ABB Relion 670 Series Applications Manual page 255

1MRK 511 401-UEN Rev. K
Bus
IEC19000651 V1 EN-US
Figure 118: Typical shunt capacitor bank configuration
The main reasons for internal element failure are:
• Transients in the system (high voltage surges or high-frequency currents)
• Poor manufacturing of any capacitor unit
• Harmonics due to non-linear loads
• Excessive operating temperature
As a result of a failure, the dielectric material in the healthy elements experiences excessive
voltage stress. This can lead to the violation of the terminal voltage of C
110% of rated RMS voltage as mentioned in IEEE standard C37.99-2000.
In this case the capacitor bank must be removed from service. Otherwise, this can lead to
cascading failure of capacitor units and severe damage of the entire bank, resulting in an
explosion or fire.
The phase voltage differential protection provides protection to both open circuit and short
circuit of capacitor elements or units using the bus voltage and tap voltage from the capacitor
bank. The phase voltage differential protection is applicable for both single and double WYE
Bay control REC670
Application manual
N
© Copyright 2017 Hitachi Power Grids. All rights reserved
L1
L2
L3
Capacitor group (C )
group
C C C
C C C
C C C
C C C
C C C
C C C
Capacitor unit (C )
unit
Section 10
Unbalance protection
Element
Branch
IEC19000651-1-en.vsdx
limits going above
unit
249