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Continuous operation: How to extend the service life of low-frequency transformers
2026-07-07
24 hours of continuous operation without interruption, effectively extending the service life of the low-frequency transformer in all directions
In the control system, a large number of low-frequency transformers need to operate continuously without interruption for 24 hours a day throughout the year, with the total operating time reaching over 8,700 hours. Transformers that operate intermittently have the opportunity to shut down for cooling, while uninterrupted power supply products have their copper loss and iron loss continuously accumulated, and the insulation materials are constantly exposed to high temperatures, accelerating their aging. Many transformers have a nominal lifespan of up to ten years, but under the all-day continuous full-load operation condition, faults such as insulation degradation, inter-turn short circuits, and coil burnout occur within just two or three years, causing significant losses to the production line and maintenance.
The service life of a transformer is largely determined by the aging rate of the insulation materials. According to the thermal aging theory, for every 8 to 10 degrees Celsius increase in winding temperature, the aging rate of the insulation materials will double. To ensure the long-term stable and continuous operation of the transformer, it is not enough to rely solely on the factory quality of the product. Instead, systematic optimization must be carried out from six dimensions: power selection, material grade, production process, heat dissipation structure, power grid protection, and daily operation and maintenance.
- The Four Major Causes Leading to Transformer Accelerated Aging under Continuous Overvoltage Conditions
1. Long-term constant high temperature leads to continuous thermal aging of insulation
For ordinary transformers that operate intermittently, the temperature fluctuates. The insulation materials have a buffer period for thermal expansion and contraction. However, for equipment that is continuously powered for 24 hours without interruption, the iron core and the coil remain in the high-temperature range all the time. The varnish coating of the enameled wire, the interlayer insulation paper, the framework, and the impregnated resin are constantly in a hot environment. The high-molecular materials gradually become brittle and crack. Once a tiny crack appears in the varnish coating, water vapor and dust invade, and it will quickly develop into a phase-to-phase short circuit. This is the main reason for the scrapping of continuous operation transformers. Many reduced-capacity transformers merely increase their power without upgrading the temperature resistance level. Running at full load for two or three years will inevitably lead to batch aging failures.
For ordinary transformers that operate intermittently, the temperature fluctuates. The insulation materials have a buffer period for thermal expansion and contraction. However, for equipment that is continuously powered for 24 hours without interruption, the iron core and the coil remain in the high-temperature range all the time. The varnish coating of the enameled wire, the interlayer insulation paper, the framework, and the impregnated resin are constantly in a hot environment. The high-molecular materials gradually become brittle and crack. Once a tiny crack appears in the varnish coating, water vapor and dust invade, and it will quickly develop into a phase-to-phase short circuit. This is the main reason for the scrapping of continuous operation transformers. Many reduced-capacity transformers merely increase their power without upgrading the temperature resistance level. Running at full load for two or three years will inevitably lead to batch aging failures.
2. Persistent fluctuations in the power grid and harmonic disturbances, repeatedly causing insulation breakdown
Industrial equipment that operates 24/7 is subject to constant voltage fluctuations, harmonic interference, and instantaneous surges. These issues persist throughout the year. Ordinary transformers can only withstand stable sinusoidal alternating current. Over time, they are exposed to fluctuating voltages and interference from various noises, causing the iron core to frequently enter a magnetic saturation state. The excitation current fluctuates greatly, and the windings repeatedly endure instantaneous large current impacts. The coil conductors generate electrodynamic forces that cause continuous vibration, and the conductors rub against each other, gradually wearing down the insulation paint layer. Over time, the originally intact insulation layer gradually deteriorates, eventually leading to leakage and breakdown.
3. The losses accumulate over time, and the internal heat cannot be naturally released.
Continuous operation for 24 hours means that copper loss and iron loss continuously generate heat. If the transformer has a compact structure and a sealed shell, the heat can only enter and cannot escape, causing the body temperature to remain persistently high. Even without overload, long-term high temperature will accelerate the degradation of the magnetic performance of the silicon steel sheets, resulting in increasing iron loss and forming a vicious cycle of "increasing heat leads to increased loss, and the loss further heats up", significantly shortening the overall lifespan of the machine.
