The Evolution of Electrical Testing
In the dynamic landscape of electrical power systems, the transition from oil-paper insulated power cables to cross-linked polyethylene (XLPE) insulated cables marks a significant technological advancement. However, the testing methodologies for these modern cables have presented unique challenges, specifically in the realm of withstand voltage testing prior to commissioning.
Challenges with Traditional DC Testing
Traditionally, Direct Current (DC) withstand tests have been the norm due to the large capacitance of these cables and limitations of test equipment. However, recent studies by numerous international and domestic research institutions have revealed that DC testing can potentially harm XLPE cables. It’s believed that the XLPE structure can store unipolar residual charges. If these charges aren’t effectively discharged post-DC testing, the combination of these residual charges and AC operational voltages can lead to cable breakdowns upon commissioning.
The Risks of DC Testing
Research indicates that during DC withstand testing of cross-linked polyethylene cables, the actual electric field strength within the insulation can be up to 11 times higher than the cable’s normal working electric field strength due to space charge effects. Even if cables pass the DC test without breakdown, serious insulation damage can occur, making these cables vulnerable to future failures.
The Shift to Non-DC Testing Methods
Consequently, there has been a growing interest in non-DC methods for withstand voltage testing of cross-linked cables. Similarly, the AC withstand voltage testing of large transformers and generators in hydro and thermal power plants is routinely conducted.
Series Resonance Test Systems: A Superior Alternative
Our company specializes in series resonant frequency automatic resonance test systems, primarily for 10kV, 35kV, and 110kV cross-linked rubber and plastic power cables, as well as 66kV, 110kV, and 220kV composite appliances (GIS), and the AC frequency withstand testing of large generators or power transformers.
The Principle of Series Resonance Testing
The fundamental principle involves using an adjustable (30–300Hz) series resonant test device in resonance with the test object’s capacitance to generate AC test voltage. Given the large capacitance of cables, traditional frequency test transformers are impractical; hence, series resonance AC withstand voltage test equipment is preferred. This method significantly reduces input power capacity, weight, and facilitates ease of use and transport.
Advantages of Series Resonance Power Supply in Power Systems
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- Reduced Power Capacity Requirements: The SXBP series resonant test device uses resonance between the reactance of the reactor and the test object’s capacitance, requiring only the active power component in the system.
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- Compact and Lightweight Equipment: Eliminates the need for bulky high-power transformers and regulators.
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- Improved Output Voltage Waveform: The resonant power supply acts as a filter circuit, yielding a better sinusoidal waveform and effectively preventing harmonic peak-induced misbreakdowns.
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- Prevention of High Short-Circuit Current: In a resonant state, if the test object’s insulation weak point is breached, the circuit immediately detunes, dropping the loop current to 1/Q of the normal test current.
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- Absence of Recovery Overvoltage: Upon breakdown, the loss of resonance conditions causes the high voltage to disappear immediately, extinguishing the arc and preventing any recovery overvoltage.
Applications of Series Resonance
This method is widely used for acceptance and preventive testing in industries like power, metallurgy, petroleum, and chemicals. It’s suitable for large capacity, high-voltage capacitive test objects, and widely applicable for XLPE power cable AC withstand voltage tests across various voltage levels, GIS AC withstand tests, and frequency withstand tests of large generator sets and power transformers.
Product Technical Parameters and Standard Configurations
The technical specifications include a working temperature range of -10 to 45℃, humidity ≤90%, altitude ≤1000m, rated power voltage: AC380V±10%, 50/60Hz, frequency power capacity of 10-500kW, rated output voltage of 0-1000kV, and working frequency range of 30-300Hz. The resonance voltage waveform is a sine wave with a waveform distortion rate of ≤1%, and the system quality factor under maximum load is ≥20. The system features IGBT, overvoltage, overcurrent, flashover automatic protection, etc.
The adoption of series resonant frequency automatic resonance test systems represents a significant advancement in electrical testing, offering enhanced safety, efficiency, and accuracy. As the electrical industry continues to evolve, these systems stand at the forefront of ensuring the integrity and reliability of modern electrical infrastructures.
