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4.4
Connecting the motor to the converter in a star or delta connection
Overview
Standard induction motors up to a rated power of approximately 3 kW are usually connected
in star/delta connection (Y/Δ) at 400 V/230 V. For a 400-V line supply, you can connect the
motor to the converter either in a star or in a delta connection.
Function description
Operating the motor in a star connection
Operating the motor in a delta connection with 87 Hz characteristic
The motor only goes into field weakening above 87 Hz.
The higher motor power when operated with an 87 Hz characteristic has the following
disadvantages:
● The converter must supply approximately 1.73x current. Select a converter based on its
rated current - and not its rated power.
● The motor temperature increases more significantly than when operated with f ≤ 50 Hz.
● The motor must have windings that are approved for a voltage > rated voltage U
● As the fan impeller rotates faster, the motor has a higher noise level than operation with
f ≤ 50 Hz.
Power Module PM240P-2
Hardware Installation Manual, 06/2020, A5E37800827C AD
4.4 Connecting the motor to the converter in a star or delta connection
In a star connection, the motor can provide its
rated torque M
in the range 0 ... rated fre-
N
quency f
.
N
Rated voltage U
= 400 V is available at a
N
rated frequency f
= 50 Hz.
N
The motor goes into field weakening above
the rated frequency. In field weakening, the
available motor torque decreases proportion-
ally with 1/f. In field weakening, the available
power remains constant.
In a delta connection, the motor is oper-
ated with a voltage and frequency above
its rated values. As a consequence, the
motor power is increased by a factor
√3 ≈ 1.73.
In the range f = 0 ... 87 Hz, the motor
can output its rated torque M
The maximum voltage U = 400 V is
available at a frequency of
f = √3 × 50 Hz ≈ 87 Hz.
Connecting
.
N
.
N
47
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