srinivasan
Member
- Location
- Bangalore,India
what is the formula to calculate the stating time of three phase induction motor in sec
starting time( %of voltage) at full load.
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kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
although I'm sure there is a method to calculate this, there are a lot of conditions that will vary the results.
In title of thread you mention "full load". Full load means nothing when the load is at rest. One load that draws full load current while at rated speed can be easier to start than another. A high inertia load will take longer time to reach full speed and could easily draw more than full load during acceleration period.
srinivasan
Member
- Location
- Bangalore,India
if you know what are the condition we have to consider while calculating. mention that. i will give my condition of motor sir.
srinivasan
Member
- Location
- Bangalore,India
that mean, it is a calculation of time of starting current.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I do not know how to calculate this. There may be a way, but I'm pretty sure it is chocked full of conditions and is not a simple calculation. I can give you many different things that I know will effect the outcome, ranging from size of the source, to mass of the load.
- Location
- San Francisco Bay Area, CA, USA
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- Electrical Engineer
There are standardized formulae for this, available in most good engineering books and on line. You have posted this question in a forum that is somewhat oriented towards the US and our National Electric Code, so we will do things in SI units, you will have to take responsibility for unit conversions, or look it up yourself elsewhere. The formula I use(d) is:
Time for motor to reach operating speed:
Seconds = Wk^2 (in ft.-lb^2) x Speed change (in RPM) / 308 x AAT (Average Accelerating Torque in lb-ft).
Wk2 = Rotor Inertia, + Inertia of load x Load RPM^2 / Motor RPM^2
AAT = [(FLT + BDT)/2] + BDT + LRT / 3
BDT = Break Down Torque, FLT = Full Load Torque, LRT = Locked Rotor Torque
If the above is over your head, perhaps you should reconsider whatever task you have taken on, this is Engineering 101 stuff.
Time for motor to reach operating speed:
Seconds = Wk^2 (in ft.-lb^2) x Speed change (in RPM) / 308 x AAT (Average Accelerating Torque in lb-ft).
Wk2 = Rotor Inertia, + Inertia of load x Load RPM^2 / Motor RPM^2
AAT = [(FLT + BDT)/2] + BDT + LRT / 3
BDT = Break Down Torque, FLT = Full Load Torque, LRT = Locked Rotor Torque
If the above is over your head, perhaps you should reconsider whatever task you have taken on, this is Engineering 101 stuff.
Last edited:
mike_kilroy
Senior Member
- Location
- United States
motor sizing
motor sizing
You've now started 3 separate threads asking small pieces of how to properly size a motor to a given load for a given application.
Perhaps a complete motor sizing program is best answer for you? If so, free good one:
http://www.kollmorgen.com/en-us/service-and-support/technical/motioneering/
motor sizing
You've now started 3 separate threads asking small pieces of how to properly size a motor to a given load for a given application.
Perhaps a complete motor sizing program is best answer for you? If so, free good one:
http://www.kollmorgen.com/en-us/service-and-support/technical/motioneering/
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