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Keyword: Asynchronous electromotor breakdown is protected

The cent of breakdown cardinal principle of electromotor is two parts: One part is mechanical reason. For example of bearing and fan wear away or damage: Another part is electromagnetism breakdown, both each other has conjunction. If bearing damages, cause the overload of electromotor, even locked-rotor, and wind leaf attaint, make electromotor winding comes loose hot difficulty, temperature rise rises, insulant ageing. The reason of electromagnetism breakdown is very much, the overload that is like electromotor, break photograph, under-voltage and short circuit enough makes electromotor damage is mixed destroy. The overload, electric current that breaks photograph, under-voltage to move to be able to make circle inter block increases, calorific quantity increases (the calorific quantity of conductor is the) that becomes direct ratio with voltaic square, and the harm that short circuit causes is greater. The difference of insulating material quality that the reason of short circuit is electromotor itself or electromotor be affected with damp be affected with damp (be in a country often happen, suffer drench for example or fall into water) , as a result the alternate with puncture at winding, cause short circuit. In addition, still electromotor park has the place of soda acid content, because suffer,be corroded and attaint is isolated from.

One, the overload of electromotor and its protection

The overload of electromotor removes afore-mentioned causes outside, still have:

A. Electromotor surroundings temperature is exorbitant, medicinal powder hot condition is poor;

B. Electromotor is slow below big starting electric current start;

C. Long-term low speed runs electromotor;

D. Electromotor starts often, have a change of luck reachs apply the brake, positive and negative to often receive apply the brake instead all right.

The overload of electromotor increases as a result of electric current, calorific leap, make its insulant is damaged thereby, shortened its service life even by burn down.

From the point of the structure of electromotor, there must be good insulant inside the chamfer that the stator core buy of squirrel cage electric machinery puts winding, winding (copper cash) the surface has insulating varnish layer, winding of rotor of electromotor of the type that wind a string and stator winding are same, winding and core chamfer line with insulant, the cupreous slip ring that place of 3 end line receives, between annulus, also each other are isolated from between annulus and runner shaft. To assure the insulation of the alternate with of electromotor, electrical body and crust, be the insulating material that uses all sorts of heat-resisting social estate normally. All sorts of insulation have be able to bear or endure certainly the index that gets working temperature. IEC85 sets class A (105 ℃ ) , E class (120 ℃ ) , B class (130 ℃ ) , F class (155 ℃ ) ... . 80 time, IEC216 raised a new heat-resisting standard, call temperature index TI(TemperatureIndex) to replace IEC85 with this. TI is silk of black of the Nero that press A (calculative of B/T of ＋ of Arrhenins) formula T=10a. In type: T, life [hour (H)>
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