Low Auxiliary Voltage Indication; Overtemperature Indication; Analogue Channels; Setting The Rated Values For The Protected Unit - ABB REX 521 Technical Reference Manual, General

REX 521
4.1.4.2.
4.1.5.
4.1.6.
4.1.6.1.
12
Protection Relay
Technical Reference Manual, General

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.

Overtemperature indication

The REX protection relay includes an internal temperature supervision function.
The CPU module issues an internal alarm signal when overtemperature has been
detected inside the relay enclosure. The alarm signal will be activated once the
temperature inside the relay enclosure increases approximately to +78
overtemperature indication can be seen on the HMI or as an event via serial
communication. The relay will go to the IRF state. See Table 4.1.11.2-1, "Fault
indications," on page 22.

Analogue channels

The protection relay measures the analogue signals needed for protection,
measuring, etc. via galvanically separated matching transformers. In addition,
current sensors (Rogowski coil) and voltage dividers developed by ABB can be used
with the REX 521.
The different versions of the REX 521 are provided with the following matching
transformers and sensor inputs:
Version Matching transformers
Basic CT1, CT2, CT3, CT4
Medium CT1, CT2, CT3, CT4, CT5, VT1
High CT1, CT2, CT3, CT4, CT5, VT1, VT2, VT3, VT4 -
Sensor CT4, CT5, VT1
A letter in the order number specifies whether the protection relay is equipped with
basic, medium, high or sensor measuring input modules. (Refer to section "Ordering
information" on page 41).

Setting the rated values for the protected unit

A separate scaling factor can be set for each analogue channel. The factors enable
differences between the ratings of the protected unit and those of the measuring
device (CTs, VTs etc.) The setting value 1.00 means that the rated value of the
protected unit is exactly the same as that of the measuring device.
1MRS 751108-MUM
Low indication level
99 V dc
88 V ac
21.6 V dc
o
C. The
Sensor inputs
-
-
RS1, RS2, RS3, VD1, VD2, VD3