Introduction
In summer thunderstorm seasons, news about “transformers being damaged by lightning strikes leading to power outages” is not uncommon. Many people may wonder: Why are these tall transformers so “vulnerable”? Are they really easy to be “struck and damaged” in thunderstorm weather? Actually, the risk of transformer damage in thunderstorms is not simply a matter of being “directly hit by lightning”, but involves complex lightning physical effects and power system protection logic. This article will deeply analyze the threats of thunderstorm weather to transformers and reveal the “hidden tips” of lightning protection designs crafted by power engineers for transformers.
Thunderstorm Threats to Transformers in Thunderstorm Weather
The threats of thunderstorm weather to transformers mainly come from two types of lightning effects: direct lightning strikes and induced lightning, with distinct damage paths and mechanisms.
A direct lightning strike refers to lightning directly hitting the transformer itself or its connected lines. The core components of a transformer, such as the iron core and windings, are made of metal materials and operate at high voltages (10kV and above) for a long time. Once hit by a direct lightning strike, the lightning voltage of hundreds of thousands or even millions of volts will instantly break down the insulation layer, resulting in winding short circuits and iron core burnout, which is often devastating. However, the probability of a transformer being directly hit by lightning is not high, as transmission lines are usually equipped with external protection facilities like lightning rods and overhead ground wires, forming a “lightning protection barrier”.
In contrast, the threat of induced lightning is more hidden and common. When lightning strikes the ground or objects near the lines, the strong lightning electromagnetic field will induce overvoltages of thousands of volts on the transmission lines, and these overvoltages will propagate along the lines to the transformer. The insulation systems inside the transformer (such as oil – paper insulation and bushing insulation) are extremely sensitive to voltage fluctuations. The overvoltages generated by induced lightning may cause partial breakdown of the insulation, leading to faults such as inter – turn short circuits and multi – point grounding of the iron core. Statistics show that over 70% of transformer lightning damage faults in power systems are caused by induced lightning.
Core Tips for Transformer Lightning Protection Design
Transformer lightning protection design is a systematic project that needs to integrate the external environment, equipment characteristics, and operation requirements to build a full – chain protection system of “prevention – interception – dredging – monitoring”.
(1) External Lightning Protection: Building the First “Physical Barrier”
The core of external lightning protection is to reduce the probability of lightning directly acting on transformers and associated equipment. In substations or distribution stations, a joint protection scheme is usually adopted: lightning rods and overhead ground wires form a “spatial protection network”, and their protection range should cover key equipment such as transformers and circuit breakers. According to the rolling ball method, the height of lightning rods should ensure that the protection angle does not exceed 45° to effectively intercept direct lightning strikes. For overhead lines connected to transformers, overhead ground wires are installed at both ends of the lines, and an “incoming line protection section” is set within 50 meters of the transformer. By increasing the number of insulator pieces and installing line arresters, the intensity of lightning incoming waves is reduced.
It should be noted that external lightning protection needs to avoid “protection blind spots”. Prominent parts of the transformer, such as bushings and radiators, are prone to lightning breakdown. Therefore, the installation position of lightning rods above them must be accurately calculated to ensure no protection dead corners. In thunderstorm – prone areas or mountainous regions, an “independent lightning rod + isolated grounding” design can also be used, where the grounding system of the lightning rod is set separately from the transformer grounding grid (with a spacing of not less than 3 meters) to prevent ground potential counterattack generated when the lightning rod is struck by lightning from affecting the transformer.
(2) Internal Lightning Protection: Accurately Intercepting “Voltage Shock Waves”
Even if external lightning protection intercepts most of the lightning, some induced lightning or residual overvoltages may still invade the transformer. At this time, internal lightning protection devices play a key role. Zinc oxide arresters are the “first line of defense” for transformers. They are installed in parallel at the high – voltage side outlet of the transformer. In normal operation, they are in a high – resistance state. When the lightning overvoltage exceeds the threshold, the arrester quickly breaks down and conducts, limiting the overvoltage within the insulation tolerance range and diverting the lightning current to the ground. High – quality zinc oxide arresters need to have the characteristics of low residual voltage and large current – carrying capacity, and the residual voltage of arresters supporting 10kV transformers should be controlled below 45kV.
In addition to arresters, insulation coordination design is also important. The insulation systems inside the transformer (such as oil – paper insulation and bushing insulation) need to match the protection characteristics of the arresters to form “step – by – step protection”. For example, the impact resistance of the winding is improved by adjusting the winding process (such as using hesitant windings), and anti – pollution porcelain sleeves or composite sleeves are selected for bushing selection to enhance the surface flashover resistance. For 35kV and above transformers, neutral point arresters are also installed at the neutral point to prevent lightning overvoltage from damaging the neutral point insulation.
Grounding System: Creating a “Safe Dredging Channel”
The grounding system is the “final destination” of lightning energy, and its performance directly determines the lightning protection effect. The grounding grid of the transformer needs to adopt a combination of horizontal grounding electrodes and vertical grounding poles. The horizontal grounding electrodes are usually made of 40mm × 4mm galvanized flat steel, laid in a mesh pattern, and the vertical grounding poles are made of galvanized steel pipes with a diameter of 50mm and a length of 2.5 meters, arranged at intervals of 5 – 8 meters. The grounding resistance of the grounding grid is a core indicator. According to specifications, the transformer grounding resistance should be ≤ 4Ω. In areas with high soil resistivity (such as mountainous areas and deserts), measures such as soil replacement, resistance – reducing agents, and deep well grounding are needed to reduce the resistance, ensuring that the lightning current can dissipate quickly and avoiding secondary faults caused by increased ground potential.
