Requirements for insulating paint of motor
When the motor is in use, it starts frequently and has high no-load speed. Sudden load jamming and even locked rotor often occur. Sometimes the instantaneous temperature of the motor used in special occasions can reach more than 200 ℃, and at the same time, it will cause severe vibration. This kind of high centrifugal force, severe vibration and instantaneous thermal shock generated at high temperature and high speed puts forward requirements for the insulation structure of the motor to be resistant to vibration, cold and thermal shock and high temperature, so as to ensure the normal operation of the motor.
The insulation process is involved in the motor from winding the coil to assembling the finished product. Motor insulation has always been an important link in motor production. Therefore, designers, technicians and operators of insulation treatment process should pay enough attention to this link in material selection and process operation. The requirements for insulation paint of motor can mainly refer to the following requirements.
(1) Electrical properties
For the motor, it is mainly the electrical strength (E) and insulation resistance coefficient of the paint（ ρ v、 ρ s) Two indicators. For these two indicators, the insulating paint produced in China can meet the requirements.
(2) Mechanical properties
For the motor, it is affected by vibration force, cold and hot impact force and rotating centrifugal force, and the instantaneous temperature rises. Therefore, it requires good adhesion of insulating paint. Especially at high temperature (such as 200 ℃ or 220 ℃), the bonding force is strong, the thermal deformation temperature of the material itself is high, and it can maintain sufficient impact strength and toughness at high temperature, so as to ensure the safe operation of the motor under the action of intense mechanical stress and long service life.
Permeability is very important in impregnating paint. The paint impregnated coil with poor permeability is easy to cause no paint in the depth, so that the performance of other insulating materials in the depth can not be improved, which is easy to cause weakness, cause breakdown or shorten service life.
(3) Thermal performance
When the motor is working, with the rise of temperature, polymer materials will produce cracking, hydrolysis and oxidation, which will make the materials hard, brittle and crack, resulting in the reduction of insulation resistance, electric breakdown strength and mechanical strength, and the increase of stress deformation. Therefore, improving the heat resistance of insulating materials is of great significance to ensure the safe operation of motor and improve motor power.
(4) Physical properties
The viscosity is required to be moderate to facilitate penetration and appropriate amount of paint hanging; The solid content should be large, and the proportion and volatilization of solvent should be reduced as much as possible; Low water absorption; Light color; The paint film has good cold and heat shock resistance.
(5) Chemical properties
Due to different application occasions of insulating paint, it is necessary to consider the resistance to damp and hot climate, solvent resistance and compatibility with other insulating materials.
(6) Process performance
Due to the large production volume of the motor, when impregnating the stator, the curing speed of the insulating paint shall be fast, but bubbles shall not be generated, so as to ensure the fast-paced production. The curing speed and the storage period of paint are a pair of contradictions. If the curing speed is fast, the storage period must be short, the storage period must be long, and the curing speed must be slow. In order to solve this contradiction, most of the drop dip paints currently supplied in the market are supplied in the form of two-component packaging of paint base and curing agent. When in use, the two-component insulating paint is mixed according to the specified proportion before use. Due to some requirements, the two-component insulating paint has long service life and good permeability after being prepared, but it also has less loss, which will not have harmful effects on other materials such as copper wire.
(7) rationality and advanced nature of technology and economy
Motor is a kind of products similar to household appliances in large quantity and wide range, and the material cost directly affects the product price. Therefore, in ensuring that products have certain advanced indicators, we must consider the economy, otherwise the products will be competitive because of their high price.
(8) Environmental requirements
In recent years, the EU has put forward RoHS Directive on restricting the use of harmful chemicals for motor materials exported to China, and requires it to be enforced.
RoHS directive has been implemented since July 1, 2006 (EU TTI group decided to advance to December 31, 2005), which means that the content of the following six hazardous substances in the products of new electronic and electrical equipment put into the EU market shall meet the following requirements:
CD (cadmium) < 100ppm
Pb < 1000ppm
Hg (mercury) < 1000ppm
Cr6 + (hexavalent chromium) < 1000ppm
PBB (polybrominated biphenyl) < 1000ppm
PBDE (polybrominated diphenyl ether) < 1000ppm
This requires the insulating paint manufacturer to prohibit the mixing of the above six hazardous substances in raw material procurement, production process, etc., and provide the "Declaration of conformity" and SGS test report to the user. When selecting insulating paint, the motor manufacturer shall ask the insulating paint manufacturer for "Declaration of conformity" and SGS test report.
