Using Three Inverters Instead of One

These numbers look a bit odd; at 345 V, an 800-KW motor ought to draw much more than 565 A.

I'm wondering if the chassis size for the overall inverter is causing it to be made up of three single-phase inverters. [??]

That part number is for a Fuji, not Mitsubishi, drive. Each drive is 3 phase, rated 585A, so each drive is capable of running that motor; I guess...

I say "I guess" because I'm not sure why you are showing 3 different RPM ratings. Is it a 3 speed motor? If so, then the nameplate would show 3 separate FLA ratings, one for each speed. I find it hard to believe however that you have a motor that is wound in such a way as to provide those speeds, it makes no sense to me. Something is amiss here, you are leaving out a lot of details, you have related the information incorrectly, or you are making this up to mess with us.

Thanks for the reply but be rest assured i am not trying to mess anything. What ever information was passed on to me i have mentioned except that on the schematic electric diagram the motors has 9 leads coming out from motor and connected to the motor terminal box and each one off the inverter is connected to 3 leads i.e. for each inverter there are 3 leads.

Sorry for the wrong information regarding the manufacturer of the inverters.Regarding 3 RPM this is mentioned on the schematic diagram.The name plate has the following data.

fuji electric 3 Phase induction motor, type MSF 9506 A.

800 Kw, Poles 6, Phase 3*3. RPM 850/1300, Hz 42.7/65.4 , Voltage 345/355, Amps 565/525

Well, it's still confusing but the motor details seem in line with the VFD selection apart from the power. (300kW?)

The 3 speeds seem to be standard rated speeds for a 6 pole so the connection of 3 VFD seems a mystery, are there switches between the VFDs and the motor?

How many terminals inside the motor terminal box, connection diagram and a good application description may help BUT what is the main point of your query or reason to enquire re this whole arrangement?

800Kw motor is installed in Aluminum file manufacturing plant in the extruder section.

Extrusion is a process in which solid thermoplastic material is melted and forced through an orfice (Die) of desired shape and then cooled.

The processing steps involved in extrusion are:

• Feeding
• Melding
• Pumping
• Forming
• Cooling

I am scanning the schematic diagrams (3No.) hope they will help to find solution to my question.

I am re-scanning the inverters drawing (only that portion which can be of help).

Regarding my basic query. My company is carrying out energy audit of the manufacturing plant and to get some technical information from the concerned dept. is hell of a job.

When I came across 800KW, connected through 3inverters my mind struck with the question that what is the use of 3 inverters is it load sharing technique or some other factors are involved. In order to clear my conception I was left with only option to get guidance from CR4 forum.

With your guide line I have come to the conclusion that as you have pointed out, VG7 only goes to 400KW rating, hence to run 800KW with 1.5 S.F (which they disclosed to-day) they need 3 inverters to run the motor.

OK, glad the information helps.

It looks like the suppressing reactor (ACL 74B) is in circuit as part of this arrangement as I suspected.

Came across something similar using a synchronising module (SIR) to enable the parallel technique using the ACReactor as depicted. In this case the supply was from phase shift transformers (to limit harmonics on the mains supply side, I suppose).

Received more information from plant which I am passing on to you please comment. 1. Large capacity motor drive The multi – windows system of VG7S is the product applicable to drive the induction motor (hereinafter called motor) with multi-winding coil (hereinafter called multi-winding) from 2 to 6 windings. This allows operation of one motor by sharing load into multiple converts. The maximum capacity of the VG7S units is 800kW. To drive the 1200kW motor, three 400kW inverters or two 630kW inverters are connected. 2. Sensorless vector control. Mulity-winding motor can be sensorless vector controlled. 3. Current sharing To drive one multi-winding motor with multiple inverter, it is necessary to mount the optical link option on each inverter. This optical link instantaneously conveys the current command to share current for each winding. Each inverter control current (feedback control) for each inverter during operation. 4. Minimized wiring Multiple inverters are defined as that one is the master and others are slaves with the switch settings on the option. The master inverter gives operation command and speed command as in a standard product and performs feedback connection (not required for the sensorless type) of the motor encoder. In contract, the function of the slave inverter is to share current. Connection for operation command or speed command is not required wiring is main circuit, alarm output to external unit and optical link. 5. Switching multi-winding motor drive/single (standard) motor drive When each inverter needs to drive an individual motor one to one (hereinafter called single motor drive) after operation of one multi-winding motor with multiple inverters, multi-winding motor drive and single motor drive can be switched with digital input signal. The constants (motor parameters) for three motors can be preset on each inverter. The motor constant (parameters which is used in switching can be switched with digital input signal. Note: I personally thank you for guiding me in the correct direction. Without your sincere guidance I would never been able to get hold of the information mentioned above from the plant management hope in future you will keep on guiding the CR4 forum members.

thanks for your e mail in response to my e mail(as mentioned Guest). once again thank you and appreciate your efforts in helping to solve my query.

salahuddin zia

well i had read all the discussion about the said topic

we are facing the same problem in our plant, in plant total three Fuji Electric inverter type FRN315VG7S-4 are installed to run the induction motor Fuji Type MSF9506A. out of these three inverter one is master while other both are Slave.

As the motor contains three windings and for each winding their is a Fuji Inverter.

we had check all the inverters individually and run the motor with no Load (coupling open) and were found normal running with low RPM. But when we connect all the three inverters to run the single motor we get Erb alarm on all the three inverters as the master drive get the signal to start.

Kindly give your expert opinion about the said problem

Very odd nameplate information. Google found no reference information on anything I could enter on that motor,must be something custom made. In that case, only the designer of the system can explain why they are using 3 inverters. Very unusual though.

How big of an extrusion press is this? what size billets/container? Is this the main drive motor?