ABB Relion 670 series - High Impedance Grounded Systems

10.3.3.4 High impedance grounded systems
In high impedance grounded systems, ground faults cause a neutral voltage in the feeding
transformer neutral. Two step residual overvoltage protection ROV2PTOV (59N) is used
to trip the transformer, as a backup protection for the feeder ground fault protection, and
as a backup for the transformer primary ground fault protection. The setting must be above
the highest occurring "normal" residual voltage, and below the lowest occurring residual
voltage during the faults under consideration. A metallic single-phase ground fault causes
a transformer neutral to reach a voltage equal to the nominal phase-to-ground voltage.
The voltage transformers measuring the phase-to-ground voltages measure zero voltage
in the faulty phase. The two healthy phases will measure full phase-to-phase voltage, as
the faulty phase will be connected to ground. The residual overvoltage will be three times
the phase-to-ground voltage. See figure
289.
3
V
0
V
_
A
V
_
B
V
_
C
V
_
B
F
V
_
C
F
V
_
C
F
ANSI07000190-1-en.vsd
ANSI07000190 V1 EN
Figure 289: Ground fault in Non-effectively grounded systems
10.3.3.5 Direct grounded system
In direct grounded systems, an ground fault on one phase is indicated by voltage collapse
in that phase. The other healthy phase will still have normal phase-to-ground voltage. The
residual sum will have the same value as the remaining phase-to-ground voltage, which is
shown in Figure
290.
1MRK 506 369-UUS - Section 10
Voltage protection
Line distance protection REL670 2.2 ANSI 577
Application manual