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Enameled wire insulation, also known as varnish, is a dense protective film formed by uniformly coating one or more layers of insulating material on the surface of copper, aluminum and other conductors through a specific process and curing at high temperature.
It is the enameled wire is different from ordinary bare wire, PVC insulated wire core features, but also the enameled wire can be in the motor winding in the dense winding, stable work of the key guarantee.
Simply put, the enameled wire insulation layer is like the enameled wire “protective armor”, not only to ensure that the conductor conducts current efficiently, but also to isolate adjacent wires, conductors and cores between the electrical connection, to avoid all kinds of electrical failures.
The function of enameled wire insulation layer is multi-dimensional, not only covers the basic electrical isolation, but also includes high temperature protection, chemical protection, mechanical protection, etc. Each function plays a key role in the working performance and service life of enameled wire.
Different types of insulation, its functional focus varies, but the core function is always around the “protection of the conductor, to protect the operation” to start, the following will be a detailed analysis of the five core functions of the enameled wire insulation.
Electrical insulation is the most core and basic function of enameled wire insulation, its core purpose is to prevent turn-to-turn short-circuit, short circuit to ground, to ensure that the current can be normally conducted along the conductor, to avoid electrical energy leakage and electrical failure.
Motor windings by a large number of enameled wire wound densely, the spacing between neighboring wires is very small, the work will produce a certain voltage difference, if the insulation layer of the electrical insulation is not enough, there will be a leakage of current, the formation of turn-to-turn short-circuit.
Turn-to-turn short circuit will lead to a sharp increase in local current in the winding, generating a large amount of heat, burned wire and insulation, and then lead to generator failure; serious cases will also lead to a short circuit to the ground, triggering leakage, fire and other safety incidents.
Enameled wire insulation layer is made of polymer material with excellent insulating properties, with high dielectric strength and insulation resistance, which can effectively block the leakage path of the current and ensure that each wire is in an independent electrical circuit.
High-temperature protection is one of the important functions of the enameled wire insulation layer, mainly used to resist the high temperature generated during the operation of the motor, to prevent the insulation layer from deterioration and damage, and to ensure that the enameled wire can still maintain stable performance in a high-temperature environment.
When the motor is running, the winding will produce Joule heat due to the passage of current, and the iron core will produce iron loss heat, resulting in the winding temperature rises, and long-term in a high temperature environment, the conductor and the insulation layer of the enameled wire will be subjected to different degrees of damage.
Insulation layer as the conductor of the “thermal barrier”, can effectively block the heat directly on the conductor, delay the conductor oxidation speed, at the same time, it can withstand a certain high temperature, to avoid high temperature caused by softening, melting, cracking and other issues.
Different types of insulation, its heat-resistant grade is different, can adapt to the maximum working temperature also varies, from 130 ℃ B insulation to 220 ℃ above the C insulation, can meet the high temperature needs of the motor under different working conditions.
Many motors, transformers and other equipment will contain oil, chemicals, refrigerants and other corrosive substances in the environment, such as industrial equipment, refrigeration equipment, new energy vehicles, etc., the enameled wire insulation needs to have a good chemical resistance to prevent erosion by corrosive substances, to ensure the stability of the insulation properties.
If the chemical resistance of the insulation layer is not enough, oil, chemical reagents and other substances will penetrate into the insulation layer, resulting in softening, cracking, peeling off the insulation layer, and then exposed to the conductor, triggering short circuit, leakage and other faults.
Enameled wire insulation layer through the selection of chemical corrosion-resistant polymer materials, can effectively resist the erosion of oil, acid and alkali reagents, refrigerant and other substances, to maintain the denseness and integrity of the insulation layer.
Enameled wire will be subjected to a variety of mechanical stresses such as stretching, bending, friction and other mechanical stresses during the production, winding and assembly process; during the operation of the motor, vibration will also be generated, resulting in friction between the enameled wires, between the enameled wires and the iron core.
If there is no protection of the insulation layer, the conductor is easy to be abraded and scratched, resulting in exposed conductors, triggering short-circuit faults; at the same time, the mechanical stress will also lead to conductor fracture, affecting the normal operation of the motor.
The enameled wire insulation layer has a certain degree of mechanical strength and flexibility, which can effectively resist the action of mechanical stresses such as stretching, bending, friction, etc., and protect the conductor from damage.
