Types of Loads acting on machine components:

There are 4 basic types of loads that are seen to act on the components of a machine. They are as follows:

• Linear loads: In this type of load, the load impedance is constant regardless of the voltage that is applied. The current of the load varies proportionally with the voltage, that is, it increases if the voltage is increased and decreases if the voltage is decreased.  A few examples of linear load are incandescent lighting, motor, heating tools, etc.
• Motor loads: Induction motor is the most commonly used as a motor load. During the start of an induction motor, a very large current is required from the source of power. This current is known as the starting current.
• Non- linear loads: in a non-linear load, the load current is not proportional to the voltage at any instant. The load current is not continuous at most times. Essential electronic loads such as a computer, UPS, motor drive with variable speed, etc. are examples of non-linear loads.
• Special loads: As the lift application since the starting of the motor is very frequent, the starting current of the motor should not exceed seventy five percent of the current that the alternator is rated at. Simply put, the Kva rating of the alternator should be thrice the HP rating of the lift motor. In a reciprocator compressor application, a maximum of sixty six percent load current can be that of the reciprocating compressor motor or a maximum current of thirty three percent of the load current should be that of the reciprocating compressing motor. If the method of starting is direct on line, then the starting current should be 6 to 7 times the full load current of motor.  If the method is star, the starting current should be 2 to 2.5 times the full load current of the motor. If it is started by rotor resistance, the starting current must be 1.5 to 2 times the full load current of the motor.

Questions:

• What is the starting current?
• Give two examples of non-linear loads.