Selecting Weighting Factor P - ABB REM 610 Technical Reference Manual

REM 610 REM 610
6.1.2.1.
126
Motor Protection Relay
Technical Reference Manual - ANSI Version
If the settings of the thermal overload protection have been defined by
means of the FLA of the motor instead of the internal FLA, they will
be valid at an ambient temperature of 40°C.
For how the ambient temperature is used to determine the internal FLA, refer to
Section 5.1.4.2. Thermal overload protection.

Selecting weighting factor p

Setting p to 100 per cent creates a pure single time constant thermal protection for
protecting cables, for instance. In this case, the allowed stall time will be only
approximately ten per cent of the safe stall time, t
Fig. 6.1.2.1.-1. At a set safe stall time of twenty seconds, the operate time when the
prior load is 1 x FLA will be only two seconds, even though the motor can withstand
a stall time of five seconds, for instance. To allow the use of the motor's full
capacity, a lower weighting factor should be used.
Normally, approximately half of the thermal capacity is used when a motor is
running at full load. By setting p to 50 per cent, the thermal overload protection will
take this into account.
In special cases where the thermal overload protection is required to follow the
characteristics of the object to be protected more closely and the thermal capacity of
the object is very well known, a value between 50 and 100 per cent may be required.
In applications where, for instance, three cold starts vs two hot starts are allowed,
setting the weighting factor to 40 per cent has at times proved useful.
Setting the weighting factor to significantly below 50 per cent may
overload the object to be protected as the thermal overload protection
may allow too many hot starts or the thermal history of the motor has
not sufficiently been taken into account.
1MRS755537
, when no prior load; see
6x