SOLUTION

The consideration involved in the selection of the type of electric drive for the Load Variation application depends upon constant Load, continuous Variable Load, pulsating Load.

Selection of Motor based on Load Variation

While selecting a motor it is necessary to consider the variation of load torque with speed and time. This is related to the torque rating of the motor i.e. how much and what type of torque motor can produce safely. The variation of load torque with speed basically decides the type of motor to be selected. While the variation of load torque with time decides the rating of the motor to be selected. Such a factor that influences the selection of rating of the motor based on the load variation with time is called the load variation factor. One cycle of variation of the load is called a duty cycle. The different types of load variations with time and corresponding examples of load are given below:

1. Continuous or constant loads: In this type of load occurs for a long time under the same conditions.
   e.g. fan type loads, paper-making machines, etc.
2. Continuous variable loads: The load is variable over a period of time but occurs repetitively for a longer duration.
   e.g metal cutting lathes, conveyors, etc
3. Pulsating loads: A torque that exhibits a combination of constant load torque superimposed by pulsations. 
   e.g. reciprocating pumps, compressors, all loads having Bank shaft.
4. Impact loads: These are peak loads that occur at regular intervals of time. Motors for such loads are provided with heavy flywheels.
   e.g rolling vanilla, presses, sharing machines, forging hammers
5. Short time internment loads: The load appears periodically on identical duty cycles, each consisting of a period of applications of load and one or rest.
   e.g. all forms of cranes, hoist, elevators.
6. Short time loads: A constant load appears on the drive and the system rests for the remaining period of the cycle.
   e.g. motor-generator sets for charging batteries, household equipment.