The volume and weight of electromagnetic equipment such as motors and transformers are important design indexes, especially small motors, micro motors, electric vehicle motors, etc., which have more stringent requirements on volume and weight.
The thickness of the insulating layer of enameled wire directly affects the volume and space utilization of the winding. Compared with ordinary PVC insulated wire, the insulating layer of enameled wire is thinner and denser, which enables more turns of wire to be wound in a limited space and improves the power density of the winding.
Ordinary PVC insulated wire insulation layer thickness is usually in the hundreds of microns or even a few millimeters, while the enameled wire insulation layer thickness is only a few microns to tens of microns, the thickness of only 1/10-1/50 of the PVC insulation layer.
This advantage makes the enameled wire can be in the narrow motor stator, rotor groove dense winding, increase the number of winding turns, enhance the motor’s magnetic field strength and power output; at the same time, it can also reduce the size of the motor, reduce the weight, to achieve the miniaturization of the motor, lightweight design.
Classification by insulation material is the core and most commonly used classification of enameled wire insulation, and the type of insulation material directly determines the performance, heat resistance level and application scenarios of the insulation layer.
At present, the commonly used insulating materials for enameled wires in the industry are mainly polymer resin materials, which can be categorized into the following categories according to the chemical structure and performance differences of the materials, and are also the core types to be analyzed in the following sections of this article.
The advantage of classifying by material is that the core performance of enameled wire can be judged directly according to the characteristics of the insulating material, which provides a direct basis for selection, and is the most commonly used classification method in the industry.
By temperature class, it is classified according to the maximum working temperature that the enameled wire insulation layer can withstand for a long time, and this classification is directly linked to the working temperature demand of the motor, which is an important reference basis for motor selection.
According to the standards of the International Electrotechnical Commission (IEC) and the National Electrical Manufacturers Association (NEMA), the temperature class of enameled wire insulation is divided into the following four categories, with different temperature classes corresponding to different insulation materials and application scenarios.
It should be noted that the classification of temperature grade is based on the aging life of the insulating layer of enameled wire. Under the specified long-term use temperature, the insulating layer is able to maintain stable insulating performance, with a service life of not less than 20,000 hours (ordinary enameled wire) or 40,000 hours (high-quality enameled wire).
The advantage of classification by temperature class is that it can quickly match the working temperature requirement of the motor, avoid insulation failure caused by insufficient insulation heat resistance class, and ensure the stable operation of the motor.
By application, enameled wire is categorized according to the environment and type of equipment, which is in line with the actual application requirements, and can provide accurate reference for the selection of enameled wire in different industries and different equipments.
According to the differences in application scenarios, enameled wire insulation can be divided into the following categories:
The advantage of categorization by application scenario is that it can directly combine with the use environment and performance requirements of the equipment to quickly screen out the appropriate type of enameled wire insulation, and improve the efficiency and accuracy of selection.
Polyester Magnet Wire Insulation is the most widely used and versatile basic insulation layer in the industry. Polyester resin is used as the core insulating material, and a dense insulating protective film is formed through coating and high-temperature curing process.
With the advantages of low cost, high versatility and good flexibility, it occupies a dominant position in the market of general enameled wires, and is widely used in domestic and small-scale industrial medium and low-temperature scenarios, and is one of the most cost-effective types of enameled wire insulation.
The core characteristics of polyester enameled wire insulation are “universal, economical and easy to process”, which are mainly embodied in the three aspects of material, process and performance, and can meet the needs of most common scenarios.
From the material point of view, polyester resin is a low-cost polymer materials, wide range of sources, processing technology is mature, can be mass production, effectively control the production cost of enameled wire.
From the process point of view, polyester enameled wire coating process is simple, can be used in a variety of ways, such as dip coating, spraying, etc., after coating by 150 ℃ -200 ℃ high temperature curing can form a dense insulating layer, high production efficiency, suitable for large-scale industrialized production.
From the performance point of view, polyester enameled wire insulation layer flexibility is excellent, can be repeatedly bending, winding without cracking the insulation layer, fall off, can adapt to the complex winding process of the motor winding; insulation performance is reliable, the dielectric strength of up to 40kV/mm-50kV/mm, can effectively prevent turn-to-turn short-circuit.
