Technical data
22
1MRS751108-MUM
Protection Relay
Technical Reference Manual, General
REX 521
5.1.2. Non-volatile memory
The protection relay is equipped with a non-volatile memory for preserving
important data during auxiliary supply breaks. For example, when a setting value is
changed, the new value is stored in the memory at the moment of sending it to the
relay, without additional store commands. The memory does not need batteries, and
a lifelong service is guaranteed.
Following data is stored in the non-volatile memory:
• Setting values
• Display state
• Lockout state
• Recorded values
1
• Last 50 events
When the relay is restarted, the LED indication and text displayed before the
auxiliary supply break are restored on the display. More information about the alarm
LEDs can be found in section “Alarm LEDs” on page 45.
Recorded values are stored from start, trip and other important events. After an
auxiliary power break, time and date and fault currents for the three last events can
be viewed by navigating to the “Recorded values” section of the function block that
caused an indication.
The last 50 events that occurred before the auxiliary power supply break can be
viewed in the HMI event buffer. Time and date for the events are also restored.
5.1.3. Real-time clock
The real-time clock (RTC) is used for time stamping of events. It is also running
during auxiliary power breaks. When the supply is re-established, the relay sets the
right time and new events are stamped accordingly.
The protection relay is provided with a 1-week capacitor back-up protection
2
that
enables the internal clock to keep time in case of an auxiliary power failure.
5.1.4. Auxiliary voltage
For its operation, the protection relay requires a secured auxiliary voltage supply.
The protection relay’s internal power supply module forms the voltages required by
the protection relay electronics. The power supply module is a galvanically isolated
(flyback-type) DC/DC converter. A green LED indicator on the front panel is lit
when the power supply module is in operation.
1. Because the storing of the recorded values is a background task, it might be affected
by a sudden auxiliary power failure.
2. Capacitor ageing may decrease the back-up time.