ABB RELION 670 Series Applications Manual page 203

1MRK 505 337-UUS A
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:
•
•
•
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. Ground-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
CBPGAPC function can be used to provide the last four types of protection mentioned in the above
list.
7.10.3 Setting guidelines
This setting example will be done for application as shown in figure 99:
Application manual
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
Section 7
Current protection
GUID-CECD6525-779C-4A77-844D-031AAEE3A5B6 v1
GUID-7C456976-BA0D-4AAC-9C7A-F73AF52B2B44 v2
197