GE 239 Instruction Manual page 66

4 PROGRAMMING
On resistance grounded systems, where the ground current is limited to safe levels longer time
delays can be used subject to co-ordination constraints. Too short time delays may cause nui-
sance tripping due to transients or capacitive charging currents and should be avoided if possi-
ble. Time delays of several hundred milliseconds are suitable for applications where the relay has
to be coordinated with other protective devices or a long delay is desired because of transients.
Time delays of several seconds are suitable for use on high resistance grounded systems where
nuisance tripping may be a problem from capacitive or induced currents during the starting
inrush. Ground currents limited by the supply ground resistance can flow for longer periods with-
out causing any damage.
The relay(s) selected in this setpoint along with the respective status indicator(s) on the front
panel of the 239 will be active upon a ground fault trip.
GROUND PRIMARY TRIP PICKUP: Ground fault trip when enabled in 6 3527(&7,21?*5281'
•
&855(17?*5281' 75,3 , will signal a trip condition when the ground current becomes equal to or
exceeds the value set in this setpoint. The amount of current that will flow due to a ground fault
depends on where the fault occurs in the motor winding. High current flows if a short to ground
occurs near the end of the stator winding nearest to the terminal voltage. Low ground fault cur-
4
rents flow if a fault occurs at the neutral end of the winding since this end should be a virtual
ground. Thus a low level of ground fault pickup is desirable to protect as much of the stator wind-
ing as possible and to prevent the motor casing from becoming a shock hazard. In resistance
grounded systems the ground fault trip level must be set below the maximum current limited by
the ground resistor or else the relay will not see a large enough ground fault current to cause a
trip.
• GROUND TRIP DELAY ON RUN: This delay is used when the motor is in a RUNNING condition.
If the ground current is equal to or above the *5281' 35,0$5< 75,3 3,&.83 setpoint value and
remains this way for the time delay programmed in this setpoint while the motor is running, the
assigned relay(s) will activate and the "CAUSE OF TRIP: GROUND FAULT" message will be dis-
played.
NOTE: When the phase current increases from 0, the *5281' 75,3 '(/$< 21 67$57 setpoint
described below is used until the 239 determines whether the motor is RUNNING or
STARTING.
Refer to Section 5.2: A1: STATUS on page 5–2 for details on how the 239 detects a start condi-
tion.
• GROUND TRIP DELAY ON START: This delay is used when the motor is in a STARTING condi-
tion. If the ground current is equal to or above the *5281' 35,0$5< 75,3 3,&.83 setpoint value and
remains this way for the time delay programmed in this setpoint while the motor is starting, the
assigned relay(s) will activate and the "CAUSE OF TRIP: GROUND FAULT" message will be dis-
played.
NOTE: When the phase current increases from 0, this delay is used until the 239 deter-
mines whether the motor is RUNNING or STARTING.
Refer to Section 5.2: A1: STATUS on page 5–2 for details on how the 239 detects a start condi-
tion.
• GROUND ALARM: For detecting momentary ground faults due to initial insulation breakdown
and arcing, this setpoint can be set to latched. This is especially useful in mines where moisture
buildup in the windings may start to cause excessive leakage. Any short duration ground fault will
then cause a latched alarm condition. Set to momentary if a ground fault alarm is required only
while the ground current is actually present. Ground fault alarm when enabled, will signal an
4-28
Courtesy of NationalSwitchgear.com
239 Motor Protection Relay
4 PROGRAMMING
GE Multilin