Performance evaluation of motor insulation
Insulation can generally be divided into gas insulation, liquid insulation and solid insulation. In practical application, solid insulation is still the most widely used and reliable insulation material. Under the action of strong current, the insulating material may be broken down and lose its insulating performance. Among the above three insulating materials, after the gas insulating material is broken down, once the external factors (strong electric field) are removed, its inherent electrical insulation performance can be restored by itself; After the solid insulation material is broken down, it will irreversibly and completely lose its electrical insulation performance. Therefore, the insulation selection of electrical lines and equipment must match the voltage level, and adapt to the use environment and operating conditions, so as to ensure the safety of insulation.
The insulation resistance of various lines and equipment under different conditions is roughly as follows: generally, the low voltage after new installation or overhaul shall not be less than 0.5 Ω; The insulation resistance of low-voltage lines and equipment in operation shall not be less than 1000 Ω / V; The insulation resistance of equipment and lines in wet places shall not be less than 500 Ω / V; Generally, the insulation resistance of control line shall not be less than 1m Ω, while the insulation resistance of high-voltage line and equipment shall not be less than 1000m Ω.
In the motor, insulation material is the weakest link. Insulating materials are particularly vulnerable to various effects that accelerate aging and damage. Generally, we evaluate the insulation performance of the motor from the following aspects.
(1) Insulation class
The insulation grade of the motor refers to the heat-resistant grade of the insulating material used, which is divided into grades A, e, B, F and H. The allowable temperature rise refers to the limit of the temperature rise of the motor compared with the ambient temperature.
(2) Heat resistance grade
The heat resistance grade indicated on an electrical product usually indicates the maximum temperature that the product can withstand when it reaches the expected service life under rated load and other specified conditions. Therefore, class F insulation indicates that the insulation heat-resistant temperature adopted by the generator is 155 ℃. When the motor is working, the user should ensure that the insulation material of the motor does not exceed this temperature to ensure the normal operation of the motor.
(3) Withstand voltage test
It is divided into turn to turn withstand voltage and ground withstand voltage. For safety, prevent breakdown. The withstand voltage test is generally required to be 1.2 ~ 1.5 times of the rated voltage, and it shall be fine after continuous power on for n hours. The instantaneous high voltage resistance is 2.5 times that required.
(4) Insulation resistance
Apply DC voltage to the dielectric. After a certain period of time, the resistance corresponding to the leakage current flowing through the dielectric is called insulation resistance. When heated and damp, the insulating material will age. The insulation resistance will be reduced, resulting in electric leakage or short circuit accidents of electrical equipment. In order to avoid accidents, it is required to measure the insulation resistance of various electrical equipment frequently. Judge whether the insulation degree meets the needs of the equipment. The measurement of common resistance usually has two methods: low voltage measurement and high voltage measurement. The insulation resistance is generally high (generally megaohm level).
Megger is the most commonly used instrument for measuring insulation resistance. It has high voltage power supply when measuring insulation resistance, which is the difference between it and resistance measuring instrument. Use a megger to measure the insulation resistance of the line and the insulation resistance of the motor. Generally, it is considered that 2 megger is insulated. You can also see the insulation grade marked on the electrical appliance, and then check the meter. Generally speaking, for low voltage, we require that the insulation resistance of lines and newly repaired Motors should be more than 0.5 megohm. Generally, the megger is used to measure the insulation resistance of the motor. The insulation resistance of each two-phase winding and between each phase winding and the casing shall be measured to judge the insulation performance of the motor.
(5) Aging test
When the motor is working, it is affected by many factors (such as temperature, electrical and mechanical stress, vibration, harmful gases, chemicals, humidity, dust and irradiation). With the increase of temperature, the polymer material will crack, hydrolyze and oxidize, so that the material becomes hard and brittle, and cracks and other phenomena occur, resulting in the reduction of insulation resistance, electrical breakdown strength and mechanical strength, and the increase of stress and deformation, so as to improve the heat resistance of the insulating material, It is of great significance to ensure the safe operation of the motor and improve the output power of the motor.