The “voltage equalization design” of the grounding system is also crucial. The potential difference between various points on the grounding grid should be controlled within a safe range. By adding voltage equalizing belts and shortening the spacing of grounding electrodes, the harm of excessive step voltage and contact voltage to equipment and personnel is avoided. In addition, non – live metal parts of the transformer, such as the shell, iron core, and clamp, must be reliably grounded to form “equipotential bonding” to prevent floating potential generated by lightning induction from breaking down the insulation.
Intelligent Monitoring: Realizing “Early Fault Detection”
With the development of intelligence in power systems, lightning protection design has upgraded from “passive protection” to “active early warning”. Modern transformers are generally equipped with online monitoring systems, which collect real – time operation data of lightning protection devices by installing zinc oxide arrester leakage current monitors, winding temperature sensors, partial discharge detectors, and other equipment. When the arrester leakage current increases abnormally or the winding insulation resistance decreases, the system will automatically send out an early warning signal, and operation and maintenance personnel can timely troubleshoot hidden dangers.
In thunderstorm – prone areas, the lightning location system can also be linked with the transformer state evaluation model. By analyzing data such as the time, location, and intensity of lightning activities, combined with the historical fault records of the transformer, the risk level of the equipment being damaged by lightning is predicted, and preventive measures such as load adjustment and temporary shutdown are taken in advance. After a power grid company applied this technology in high – risk thunderstorm areas, the repair time for transformer lightning damage faults was shortened by 40%, and the power supply reliability was significantly improved.
Lightning Impulse Test: Verifying the Effectiveness of Lightning Protection Design
The Lightning Impulse Test is a crucial link to verify whether the transformer can withstand lightning overvoltage impacts and ensure the reliability of the lightning protection design. Its core purpose is to simulate the lightning impulse voltage that may occur in actual operation on the transformer in a laboratory environment, test the insulation performance and structural stability of the transformer under extreme voltage conditions, and provide a reliable basis for the optimization of the lightning protection design.
There are two main types of Lightning Impulse Tests: full – wave impulse test and chopped – wave impulse test. The full – wave impulse test simulates the complete process of lightning overvoltage propagating along the line, applying a standard lightning impulse voltage waveform (1.2/50μs) to the transformer winding. This test can effectively detect whether there are insulation defects such as weak points in the winding that are prone to breakdown under lightning overvoltage. The chopped – wave impulse test is to cut off the lightning impulse voltage wave in advance (usually cutting off the wave tail within 2 – 5μs after the wave front), which is more severe than the full – wave test. It is mainly used to test the insulation strength of the transformer’s oil – paper insulation and bushing under the action of steep – front overvoltage, and verify whether the insulation can still maintain its performance when the lightning overvoltage changes suddenly.
During the test, key indicators such as the breakdown voltage value, partial discharge amount, and insulation resistance change of the transformer are monitored. If the transformer can withstand the specified number of impulse voltages without breakdown, flashover, or significant changes in insulation parameters, it indicates that its insulation system meets the lightning protection requirements. Otherwise, it is necessary to find out the causes of insulation weaknesses, such as improper winding arrangement or unqualified insulation materials, and optimize the design.
The Lightning Impulse Test is not only a necessary test before the transformer leaves the factory but also an important means for operation and maintenance units to evaluate the aging state of the transformer’s insulation during its service life. By comparing the test data of the same transformer in different periods, it can be judged whether the insulation performance of the transformer has degraded, so as to take maintenance or replacement measures in advance and avoid lightning damage faults caused by insulation aging.
Hidden Details and Maintenance Points of Lightning Protection Design
The effectiveness of lightning protection design not only depends on the initial scheme but also needs to pay attention to detail optimization and daily maintenance. During transformer installation, high – voltage side cable incoming lines need to be laid through pipes, and both ends of the metal pipe should be reliably grounded to form an “electromagnetic shielding layer” to reduce the overvoltage generated by induced lightning in the cable. For oil immersed transformers, the silica gel in the breather should be kept dry to avoid reducing insulation performance after moisture absorption; for dry type transformers, the surface dust should be cleaned regularly to prevent surface flashover caused by dirt accumulation.
The maintenance of the grounding grid is a key link that is easily ignored. Soil corrosion and settlement may cause grounding electrode fracture or grounding resistance increase. Therefore, the grounding resistance should be measured every year, and a grounding grid conduction test should be carried out every 3 years to ensure reliable connection of grounding electrodes. Arresters need to undergo DC reference voltage tests and leakage current tests every 1 – 2 years, and aging or performance – degraded arresters should be replaced in time to prevent them from failing in thunderstorm weather.
Conclusion
The risk of transformers being “struck and damaged” in thunderstorm weather is not uncontrollable. Through scientific lightning protection design and refined operation and maintenance, the probability of lightning damage faults can be reduced by more than 90%. From the accurate layout of lightning rods to the millisecond response of zinc oxide arresters, from the low – resistance dredging of the grounding grid to the real – time monitoring of intelligent systems, and then to the strict verification of the Lightning Impulse Test, every lightning protection skill reflects the engineering wisdom of “active defense”. With the application of new materials (such as nano – composite insulation materials) and new technologies (such as artificial intelligence early warning), the transformer lightning protection system will be more reliable, providing a “lightning protection umbrella” for the safe and stable operation of the power system.
