Eaton PowerXL DC1, Manual

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2 Engineering
2.5 Motor and Application
38
DC1 Frequency Inverter 10/12 MN04020003Z-EN www.eaton.com
2.5 Motor and Application
2.5.1 Motor Selection
General recommendations for motor selection:
• For a frequency-controlled magnet system (PDS), use three-phase AC
motors with squirrel-cage rotors and surface cooling, also known as
three-phase asynchronous motors or standard motors. Other types of
motors, such as external rotor motors, wound-rotor motors, reluctance
motors, permanent-magnet motors, synchronous motors, and servomo-
tors can also be operated with a frequency inverter, but normally require
additional engineering in consultation with the motor's manufacturer.
• Using single-phase AC motors (shaded-pole motors, permanent-split
capacitor motors) requires a DC1-S… frequency inverter.
• Only use motors that have insulation class F (maximum steady state
temperature of 155 °C ) at least.
• Choose 4 pole motors preferably (synchronous speed: 1500 min
-1
at
50 Hz and 1800 min
-1
at 60 Hz).
• Take the operating conditions into account for S1 operation (IEC 60034-1).
• When operating multiple motors in parallel on one frequency inverter,
the motor output should not be more than three power classes apart.
• Ensure that the motor is not overdimensioned. If it is underdimensioned
in the “speed control“ (slip compensation) operating mode, the motor
output may only be one single assigned output level lower.
2.5.2 Parallel connection of motors
The DC1 frequency inverters allow parallel operation of several motors in
“V/f control mode“:
• With multiple motors with the same or different rated operational data:
The total of the motor currents must be less than the rated operational
current of the frequency inverter.
• Connecting and disconnecting individual motors: The total of the motor
currents in operation, plus the motor's inrush current, must be less than
the rated operational current of the frequency inverter.
Parallel operation at different motor speeds can be implemented only by
changing the number of pole pairs and/or changing the motor’s transmission
ratio.
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 12) in the output of the frequency inverter ( ￫ Section 9.8, „Motor
reactors“, page 182).