Calculating motor decelleration times 1

[JY]

I am looking into a review of motor re-acceleration times where I work. What I need is a reference on how to determine the speed of a motor driving a load (compressor, pump ...) at any time after a complete power loss. If anyone has any good links or references they would be appreciated.

Working on the basis that if the machine still has greater than 90% speed it shouldn't draw starting current etc.

Thanks

Jason

 

[electricpete]

Torque = Moment of Inertia * d/dt (angular velocity)
(this is same as F=MA for rotating components).

You need to develop a Torque-speed curve for use during acceleration. The load (pump) has a torque speed curve. You may have to investigate with mechanical engineer whether this curve holds true for deccelaration (it is normally used for starting studies). If load torque is high then friction can probably be neglected.

T(w(t)) = J d/dt(w(t)).
T = Torque
J = rotating moment of inertia
w = angular speed

w(t) = 1/J * Integral (T(w)) dt.
Using numerical instegration with t=k*delta_t
w(k) = w(k-1) + delta_t * 1/J * T(w(k-1))
w(0) = known operating speed before loss of power.

There may be a little more sohpisticated implementation which will give less errors.
(there is error to applying T(w(k-1)) over the interval centered on k-0.5.)

 

[jbartos]

Suggestion: Reference:
IEEE Std 399-1997 "IEEE Recommended Practice for Industrial and Commercial Power System Analysis" (Brown Book) page 253 Section 9.6.5 The speed-torque and motor-accelerating time analysis
It may be a good idea to search for some suitable motor-starting program/software package since it will save you a lot of time.