The coil insulation of high voltage motor has a great impact on the service life and economic effect of the motor, which is a problem that every designer and technician must carefully consider. The high-voltage coil can be called the heart of the motor to some extent, which directly determines the service life of the motor, and the performance of the insulating material, which is an important component of the coil, is crucial.
The insulation structure and treatment process of high-voltage motors in various countries can be roughly summarized as follows:
(1) Multi-adhesive mica tape is continuously wrapped, vacuum dried, and then hot pressed (moulded or hydraulic).
(2) Multi-adhesive mica tape is continuously wrapped, without vacuum drying, and directly formed by hot molding.
(3) Less adhesive mica tape is continuously wrapped, vacuum immersed in solventless resin, and then hot press forming.
(4) The mica tape (or white embryo tape) is continuously wrapped, that is, the line is scattered, and then the solvent-free resin is impregnated as a whole.
In addition, there are silicone rubber insulation, as well as silicone rubber and mica tape mixed insulation. The heat resistance, cold resistance, moisture resistance and corrosion resistance of silicone rubber are excellent, but the electrical performance and tear strength are poor, and it is only used for high-voltage motors operating in special environments below 6 kV.
Basic requirements for high voltage coil insulation:
Sufficient electrical strength
On the one hand, it is desirable that the insulation of motors be as thin as possible, but on the other hand, it is required to have a certain margin in terms of electrical strength. Because the motor in operation, will be subject to atmospheric overvoltage and operational overvoltage impact: sudden short circuit, temperature and voltage of the long-term role, the insulation will gradually aging, vibration and mechanical stress will also damage the insulation, in addition, in the manufacturing process to carry out a number of withstand voltage test, every time, will produce a certain subtle deterioration traces of the insulating structure, that is, the so-called cumulative effect. All these will make the insulation electrical strength decline. Therefore, when designing the coil structure, there must be a certain safety factor.
Low dielectric loss
Dielectric loss occurs when an insulating structure is subjected to an alternating electric field. Dielectric loss of the average heat, although not large, but in individual weak points on the heat is particularly concentrated, if the weak points on the heat caused by the dielectric loss more than the heat emitted, the local temperature of the insulation will continue to rise, the rising temperature and promote further increase in the dielectric loss, the insulation of the electromechanical performance will be a sharp decline in the severity of the weak points of the local thermal breakdown will be caused. Therefore, in the high-voltage motor dielectric loss should not exceed the specified value.
Good corona resistance
When high-voltage motors are in operation, corona phenomenon may occur both inside and on the surface of the insulation, accelerating the aging and corrosion of the insulation. Therefore, for generators of 6.3kV and above and motors of 6kV and above, their coils should take anti-corona measures. The coil of 6kV motor can not be anti-corona treatment in general, but it should be anti-corona treatment for the motors which are used in poor environment or with large capacity.
Good thermal aging performance
The heat resistance of the thermal insulation structure should meet the heat resistance grade required by the product. Under the long-term action of the working temperature, the normal service life of the insulation can be guaranteed.
Motor insulation is usually divided into A, E, B, F, H five heat resistance grades. During operation, the temperature of the most hot spot in the motor winding insulation shall not exceed the maximum temperature specified in the insulation class. Generally, it is necessary to leave a margin of 5~10℃. If the insulation structure is composed of insulation materials of different heat resistance grades, its heat resistance grade can be simulated and comprehensively evaluated through its structural model.
Can withstand the role of mechanical stress
The insulation of the coil must be able to withstand a certain amount of mechanical stress without breaking or causing harmful deformation. Coil in operation due to the expansion coefficient of wire and insulation is not the same, temperature changes, insulation will be subject to tension, the longer the motor, the greater the impact; Because of the electromagnetic force, the end of the coil will also produce vibration, especially when the motor is affected by short circuit, starting and braking current, the electromagnetic force often causes the coil to deform; Therefore, the insulation is required to have a certain elasticity and mechanical strength.