4. Environmental dust and moisture continuously erode the insulation
The electric control box operates continuously without being turned off for years, and the internal air keeps circulating. Dust and moisture continuously adhere to the surface of the coils. Under the alternating conditions of heat and cold, condensation forms and gradually seeps into the gaps of the varnish layer, causing the insulation resistance to decline year by year. Even in an indoor environment that is slowly deteriorating, if it is in a damp dust environment such as underground, near the sea, or in a workshop, the insulation failure rate will increase exponentially.
- Ensure sufficient margin in selection and avoid long-term overloading
For transformers that operate continuously without interruption, the selection must not be exactly at the rated power. This is the most fundamental and crucial step in extending the lifespan. For intermittent equipment, a 20% power margin is sufficient, while for motor-type equipment operating 24 hours a day, the safety margin must be increased to 30% to 40%. For example, if the continuous load at the rear end is 200VA, one cannot choose a 200VA transformer; instead, a transformer of 260 to 280VA should be selected. Reducing the current density can significantly lower the winding operating temperature, thereby significantly slowing down the rate of thermal aging.
At the same time, it is essential to strictly distinguish between apparent power and active power. For rectifier loads and inductive loads, the capacity must be calculated based on the power factor. Directly using wattage instead of volt-ampere is not allowed to avoid hidden long-term overloading. Firmly resist low-quality products with falsely labeled capacity, reduced copper wire, and small iron cores. Many purchases only compare unit prices and choose transformers with reduced wire diameters and smaller iron cores. They can barely carry the load temporarily, but after running continuously for two years, they will overheat and be damaged extensively. The overall replacement cost is much higher than that of genuine products with adequate materials and specifications.
In addition, frequency matching must be strictly adhered to. For equipment operating on a 50Hz grid for a long time, transformers designed for 60Hz must not be used; otherwise, the iron core will be magnetically saturated for a long time, the no-load loss will remain high, and continuous heating will quickly deplete the insulation lifespan.
At the same time, it is essential to strictly distinguish between apparent power and active power. For rectifier loads and inductive loads, the capacity must be calculated based on the power factor. Directly using wattage instead of volt-ampere is not allowed to avoid hidden long-term overloading. Firmly resist low-quality products with falsely labeled capacity, reduced copper wire, and small iron cores. Many purchases only compare unit prices and choose transformers with reduced wire diameters and smaller iron cores. They can barely carry the load temporarily, but after running continuously for two years, they will overheat and be damaged extensively. The overall replacement cost is much higher than that of genuine products with adequate materials and specifications.
In addition, frequency matching must be strictly adhered to. For equipment operating on a 50Hz grid for a long time, transformers designed for 60Hz must not be used; otherwise, the iron core will be magnetically saturated for a long time, the no-load loss will remain high, and continuous heating will quickly deplete the insulation lifespan.
- Upgrade material grades and enhance the foundation of high-temperature resistance and anti-aging capabilities
The insulation grade directly determines the service limit of the transformer. For products that operate continuously around the clock, the conventional B-grade insulation configuration must be abandoned.
1. Upgrade of insulation grade: Most civilian transformers use B-grade insulation, and the long-term allowable operating temperature is only 80℃. Continuous operation models are uniformly upgraded to F-grade insulation, with a long-term temperature resistance of 105℃; for sealed equipment without ventilation, high-grade H-grade heat-resistant materials are directly selected, with a temperature resistance of up to 180℃. The insulation paper for high-temperature resistance, high-temperature enamel-coated wire, and high-temperature curing insulating paint are all upgraded in a coordinated manner, significantly delaying the thermal decomposition rate of high-molecular materials.
1. Upgrade of insulation grade: Most civilian transformers use B-grade insulation, and the long-term allowable operating temperature is only 80℃. Continuous operation models are uniformly upgraded to F-grade insulation, with a long-term temperature resistance of 105℃; for sealed equipment without ventilation, high-grade H-grade heat-resistant materials are directly selected, with a temperature resistance of up to 180℃. The insulation paper for high-temperature resistance, high-temperature enamel-coated wire, and high-temperature curing insulating paint are all upgraded in a coordinated manner, significantly delaying the thermal decomposition rate of high-molecular materials.
