ABB REX 521 Technical Reference Manual, Standard Configurations Download

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1MRS751802-MUM

Protection Relay

Technical Reference Manual, Standard Configurations

REX 521

highest phase current value. The 3Ith> applies the thermal model of one time-
constant for temperature measurement, which means that both the temperature rise
and the cooling follow an exponential curve.

The following set values have to be defined for the 3Ith>: the time constant for the
rise and cooling of the cable, the maximum rated load current for the cable, the
maximum temperature allowed for the cable and the reference temperature in which
the rated current has been defined.

The Start output becomes active when the calculated conductor temperature exceeds
the setting of the

Prior alarm

parameter that can be given a value in the range

40% to 100%. The trip output is activated if the conductor temperature-rise
measured in per cents exceeds the value of the

Trip temperature

parameter

that can be set in the range 80% to 120%. The delayed trip is set into use by giving
the

Trip temperature

parameter a value higher than 100% and the

Trip

delay

parameter one higher than 0. For example, the trip temperature can be set to

120% and the trip delay to 60 min, in which case the function block trips when the
cable load remains above 100% for 60 minutes but does not exceed 120%.

The CU_ALARM output alarms when the measured current has exceeded the level
where, if it remains the same, the cable temperature will reach the maximum
temperature set for the cable.

After the thermal overload protection has tripped, reclosing is not possible until the
calculated conductor temperature falls below the value set for the

Reclosure

temp

parameter, because the function block holds the trip output active. If the re-

closing inhibit is chosen not to be used, the parameter is set to 100%.

In the initializing stage, that is, when the auxiliary voltage is connected to the relay,
the function block assumes that the cable temperature has risen to 50% of the
difference between the parameter values

Maximum temp

and

Ambient temp

For example, if the maximum temperature has been set to +90°C (cable with PEX
insulation) and the ambient temperature is set to +20°C, the relay assumes a
temperature of +55°C for the cable.

The necessary settings for the thermal overload protection can be found in:

Main menu\Protection\3Ith>\Setting group 1\

The calculated temperatures of the conductor can be viewed in:

Main menu\Protection\3Ith>\Output data\

9.1.4.

Connections and signal routings

All the necessary settings for the connected signals can be set via the Relay Setting
Tool or the local HMI.

9.1.4.1.

Protection signal routing

The protection trip signal, Trip 1, is routed to the high-speed power output HSPO1,
(x4.2.1/2/3/4) as well as the control-open signal to the circuit breaker. The trip
signals from the protection functions are routed to the output relay via the output
switchgroups. These settings can be found in

Main menu\Configuration\Output SWGRP\