Drives and Motors

What type of drives are you using? Variable speed control, Soft-starter? Everything is possible but your information is not enough to help you.

Dear,

In principle, Every thing is possible, but not above the rating limit of the drive. In this case, starting torque of drive should be able to take up the starting torque of load on motor.

Over loads capacity of drive shall be less then that of motor & gear mechanism. In cases of faults, effect would be on the drive first, activating the protections like current limit, motor stall condition protection etc.... In case of delayed protections, drive power components may damage first, & Main power MCCB may not trip.

With the above practical aspects, you may chose.

ABB drive 200kW, output current 445A...

my motor ratings are 250kW at FLC-428A....

Drives do not "care" about kW ratings, only current and more specifically, current both continuously and for limited amounts of time when delivering overload current. To that end then, VFD mfrs rate drives based on the expected OL current capability of a specific type of load that is connected.

A centrifugal pump or fan is called a "Variale Torque" load, also called a "Quadratic" load and VFD mfrs will de-rate a VFD for use on these loads because it is expected that they will never need to deliver high current for more than a few seconds at start-up. A typical VT over load current capacity rating for a VFD is 105% current for 30 seconds, plus the continuous current rating is higher because it is acknowledged that a centrifugal load will only require the highest continuous current when running at lower speeds and thus the switching losses inside the VFD are lower.

But a "Constant Torque" load may require more capacity in the VFD, not only during start-up, where it is typically required to be capable of delivering 150% current for 60 seconds, but also the continuous current rating is comparatively lower. That's because in a CT load, you may be needing full current even at full speed when switching losses in the VF are the highest. Higher switching losses inside the VFD mean more cooling is required, or lower current ratings on the components.

So without more information on your drive and load, it's impossible to determine if your drive will work adquately. You may have a VT rated drive and a CT load. If that's the case, it ill not likely perform to any degree of satisfaction. But if you have a CT drive and a VT load, no problem at all. Then if you have a CT drive and a CT load, or a VT / VT combination, it may work to accelerate the motor but not to keep in running at full speed under load. Most VFDs can do what is called "Current Limit" to protect themselves from overloading by artificially reducing the output frequency as a way to cut loading. This may get in the way of a successful application.

yap definetly the drive will allow the motor to be run without load and if the load is 250kw and the drive u have is the capacity of 200kw then change the module inside then it will easily support ur motor to be run but u not to change the drive board inside drive okzzzzzzzzzzzzzzzzzzzzz thankz bye

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as a general rule of thumb; something rated less than it's load, will not operate it properly

Hi Jaganath.

The comments by JRaef cover your problem / questions excellently - especially without you having included what load you intend to drive and at what duty point.

I would add two things:

Firstly, the obvious question of what your load is and the approximate duty point.

Secondly, most ABB variable speed drives perform an "ID run" on a motor to identify its (the motor's) parameters and run it optimally. While your motor rating is higher than that of the drive, it is only marginally higher so the drive should be able to start and run the motor.

The last point is very important and identified by JRaef by considering the load torque characteristic: The drive has to START and RUN the motor; for the drive there is almost no difference because the duty point is so variable that it often occurs somewhere along the speed curve which is normally the "Start" of a Direct-On-Line application. So IF your load is a centrifugal law type (pump, fan, compressor) with not too arduous a starting torque (bearing stiction etc.) AND you your motor is over-rated for the load duty point (as are almost all inductrial applications) then it is very likely that you will be able to start and run your motor WITH its load - and quite efficiently in fact because your fixed losses will be comparitively lower than a larger drive and motor driving the same load.

Good Luck and thanks.

Rob Melaia (Jhb, South Africa)

melaia@mweb.co.za

Most decent VFD's rated at 200kW (notional) will drive a 250kW motor, no problem.

The load limitation will normally be dictated by the load current required, so, e.g. if you have a 420A VFD and a 450A motor then you should be OK up to 420A load. If no load current is 100 A, say, this means you have approximately (420-100) / (450-100) = 300/350 = 6/7 capacity available to you of motor rated torque (or power at full speed approx 210kW in above example).

The same applies for any overload rerquirement, taking the inverter overload available compared to motor rating to approximate maximum short term performance capability.

So, if its an easy application, like a fan, maybe this may mean you cannot reach max speed / flow because of VFD capacity.

That's "nominal", chief.

I don't really understand what you're saying. If you mean my comment is lacking in substance or made for the sake of it (nominal) then I can say that I was only trying to add to the discussion for the benefit of understanding re the original question.

If you are querying my use of 'notional', I am trying to say that a '200kW' rated VFD is only a theoretical and loose description and the real power is related to VFD and motor data as also outlined elsewhere.

I hope this clears up any queries and you catch the gist of my original reply OK.

Exactly. Good answer.

Reply: First and foremost, what is the difference between the drive and motor?. Ithink that it is the motor to drive and not a drive to run the motor.And the drive system includes the motor and the gearing system.Therefore the answer to your question is the reverse of your question.

yours, mwesigye charles, uganda