Hermetic Refrigerant Compressor Motors - ABB MS116 Manual

MA N UA L MOTOR START ER G UI D E
Different load conditions
All motors are used for starting and running different applications. These applications will result in different load
conditions for the motor. This is a direct braking force on the motor shaft. To be able to accelerate, the motor must
be stronger than the load. The accelerating torque is the difference between the available motor torque and the load
toque. Many starting methods will reduce the torque of the motor and thereby reducing the accelerating torque
which will give a longer starting time. The accelerating torque = the available motor torque – the braking load torque.
The load curve can have different characteristic depending on the application. Some of the common load types can
be seen below.
Figure 23: Diagram of the torque vs. speed for different load conditions.
Many applications are started unloaded, and the load is applied first when the motor has reached the rated speed.
This will reduce the load torque to about 10-50% of the load torque of a loaded start.
Manual motor starters are well suited for both the control and protection of motors, including high-efficiency types.
Since the tests for IEC utilization category AC-3 and UL/CSA "AC Motor" have yet to be fully harmonized, manual mo-
tor starters carry both ratings to ensure international acceptability.
For additional information regarding IE3 high-efficiency motors, please click the "Info on IE3 Motors" link in the Se-
lected Optimized Coordination (SOC) selection tool (http://applications.it.abb.com/SOC/page/selection.aspx).

3.3 Hermetic refrigerant compressor motors

A hermetic refrigerant compressor motor is a combination of a compressor and a motor, both of which are enclosed
in the same housing, with no external shaft or shaft seals, with the motor operating in refrigerant. These motors are
commonly used in air-conditioning and refrigeration equipment. Two harmonized utilization categories exist for
these types of loads: AC-8a and AC-8b. AC-8b is an additional test accompanying AC-8a and is referred to as a "recy-
cle rating", which covers applications where overload releases are automatically reset. Manual motor starters can be
used for manual control and protection of these motors. For control, use AF contactors.
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