5.4
Connecting the motor to the inverter in a star or delta connection
Standard induction motors with a rated power of approximately ≤ 3 kW are normally connected
in a star/delta connection (Y/Δ) at 400 V/230 V. For a 400‑V line supply, you can connect the
motor to the inverter either in a star or in a delta connection.
Operating the motor in a star connection
I
I
1
8
8
1
I
0
0
1
I
3
3
1
9
+]
9
8
8
:
8
8
9
9
:
:
In a star connection, the motor can provide its
rated torque M
N
in the range 0 … rated frequen‐
cy f
N
.
Rated voltage U
N
= 400 V is available at a rated
frequency f
N
= 50 Hz.
The motor goes into field weakening above the
rated frequency. In field weakening, the availa‐
ble motor torque decreases linearly with 1/f. In
field weakening, the available power remains
constant.
Operating the motor in a delta connection with 87 Hz characteristic
I
I
1
෭෪I
1
8
8
1
෭෪8
1
෭෪3
1
9
9
+]
+]
I
0
0
1
I
3
3
1
9
8
8
:
8
8
9
9
:
:
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
N
.
The maximum voltage U = 400 V is avail‐
able at a frequency of f = √3 × 50 Hz ≈
87 Hz.
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 inverter must supply approximately 1.73x current. Select an inverter 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
N
.
● As the fan impeller rotates faster, the motor has a higher noise level than operation with
f ≤ 50 Hz.
Connecting-up
5.4 Connecting the motor to the inverter in a star or delta connection
Power Module PM240-2
66
Hardware Installation Manual, 08/2017, A5E33294624B AG