2. Select high-quality pure copper enamel-coated wire for the winding: Copper-aluminum wire has a high resistivity and generates a large amount of heat during continuous operation, and must not be used in 24-hour non-stop operation conditions. The winding must use high-purity purple copper high-temperature-resistant enamel-coated wire, and the wire diameter should be appropriately enlarged to reduce the current density, keeping the copper loss at the lowest level. The lower the wire temperature, the slower the insulation aging.
3. Select high-conductivity and low-loss oriented silicon steel sheets for the core: High-quality silicon steel sheets have lower hysteresis loss and eddy current loss, and generate less no-load heat. Low-quality recycled silicon steel sheets have high iron loss and generate continuous heat when powered on, even without a load, and the body remains in a high-temperature state for a long time. Continuous operation models must use brand-new genuine silicon steel sheets, strictly control the iron loss indicators, and keep the no-load temperature rise to the lowest level.
- Strengthen production processes and solidify the windings to prevent vibration-induced wear
Loose coils and wire friction are significant causes of chronic inter-turn short circuits. Under continuous power supply, the electromagnetic force acts repeatedly, causing the loose windings to continuously generate minor vibrations. To prevent wear, two key production processes must be implemented.
First, the winding process is neat and compact. The wires are neatly arranged, and there is no cross-interference or squeezing between layers, which prevents the wires from colliding and causing damage to the paint film. The tension of the windings is uniform, and there is no local loosening.
Second, perform vacuum pressure impregnation. Ordinary surface painting can only seal the exterior. The coil has internal cavities, and when heated, air expands continuously, accelerating the insulation aging process. After vacuum impregnation treatment, the insulating paint fills all the gaps in the coil, and after drying and curing, the iron core and the coil form a solid whole. The wires are completely wrapped in resin and will not experience relative vibration and friction, which not only reduces noise but also prevents moisture and dust from entering. The insulation stability is improved by several times.
The root of the leads is reinforced and insulated wrapped to prevent the leads from breaking at the root due to long-term power-on vibration and insulation cracking. The iron core is fully compressed, and clamping fasteners are added to reduce the additional heat generated by the vibration of the silicon steel sheets.
- Optimize the heat dissipation structure to lower the operating temperature
Temperature is the greatest enemy of lifespan. By ensuring proper heat dissipation, the lifespan can be directly doubled.
1. Prioritize retaining natural ventilation space. The transformer should not be placed closely against the metal casing. Leave sufficient air convection gaps around it to utilize natural convection to remove heat. The sealed electrical control box must have ventilation louvers, and in necessary cases, add small cooling fans to form an airflow circulation to avoid heat accumulation.
2. Install an insulating and shock-absorbing base at the bottom of the transformer. Do not directly attach it to the iron plate to reduce heat conduction to the box and also isolate vibrations.
3. For high-power continuous operation models, add metal heat dissipation plates to expand the heat dissipation area and quickly disperse the core heat outward. Strictly control the steady-state temperature rise. After continuous operation at full load for 3 hours, the shell temperature should not exceed 75℃. The lower the temperature, the slower the insulation aging.
1. Prioritize retaining natural ventilation space. The transformer should not be placed closely against the metal casing. Leave sufficient air convection gaps around it to utilize natural convection to remove heat. The sealed electrical control box must have ventilation louvers, and in necessary cases, add small cooling fans to form an airflow circulation to avoid heat accumulation.
2. Install an insulating and shock-absorbing base at the bottom of the transformer. Do not directly attach it to the iron plate to reduce heat conduction to the box and also isolate vibrations.
3. For high-power continuous operation models, add metal heat dissipation plates to expand the heat dissipation area and quickly disperse the core heat outward. Strictly control the steady-state temperature rise. After continuous operation at full load for 3 hours, the shell temperature should not exceed 75℃. The lower the temperature, the slower the insulation aging.
