Motor Starting Times

[nightfox1925]

Dear all,

Is there any typical formula to estimate the starting times (No load and Full Load) of pump, fan and conveyor motors. The Data I have at the moment are the motor rating, voltage, and estimated BHP. I am going to use this data on my load flow and static motor starting studies on a conceptual project I am working on.

I hope motor and plant experts can give me a hand or guidance.

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[nightfox1925]

By the way, how many seconds do we typically set the transition timers of an Y-D starter?

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[jraef]

There is a formula, but you need a lot more information, mainly regarding the connected load.

Time for a motor to reach operating speed:

Seconds = WK² x Speed Change (RPM)
308 x AAT

AAT (Average Accelerating Torque) = {(FLT + BDT)/2} + BDT + LRT
3

Where;
BDT = Breakdown Torque
LRT = Locked Rotor Torque
FLT = Full Load Torque
WK² = Total inertia (motor rotor plus load inertia)

 

[aolalde]

Induction Motors up to 500 HP, 4 Poles, manufactured under Standard NEMA MG1, will be able to have two starts in succession when the motor temperature is at ambient and one start when it has the operating temperature, provided that the load moment of inertia (WK2) does not exceed the values stated in the same standard for the listed power (HP) and speed (Poles).
Normally the load inertia of centrifugal pumps is quite under the figures allowed by such standard. However conveyors could have high moment of inertia. Make a research for your application figures.

 

[nightfox1925]

Thank you guys for the inputs, I will deal with our process and rotary equipment for more details.

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[cherry2000]

I had adopted a long & laborious method to derive starting time of a induction motor. It can be done using the Driven & driving torque curves ( driving torque needs to be derated based on the anticipated voltage drop since Torque is proportional to Terminal Voltage square ). The equations used is similar to that jraef. I had pretty accurately derived the starting time for the motor which compared well with the field results.

 

[electricpete]

Sine you mention numerical
Taccelerating(w)=Telec(w)-Tmech(w) = J dw/dt
w = (1/J) Integral[Taccelerating(w)] dt

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[electricpete]

I guess that would give you a time simulation of w and you could see how long to get to w=wfinal.

Another more direct approach:
Taccel(w) = J dw/dt
dt = (J/Taccel(w))dw
T = Integral [J/Taccel(w)] dw from w=0 to wfinal

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[electricpete]

where T (without any subscript) is the time to acclerate

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