10.6 100% Stator ground fault protection, 3rd harmonic
based STEFPHIZ (59THD)
SEMOD156719-1 v3
10.6.1 Identification
SEMOD158987-2 v4
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
100% Stator ground fault protection,
3rd harmonic based
STEFPHIZ - 59THD
10.6.2 Application
SEMOD143260-4 v6
The stator ground-fault protection of medium and lar
ge generators connected to their
power transformers should preferably be able of detecting small ground current
leakages (with equivalent resistances of the order of several kΩ) occurring even in the
vicinity of the generator neutral. A high resistance ground fault close to the neutral is
not critical itself, but must anyway be detected in order to prevent a double ground
fault when another grounding fault occurs, for example near the generator terminals.
Such a double fault can be disastrous.
Short-circuit between the stator winding in the slots and stator core is the most
common type of electrical fault in generators. Medium and large generators normally
have high impedance ground, that is, grounding via a neutral point resistor. This
resistor is dimensioned to give an ground fault current in the range 3 – 15 A at a solid
ground-fault directly at the generator high voltage terminal. The relatively small
ground fault currents (of just one ground fault) give much less thermal and mechanical
stress on the generator, compared, for example to short circuit between phases.
Anyhow, the ground faults in the generator have to be detected and the generator has to
be tripped, even if longer fault time, compared to short circuits, can be allowed.
The relation between the magnitude of the generator ground fault current and the fault
time, with defined consequence, is shown in figure
212.
Section 10 1MRK 502 071-UUS A
Voltage protection
464 Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual
To Next Page
Loading...
