Rotating motorThere are many kinds of.It can be divided intoalternatorandMotor, divided intoDC motorAndalternating current dynamo, divided intoSynchronous motorandAsynchronous motor。Asynchronous motors can be divided intoThree phase asynchronous motorandSingle phase asynchronous motor；According to the different rotor structures, it can be divided into cage type and wound rotor type. Cage type three-phase asynchronous motor is the most widely used and the largest demand in various motors because of its simple structure, convenient manufacturing, cheap price and reliable operation.
The lightning protection of rotating motors (generators, condensers, large motors, etc.) is much more difficult than that of transformers, and the lightning accident rate is often higher than that of transformers.This is because rotating electrical machines have some characteristics different from transformers in insulation structure, performance and insulation coordination.
(1) Among the electrical equipment of the same voltage level, the impulse withstand voltage level of the insulation of the rotating motor is the lowest.
The reasons are as follows: ① The motor has high-speed rotationrotorTherefore, only solid dielectric can be used, rather than solid liquid (transformer oil) dielectric combination insulation, as can be used for transformers: during the manufacturing process, solid dielectric is easy to be damaged, and holes or gaps are easy to appear in the insulation, so partial discharge is easy to occur during operation, leading to insulation degradation; ②The operation condition of motor insulation is the most severe, which is subject to the combined effect of heat, mechanical vibration, moisture in the air, pollution, electromagnetic stress and other factors, and the aging speed is fast; ③The electric field of the motor insulation structure is relatively uniform, and its impact coefficient is close to 1. The electrical strength under overvoltage is the weakest link.Therefore, the rated voltage and insulation level of the motor cannot be too high.
(2) The residual voltage of the arrester used to protect the rotating motor is very close to the impulse withstand voltage value of the motor, and the insulation margin is very small.
For example, the delivery of generatorImpulse withstand voltage testValue ratioZinc oxide arresterThe 3kA residual pressure value of is only 25%~30% higher than that of,Magnetic blow arresterThe margin is smaller, and the insulation margin will be lower with generator operation.Therefore, it is not enough for the motor to be protected only by lightning arrester. It must also be protected together with capacitors, reactors, cable sections, etc.
(3) Interturn insulation requires that the steepness of the intrusion wave be strictly limited.
Because the inter turn capacitance of the motor winding is very small and discontinuous, the overvoltage wave forced into the motor winding can only travel along the winding conductor, and the length of each turn winding is far larger than that of the transformer winding. The overvoltage acting on the adjacent two turns is proportional to the gradient of the intrusion wave.In order to protect the turn to turn insulation of the motor, the steepness of the intrusion wave must be strictly limited.
In a word, the lightning protection requirements of rotating motors are high and difficult, and the protection requirements of main insulation, turn to turn insulation and neutral point insulation of windings need to be fully considered.[1]
principle
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Principle of conservation of energyIt is a basic principle of physics.The implication of this principle is that in a physical system with constant mass, energy is always conserved;That is, energy can neither be generated nor destroyed out of thin air, but can only transform its form of existence.
In traditional rotating motorElectromechanical systemIn, the mechanical system is the prime mover (for the generator) or the production machinery (for the motor), the electrical system is the load or power supply of electricity, and the rotating motor connects the electrical system with the mechanical system.In the process of energy conversion inside the rotating motor, there are mainly four forms of energy: electrical energy, mechanical energy, magnetic field energy storage and thermal energy.In the process of energy conversion, there are losses, namely resistance loss, mechanical loss, core loss and additional loss.
For rotating motors, the loss consumption converts all of them into heat, causing motor heating, temperature rise, affecting the output of the motor, and reducing its efficiency: heating and cooling are common problems for all motors.The problem of motor loss and temperature rise provides an idea for research and development of new rotating electromagnetic devices, that is, electric energy, mechanical energy, magnetic energy storage and thermal energy constitute a new rotating motorElectromechanical systemSo that the system does not output mechanical energy or electrical energy, but uses the electromagnetic theory and the concept of loss and temperature rise in rotating motors to completely, fully and effectively convert the input energy (electrical energy, wind energy, water energy, other mechanical energy, etc.) into heat energy, that is, all the input energy is converted into effective heat energy output as "loss".
