Extreme Temperature of Increased Safety Electrical Equipment

The maximum heating temperature of components that may contact flammable gas-air mixtures in increased safety electrical equipment is a critical factor in determining the explosion-proof safety of electrical devices. Current-carrying components, especially power components like windings and heating elements, act as heat sources in electrical equipment.

The maximum heating temperature should not exceed the limit temperature of increased safety electrical devices. The term ‘limit temperature’ refers to the highest permissible temperature of explosion-proof electrical equipment, which is the lower of the temperature determined by the equipment’s temperature class and the temperature at which the materials used achieve thermal stability. This limit temperature is the “threshold” for ensuring the explosion-proof safety performance of increased safety electrical products. If the maximum heating temperature exceeds the limit temperature, it could ignite the corresponding explosive gas-air mixture or damage the mechanical and electrical properties of the materials used. For example, for insulated windings, a sustained temperature beyond the stability temperature can halve its lifespan for every 8-10°C increase.

For insulated windings, their maximum heating temperature must not exceed the standard stipulated in the table.

Limit Temperature of Insulated Windings

Characteristic Items	Temperature Measurement Method	Heat Resistance Level Of Insulation Materials
-	-	A（105℃）	E（120℃）	B（130℃）	F（155℃）	H（180℃）
Maximum Temperature During Rated Operation/℃
Single Layer Insulated Winding	Resistance Method Or Thermometer Method	95	110	120	130	155
Other Insulated Windings	Resistance Method	90	105	110	130	155
Other Insulated Windings	Thermometer Method	80	95	100	115	135
Extreme Temperature During Stall/℃
Extreme Temperature At The End Of TE Time	Resistance Method	160	175	185	210	235

For conductors carrying electrical current, at the maximum heating temperature, the material’s mechanical strength should not be reduced, there should be no deformation beyond what the permissible stress allows, and adjacent insulation materials should not be damaged. For instance, in the case of increased safety three-phase asynchronous motors, the rotor’s heating temperature will not harm the insulation of the stator windings.

In the design of increased safety electrical equipment, to prevent certain components’ temperatures from exceeding their limit temperature, designers should consider incorporating appropriate temperature protection devices, in addition to the electrical and thermal performance of the electrical components, to prevent overheating beyond their limit temperature.