200 HP Motor Start Time

[plangetee]

Hello all, I've got a 200 HP Motor powered by a 400 kVA transformer with 3.68% impedance. This motor is full-line starting. This motor is the only load on this transformer other than a small lighting panel ~20 kVA.

Having said this, the customer who owns this transformer is telling me the 200 HP motor is taking 10 seconds to start. The motor has been operating like this for a few years now and has not had any "problems" starting in this fashion.

For someone who has worked with motors this large, Is the starting time I described typical for a motor this large or unusual? What would be a typical start time for a motor this large?

 

[waross]

Often the the load has the most effect on starting time of a motor and you haven't told us what the load is. 10 seconds may be a little long for a design B motor but not nearly as serious for a design D motor.

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

 

[plangetee]

Thanks Bill.
This is a NEMA Design B motor. KVA Code = "H". FLC = 231 Amps.

I will try to find what the load typically is during this investigation.

I do know the motor is started/stopped around 6 times a day.

 

[LionelHutz]

It sounds longer than most typical application when full-voltage starting. But, most typical applications are easy to start pumps and fans. It could easily be correct for a more difficult load.

 

[waross]

The best option may be to search the manufacturers literature to find the allowable starting times. 10 seconds seems a little long and is certainly grounds for investigation but it may be within the manufacturers allowable starting time.
The inertia of the load is the most important but a motor with a cyclic load that starts and idles before full load is applied or a motor with less than the full 200 HP load may be more forgiving than a motor that starts loaded and continues to run at 100% load.

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

 

[jraef]

You may also have an inadvertent Reduced Voltage Starter there as well. That transformer may be a little on the small side for Across-the-Line starting of that motor and is saturating, which is effectively limiting the current the motor can draw, just like an Auto-Transformer starter or Reactor Starter would. With that low of a duty cycle and no history of tripping on Overload, I wouldn't be too concerned about it, as long as nobody else complains about the dimming lights.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[jraef]

... but that said, I personally would not be starting a 200HP motor ATL anyway, I would use a soft starter.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376