Heat resistance of motor winding insulation.
?Insulation
Electrical insulation (EI) is an element of equipment construction that prevents electric current from passing through it. Materials with dielectric properties are used for insulation: glass, ceramics, numerous polymers, mica.
Main characteristics:
- Dielectric permittivity
- Mechanical strength
- Temperature resistance. Determines how well the insulation retains its properties under different temperature conditions. This is critical because machines can get hot during operation.
- Moisture resistance
- Loss rate. Tangent delta. Determines the ratio of active power (losses) to reactive power in the dielectric. This ratio allows the quality of the insulation to be assessed.
Main insulation is the outer insulation of the coil, insulating it from the walls of the grooves in the cores (slot/groove insulation) and from other metal parts of the machine (mainwall insulation). The purpose of the main insulation is to separate the conductors from the iron of the machine or the magnetic core. The main insulation is followed by cover insulation, which protects the main insulation from mechanical damage.[1]
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It is worth mentioning that there are different technologies of winding production. Rem&Coil uses Flat Coil technology, which differs from the classical method of insulation application. The peculiarity of Flat Coil is that the insulation is applied to the winding blank before the moulding stage. The main advantage of Flat Coil technology is the possibility to use automated machines at the stage of winding insulation application.
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Insulation classification: temperature class
The service life of electrical machines depends to a large extent on the condition of the stator winding insulation. Damage to the winding insulation leads to short circuits, which account for more than three quarters of all electrical equipment failures.
In addition to natural ageing, moistening and contamination of the winding, the causes of damage include long-term excessive temperature conditions that do not meet the requirements of operation, as a result of which the insulation strength drops sharply. Therefore, heat resistance classes
Windings are the least heat-resistant part of the motor structure. Therefore, the operating temperature limit of the whole device is determined by the temperature at which they burn out.
The following classes of winding insulation heat resistance are distinguished:
Y (maximum temperature - 90 degrees Celsius). Windings are made of paper or natural fabrics without additional insulation impregnation;
A (maximum temperature - 105 degrees Celsius). Wraps are made of paper or natural fabrics with additional insulating impregnation;
E (maximum temperature 120 degrees Celsius). Wraps made of organic film of synthetic origin;
B (maximum temperature 130 degrees Celsius). Windings made of glass fibre or mineral compositions;
F (maximum temperature 155 degrees Celsius). F (maximum temperature - 155 degrees Celsius); F (maximum temperature - 155 degrees Celsius); F (maximum temperature - 155 degrees Celsius); F (maximum temperature - 155 degrees Celsius);
H (maximum temperature 180 degrees Celsius). Fibreglass or mineral wrap with organosilicon binder impregnation;
C (maximum temperature from 180 degrees Celsius). Wraps made of heat resistant materials with or without inorganic binder impregnation.
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Electric machines with class A insulation are practically not manufactured, and class E insulation is of limited use in low-power machines. Class B and F insulation is mainly used, and in special machines operating under severe conditions (metallurgy, mining equipment, transport) - class H and C. As a result of use of more heat-resistant materials, improvement of properties of electrical steels and improvement of constructions for the last 60-70 years it was possible to reduce the weight of electric machines in 2,5-3 times.
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Types of insulation materials?
For long-term use of insulation, it is necessary to contact proven and reliable winding contractors and purchase quality materials. Electric motor manufacturers and repair organisations can turn to the Russian plant Rem&Coil, which since 2006 has been producing any type of sections as well as stator winding rods for AC and DC electric motors and generators. Due to the perfect geometry, section laying will take 1-2 days. And in production we use only high quality copper of M0 and M00 grades, and insulation of F, H, C heat resistance classes of leading world manufacturers.
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Types of insulation materials used at Rem&Coil plant
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ELECTRICAL INSULATING TAPES FOR RESIN RICH TECHNOLOGY
- Elmikatherm 524019
Mica tape consisting of PET film, mica paper, glass substrate. Mica content not less than 40 %. Heat resistance class F(155°C).
- Elmikatherm 52409
Mica tape consisting of mica paper, glass substrate. Mica content of at least 50%. Heat resistance class F(155°C).
- Elmikatherm 529029
Mica tape consisting of polyimide film, mica paper, glass substrate. The mica content is at least 35%. It is used for manufacturing sections of asynchronous motor stator winding for traction electric machines. Heat resistance class H(180°C).
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- Elmikatherm 525029
Mica tape consisting of polyimide film, mica paper, glass substrate. The mica content is at least 35%. It is used for manufacturing of stator winding sections of three-phase asynchronous motor stator winding for traction electric machines. Heat resistance class C (200°C).
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ELECTRICAL INSULATING TAPES FOR VPI TECHNOLOGY
- Elmikapor 523119
Mica tape consisting of PET film, mica paper, glass substrate. The mica content is at least 60%. Heat resistance class F(155°C).
