general equation for estimating rotor weight
general equation for estimating rotor weight
(OP)
Does anyone have a general/approximate relationship for estimating rotor weight, given horsepower and speed of an integral-horsepower horizontal motor?
=====================================
Eng-tips forums: The best place on the web for engineering discussions.





RE: general equation for estimating rotor weight
when we first started our repair shop, we did not have any means to weigh the rotors for balancing purposes. So, back to basics - take the cross section and length of each section of the rotor, then calculate the weight with a density of 8 gm/cc.
Nowadays, I simply use a digital crane scale. Saves time but my math is getting a bit rusty.
kumar
RE: general equation for estimating rotor weight
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: general equation for estimating rotor weight
For the core lamination:
RW (rotor weight) =(OD2^2*pi/4)*L*d
SW (stator core weight) = (OD1^2*pi/4)*L*d - (OD2^2*pi/4)*L*d
= (OD1^2 – OD2^2)*pi/4*L*d
L= core length and d steel lamination density.
SW/RW= (OD1^2-OD2^2) /OD2^2 = R^2-1
The windings could be considered following the same relation, most of the rotor bars are aluminum.
In general the laminations have three ratios:
for 2 poles R=2
for 4 poles R=1.666
For 6 or more poles R=1.5
For a given frame size the Frame, End-brackets, bearings and shaft are constant and will take around 25% of the total weight for ODP and 35% for TEFC.
EG. 50 HP, 4 Poles, 60 HZ. 460 V, TEFC, Frame 326T, Total Weight 795 LB.
Structure weight~ .35*795 = 278.25 LB
then;
SW + RW = 795-357.75 = 516.75
SW/RW=1.666^2-1 = 1.775
Solving the two equations,
SW= 330.53 Lb
RW=186.22 Lb
This is only an approximation; the variation of results could be very rough from motor to motor.