Can 50HP Motor be accelerated from 0 to full speed in 1 second? 1

[AndreyG]

Hello,

Can 50HP motor be accelerated in 1 second from zero to full speed?
And then decelerated in 1 second time?

This question may sound naïve but this is really what I need to figure out. The RPM value is not important as I learned.

The motor will be driving the pump and the pump is expected to provide some load. But even without load, is it physically possible to accelerate/decelerate 50HP motor in 1 sec?

The drive method: VFD, driving voltage assumed 220 - 500 V, assume infinite current supply available.

 

[jraef]

Well, you cannot assume "infinite" current available from a VFD, unless you are willing to concede an infinitely sized VFD! Any VFD will have a maximum current it can deliver, so that will always be a limitation.

That said, you can assume, for lack of any other realistic information, that you size the VFD to be capable of providing Locked Rotor Current of the motor instantaneously (no point in sizing it any higher). LRC is typically defined as 600% of FLC, and VFDs are typically capable of delivering 150% of rated current. So if the VFD is sized as 400% of FLC of the motor, i.e. a 200HP VFD connected to a 50HP motor, then it is possible to accelerate an UNCOUPLED motor in less than 1 second for sure.

Now the other nasty little bit of reality sneaks in, the LOAD on the motor. The LOAD on the motor would be defined as the inertia of the pump itself, plus any additional torque required as the pump begins to pump. Without knowing what kind of pump we are discussing here and what you are puming (it is anhydrous amonia or peanut butter?), it's not possible to do any better than a slightly educated crap shoot. So to that definition within the above defined conditions, I say, ....

Maybe...

"Will work for (the memory of) salami"

 

[LionelHutz]

It's possible to accelerate and decelerate a 50hp motor in 1 second. Will your motor accelerate and decelerate in 1 second? o-one can tell from the little info you provided.

Why do you want to accelerate and decelerate a pump in 1 second anyways?

 

[Strong]

"Why do you want to accelerate and decelerate a pump in 1 second anyways?"
Possibly to:
Create water hammer
Break a shaft or coupling
Waste energy
Dim the lights!

Walt

 

[KllrWolf]

I agree, not much information here to make the call for your specific configuration. Using a VFD adds even more complexity to the problem.

The motors I deal with, with DOL start, will be up to full speed in less than 1 second. This is with the load being a centrigugal pump and a stiff enough power supply that the voltage sag does not slow the start. It is with VFD and soft starts, which lengthen the motor start time, that can cause problems with the type of bearings we use. The stop time at load is not something we have concerned ourself with, as the systems our motors are in have other ways to immediately stop the pump output as the motors slows.

The size of motors we normally make are 5-350 Hp, with a few past 1000 Hp. However, our motors are a bit different than your standard electric motor, and the differences matter.

 

[waross]

If you can find a supplier of "U" frame motors you may "plug" them to a stop almost instantly. I wouldn't try it with a "T" frame motor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[AndreyG]

You mentioned your special motors KllrWolf. Are fluid filled motors any better then regular 3 phase inductance motors for applications with rapid changes of motor operation?

 

[KllrWolf]

Our specific type of fluid filled motors are much skinner and longer than a standard motor. Standard motors use the letter designation for a certain frame type, we use the inch diameter of the hole it will fit into. We have 300Hp 2 pole 460V that is designed to go into a 12” diameter hole. The rotors have a much smaller diameter than a standard motor, thus the moment of inertia of the rotor is actually very little. This allows them to accelerate very quickly. However, the design does have tradeoffs, to get the performance in such a shape.

 

[AndreyG]

Thank you everybody for sharing opinions.
Basically you proved that my idea was possible however I did not win and system with hydraulic accumulator will be used to provide required hydraulic 'pulses'.

 

[KllrWolf]

To answer your question about starting and stopping our fluid filled motors, the rapid start stop cycles would have them dead in minutes, if not faster. Either you would overheat the motor with the starts or snap/twist/warp something if you tried to stop it that fast. Our motors love to be turned on and then just fed clean power. Give them that, and the pumps they are attached to will wear out long before the motor even needs to be thought of. (32 years straight operation is the current leader in the "give it a quick clean and repaint, and send it back out")