GE UR Series C70, Инструкция по эксплуатации

Страница: 430 / 614

10-16 C70 Capacitor Bank Protection and Control System GE Multilin
10.4 SETTING EXAMPLE 10 APPLICATION OF SETTINGS
10
To check the limits of protection sensitivity, the same calculations are repeated for the minimum system conditions, which
are considered to be 0.85 pu of nominal system voltage.
The minimum line to neutral system voltage is:
(EQ 10.21)
The following table summarizes the unbalance values during minimum system conditions.
The balance values during minimum operating conditions may be used to check sensitivity.
10.4.5 BANK VOLTAGE DIFFERENTIAL SETTINGS
The bank configuration, CT location, and VT locations allow applying three voltage differential elements:
• An 87V-1 differential element measuring the differential voltage between the two bottom taps.
• An 87V-2 differential element measuring the differential voltage between the upper capacitor string and bottom capaci-
tor can for string 1.
• An 87V-3 differential element measuring the differential voltage between the upper capacitor string and bottom capaci-
tor can for string 2.
Two voltage differential (87V) stages provide trip and alarm levels during capacitor unit failures in each differential element.
The capacitor units are subject to overvoltage if one or more capacitors units are shorted out. The voltage differential trip
pickup setting is programmed for value of 110% of capacitor rated voltage. As seen from the
Unbalance values for maxi-
mum system conditions table above, a failure of four capacitor elements causes a 10.5% overvoltage.
The pickup setting for the stage 1 differential alarm element is chosen for one element failure.
(EQ 10.22)
The alarm delay is set to 10 seconds to avoid alarming during transient conditions.
The pickup setting for the stage 2 differential trip element is programmed as the differential voltage during maximum system
conditions midway between the third and fourth capacitor element failure differential voltages.
(EQ 10.23)
Therefore, the trip delay is set to 50 ms.
Table 10–2: UNBALANCE VALUES FOR MINIMUM SYSTEM CONDITIONS
0 1894.42
Ω
1894.42
Ω
145.70 V 145.70 V 67577.30 V 1.000 pu 0.0000 pu 0.0000 pu 0.0000 pu
1 1894.42
Ω
1849.41
Ω
145.70 V 149.24 V 67573.76 V 1.024 pu 0.0207 pu 0.0207 pu 0.0174 pu
2 1894.42
Ω
1804.40
Ω
145.70 V 152.97 V 67570.03 V 1.050 pu 0.0424 pu 0.0424 pu 0.0357 pu
3 1894.42
Ω
1759.39
Ω
145.70 V 156.88 V 67566.12 V 1.077 pu 0.0652 pu 0.0652 pu 0.0549 pu
4 1894.42
Ω
1714.38
Ω
145.70 V 161.00 V 67562.00 V 1.105 pu 0.0893 pu 0.0893 pu 0.0751 pu
5 1894.42
Ω
1669.38
Ω
145.70 V 165.34 V 67557.66 V 1.135 pu 0.1146 pu 0.1146 pu 0.0964 pu
6 1894.42
Ω
1624.37
Ω
145.70 V 169.92 V 67553.08 V 1.167 pu 0.1413 pu 0.1413 pu 0.1189 pu
7 1894.42
Ω
1579.36
Ω
145.70 V 174.76 V 67548.24 V 1.200 pu 0.1696 pu 0.1696 pu 0.1426 pu
8 1894.42
Ω
1534.35
Ω
145.70 V 179.89 V 67543.11 V 1.235 pu 0.1995 pu 0.1995 pu 0.1678 pu
9 1894.42
Ω
1489.34
Ω
145.70 V 185.32 V 67537.68 V 1.273 pu 0.2312 pu 0.2312 pu 0.1945 pu
10 1894.42
Ω
1444.34
Ω
145.70 V 191.10 V 67531.90 V 1.313 pu 0.2649 pu 0.2649 pu 0.2228 pu
V
min
0.85 V
nom
×
3
-------------------------------
0.85 138000 V
×
3
--------------------------------------------
67723 V
= = =
n
f
Z
C
s
Z
C
sf V
tap 1
V
tap 2
V
top
OV V
diff tap
( )
V
diff string
( )
I
unbal
87V alarm 0.9 V
diff f1_max
( )
0.9 0.0249 pu
×
0.0224 pu = = =
87V trip
V
diff f4_max
( )
V
diff f3_max
( )
+
2
------------------------------------------------------------------
0.1074 pu 0.0785 pu
+
2
------------------------------------------------------------
0.093 pu
= = =