CALCULATING STARTING TIME - 0% & 100% LOAD 2

[JZA10]

How do I calc the starting time of a motor at no-load & full-load, given the following?

Motor Data:

30Hp, 1200Rpm, 326U, 480V/3/60Hz.
NLA=17A, FLA=36A, LRA= 275A
FL RPM=1174, FLT=134#, BDT=405#, LRT=260#
EFF=91.1 & PF=80.8 @ Rated Load.
Rotor inertia=10.0 lb.ft^2.

Thanks in advance for your help.

 

[jraef]

You need to know the WK^2 for the load.

The formula is
Seconds = [Total WK^2 (lb-ft^2) x Speed Change (RPM)] / 308 x AAT (Average Accelerating Torque)

AAT = {[(FLT + BDT)/2] + BDT + LRT} / 3

Total WK^2 = Rotor Inertia + (Load Inertia x Load RPM^2 / Motor RPM^2)

"Venditori de oleum-vipera non vigere excordis populi"

 

[aolalde]

Use the formula:

t=(WK^2*DeltaRPM)/(308*Tave)

t= time to accelerate the inertia (sec).
WK^2= total inertia constant of the part being accelerated (Lb*FT^2).
DeltaRPM = Final speed minus Initial speed (RPM)
308 = constant for units
Tave = Average accelerating torque (LbxFt).

You do not provide the load data ( WK^2 and speed torque curve) then, only the no load accelerating time could be calculated.

Note that Tave is the net difference between the motor torque minus the load torque averaged for a speed range.

For no load condition at full voltage start, I considered the influence of the BDT for 1/10 of the speed range and the LRT for the remaining 90%.
Tave = 0.9x(260*9+405)/10 = 247 Lb-Ft. The initial speed is 0 RPM (stand still).

t = (10x1174)/(308x247) = 0.154 sec

 

[jraef]

LOL, we must have been typing at the same time!

"Venditori de oleum-vipera non vigere excordis populi"

 

[JZA10]

Thanks for all your help.

JZA10