Shaft Torque (Tsh)
The torque which is available at the motor shaft for doing useful work is known as shaft torque. It is represented by Tsh. Fig. (4.9) illustrates the concept of shaft torque. The total or gross torque Ta developed in the armature of a motor is not available at the shaft because a part of it is lost in overcoming the iron and frictional losses in the motor. Therefore, shaft torque Tsh is somewhat less than the armature torque Ta. The difference Ta – Tsh is called lost torque.
Ta - Tsh =9.55 × iron and frictional losses/N
For example, if the iron and frictional losses in a motor are 1600 W and the
motor runs at 800 r.p.m., then,
Ta - Tsh =9.55 × 1600 /800 =19.1 N-m
As stated above, it is the shaft torque Tsh that produces the useful output. If the speed of the motor is N r.p.m., then,
Output in watts= 2πN Tsh/60
or Tsh =Output in watts /(2πN /60 ) N-m
or Tsh = 9.55 ×Output in watts /N N-m
Brake Horse Power (B.H.P.)
W.D./revolution = force x distance moved in 1 revolution
F × 2π r = 2π×Tsh J
W.D./minute = 2π N Tsh J
W.D./ sec= 2πNTsh J/60 jS-1 or watt=2πNTsh J/(60 ×746) H.P.
Useful output power =2πNTsh J/(60 ×746) H.P.
or B.H.P. =2πNTsh J/(60 ×746)
Written by arjun on September 14th, 2009 with
no comments.
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