Various Methods of Heating the Machine

Various Methods of Heating the Machine

Q. Explain the various methods of heating the machine.

The various methods of heating the machine are as follows :

External heat :

It is the method of drying insulation most frequently used. The various methods of applying external heat are : 

  1. Baking in the oven : It is conveniently carried out by placing the machine, having winding. The winding of machine with varnish is dried in baking oven at constant temperature. The temperature is kept constant with the help of thermostatic control. 
  2. By using boiler : The steam from the boiler heats up the top of machine . The heat raises the temperature of the windings and dries the windings. The temperature of the windings is measured by thermometers attached to the coils should not exceed 90°C.
  3. By electric lamps, heaters : Electric heaters are kept surrounding the machine to dry the insulation. Sometimes the heat of 200 watt, 500 watt lamp is used to dry the insulation. The drying takes place through radiation of heat. Hot air furnace can used for bring the insulation.

Internal heat : 

The insulation of the winding can be dried with the help of heat produced in the winding, by I2R loss. The d.c. voltage can be obtained with the help of rectifier. Low d.c. current is passed through the field winding and armature is short circuited. For induction motor apply reduced voltage to stator and block the rotor such that rated current will pass through the stator. The copper losses are converted into heat, which is used to dry the insulation. Even for transformer secondary is short circuited reduced voltage is applied to primary. The copper losses (I2R ) are used to heat the winding. 
Various Methods of Heating the Machine

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