Page 873 - Industrial Power Engineering and Applications Handbook

Making capacitor units and ratings of switching devices 25/825

60549i 1'176 Ili~h-\oltnge fuse\ for shunt power capacitors 9402/1992 BS 55641992
6llh-131 I979 Specification for high-voltage fuse-links for motor - BS EN 606441993
circuit applications
60947-3/1 u9x Specification for LV switchgear and controlgear 13917-3/1993 BS EN 60947-3/1992
S\vitche\. disconnectors, switch-disconnectors and
luse comhination units
611947-4- 111 990 ILow \oltage switchgear and controlgear
F.lectroinechanical contactor\ and motor \tarter\
Relevant US Standards ANSYNEMA and IEEE

ANSI!IEEE Giiitie tot pi-otecuoii of shun1 capacitor banks
(' 37.W/IW4
Inchstrial control and \y\teins. controllers. contactors and overload relays. rated not inore than
N m1, \/I(.S ~
2/1')91 2000 V J.C. or 750 V d.c.
Y 131 ,W.I'- Ezrernal f iises for shunt c;ipacitors
'I/ I 99'
N Ehl A tT .- Lo\\ \ olrage cartridge fures
I / 19x11
NEM.\ SG High \oltayc I'USC\
21 I 9') 3
,V(l/?\
I In the table\ oi'Rclcvanr Standards in this book while the latest editions ofthc standard5 are provided. it i\ possible that revi\cd edition\
Iha\t. become a\ailable. With thc advances 01' technology and/or its application, the updating of Standards ih a continuous process by
tiilferciir ~t:ii)ti;t~d~ or-ganiiations. 11 is therefore advisable that for more authentic references. reader\ should conhuh the iclevilnt
or~ani/ati(iii~
1.o~ the latest \ersion of a standard.
2 Soine ot the BS or IS standards mentioned again\[ IEC may not be identical
3 'The hex noted .iyin\t each Standard may ;d\o refer to the year of its last aniendment and no( nece\?arily the year of publication

List of formulae used (iii) Double-star capacitor banks
Precautions against overvoltages on the failure % over voltage = 6.N.N) -5N x lOO(25.4)
of some units 6N2 . N, - 6N. N, i 5N

Discharge devices
(i) Single-phase units connected in parallel
./
(25. I) (i) The value of discharge resistance
V, = enhanced voltage across the healthy units on the R, = (35.5)
failure of one unit C
2'-
. , - no. of units in parallel R, = discharge resistance in 0.
C = capacitance in farad
T = time constant in seconds
(ii) Single-star capacitor banks t
3 N N, -2N r= d3. V, (35.6)
('1) '4 oven oltage = k ' log,
3NL N, -3N N, +2N ~ u
(25.2) t = changeover time or required discharge time in
N = number of units failed seconds
N, = number of units in series per group per phase V, = system voltage in volts
N2 = number of units in parallel per group per phase u = residual voltage
(b) Fault current k = a constant that will depend upon the confip-ation
of the capacitor unit and its discharge resistance
(25.3)
(ii) The value of a series inductor
I, = fault current on failure of one unit
f,. = rated current of one unit (25.7)