GE C70, Instruction Manual

Page: 464 / 708

9-12 C70 Capacitor Bank Protection and Control System GE Multilin
9.4 SETTING EXAMPLE 9 APPLICATION OF SETTINGS
9
9.4SETTING EXAMPLE 9.4.1 DESCRIPTION
Consider protection of a capacitor bank with the following characteristics:
• V
LL
= 138 kV fuseless.
• Q
B
= 21 Mvar.
• Two parallel strings ( S = 2) in each phase with N = 7 capacitor units rated Q
C
= 500 kvar, V
C
= 11.62 kV.
• Each capacitor unit consisting of n = 6 series capacitors.
Refer to the diagram below for details. Phase capacitors are connected to ground through a neutral capacitor rated
Q
CN
= 167 kvar, V
CN
= 0.825 kV.
Figure 9–12: SAMPLE CAPACITOR BANK CONFIGURATION
Based on the bank configuration, CT connections, and VTs connections, a C70 model is chosen with three CT/VT modules:
two type 8L modules (in slots F and U) and one type 8V module (in slot M) to provide following protection functionality.
• Negative-sequence instantaneous overcurrent (ANSI 50_2) to provide fast backup protection against arcing within
capacitor bank.
• Phase overvoltage (ANSI 59B) to provide protection against overvoltages.
• Bank overcurrent protection, phase instantaneous overcurrent (ANSI 50P), neutral instantaneous overcurrent (ANSI
50N) and phase time overcurrent (ANSI 51P) to provide protection against major faults within the capacitor bank.
• Bank undervoltage (ANSI 27P) to detect loss of bus voltage and trip the bank.
• Voltage differential (ANSI 87V) to detect failure of one or more capacitor elements in a given string. Three voltage dif-
ferential elements can be set for this application: one between two tap voltages (ANSI 87V-1) and two between the bus
voltage and tap voltage in both strings (ANSI 87V-2 and 87V-3).
• Phase current unbalance (ANSI 60P) to detect failure of one or more capacitor elements in a given string.
9.4.2 VT AND CT SETUP
The CT and VT connections are shown in the figure above. The CT channels are connected as follows.
• The type 8L CT/VT module F1 to F3 three-phase CT channels are connected to the bus side three-phase CTs with a
120 / 5 A ratio.
F1-3
F5-7
59B
87V
51N
C70 CAPACITOR BANK RELAY
U1-3
60P
(A)
60P
(B)
60P
(C)
138 kV
138 kV/
0.115 kV/
500 kvar
11620 V
120/5A
50/5A
50_2
50P
51P
27P
1250/250 V
167KVAR,
825V
`
L4-7
L1-3
3
834764A1.CDR