Auxiliary Voltage; Power Supply Versions; Low Auxiliary Voltage Indication - ABB REX 521 Technical Reference Manual, General

REX 521
4.1.4.
4.1.4.1.
4.1.4.2.
18
Protection Relay
Technical Reference Manual, General

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.

Power supply versions

There are two basic versions of power supply modules available for 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 56).
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 also lower rated input voltage.
The auxiliary voltages of power supply modules and the corresponding rated input
voltages of digital inputs are:
Power supply module
PS_87H
PS_87L
For further technical data of the power supply, see Table 4.2.1-2 on page 44.

Low auxiliary voltage indication

The relay is provided with a low auxiliary voltage indication feature. The power
supply module issues an internal alarm signal when a drop in the power supply
voltage is detected. The alarm signal is activated if the power supply voltage falls
about 10% below the lowest rated DC input voltage of the power supply module, see
the table below:
Rated input voltage
PS_87H
• Rated input voltage 110/125/ 220 V DC
• Rated input voltage 110/120/220/ 240 V AC
PS_87L
• Rated input voltage 24/48/60 V DC
The indication of a low auxiliary voltage (ACFail) can be seen as an event via serial
communication.
Rated input voltage
of power supply
110/120/220/240 V AC
or 110/125/220 V DC
24/48/60 V DC
1MRS 751108-MUM
Rated input voltage
of digital inputs
DI1...DI8: 110/125/220 V DC
DI9: 24/48/60/110/125/220 V DC
DI1...DI9: 24/48/60/110/125/220 V DC
Low indication level
99 V DC
88 V AC
21.6 V DC