Page 867 - Industrial Power Engineering and Applications Handbook

Table 25.2 Rating and selection of components for capacitor duty

Type of Reference voltage class Insulation level Current rating Fault level Any other requirement
component Standard (M and time)

1 2 3 4 5 6 I
Isolator LT ~ IEC 60947-3 As per the As in Tables As for the For LT isolators minimum duty AC23.
HT - IEC 60129 voltage rating 13.2 and 14.3 main system. (Table 12.5)
of the capacitor for Series I or Minimum 150% of
banks (Section the rating of the
23.12.1) Table 14.1 for capacitor banks.
(average voltage) Series I1 voltages For systems prone
to generating
HRC fuses LT ~ IEC 60269 excessive
HT - IEC 60282-1, harmonics, and
60549 and 60644 when the size of the
reactor, if used, is
Circuit LT - IEC 60947-4- I not sufficient to 1 For LT systems, it may be a switch and
interrupter (for contactors) suppress these, ratings a contactor, ACB or MCCB. When a
HT ~ IEC 600.56 up to 200% are contactor, they would be minimum AC3
(for circuit breakers) recommended. or AC6b duty. (Table 12.5).
2 For HT systems, refer to Table 19.1,
for the selection of interrupters for
capacitor duty. The breaker should be
chosen restrike free, as far as possible.

Cables and Refer to Table
conductors A16.1 in Chapter 16
._ __ ~
Series reactor IEC 60289 Refer to column 5 I For smaller units, they Refer to 1 For limiting inrush currents: Generally,
are used to limit only column 5 it is not required for the LT systems.
the inrush currents For larger banks, however, say, 500 kVAr
during a parallel and above, when they are installed
operation and may be close to the supply source, so that the
rated for 0.2% of the line reactance up to the bank is too
capacitors’ kVAr small to limit the switching currents,
rating. They must be the use of reactor would be advisable.
connected on the
neutral side of a star- 2 For suppressing harmonics: since on an
connected capacitor LT system, the capacitor banks are
bank. Also refer to normally small, there is generally no
the notes below step 4 need to provide a reactance to suppress
of Example 23.4. the harmonics. It is, however, advisable
The series reactor to provide this for larger banks above
may not be suitable to 500 kVAr to contain the overvoltages
withstand the system on account of this, to save the other
fault level, nor add devices also operating on the same
significantly, to the system. For the likely magnitudes of
circuit impedance to harmonics on an LT system, refer to
diminish its fault level. Table 23.1.