Voltage; Current - ABB MS116 Manual

MA N UA L MOTOR START ER G UI D E

3.2.5 Voltage

Three-phase single speed motors can normally be connected for two different voltage levels. The three stator wind-
ings are connected in star (Y) or delta (D) configurations. If the rating plate on a squirrel cage motor indicates
voltages for both the star and delta connections, it is possible to use the motor for both 230 V AC, and 400 V AC as
an example.
The winding should be a delta configuration if connected at 230 V AC and if the main voltage is 400 V AC, a star con-
nection is used.
When changing the main voltage, it is important to remember that for the same power rating the rated motor cur-
rent will change depending on the voltage level. The method for connecting the motor to the terminal blocks for star
or delta connection is shown in the picture below.
Figure 19: Voltage connection at the motor.

3.2.6 Current

The rated current of the motor, which can be found on the motor nameplate, is the current used by the motor when
fully loaded and while up in full speed. An unloaded motor will use far less current and an overloaded motor will use
more current. During a direct on-line start, the current used by the motor is far higher than the rated current.
This is usually between 6-13 times the rated current (for IE3 motors), but it can be more than 10 times the rated cur-
rent. This can be clearly seen in a speed-current diagram for the motor. As the motor accelerates the current will drop
and when reaching the rated speed, the current will have dropped to the rated current. ≈ 6 -13 × I
e
I
e
Figure 20: Diagram of the current vs. speed.
The required increase in efficiency of the IE3 motors is usually achieved by lower rated currents of the motors. In the
small power ranges, the required increase in efficiency is greater, so that the deviation of the rated current is greater
there. The higher the power, the lower the deviation of the rated currents compared to IE1 / IE2 motors.
Increasing starting current conditions
The starting current conditions (ratio of the starting current to the rated current, steady state, stalled rotor) increase
with an increasing IE class.
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