Based on the above ideas, the author proposes an electromechanical thermal transducer based on the rotating electromagnetic theory. Its rotating magnetic field is similar to that of a rotating motor, which can be generated by multi-phase energized symmetrical windings or by multipolar rotating permanent magnets. Using appropriate materials, structures and methods, the combined effects of hysteresis, eddy current and secondary induced current in a closed loop are utilized,The input energy is fully converted into heat energy, that is, the traditional "loss" of rotating motor is converted into effective heat energy.It combines electrical, magnetic, thermal systems and heat exchange systems with fluid as the medium.The new electromechanical thermal transducer not only has the research value of inverse problem, but also broadens the function and application of traditional rotating motors.[2]
heat exchange
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First, timeharmonicAnd space harmonics have a very rapid and significant effect on the generation of heat, which is rarely mentioned in the design of motor structure.Because the application of chopper power supply voltage is less and less, in order to make the motor rotate faster, it is necessary to increase the frequency of the active component of the current, but this depends on the large increase of the current harmonic component.stayLow speed motorIn, the local change of magnetic field caused by tooth harmonics will cause heating. We must pay attention to this problem when selecting the thickness of metal sheet and cooling system.The use of the strap should also be considered in the calculation.
As we all know, superconducting materials work at low temperatures, which leads to two situations:
The first is to predict the location of hot spots in the composite superconductor used in the motor coil winding.
The second is to design a cooling system that can cool any part of the superconducting coil.
It is very difficult to calculate the temperature rise of motor because many parameters need to be processed.These parameters include the geometry of the motor, rotation speed, material unevenness, composition of constituent materials, andSurface roughnessEtc.Due to the rapid development of computer and numerical calculation methods, the progress of motor temperature rise calculation has exceeded other fields by combining experimental research with simulation analysis.
The thermal model should be global and complex, without generality. Every new motor means a new model.[3]
Insulating material
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The motor insulation in operation shall withstand the influence and effect of various internal and external factors.The internal factors mainly include electric field, heat and mechanical stress;External factors include mechanical force, environmental conditions of the motor (temperature, humidity, pollution and the role of chemical composition), etc. All these factors constitute the working characteristics of motor insulation.In addition,High voltage motorCompared with other electrical equipment of the same voltage level, the electrical strength of insulation is lower, which has a certain impact on the operation.It is required that the motor insulation shall be able to withstand the independent or combined action of the above factors and operate safely and reliably for a long time.
Mica and mica products
micaIt is a kind of silicate mineral crystal with high electrical strength.It also has the advantages of high temperature resistance, flame resistance, stable chemical performance, poor water absorption, corona resistance, etc. It is an idealHigh voltage motorInsulation material.
Mica products can be divided into three categories: mica tape, mica plate and mica foil.All kinds of mica products include micaReinforcing materialAnd adhesive.Mica is used as the basic insulation barrier to ensure high electrical strength under long-term operation;Reinforcing materials are used to improve mechanical strength;The adhesive binds the two together.Mica products must have high electrical strength and sufficient mechanical strength.
Insulating paint
Insulating paint is composed of three parts: paint base (resin, asphalt, drying oil, cellulose, etc.), flux or diluent (benzene, toluene) and auxiliary materials (desiccant, pigment, antitoxic agent).It can be divided into impregnating paint, covering paint and adhesive paint according to the use.
(1) Impregnating varnish.Used for impregnating motor windings and fiber materials to improve the electrical performance, thermal conductivity, heat resistance, moisture resistance of insulation and the integrity of windings.In recent years, solvent-free impregnating varnish has been developed, and polyester and epoxy are the most widely used, gradually replacing the polycyandiamide alkyd paint.
(2) Cover paint.It is also called painting or coating. It is used to apply the paint on the impregnated insulation surface to form a smooth, smooth and water resistant insulation paint film with good mechanical properties to enhance the moisture-proof ability and prevent the effects of dust, dirt and chemical substances on the insulation, such as enamelled wire paint, silicon steel sheet paint, semi conductor paint, etc.
(3) Adhesive paint.Used to bond various insulating materials, such as mica, paper, cloth, etc.In addition to electrical properties, especially strong adhesion.The commonly used bonding paints are alkyd resin paint, shellac paintPhenolic resin paint, epoxy polyester paint, etc.
Lacquer cloth, film and composite products
Lacquer cloth is a soft insulating material made of cloth or glass cloth soaked in insulating varnish and dried. It must have certain mechanical strength, flexibility, electrical performance, heat resistance and thermal conductivity.
Compared with lacquered cloth, the film has the advantages of high electrical strength, good mechanical properties, small thickness and saving cotton cloth.High voltage motorPolyimide film is mostly used for insulation.[4]
