High voltage with a recommendation to start with a softstarter 1

[panter]

Hello everyone ,
I recently saw at manual for Westinghouse High voltage motor that as starting method was given soft starter only . In your opinion, what should be structural difference compared to the motor with a DOL start .

 

[jraef]

Details, and in this case context, matters…

What do you mean by “high” voltage? Per IEC standards that is just anything over 1,000V, but by ANSI standards that term applies to 115kV and above!

What do you mean by “structurally”? I mean, yes, ANY form of “soft starting” is going to be different from Across-The-Line (DOL) starting.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[waross]

Either high inertia or thermal limits may be pertinent.
And high inertia interacts with thermal limits.
Consider a standard motor suitable for DOL starting.'
That motor is now connected to a high inertia load.
The high starting inertia may cause the thermal limit to be exceeded and some sort of reduced current starting is now mandatory.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[LionelHutz]

Reduced-current starting doesn't help with any thermal limits. It uses more thermal capacity.

It's likely specified to reduce mechanical stresses. Why - you'd have to find out from the motor designer.

 

[Gr8blu]

Again - more details are important.
1) Was the machine a wound rotor (or squirrel cage) induction design?
2) Was it synchronous - and if so, brushed or brushless?
3) Is it intended for multiple consecutive starts in a short time period - or the usual "2 cold, 1 hot" requirement?
4) What is the driven load? Some loads have much higher mechanical inertias, which means a longer acceleration time - and although the DOL method produces more torque, there is no way to regulate the amount of current flowing during the start. This may create an unsafe (or at least undesirable) condition inside the motor winding(s) - usually at the bar-to-cage joint.
5) What is the allowable voltage dip on the bus supplying the machine? A Direct On Line start may draw enough current to temporarily drop the voltage to where protection trips on under-voltage either due to the actual amplitude or duration of the dip, or possibly both.

Most likely the design does not have sufficient material (mass) in rotor bar, shorting ring, or both to accommodate the heating associated with the relatively high inrush currents (and length of time to accelerate), which then requires that there be some means of controlling that current to a lower setpoint - which is accomplished by the soft starter. There will be no mechanical (i.e. "structural") difference where steady-state operation at rated power/speed/voltage is concerned.

Converting energy to motion for more than half a century

 

[panter]

I was on the road and did not provide minimum information related to my question
It's about 6kV ,3,5MW motor that was talked about a lot and it was used to drive the fan .
Link
Now it is considers that this motor should be used to drive one pump where we have motors with same voltage and power instead old wound rotor which have starting method with a resistor in rotor circuit .


In order to use it now to drive the pump, we are considering a softstarter or a frequency regulator but we will also include an external company with experience in this type of work .