Hardware and Engineering DF6-340-... Frequency ... - Moeller.com.tr

Installation01/02 AWB8230-1413GBParallel connection of motors to a single frequencyinverter<strong>DF6</strong> frequency inverters can control several parallel-connectedmotors. If the motors are to run at different speeds, this must beimplemented through the number of connected pole pairs <strong>and</strong>/orthe gear transmission ratio.K1MK2MK3MF1U1 V1 W1F2U1 V1 W1F3U1 V1 W1M1M3˜M2M3˜M3M3˜Figure 31:Parallel connection of multiple motorsCaution!If a frequency inverter controls a number of motors inparallel, the contactors for the individual motors must bedesigned for AC-3 operation. Do not use the mainscontactors listed in table in the appendix (section “Mainscontactors”, page 165). These mains contactors aredesigned only for the mains (primary) currents of thefrequency inverter. If they are used in multiple-motorcircuits, their contacts may weld.If motors with widely differing ratings (for example 11 kW <strong>and</strong>30 kW) are connected in parallel to the output of a frequencyinverter, problems may arise during starting <strong>and</strong> at low speeds.Motors with a low rating may be unable to develop the requiredtorque. This is due to the relatively high ohmic resistances of theirstators. They require a higher voltage during the start phase <strong>and</strong>at low speeds.Connecting motors inparallel reduces the load resistance at thefrequency inverter output, reduces the total stator inductivity is<strong>and</strong> increases the leakage capacitance. As a result, the currentdistortion is larger than it is in a single-motor circuit. To reduce thecurrent distortion, chokes or sinusoidal filters can be connected atthe frequency inverter output.hhThe current consumption of all connected motors mustnot exceed the rated output current I 2N of the frequencyinverter.Electronic motor protection can not be used whenoperating the frequency inverter with a several connectedmotors. You must however, protect each motor withthermistors <strong>and</strong>/or overload relays.36