provided by
using PHPIOC, OC4PTOC, CVGAPC, T2WPDIF/T3WPDIF or HZPDIF
functions)
2. Earth-fault protection for SCB and connecting leads (can be provided by using
EFPIOC, EF4PTOC, CVGAPC, T2WPDIF/T3WPDIF or HZPDIF functions)
3. Current or Voltage based unbalance protection for SCB (can be provided by
using EF4PTOC, OC4PTOC, CVGAPC or VDCPTOV functions)
4. Overload protection for SCB
5. Undercurrent protection for SCB
6. Reconnection inhibit protection for SCB
7. Restrike condition detection
1MRK 511 401-UEN A
Bay control REC670 2.2 IEC
Application manual