Engineering manual - SAB 193-233-283 S A-frame (including ATEX)
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008831 en 2022.02
6.6
Selecting electric motor
The IEC electric motor types IP23 or IP54 (55) are the motors normally used to drive the
compressors.
Fig. 67: IP23 Drip-proof motor
When selecting an electric motor, the aspects discussed below should be taken into
consideration.
6.7
Motor dimension
The motor size is determined on the basis of power demands of the compressor during the cur-
rent operating conditions calculated by the Sabroe COMP1 program. Always choose a motor a
little bigger, however:
a.
To ensure that the motor has sufficient driving power both during start-up, at minor devi-
ations from the calculated operating conditions and with regard to mechanical transmis-
sion loss, the calculated power demand should be increased by one of the following
factors:
1) Air conditioning plant: factor 1.10
2) Other refrigeration plants: factor 1.15
b.
Consider which type of plant the compressor is going to work on. The motor must be di-
mensioned in accordance with the following rules:
•
For plants where a high ET may be expected, consequently also a higher CT in
the start-up phase, the motor must be dimensioned to meet the high operating
temperatures. Usually, there is no need to incorporate factors 1 and 2.
For booster compressors, special consideration should also be given to the
choice of motors.
•
Alternatively, the motor can be connected to a system for ampere limitation,
which reduces the compressor capacity until the planned operating tempera-
tures have been reached. This element is found in UniSAB III, which must be
linked to the Amp. signal. Also in this case, disregard factors 1 and 2.
Note:
Please note that for class F insulation motors (105K) for operating conditions like for
class B (90K), approximately 10% continual overloading of the motor is acceptable in relation
to the marking effect.