Month: agosto 2017

Stator Insulation

In electric motors the insulation of the stator winding is responsible for preventing the passage of electric current from the conducting wires to the stator plating.

It protects the winding of erosive agents from the environment and helps in conducting the heat generated by the losses to the outside. The MIT being a robust machine is dimensioned so that its useful life is determined by the longevity of the stator winding insulation.

The life of the insulation is reduced due mainly to the temperature, but also due to the action of humidity and vibration, until it can not withstand the applied voltage and cause a short circuit.

An increase of 10ºC above the thermal class limit of the insulation can reduce the half-life of the motor coxreels 1125. The total insulation of the winding involves a combination of insulation from the groove where the coils are inserted, the winding impregnation resin, the enamel on each winding wire and the insulation between phases.

The standard establishes the classes of insulation, each with its temperature limit, that is, by the higher temperature that the insulation system can withstand without affecting its useful life.

Temperature Control

The maximum temperature that can be supported by the insulation-based components found in the electric motor is usually calculated to ensure effective operation in an environment with an average temperature of approximately 40 ° C.

It is therefore extremely important that the technician responsible for the maintenance process properly checks and controls the ambient temperature to ensure that it does not exceed the values ​​for which the engine was originally produced.

There are care with the voltage variations that need to be rigorously taken. The thermal balance of an engine may vary depending on the change in the supply voltage. A voltage drop makes it possible to limit the flow of the magnetic circuit, thereby reducing the losses in the iron and the no-load current. However, the motor torque will need to overcome the resistant torque, so as to prevent a high increase in slip.

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As the motor conjugate results from the process between the flow and the intensity of the absorbed current, if the flux reduces, the current intensity increases. With the load current significantly increased by the voltage drop, the motor can heat up, causing losses.

Minimum and Maximum Conjugation

Briefly, in practice, the locked rotor torque needs to be as high as is feasible, so that the rotor can overcome the initial inertia of the load and can accelerate it rapidly, especially if the starting becomes less tension . The minimum torque is the smallest torque developed by the engine when accelerating from zero speed to the speed corresponding to the maximum torque.

Therefore, this value can not be very low, ie the curve should never present a marked depression in the acceleration process, so that the start is not very long and can result in overheating of the electric motor, especially in cases of high inertia Or starting with reduced voltage.

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The maximum torque is the largest torque developed by the motor, under nominal voltage and frequency, without any possibility of extreme speed drop. In practice, the maximum torque must be as high as possible, for two main reasons, and the motor must be capable of overcoming any load peaks that may occur, as in specific applications. The engine can not lower, ie abruptly lose speed if excessive voltage drops occur.