Parallel Connection Of Motors - Danfoss VLT AutomationDrive FC 300 Design Manual

Electrical Installation

7.4.2 Parallel Connection of Motors

The frequency converter can control several parallel-connected motors. When using parallel motor connection, observe the
following points:
•
Run applications with parallel motors in U/F mode (volts per hertz).
•
plus
VCC mode may be used in some applications.
•
Total current consumption of motors must not exceed the rated output current I
•
Problems may arise at start and at low RPM if motor sizes are widely different because the small motors' relatively
high ohmic resistance in the stator demands a higher voltage at start and at low RPM.
•
The electronic thermal relay (ETR) of the frequency converter cannot be used as motor protection. Provide further
motor protection by including thermistors in each motor winding or individual thermal relays.
•
When motors are connected in parallel, 1-02 Flux Motor Feedback Source cannot be used, and 1-01 Motor Control
Principle must be set to Special motor characteristics (U/f).
Illustration 7.34 Different Parallel Connections of Motors
A Installations with cables connected in a common joint as shown in A and B are only recommended for short cable lengths.
B Be aware of the maximum motor cable length specified in 4.3 General Specifications.
C The total motor cable length specified in 4.3 General Specifications is valid as long as the parallel cables are kept short less than 10
m each. (Example 1)
D Consider voltage drop across the motor cables. (Example 1)
E Consider voltage drop across the motor cables. (Example 2)
F The total motor cable length specified in 4.3 General Specifications is valid as long as the parallel cables are kept less than 10 m
each. (Example 2).
Table 7.65 Legend to Illustration 7.34
®
VLT AutomationDrive FC 300 Design Guide 90-1200 kW
A
B
C
MG34S202 - Rev. 2013-08-19
for the frequency converter.
INV
D
E
F
7 7
199