ABB MS116 Manual page 36

3.2.3.6 What differs an IE3/IE4 motor from motors with lower efficiency?
IE3 motors are able to achieve higher efficiency thanks to innovative designs and the use of better conducting mate-
rial. The higher efficiency design will ultimately show a lower rated motor current for any given kW rating. However,
during the starting phase of the motor there may be an increase of inrush and starting current. The increased inrush
and starting current can in some cases affect the selection of the starter components as well as the short- circuit
protection device.
If a motor is directly connected to the line, the current drawn will be very high at the start-up, which is mostly reac-
tive. The line in the following figure shows a typical starting RMS current curve for an IE3 motor in a direct online
connection. In general, the motor draws current in three steps:
− Shortly after starting, during the first 20 ms to 30 ms: I
−
Between the inrush and 0.5 s to 10 s (depending on rated power and inertia), a steady-state current I
rent remains constant as long as the rotor starts revolving; its duration depends on the motor's load and
design.
−
After 0.5 s to 10 s: the rotor accelerates and reaches its final speed. The current stabilizes to reach the motor's
rated current I
I
I
peak (RMS)
I
d
I
n
To be able to offer the best possible starter solutions, ABB performed many tests on different motors, to map the
relevant data when starting the motors, also taking into consideration the findings of ABB's own motor manufacturing
units. The tests and analyses clearly show that premium efficiency motors (IE3 motors) in general will draw a higher
starting current than IE1 and IE2 motors. There is an estimated 15 % higher starting current compared to IE2 motors.
Once the IE3 motor reaches full speed, the rated motor current is lower for the same load conditions, because of the
higher efficiency and the desired energy savings.
≈ 6 -13 × I
APR I L 19
MA N UA L MOTOR START ER G UI D E
at full load.
n
I
peak
I
RMS
20-30 ms
Figure 16: Diagram with the Currant at the start of a IE3 motor.
I
IE3 current RMS
IE3
peak
e IE2 current RMS
IE3 I
d
IE2 I
d
I
n
Figure 17: Diagram showing the different currents for the IE3/IE2 motors.
a high peak current (inrush).
peak
0.5-10 s
This cur-
d.
t
t
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