Field Ground Fault Protection - GE G60 Instruction Manual

CHAPTER 5: SETTINGS

5.7.18 Field ground fault protection

5.7.18.1 Menu
SETTINGS  GROUPED ELEMENTS  SETTING GROUP 1(6)  FIELD GROUND PROTECTION
 FIELD GROUND
 PROTECTION
The figure shows a field ground detection scheme using the G60 and the GPM-F. The field winding of a synchronous
generator is represented electrically by the impedance Z
ungrounded. The capacitance C
represents the only path for current to flow to ground under normal conditions.
The resistance R represents a breakdown of the field winding insulation providing a resistive path to ground through the
G
field grounding brush. The insulation failure can occur anywhere, so the impedances Z
impedance R is also unknown. The purpose of the field ground detector is to measure this resistance.
G
Measurement of R is accomplished by injecting a voltage, V
G
algorithm must be capable of discriminating between capacitive current due to C
current due to a fault. The exciter voltage, V
essentially resistive. The current I
G60 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
 FIELD

 GROUND
 FIELD

 CURRENT
= Z
F
is the stray capacitance of the field, distributed along the field winding. This capacitance
F
Figure 5-180: Field ground fault detection
INJ
is a DC value with a small ripple such that the impedance of the field is
FLD
is a DC current with a range of tens, hundreds, or thousands of amps.
FLD
See page 5-313
See page 5-315
+ Z . Under normal conditions, the field circuit is
F1 F2
and Z
F1
and measuring the resulting current, I
(which can be significant) and resistive
F
GROUPED ELEMENTS
are unknown. The fault
F2
. The measurement
G
5-311
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