Active Load Torques: Torques: Load torques torques which have the potential potential to drive the the motor under under equilibrium conditions are called active load torques. Load torques torques usually retain sign when the drive rotation rotation is changed. changed. Active Load Torques
Passive Torque: Load torques which always oppose the motion and change their sign on the reversal of motion are called passive load torques. Torque Torque due to friction cutting – Passive Passive torque.
omponents of load torques! 1. "riction Torque #T"$ The friction torque torque #T"$ is the equivalent equivalent value of various various friction torques referred to the motor shaft. 2. %indage Torque Torque #Tw$ #Tw$
%hen a motor runs& the wind generates a torque opposing the motion . This is 'nown as the winding torque. (. Torque required required to do useful useful mechanical wor' # Tm$
Nature Nat ure o the the torqu tor que e depan depands ds o type type o load: )t may be constant and indeoendent of speed& *ome function of speed& may be time invariant or time variant. The nature of the torque may may change with the change in the loads mode of operation.
Characteristics o dierent types o load: )n electric drives the driving equipment is an electric motor. + ,i-erent types of loads ehibit di-erent speed torque characteristics. + /ost of the industrial loads can be classi0ed into the following general categories! 1. onstant torque type load. 2. Torque proportional to speed #generator type load$ (. Torque proportional to square of the speed #fan type load$ . Torque inversely proportional to speed #const power type load$ 1.onstant Torque haracteristic !
The speed – torque characteristic characteristic of this type of of load is given given by T3. %or'ing motor have each mechanical nature of wor' li'e shaping & cutting& grinding or sharing& require require constant torque irrespective irrespective of speed. *imilarly cranes during the hoisting. *imilarly cranes during the hoisting and conveyors handling constant weight of material 4 unit& time also ehibit this type of characteristics.
Torque proportional to speed:
*eparately ecuted ecuted dc generators connected to a constant resistance load& eddy current bra'es and calendaring m4cs have a
speed torque characteristics m4cs have a speed – torquecharacteristics given by T 3w.
Torque propositional to square o the speed :
Load Torque Torque *quare *qua re of speed 5ample ! "ans & 6otary pumps & compressors & ship propellers. The speed – torque characteristicsof this type of load is given by
Torque inversely propositional to speed:
+ )n such types of loads & torque is inversely proportional to speed or load power remains const+ 5q! Lathes& boring m4cs& milling m4cs & steel mill colier and electric traction load. + This type of characteristics is given by
+ /ost of the load require etra e-ort at the time of starting to overcome static friction. )n power application it is 'nown as bra'e bra'e away torque and load contengineers call it 7stiction8 . 9ecause of slition & the speed torque characteristics of the load is modi0ed near to :ero speed.
