the formula to calculate the rotor motor inertia for 3 phase induction motor. in kg-m2
the formula to calculate the rotor motor inertia for 3 phase induction motor. in kg-m2
There is no special way to calculate motor rotor inertia. It is calculated the same way you would calculate the inertia of anything else. To do so you need to know the shape of the thing and its mass. Most of the time you can get this information from the manufacturer fairly easily.
Bob
I assume you mean motor rotor inertia rather than rotor motor inertia?
As petersonra has stated, the rules are no different for this.
The difficulty here it that it is a complex assembly with different materials and usually with some holes.
Depends on how accurately you want it and for what purpose. For a quick and dirty approximation I'd take a solid steel cylinder the length and diameter of the rotor and the steel shaft, also as a cylinder and add the two together. This is likely to give you a worst case.
FWIW, solid cylinder inertia is
I = m*r^{2}/2
m being mass.
m = pi(r^{2}) * length * material density.
The density of steel is around 7,800kgm^{-3}
I don't know what application you require this for.
In most that I've dealt with where inertia calculations are required, the load inertia has greatly exceeded motor inertia when referred to either load or motor relative speed.
This data is typically provided by the supplier.
The formula -
H = 5.48E-9 * WR^{2} * RPM^{2} / MVA (When WR^{2} is in kg-m^{2})
Total RPM
The total RPM is equal to the Motor RPM.
Total WR2
The total WR2 is calculated based on the Total RPM and Total H using the equation above.
Total H
This is the arithmetic sum of the Motor, Coupling and Load H in MW-sec/MVA.
"Just because you're paranoid, doesn't mean they're not out to get you"
You'll notice that the formula is for H when inertia and RPM are known, or to calculate inertia when H and RPM are known.
It does give the inertia when no other info is known.
Sorry if it was misleading, maybe should have clarified better. ETAP uses this info to do motor starting dynamic analysis.
"Just because you're paranoid, doesn't mean they're not out to get you"
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