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1MRS 751108-MUM
Protection Relay
Technical Reference Manual, General
REX 521
11
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.
4.1.3.
Real-time clock (RTC)
The 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
1
that
enables the internal clock to keep time in case of an auxiliary power failure.
4.1.4.
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.
4.1.4.1.
Power supply versions
There are two basic versions of power supply modules available for the REX 521
protection relays: type PS_87H and type PS_87L.
The input voltage range of the power supply module is marked on the front panel of
the REX 521 unit. The power supply version is specified by a letter in the order
number of the protection relay (refer to section “Ordering information” on page 41).
The voltage range of the digital inputs is tied to the selected power supply. If a power
supply version with the higher rated input voltage is selected, the protection relays
will be delivered with digital inputs that also have the higher rated input voltage. The
digital input, DI9, on the CPU module has always lower rated input voltage.
The auxiliary voltages of power supply modules and the corresponding rated input
voltages of digital inputs are:
For further technical data of the power supply, refer to Table 4.2.1-2 on page 30.
1. Capacitor ageing may decrease the back-up time.
Power supply module
Rated input voltage
of power supply
Rated input voltage
of digital inputs
PS_87H
110/120/220/240 V ac
or 110/125/220 V dc
110/125/220 V dc
PS_87L
24/48/60 V dc
24/48/60/110/125/220 V dc
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