In case of kiln drives
Right Answer is:
Starting torque is more than double the running torque.
Kiln drives: The rotary kiln is an indispensable part of a cement plant. The rotary kiln drives depend upon the type of cement-making process (wet or dry). These are, in general, tubular tilted from the horizontal position with a ring fitted around them. This ring gear engages with one or two pinions. A variable-speed motor drives the pinion.
The requirements of a kiln motor are the following:
- Power requirement is very high
- The speed control ratio is 1:10. Very low creeping speeds of 1 rpm may be required.
- Starting torque should be in the range of 200 to 250% of full load torque.
- The acceleration of the drive should be completed in about 15 s.
- For small periods an overload capacity of 200-250% may be required.
- The motor must have suitable control for inching and spotting during maintenance.
The motors that meet the above requirements are as follows:
- A.C. motors with speed control.
- Slip ring induction motor.
- Ward Leonard controlled the D.C motor.
- Three-phased shunt-wound commutator motor.
- Cascade controlled A.C. motor.
- D.C. motor with transformer step switch control.
In kiln drives starting torque is double that of running torque. Hence for kiln drives Ward Leonard controlled DC shunt motors, slip ring IM, cascade controlled AC motors are employed.