ABB Relion 670 Series Applications Manual page 266

Section 10
Unbalance protection
C
L 1
IECEQUATION19275 V1 EN-US
C
L
IECEQUATION19276 V1 EN-US
Where,
C
L1
C
L2
C
L3
For an ungrounded capacitor bank configuration, the differential voltage is calculated by using
the bus voltage, tap voltage, and neutral voltage from the bank with the corresponding
voltage ratio for phase L1 as follows:
• The tap voltage and capacitor bank neutral voltage are calculated as follows:
U
N
IECEQUATION19277 V1 EN-US
U
TapL
IECEQUATION19278 V1 EN-US
Where,
U
L1
U
TapL1
U
N
• The differential voltage for phase L1 is calculated as follows:
IECEQUATION19128 V1 EN-US
Where,
UDIFL1 is the differential voltage of phase L1
• The phase differential voltage are expressed in percentage of base voltage UBase as
follows:
PUDIFL
IECEQUATION19129 V1 EN-US
Where,
PUDIFL1 is the differential voltage of phase L1 in % of UBase
The percentage voltage increment on the healthy unit due to unit failure is calculated as
follows:
• The voltage across the faulty unit is calculated as follows:
260
æ ö
´
C C
= ç
1 2
÷
+
è ø
C C
1 2
´
P C
= = =
u u
C 18 C
2 L 3 e
S
u
is the capacitance of phase L1
is the capacitance of phase L2
is the capacitance of phase L3
æ ö
-
C C
= ´ ç
L 1 L 2
÷
U
L 1 +
è ø
2 C C
L 2 L 1
æ ö
C
= ´ ç
1
÷
U
1 L 1 +
è ø
C C
1 2
is the measured bus voltage of phase L1
is the measured tap voltage of phase L1
is the measured neutral voltage of capacitor bank
1
 
  
1
UDIFL U U
L 1 N
USEDURATL
UDIFL 1
= ´
1 100
UBase 3
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 
 
U U
TapL 1 N
1
1MRK 511 401-UEN Rev. K
(Equation 142)
(Equation 143)
(Equation 144)
(Equation 145)
(Equation 146)
(Equation 147)
Bay control REC670
Application manual