GE Industrial Solutions Entellisys 4.0 System User Manual - Manual (Page 88)

Single point functions 88
5
5.2.9 High Resistance Ground Fault Location Relay
The Entellisys system provides High Resistance Ground Fault Location (HRGF Location) for up to
4 mains which locates a fault by analyzing system currents while operating the ground resistor
pulsing contactor.
For example, in a typical High Resistance system, a phase to ground fault will be limited to 5-15
Amps allowing the breaker to remain closed. To locate, a ground contactor will short some of
the resistor effectively reducing the ground resistance and increasing the ground current at a
periodic rate. Location systems will use this amperage modulation to locate the fault to the
specific breaker(s) affected.
Unlike traditional systems, Entellisys does not require additional sensors to locate a ground
fault, rather it utilizes a signal processing algorithm to detect the low magnitude ground signal
in the presence of large phase currents. Entellisys then reports all breakers that are seeing the
modulated current - including mains and ties.
Highlights
Manual Mode will pulse the contactor indefinitely until stopped by the user.
Tripping Option: When a ground fault occurs and has been successfully located, the relay
will begin timing to trip the faulted breaker. If the fault continued uninterrupted for the
specified number of hours, the feeder breakers reported by this function will be tripped.
Tripping Priority: If a breaker faults to ground while a HR fault already exists there will be
what amounts to a phase to phase fault through ground. In High Resistance systems, only
one breaker needs to be tripped. Entellisys allows the user to configure a tripping priority to
each breaker. (See
Ground Fault Tripping priority on page 126 )
Operation
the location relay can be set to automatically operate when a fault is detected. Once the
detection relay is in pickup, the location relay automatically starts to locate the fault by pulsing
the grounding contactor through the discrete I/O for 1 minute.
The CPU locates the ground fault by creating a tracing signal in the ground current using a
pulsing contactor toggled by a Flex Logic contact output “HRGF Pulse contactor output 1-4”
routed to an appropriate discrete output to pulse the contactor.
When the contactor is ON, the resistance value will be lowered and the ground current will be
increased, thus creating a tracing pulse current through the ground resistor. Only one contactor
among of the available contactors (maximum of 4) will be operating at any point of time. The
contactor pulsing can be manually initiated under any condition.
The pulsing contactor connected to the discrete I/O must have a coil current less than 1 Ampere
of 120VAC current when closed. The contact ratings must be at least 10A @ 600VAC when
closed and while opening.
The user must go to the Event screen to view the results of the HRGF location relay. From the
HRGF events, the user will be able to determine that a ground fault has occurred and if the
system has located the responsible feeder. There are also several alarms to help alert the user.
(See
Events and Alarms on page 94 )