GE G60 Instruction Manual page 412

5.6 GROUPED ELEMENTS
Where C is in microfarads. Some example injection frequency settings are given in the table below for various field
F
winding capacitance values. For field winding capacitances greater than 10 μF, resistance measurements will be less
accurate.
Table 5–31: EXAMPLE INJECTION FREQUENCY SETTINGS
C
F
1 μF
2 μF
3 μF
4 μF
5 μF
6 μF
7 μF
8 μF
9 μF
10 μF
• INJ CONNECTION TYPE: Field ground protection can be implemented by injecting a low frequency signal either into
both positive and negative terminals of the field winding or only into the negative terminal of the field winding. Refer to
the instruction manual of the field ground module for wiring difference between single point and double point injections.
For single point injection, the G60 provides the feature of fault location. In case of a field ground fault, the G60 displays
the location of the fault in the field winding as a percentage of the winding from the negative terminal. If the preference
is to keep the injection symmetrical into the field winding, then double point injection has to be done but the fault loca-
tion feature is not available. This setting has to match the type of connection on the field ground module.
5
• FIELD GROUND STG1 PICKUP: If the measured ground resistance is less than the value specified by this setting,
then the stage 1 element will pickup. Normally stage 1 is used to raise alarms and typical settings may fall in the range
of 10 to 40 kΩ.
• FIELD GROUND STG1 DELAY: This setting specifies a time delay for stage 1. Typical settings are in the range of 10
to 15 seconds. This delay will have to be added to the operating time of the element to obtain the overall delay.
• FIELD GROUND STG2 PICKUP: If the measured ground resistance is less than the value specified by this setting,
then the stage 2 element will pickup. Normally stage 2 is used to raise trip signals and typical settings may fall in the
range of 2 to 5 kΩ.
• FIELD GROUND STG2 DELAY: This setting specifies a time delay for stage 2. Typical settings are in the range of 3 to
5 seconds. This delay will have to be added to the operating time of the element to obtain the overall delay.
• FIELD GROUND UC PICKUP: This setting specifies the ground undercurrent level below which a brush open condi-
tion shall be detected. A brush lift-off condition will prevent the field ground detector from operating. This is detected by
calculating the RMS value of the ground current. It will normally have a non-zero value due to the capacitance of the
field winding. A drop in this signal indicates an open circuit in the injection path. To set this value, the ground current in
a healthy operating condition preferably with zero field voltage should be recorded from G60 actual values display
(performed during commissioning). Configure this setting to be 60 to 70% of that normal value.
• FIELD GROUND UC DELAY: This setting specifies a time delay for field ground undercurrent element. Typical settings
are in the range of 20 to 30 seconds. This delay will have to be added to the operating time of the element to obtain the
overall delay.
• FIELD GROUND FUNCTION BLK: This setting selects a FlexLogic operand to block the field ground function.
5-252
F
INJ
2.50 Hz
1.50 Hz
0.83 Hz
0.63 Hz
0.50 Hz
0.42 Hz
0.36 Hz
0.31 Hz
0.28 Hz
0.25 Hz
G60 Generator Protection System
5 SETTINGS
GE Multilin