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The auxiliary fault relays operate exclusively in the shunt (non-failsafe) mode. When the SIGMA-MD monitor relay is
operating and no fault condition is present, the auxiliary fault relays are idle or de-energized. If a fault condition is
detected and qualified, the appropriate auxiliary fault relay is tripped or energized.
The SIGMA-MD monitor relay uses non-volatile memory to store the states of the trip and auxiliary fault relays in
case of a loss of control power.
If the trip memory option is ON and the SIGMA-MD monitor relay is powered down while indicating a fault condition,
the trip, NGR and GND auxiliary fault relays are restored to the states these relays were in at the time of the power
loss when control power is restored. If an NGR Fault was indicated at the time of the loss of control power, the NGR
fault relay will be restored to a tripped state when control power is restored. Similarly, if a GND fault was indicated
at the time of the loss of control power, the GND fault relay will be restored to a tripped state when control power is
restored. The main trip relay will be set to a trip state if either of the NGR or GND auxiliary fault relays is restored to a
trip state.
If the trip memory option is ON and, when control power is restored, if the NGR or GND fault relays are restored to a
trip state, the LED associated with the fault relay, i.e. NGR Fault or GND fault is set flashing. The trip relay, auxiliary
fault relays and associated LED will remain as such indefinitely regardless of whether a fault is present on the
system and until the conditions which caused the trip are cleared and the relay is manually reset.
When SIGMA-MD monitor relay is manually reset, the states of the trip relay and auxiliary fault relays are set to their
respective idle states in the relay’s operating memory and are then stored in the non-volatile memory.
6. LED INDICATORS AND DIAGNOSTICS
The SIGMA-MD monitor relay has four light emitting diodes (LEDs) located on its front panel. These LEDs are the
Green PWR (Power) LED; the Red GND (Ground) FAULT and NGR FAULT LEDs; and the ZONE GR (Zone Grading) LED.
6.1 START-UP AND RESET INDICATIONS
The SIGMA-MD monitor relayhas a start-up sequence where the Red GND FAULT, NGR FAULT and ZONE GR. LEDS
flash ON and OFF twice before being turned OFF. The Green PWR (Power) LED may also flash before it is turned ON.
These indications will be the same whether the start up is a result of a manual reset or the application of control power.
During a manual reset the Red GND FAULT, NGR FAULT and ZONE GR. LEDs are turned ON for two seconds as an
indication that a reset sequence is taking place. During this time the Green PWR (Power) LED will be FLASHING.
After these indications the SIGMA-MD monitor relay resets giving the start-up indications described above.
After the SIGMA-MD monitor relay has gone through the start-up sequence and is operating normally the Green
PWR (Power) LED will be ON and the Red GND, FAULT, NGR FAULT and ZONE GR LEDS will be OFF.
