Chapter 5—Motor and Application
20
DG1 Series VFD
MN040002EN—March 2014
www.eaton.com
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
1
in
Figure 11
) in the output of the
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.
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.
Summary of Contents for PowerXL DG1-32011FB-C21C
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