In addition, polyester enameled wire insulation layer of wear resistance, anti-aging performance is better, can adapt to the erosion of the conventional working environment, longer service life; at the same time, its coloring is better, according to the demand for different colors of enameled wire, easy to distinguish between different windings.
The heat-resistant grade of polyester enameled wire insulation is mainly B grade (130℃) and F grade (155℃), which is a typical medium-low temperature insulation layer and can adapt to the working temperature of most common motors.
Class B polyester enameled wire insulation has a long-term maximum working temperature of 130℃ and a short-term overload temperature of no more than 150℃, which is suitable for lower working temperature scenarios, such as ordinary household motors, small instrumentation motors, etc., with a thermal life of more than 20,000 hours at 130℃.
Class F polyester enameled wire insulation layer of the long-term maximum operating temperature of 155 ℃, short-term overload temperature does not exceed 175 ℃, applicable to the working temperature of a slightly higher temperature scenarios, such as small industrial motors, air-conditioning fan motors, etc., and its thermal life in the 155 ℃ environment can be up to more than 15,000 hours.
It should be noted that the heat resistance of polyester enameled wire insulation is limited, and if it works for a long time in an environment that exceeds its rated temperature, it will accelerate the aging and cracking of the insulation layer, resulting in a decline in insulation performance and even insulation failure.
Therefore, when selecting the type, it is necessary to choose the polyester enameled wire with the corresponding temperature rating according to the actual working temperature of the motor, so as to avoid motor failure due to insufficient heat-resistant rating.
Polyurethane Magnet Wire Insulation is an insulating protective film formed by coating and high temperature curing with polyurethane resin as the core insulating material.
Its most outstanding feature is that it is directly weldable (solderable) without removing the insulating layer in advance, which can greatly simplify the production process of motor winding, and at the same time, it has excellent high-frequency performance, which is widely used in high-frequency equipments in the fields of electronics, communication, instrumentation and so on.
Polyesterimide Magnet Wire Insulation is a medium to high end type of insulating layer which is formed by coating and curing at high temperature with polyesterimide resin as the core insulating material.
Its core advantage is a higher heat resistance level, while taking into account the cost-effectiveness of polyester enameled wire and the high temperature resistance of polyimide enameled wire, chemical resistance, mechanical properties are also superior to polyester enameled wire, widely used in industrial motors, medium and high voltage motors and other medium and high temperature scenarios.
The core temperature class of polyesterimide enameled wire insulation is Class H (180°C), which is the key feature that distinguishes it from polyester enameled wire, and also its core advantage for medium and high temperature scenarios.
The long-term maximum working temperature of Class H polyesterimide enameled wire is 180℃, and the short-term overload temperature does not exceed 200℃, which is able to adapt to the use of medium and high temperature scenarios, and its thermal life can reach more than 20,000 hours in 180℃ environment, and more than 40,000 hours in 155℃ environment.
Polyesterimide enameled wire has better thermal shock performance, which can withstand sudden temperature changes when the motor is started, braked or when the load changes suddenly, avoiding cracking of the insulation layer, and is suitable for industrial motors with frequent starting and stopping.
Compared to polyester enameled wire, polyester-imide enameled wire has a significant improvement in heat resistance and is able to adapt to the high temperature working environment of industrial motors. Compared to polyimide enameled wire, it is lower in cost and more cost-effective, making it the preferred type of insulation for medium to high temperature scenarios.
Polyamide-Imide (PAI) wire enameled insulation is a high-end insulating and protective film formed by coating and high temperature curing with polyamide-imide resin as the core insulating material, and is one of the insulation types with the best overall performance in the industrial field.
Its core features are ultra-high heat resistance, abrasion resistance, refrigerant corrosion resistance, while taking into account the excellent electrical insulation and mechanical properties, can adapt to new energy, industrial high-end equipment and other harsh working environments, and is widely used in electric vehicle drive motors, refrigeration compressors and other demanding performance scenarios, is the core insulating material for high-end enameled wires.
The core characteristics of polyamideimide (PAI) insulation layer are “ultra-high heat resistance, strong protection, high reliability”, its molecular structure combines the flexibility of polyamide and high temperature resistance of polyimide, and its comprehensive performance far exceeds that of polyester, polyurethane, polyesterimide and other insulating layers.
