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micromaster 420 or vfd

Created by: saeedplc at: 6/23/2011 5:52 PM (3 Replies)

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6/23/2011 5:52 PM	Rate (0)
saeedplc Posts: 288 Rating: (4)	hello all expert. i have read more about vfd and i know that vfd keep torque constant between 0 to 50hz with v/f ratio constant. i have installed micromaster 420 on one of our machine for spindle speed control.the motor is 3.5kw , 1365 rpm , 50hz , 380v , 6.6 amp asynchronise motor. i read output current on display during working and it was 4.6 amp at 10hz , 4 at 20hz , 3.8 at 30hz , 3.65 at 45 hz . shoudn't current be 6.6 amp in all speeds?(beacuse v/f is constant so flux and current and torque should be constant!) what is current depending on wile the drive keep torque constant? why does current change in different speed? thanks . best regards.
saeedplc Posts: 288 Rating: (4)
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6/24/2011 6:03 AM	Rate (0)
PISCEAN 2010 Diamond Member Joined: 4/23/2010 Last visit: 11/23/2024 Posts: 8092 Rating: (882)	Hello, The current what is displayed is magnetizing current + no load motor current. Since this is spindle motor, at different speeds the load torque & power requirement varies. When drive is configured as simple V/F mode, it means your motor speed is linearly varied by maintaining V/F ratio. Depending upon load requirement, current drawn by motor shall vary & the same shall be supplied by drive. During this period drive shall maintain V/F ratio constant to meet load requirement. Hope this helps you.

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6/24/2011 2:11 PM

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saeedplc

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thanks a lot for your reply.

are you mean that torque is constant in all speed and it is permissible the motor take up to 6.6amp depending on load but in all amps the drive keep torque constant with keeping v/f ratio contant.?

mr deepstr2010 i want you to confirm my understanding please:

when we use a vfd to control speed of a motor with v/f contant
control , because the drive keep v/f ratio constant
so flux and torque are constant beween 0 to 50hz
and in different speed only hp(or kw)
change and current drawn by the motor
depends on the load for example if i put a higher
load on the motor higher current will be drawn
from the drive ( it must be in range of motor current
in my example 6.6 amp and if it become higher
than 6.6 amp the drive will trip) then:
torque is constant between 0 to 50hz
(because the drive can rotate spindle without any problem).
current drawn by the motor from drive is depending on
the load between no load current and 6.6 amp but in this current range torque in constant.
best regards.

6/25/2011 12:58 PM	Rate (0)
PISCEAN 2010 Diamond Member Joined: 4/23/2010 Last visit: 11/23/2024 Posts: 8092 Rating: (882)	Hello, In simple V/F mode, motor speed is varied by keeping V/F ratio constant. What torque constant is meant by, whenever there is requirement of constant torque during the complete range i.e. say from 1 to 50 Hz, drive will supply & at the same time motor will draw rated current, say in your case 6.6 Amp. As long as drive part is considered, there will not be any problem. But the motor at low RPM say at 1 Hz, should be capable to deliver the torque & heat dissipation must be OK. Otherwise because of overheating & longer time duration of operation, motor may fail.

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micromaster 420 or vfd

Created by: saeedplc at: 6/23/2011 5:52 PM (3 Replies)

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saeedplc

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