Manual 37353A
MFR 13 Packages - Protection Relay
Page 54/91
© Woodward
Ground Fault Monitoring, Calculated (
Packages GP
/
K08
)
Ground fault monitoring for low-impedance or solidly grounded systems.
Function:
The ground fault monitoring can be configured for two threshold limits. The third harmonics single-
phase components may result in false currents being monitored on the grounding circuit. A digital anti-aliasing
filter is utilized to separate theses harmonics and prevent inaccurate values caused by harmonics from being dis-
played. If the actual sine wave of the ground current exceeds the configured threshold, an alarm message is dis-
played. This message can
be suppressed with the discrete input "Blocking of protective functions / remote ac-
knowledgement".
Acquiring the measured value:
•
The ground current is measured by calculating the vectorial sum of the three monitored phase currents. The
current transformer should be sized so that the configured ground current threshold is at least 10% of the
transformer's current rating to ensure proper operation.
Earth current
monitoring ON
Ground fault monitoring
ON/OFF
ON
................Ground fault monitoring is enabled. The subsequent screens of this
function are displayed.
OFF
..............Ground fault monitoring is disabled. The subsequent screens of this
function are not displayed.
Earth current 1
Response = 000%
Threshold ground fault, level 1
10 to 300 %
Ground fault current (level 1) is defined by this parameter. The percentage config-
ured here refers to the configured rated current (refer to page 36). If this limit is
reached or exceeded, the unit outputs the message "
Earthcur.1
". If a relay was
assigned to this function in the relay manager, that relay will be energized.
Earth current 1
Delay 00.00s
Pickup delay, level 1
0.02 to 99.98 s
In order to initiate a ground fault current (level 1) alarm, the measured ground fault
current must exceed and remain above the configured threshold without interrup-
tion for at least the period of time specified in this screen.
Earth current 2
Response = 000%
Threshold ground fault, level 2
10 to 300 %
Ground fault current (level 2) is defined by this parameter. The percentage config-
ured here refers to the configured rated current (refer to page 36). If this limit is
reached or exceeded, the unit outputs the message "
Earthcur.2
". If a relay was
assigned to this function in the relay manager, that relay will be energized.
Earth current 2
Delay 00,00s
Pickup delay, level 2
0.02 to 99.98 s
In order to initiate a ground fault current (level 2) alarm, the measured ground fault
current must exceed and remain above the configured threshold without interrup-
tion for at least the period of time specified in this screen.
Earth current
Hysteresis 000%
Hysteresis for the ground fault monitoring, levels 1+2
1 to 300 %
In order to prevent system fluctuations from continually initiating ground fault cur-
rent alarms (levels 1 & 2), a lower release point is defined here. If the control moni-
tors the current above the permissible limit, the current must drop below that
threshold and the current level defined here for the fault condition to be recognized
as no longer existing.
Example: If a 1000A system has a ground fault current limit 1 of 5% (50A) and a
hysteresis of 2% (20A), the monitored current for a ground fault current alarm must
drop below 20A to reset the alarm.