- Elmicapor 523199
Mica tape consisting of mica paper, glass substrate. Mica content of at least 50%. Heat resistance class F(155°C).
- Elmikapor 53319
Mica tape consisting of mica paper, glass substrate. Mica content of at least 80%. Heat resistance class F(155°C).
- Elmicapor 525029
Mica tape consisting of polyimide film, mica paper, glass substrate. The mica content is at least 35%. Used for manufacturing sections for traction electric machines. Heat resistance class H/C (180 - 200°C).
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PROTECTING TAPES
- Glass fibre tape LES
Designed for protection of body insulation from mechanical influences.
- LPP-400
Designed to protect the case insulation from external partial discharges in groove parts.
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Temperature operation mode of electric motors
Normal values of ambient temperature at which the electric motor operates with rated power are determined by the climatic version of the electric motor. Thus, machines with N1 and F1 version are designed for operation at ambient temperature up to +40 degrees Celsius, N3 and T2 - up to +45 degrees Celsius, T1 - up to +50 degrees Celsius. If the ambient temperature exceeds this parameter and it is not possible to organise cooling, it is necessary to reduce the load on the used electric motor[3].
For temperature control, the supply voltage must be monitored. If the voltage drops to 95% of the nominal voltage or lower, the motor is supplied with increased current, which leads to overheating of the device. The same phenomenon is observed when the voltage rises to 110% and above of the nominal voltage, as eddy currents cause the stator to heat up.
According to statistics, the life of the insulation when the temperature rises 8 degrees above the permissible limit halves its operating period. Therefore, in order to maintain the performance of the machine, it is worthwhile to find out the permissible operating temperature, avoid overheating and avoid exceeding (or reducing) current loads.
Temperature exceedances under the above conditions (gaseous cooling medium temperature of 40 °C and altitude not exceeding 1000 m above sea level) must not exceed the values given in Table 3 (for air cooling) or Table 4 (for hydrogen cooling). For other on-site operating conditions for typical modes other than S1 and for nominal machine voltages above 12000 V, the tolerance limits must be adjusted according to GOST R 52776-2007 (IEC 60034-1-2004).
More details - https://disk.yandex.ru/i/baf_RJWt8CK73g
The ambient air temperature at which a general industrial electric motor can operate at rated power is considered to be 40oC. If the ambient temperature is higher or lower than +40 for the general industrial version of the electric motor, the standard allows certain modifications of the permissible temperature exceedances.?
! When the ambient air temperature rises above 40oC, the load on the electric motor must be reduced so that the temperature of its individual parts does not exceed the permissible values.? When the machine is operated in mountainous areas where the heat dissipation is impaired due to lower atmospheric pressure, the standard provides for some reduction of permissible temperature exceedances.
Regardless of the decrease in ambient temperature, it is not allowed to increase the current loads by more than 10% of the rated current. With induction motors, this can be affected by changes in the supply voltage; as the supply voltage decreases, the power at the motor shaft squared decreases and, in addition, a voltage decrease below 95% of the nominal voltage leads to a significant increase in motor current and heating of the windings. Increase in voltage above 110% of rated voltage also leads to increase in motor winding current, stator heating due to eddy currents increases.
As the temperature rises, many of the materials begin to char and become conductive. All materials become brittle from prolonged exposure to elevated temperatures long before charring, easily break down and lose their insulating properties. This process is called thermal ageing
Technological overloads of working machines or voltage fluctuations in the supply network lead to an increase in the current in the windings of machines and exceed the temperature of the windings above the permissible for this class, as a result, the service life of machines is quickly reduced.?
Temperature is the most important factor affecting the service life of a motor. If the operating temperature constantly exceeds the operating limit temperature of the insulation material, the insulation deteriorates faster. This accelerated ageing process significantly reduces the service life of the motor. Maintaining the motor operating temperature within the specified limits is therefore essential to ensure longevity and reliable operation.
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More details on testing:
Organisation Standard 34.01-23.1-001-2017 - https://stds.ru/document/%D0%A1%D0%A2%D0%9E%2034.01-23.1-001-2017.pdf?
Useful materials on insulation and sections:
Sources:
[1] The cover insulation protects not only against mechanical damage, but also against moist external environment (Eliflex 19), against partial discharges - anti-corona/conductive tape (LPP-400 + LPP-1000). Everything depends on the tapes applied.?
[2] Consolidation = сoncatenation
[3] Climatic version: N - temperate macroclimatic area; F - cold macroclimatic area; NF - combination of temperate and cold macroclimatic areas; T - tropical macroclimatic area; U - general land area, excluding areas with very low temperatures; M - macroclimatic area with moderately cold maritime climate; B - all areas of the globe, excluding parts of the earth with very low temperatures (e.g. Antarctica). https://relsib.com/uploads/tiny/documents/gost_15150_69_klimat_ispolneniya.pdf