As a supplier of Extra High Voltage (EHV) transformers, I have witnessed firsthand the crucial role these electrical giants play in power systems. However, like any complex electrical equipment, EHV transformers are not without their challenges, and one of the most significant issues we often encounter is corona discharge.
Understanding Corona Discharge
Corona discharge is a type of electrical discharge that occurs when the electric field strength around a conductor exceeds the breakdown strength of the surrounding medium, typically air. In EHV transformers, this phenomenon can happen due to several factors. Firstly, the high voltage levels involved in EHV systems create strong electric fields. When the electric field intensity at the surface of a conductor, such as a high - voltage winding or a bushing, reaches a critical value, the air molecules around it become ionized.
The ionization process starts with the detachment of electrons from air molecules, creating a plasma region near the conductor. This plasma region can conduct electricity to a certain extent, and it emits visible light, often appearing as a faint glow around the conductor. The corona discharge can be classified into different types, such as positive and negative corona, depending on the polarity of the voltage on the conductor.
Causes of Corona Discharge in EHV Transformers
- High Voltage Levels
- EHV transformers operate at extremely high voltages, often in the range of hundreds of kilovolts or even higher. These high voltage levels can easily generate strong electric fields that exceed the breakdown strength of air. For example, in a Power Transformer in Power Plant, the high - tension windings are designed to handle large amounts of electrical energy at high voltages. If the insulation design is not optimized, the electric field around the windings can become concentrated, leading to corona discharge.
- Sharp Edges and Protrusions
- Any sharp edges or protrusions on the conductors or other components of the transformer can cause a local increase in the electric field strength. In the manufacturing process, if the conductors are not properly smoothed or if there are burrs on the metal parts, the electric field will be concentrated at these points. This local increase in the electric field can trigger corona discharge even at relatively lower overall voltage levels.
- Contaminants and Moisture
- Contaminants on the surface of the transformer's insulation or conductors can also contribute to corona discharge. Dust, dirt, and other particles can change the electrical properties of the surrounding air and create areas of higher electric field intensity. Moisture is particularly problematic, as it can lower the breakdown strength of air. When the air around the transformer is humid, the likelihood of corona discharge increases significantly.
Effects of Corona Discharge
- Power Loss
- Corona discharge is an inefficient process that consumes electrical energy. The energy dissipated in the form of heat, light, and sound during corona discharge represents a loss of power from the transformer. This power loss not only reduces the overall efficiency of the transformer but also increases the operating costs. In large - scale power systems, even a small amount of power loss in each transformer can add up to a significant figure over time.
- Insulation Degradation
- The ionized air in the corona discharge region contains reactive species such as free radicals and ozone. These reactive species can react with the insulation materials of the transformer, causing chemical degradation. Over time, the mechanical and electrical properties of the insulation can deteriorate, reducing its effectiveness in preventing electrical breakdown. This can lead to more serious insulation failures and potentially cause the transformer to malfunction.
- Electromagnetic Interference (EMI)
- Corona discharge generates electromagnetic waves in a wide frequency range. These electromagnetic waves can interfere with nearby communication systems and electronic devices. In a power substation, the EMI from corona discharge can disrupt the normal operation of control and monitoring equipment, leading to inaccurate readings and potentially dangerous situations.
Detection and Prevention of Corona Discharge
- Detection Methods
- There are several methods for detecting corona discharge in EHV transformers. One of the most common methods is visual inspection. Since corona discharge often produces a visible glow, trained technicians can use specialized cameras or binoculars to look for the presence of the glow during the night or in low - light conditions. Ultrasonic detectors can also be used to detect the high - frequency sound waves generated by corona discharge. Another method is the use of electrical measuring devices to detect the current and voltage changes associated with corona discharge.
- Prevention Techniques
- Design optimization is crucial in preventing corona discharge. Transformers should be designed with smooth conductors and rounded edges to reduce the concentration of electric fields. The insulation materials should be carefully selected and properly installed to ensure that they can withstand the high - voltage environment. For example, using high - quality insulation materials with good dielectric properties can improve the breakdown strength of the insulation system.
- Environmental control is also important. Transformers can be installed in enclosures or outdoor areas with proper ventilation and dust - proofing measures. In areas with high humidity, dehumidification equipment can be used to reduce the moisture content in the air around the transformer.
Examples of EHV Transformers and Their Corona Discharge Considerations
We offer a wide range of EHV transformers, such as the UL Certificate 35kV Liquid Filled Substation Power Transformer and Electric Power Station Transformer. These transformers are designed with the latest technology to minimize the risk of corona discharge.
For the 35kV Liquid Filled Substation Power Transformer, the liquid insulation provides better dielectric properties compared to air. This helps to reduce the likelihood of corona discharge even at higher voltage levels. The design of the windings and bushings is carefully optimized to ensure a uniform electric field distribution.
In the case of the Electric Power Station Transformer, which is typically used in large - scale power generation plants, the high - voltage components are subject to extremely high electric stresses. To prevent corona discharge, we use advanced insulation materials and manufacturing techniques. The transformer is also equipped with monitoring systems to detect any early signs of corona discharge, allowing for timely maintenance.
Conclusion
Corona discharge is a significant issue in EHV transformers, with far - reaching consequences for power system efficiency, reliability, and equipment lifespan. As a supplier of EHV transformers, we are committed to providing high - quality products that are designed to minimize the risk of corona discharge. Through continuous research and development, we strive to improve the design and manufacturing processes to ensure the optimal performance of our transformers.
If you are interested in our EHV transformers or have any questions regarding corona discharge or other technical issues, we welcome you to contact us for procurement discussions. Our team of experts is ready to provide you with detailed technical information and customized solutions to meet your specific needs.
References
- Grover, A. K. "Electrical Machine Design." New Age International, 2007.
- Blackburn, J. L. "Protective Relaying: Principles and Applications." Marcel Dekker, 1998.
- Westinghouse Electric Corporation. "Electrical Transmission and Distribution Reference Book." Westinghouse Electric Corporation, 1964.