Multifunction Protection and Switchgear Control unit REF542plus
Manual: Motor Protection with ATEX-Certification
5.1 Rotor block protection
The rated motor current is known. Since the primary current transformer rated current
is 100A, the rated motor current or the motor current Ie at the REF542plus has to be
set to
In 0,91 In
100A
91A
IMn ==
For detecting a rotor blocking, only the overcurrent criterion is to be used. In this
case, a rotor blocking is assumed to be present if the motor current is at 90% of the
blocking current. Thus, the starting value is
IMn 7.11 Ie 7.9 0.9 Start
×=
The time setting is selected as the following:
ms 8000 s 8.0 Time
=
5.2 Motor start protection
For the motor startup monitoring function, the setting for the rated motor current or
motor current IMn is done in the same way as for the rotor blocking monitoring de-
scribed earlier. After that, the starting value and the time can be defined in accor-
dance with the motor data:
IMn 7,9 Start =
and
ms 8000ly respective s 8 Time =
The motor startup is set to the following setting:
Is 0.7 Motorstart =
Thereby Is means the setting for the starting value.
5.3 Thermal overload protection
For this function, the rated motor current can be entered.
A91IMn =
The motor winding is specified at thermal class B. In this context, it is assumed that
the ambient temperature is
C 40Tenv °=
As a result of the thermal class and the temperature class indicated above, according
to table 2 and 3 the rated temperature for the REF542plus will be
C 110)7040(Tnom °
°
= C
and the maximum temperature for tripping:
C 145Tmax °=
Setting constant k can be calculated by applying equation (10).
1VTA100114-Rev. 04 en PTMV, 19.01.05 Motorprotection 33 / 66
Valid from Version V4D02
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