- Enhance front-end circuit protection to withstand grid surges
Continuous power supply equipment is always connected to the power grid. Surge, voltage spikes, and harmonics can always impact the windings, damaging the insulation. At the input end, add voltage-sensitive resistors, fuses, and common-mode filter inductors to suppress instantaneous high voltage surges from the grid and prevent the windings from being damaged by instantaneous overvoltage due to breakdown of the insulating layer. For rectifier DC loads, add a buffer absorption circuit in the circuit to reduce the magnetic deflection caused by the DC component and prevent the core from operating abnormally due to long-term semi-saturation and abnormal heating. In conditions permitted, add a voltage stabilizing device to stabilize the input voltage within the rated range, avoiding excessive flux and increased iron loss caused by excessively high voltage.
- Daily preventive maintenance to reduce environmental erosion
For equipment operating 24/7, it is impossible to stop the operation for cooling. Therefore, environmental control must be strengthened:
1. Install dust-proof seals on the electrical control boxes and regularly clean the dust inside the boxes to prevent dust from accumulating on the coil surface and forming a heat-insulating layer, which prevents heat from dissipating.
2. Install desiccants or small heaters in damp workshops or outdoor control boxes to eliminate condensation inside the boxes and prevent the windings from getting damp, which leads to a gradual decline in insulation.
3. Conduct insulation resistance tests on the windings once every six months using an ohmmeter to track changes in insulation values. If the insulation resistance slowly decreases, carry out drying and painting treatment in advance instead of waiting until an electrical leakage trip occurs for repair.
4. Regularly inspect the connection terminals to prevent oxidation and false connections at the terminals, which may cause additional heating and prevent high temperatures from being conducted to the ends of the windings.
1. Install dust-proof seals on the electrical control boxes and regularly clean the dust inside the boxes to prevent dust from accumulating on the coil surface and forming a heat-insulating layer, which prevents heat from dissipating.
2. Install desiccants or small heaters in damp workshops or outdoor control boxes to eliminate condensation inside the boxes and prevent the windings from getting damp, which leads to a gradual decline in insulation.
3. Conduct insulation resistance tests on the windings once every six months using an ohmmeter to track changes in insulation values. If the insulation resistance slowly decreases, carry out drying and painting treatment in advance instead of waiting until an electrical leakage trip occurs for repair.
4. Regularly inspect the connection terminals to prevent oxidation and false connections at the terminals, which may cause additional heating and prevent high temperatures from being conducted to the ends of the windings.
The low-frequency transformers that operate continuously for 24 hours have their lifespan shortcomings mainly concentrated in two issues: insulation thermal aging and insulation damage. To significantly extend the service life, it is not enough to rely solely on product quality; a complete protection system needs to be established:
First, reserve a 30% to 40% power margin to avoid long-term full-load operation, thereby reducing the working temperature from the source;
Second, comprehensively upgrade F-class and H-class high-temperature-resistant insulating materials, combined with low-loss silicon steel sheets and sufficient pure copper wires, to reduce losses and the speed of thermal aging;
Third, strictly implement the vacuum impregnation process, solidify the windings, and eliminate the vibration and wear of the wires;
Fourth, optimize the ventilation and heat dissipation structure to control the steady-state temperature rise;
Fifth, add grid surge protection to reduce the damage to insulation caused by voltage shocks;
Sixth, regularly clean and dehumidify to continuously maintain the insulation of the windings in a good state.
For every 10-degree Celsius reduction in operating temperature, the insulation aging rate can be halved, and the overall service life of the equipment can be extended by more than double. By controlling the temperature rise during continuous operation properly, and by doing a good job in material selection, process, heat dissipation and circuit protection, a power frequency transformer can operate stably and reliably for over ten years, significantly reducing the overall costs associated with equipment replacement and downtime maintenance, and truly achieving zero-fault long-term uninterrupted power supply.
Shenzhen Cxwon Technology Co., Ltd. has been specializing in manufacturing low-frequency transformers, high-frequency transformers, network transformers, custom coils, inductors and other products for over a decade. It has its own factory, R&D team, and can quickly respond to various demands of customers. We welcome communication and exchanges among all industries!
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