ABB Industrial IT enabled REX 521 - Auxiliary voltage; Power supply versions; Low auxiliary voltage indication

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Technical Reference Manual, General
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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.
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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 48).
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:
For further technical data of the power supply, refer to Table 4.2.1-2 on page 37.
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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:
The indication of a low auxiliary voltage (ACFail) can be seen as an event via serial
communication.
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PS_87H 110/120/220/240 V ac
or 110/125/220 V dc
DI1...DI8: 110/125/220 V dc
DI9: 24/48/60/110/125/220 V dc
PS_87L 24/48/60 V dc DI1...DI9: 24/48/60/110/125/220 V dc
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PS_87H
• Rated input voltage 110/125/ 220 V dc 99 V dc
• Rated input voltage 110/120/220/ 240 V ac 88 V ac
PS_87L
• Rated input voltage 24/48/60 V dc 21.6 V dc