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Views: 0 Author: Site Editor Publish Time: 2025-12-04 Origin: Site
Lightning Impulse Test System in Transformer Manufacturing Plants
The Lightning Impulse Test System is a core high-voltage testing facility in a transformer factory. Its primary function is to simulate and verify the reliability of a transformer's insulation system when subjected to extreme transient overvoltages—like those from lightning strikes—that it may encounter during operation.
In simple terms, it uses artificially generated "man-made lightning" to strike the transformer before it leaves the factory, testing whether its insulation can "withstand" the test of a real lightning strike.
Transformers in the grid face two main types of transient overvoltage threats, which the impulse test system is designed to simulate:
Lightning Impulse: When transmission lines are struck directly or indirectly by lightning, an extremely high-voltage, short-duration (microsecond-level) impulse wave propagates along the line into the transformer.
Switching Impulse: Operations within a substation, such as circuit breaker switching or fault clearing, can also generate overvoltages with a slightly longer duration (millisecond-level).
The peak value of these impulse voltages can be several times or even more than ten times the transformer's rated operating voltage. If there are weaknesses in the transformer's insulation design or manufacturing (between windings, from windings to ground, or inter-turn), a breakdown may occur under such impulses. This could leave a latent defect in the equipment before it even enters service, potentially causing complete failure during a thunderstorm.
Core Purpose: To proactively identify and eliminate insulation defects within the factory, ensuring the transformer can withstand voltage surges from nature and the power grid throughout its decades-long service life. It is a critical quality control checkpoint for guaranteeing long-term operational reliability.
Its operation can be divided into three main phases:
Energy Storage Phase: The system contains a large-capacity impulse capacitor bank. Before the test, a DC high-voltage source slowly charges these capacitors over seconds, storing immense energy (which can reach hundreds of kilojoules).
Instantaneous Release Phase (Simulating "Lightning"): When the capacitor voltage reaches the preset value, a computer-controlled trigger switch (e.g., a sphere gap) closes within microseconds. The stored energy is released abruptly through a wave-shaping resistor and inductor network, generating an impulse voltage wave that conforms to international standards (e.g., IEC 60076-4), simulating a real lightning impulse wave.
Application and Evaluation Phase: This standardized impulse voltage wave is applied to the designated winding of the transformer under test (with other windings grounded). Simultaneously, high-voltage probes, dividers, and digital recorders precisely capture and record the applied voltage waveform and the transformer's current response waveform. Engineers analyze whether the waveform is distorted (e.g., chopped, oscillating) to determine the integrity of the insulation.
Two main standard tests are performed:
Full Lightning Impulse Withstand Test: A standard full lightning impulse wave is applied (typically a 1.2/50 µs wave, meaning a wavefront time of 1.2 µs and a time to half-value on the tail of 50 µs). This is the fundamental test.
Chopped Lightning Impulse Withstand Test: Simulates a more severe condition—when an insulator near the transformer (e.g., a bushing) flashes over under lightning, causing a sudden voltage collapse. The test involves artificially chopping the voltage wave approximately 2-6 µs after the peak, testing the insulation's ability to withstand this abrupt voltage change.
Key Pass/Fail Judgment Criteria (strict adherence to standards is required):
Waveform Comparison Method: This is the most critical method. First, a "reference waveform" is recorded at a reduced voltage level (e.g., 50%-75% of the rated impulse voltage). Then, three consecutive full-voltage impulses are applied. The waveforms from the full-voltage tests are strictly overlaid and compared on a computer with the reference waveform.
Pass Judgment: If the waveforms after the full-voltage impulses substantially overlap with the reference waveform in their main parts (wavefront, wavetail) with no significant distortion, the insulation is considered to have passed. If the waveform shows obvious oscillation, amplitude change, or chopping, it indicates that partial discharge or breakdown may have occurred within the insulation, requiring internal inspection.
"Final Gatekeeper" for Quality: Together with the "Induced Voltage Withstand Test," it forms the two most stringent lines of defense for testing transformer insulation performance, typically conducted after all routine tests.
"Touchstone" for Design and Craftsmanship: Test results directly verify whether the transformer's insulation structure design, material selection, and manufacturing processes (e.g., winding tightness, insulation wrapping quality) are excellent.
High-Value, High-Requirement Equipment: The impulse test system itself is expensive, occupies significant space, and requires highly specialized technicians and strict safety protocols for operation and maintenance (due to the ultra-high voltages and energies involved).
Symbol of Qualification and Capability: Possessing complete impulse testing capability is a crucial indicator that a transformer manufacturing plant has the qualification and technical prowess to produce high-voltage class products (typically 110kV and above). It is also a key qualification for securing orders from national grid companies and large-scale projects.
In summary, the Lightning Impulse Test System acts as the transformer factory's "lightning simulator" and "insulation health examination center." It ensures, in the most severe manner, that every transformer leaving the factory has a "strong heart" capable of withstanding natural lightning.
