ABB REM 610 Technical Reference Manual page 23

1MRS 752263-MUM
Motor protection Relay
Technical Reference Manual
The full load current of the motor is defined by means of the protected unit scaling
factor and determines the thermal trip level of stage θ>, θ
t , determines the operate time of the stage for a load current of 6 x FLC without
6x
prior load.
If the RTD module has been installed, RTD6 can be selected to measure the ambient
temperature. The selection is made in SGF4. However, if RTD6 is not used for
measuring the ambient temperature or if the RTD module has not been installed, the
thermal protection will use the set ambient temperature, T
The ambient temperature is used to determine the internal FLC. The table below
shows how the internal FLC is modified.
Table 4.1.4.2-1 Modification of internal FLC
Ambient temperature Internal FLC
<+20°C
20...<40°C
40°C
>40...65°C
>+65°C
There are two thermal curves, one which characterizes short- and long-time
overloads and which is used for tripping and another which is used for monitoring
the thermal condition of the motor. Weighting factor p determines the ratio of the
thermal increase of the two curves. For direct-on-line started motors with hot spot
tendencies, the weighting factor is typically set to 50 per cent. When protecting
objects without hot spot tendencies, e.g. motors started with soft starters, and cables,
the weighting factor is set to 100 per cent.
When one or several phase currents exceed the internal FLC by more than five per
cent, the whole thermal capacity of the motor will be used after a time determined
by the internal FLC, the set safe stall time and the prior load of the motor. When the
thermal level (influenced by the thermal history of the motor) exceeds the set prior
alarm level, θ
>, the stage will generate an alarm signal, and when the thermal level
a
exceeds the set thermal restart inhibit level, θ
inhibit signal. The time to the next possible motor start up can be read with SPA
parameter V52 or via the HMI. When the thermal level exceeds the trip level, θ
the stage will generate a trip signal. For operate times, see Fig. 4.1.4.2.-1...Fig.
4.1.4.2.-4.
The thermal protection operates differently depending on the value of weighting
factor p. For instance, if p is set to 50 per cent, the thermal protection will consider
the hot spot tendencies of the motor and distinguish between short-time thermal
stress and long-time thermal history. After a short period of thermal stress, e.g. a
motor start up, the thermal level will start to decrease quite sharply, simulating the
levelling out of the hot spots. As a consequence, the probability that successive start
ups will be allowed increases.
If p is set to 100 per cent, the thermal level will decrease slowly after a heavy load
condition. This makes the protection suitable for applications where no hot spots are
expected.
FLC x 1.09
FLC x (1.18 - T x 0.09/20)
amb
FLC
FLC x (1 - [(T - 40)/100])
amb
FLC x 0.75
>, the stage will generate a restart
i
REM 610
. The set safe stall time,
t
.
amb
>,
t
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