Parallel Connection Of Several Motors To One Frequency Inverter; Motor And Circuit Type; Figure 11. Parallel Connection; Figure 12. Example Of A Motor Ratings Plate - Eaton PowerXL DG1-323D7FB-C21C Installation Manual

Chapter 5—Motor and Application
Parallel Connection of Several Motors to One
Frequency Inverter

Figure 11. Parallel Connection

Connecting motors in parallel reduces the load resistance at
the frequency inverter output. The total stator inductance is
lower and the leakage capacity of the lines greater. As a
result, the current distortion is greater than in a single-motor
circuit. To reduce the current distortion, you should use
motor reactors (see in Figure 11) in the output of the
1
frequency inverter.
The current consumption of all motors connected in parallel
must not exceed the frequency inverter's rated output
current I .
2N
Electronic motor protection cannot be used when operating
the frequency inverter with several parallel connected
motors. You must, however, protect each motor with
thermistors and/or overload relays.
The use of a motor protective circuit breaker at the frequency
inverter's output can lead to nuisance tripping.
20 DG1 Series VFD MN040002EN—March 2014 www.eaton.com

Motor and Circuit Type

The motor's stator winding can be connected in a star or
delta configuration, in accordance with the rated operational
data on the nameplate.

Figure 12. Example of a Motor Ratings Plate

Figure 13. Star and Delta Circuit Types

The three-phase motor with the rating plate based on
Figure 13, can be run in a star or delta connection. The
operational characteristic curve is determined by the
ratio of motor voltage and motor frequency, in this case.
87 Hz Characteristic Curve
In the delta circuit with 400V and 87 Hz, the motor shown
in Figure 13 was released with three times-fold output
(~1.3 kW).
Because of the higher thermal loading, using only the next
higher motor output according to the list (1.1 kW) is
recommended. The motor (in this example) therefore still has
1.47-fold higher output compared with the listed output
(0.75 kW).
With the 87 Hz characteristic curve, the motor also works in
the range from 50 Hz to 87 Hz with an un-attenuated field.
The pull-out torque remains at the same level as in input
operation with 50 Hz.
The heat class of the motor must be at least F in 87 Hz
operation.