Insulation & Thermal Classes for Rotating Machines
This blog is describe the recognized system of thermal classes for the insulation used for electro-magnetic or electric equipments.As we know that most of the product failure is due to failure of insulation of the product or motor. There are different factor which are affected on insulation these are follows:
1. Ageing Factor: Insulation of motor is failure due to ageing factor .Such as temperature, electrical & mechanical stress, vibration, deleterious atmosphere, chemicals, moisture ,dirt & radiation .
§ Temperature: As the temperature of motor is increase above the insulation class used .Then there is chance of insulation failure. To avoid such failure select proper insulation class for the motor as per mention below.
§ Electrical & Mechanical stress: There is unbalance in supply or suddenly increases of supply, due to this increase in motor current & it will increases the losses in motor & temperature. Also coupling of motor is tight or unbalance in connected load, motor mounting is not proper .Then there is chance of mechanical stress & vibration. Due to the mechanical failure lose part or touching the part or insulation & it will damage the insulation.
§ Deleterious Atmosphere : All product are design to operate in particular atmosphere or specific temperature. If the atmosphere condition change or motor operate above their altitude level then there is also change motor performance. Also motor is operated above or below its operating temperature then there is also chance of insulation failure.
§ Chemical : Electric equipment or motor insulation come to contact with chemical then its affect or lower the insulation resistance . Due to this life of insulation is decreases.
§ Moisture : As explain above moisture also affect the insulation failure.
§ Durt & Radiation : If the motor or product operating under dusty environment & there is dust on motor or equipment ,then due to this there is increase of motor temperature as there is no proper cooling on motor surface. Also if dust contain moisture then there is failure of insulation as discuss earlier. Radiation also affect the motor insulation .
2. Wrong Selection : If there is no proper selection of motor or product or lower rating product is used. Then there is chance of insulation failure due excess of current flow through the motor or product.
3. Insulating Material : For particular temperature ,there is thermal class of insulation is specified.If the wrong insulation is used then there is chance of insulation failure.
4. Operation of Product : Actual performance of insulation is depend upon particular conditions ,such as environmental exposure ,duty cycle & type of product .Further the intended performance in service varies greatly depending on relative importance of size ,reliability ,desired period of used of associated equipment & economic consideration.
Thermal Classes : Following are the thermal classes & the temperature assigned to them -
Thermal Class → Temperature in ℃
Y → 90
A → 105
E → 120
B → 130
F → 155
H → 180
200 → 200
220 → 220
250 → 250
Temperature above 250°C should increase by 25°C intervals starting from 250 °C.When a thermal class is describes an electromecanical or electrotechnical equipment it normally represent the maximum temperature appropriate to that product under rated load & other condition.Thus,the insulation subjected to maximum temperature will need to have thermal capability at least equal to temperature associated with thermal class of product or motor as per above table.
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