High-voltage cables, as the "arteries" of power systems, their stable operation is crucial. In the event of a fault, rapid and accurate location and diagnosis are key to restoring power supply. The following is a professional high-voltage cable fault detection process:
Safety First, Thorough Preparation
Strictly implement safety regulations: Confirm that the cable is completely de-energized and reliably grounded, post warning signs, implement the work permit and operation permit system. Operators must wear qualified protective equipment, and designated personnel shall provide full-time supervision.
Information collection and analysis: Review in detail cable route drawings, historical test data, laying methods (direct burial, pipe jacking, tunnel, etc.), service life, environmental conditions, and fault phenomena (trip type, protection action information, etc.), to preliminarily judge the possible fault nature (low-resistance, high-resistance, flashover, or open-circuit).
Preliminary Diagnosis and Fault Classification
Insulation resistance test: Use a high-voltage megohmmeter (2500V or 5000V) to measure the insulation resistance between each phase conductor and ground as well as between phases, preliminarily determining whether there is severe insulation deterioration or penetrating faults.
Continuity test: Use a multimeter or low-resistance tester to check the integrity of each phase conductor of the cable and confirm whether there is an open-circuit fault.
Preliminary judgment of fault nature: Combining the insulation resistance value and multimeter measurement results, distinguish between low-resistance faults (usually less than several hundred ohms), high-resistance faults (several hundred ohms to megaohm level), or flashover faults (breakdown during withstand voltage test).
Core Methods for Precise Location
- Low-Voltage Pulse Reflection Method (for low-resistance and open-circuit faults)
Principle: Inject low-voltage pulses into the cable, which generate reflected waves when encountering fault points (impedance discontinuities).
Application: Precisely measure the total length of the cable and locate low-resistance grounding, short-circuit, and open-circuit faults. It is particularly effective in solving open-circuit problems.
- High-Voltage Bridge Method (for low-resistance faults)
Principle: Utilize the Wheatstone bridge balance principle to calculate the fault distance by comparing the loop resistance ratio between the faulty phase and the intact phase.
Application: High positioning accuracy and strong anti-interference ability for stable low-resistance grounding or short-circuit faults.
- Secondary Pulse Method (for high-resistance and flashover faults)
Principle: It is the current mainstream advanced method. First, apply high-voltage pulses to breakdown the high-resistance fault point into a transient low-resistance state, and simultaneously transmit low-voltage measurement pulses to capture clear reflected waveforms at the moment of breakdown.
Application: Especially suitable for high-resistance leakage faults and flashover faults, with high positioning accuracy and waveforms easy to interpret.
- Acoustic-Magnetic Synchronous Positioning Method (precise pinpointing of fault points)
Principle: Apply high-voltage pulses to make the fault point discharge periodically. Use a probe to synchronously receive acoustic waves (vibrations) and electromagnetic signals generated by the discharge. When the time difference between acoustic and magnetic signals is minimal (or the instrument indicates synchronization), the fault point is directly below the probe.
Application: An indispensable step for final precise pinpointing, especially for directly buried cables. The environment needs to be relatively quiet, and the detection depth can usually reach several meters.
Post-Location Processing and Verification
After precise pinpointing, carefully excavate to expose the cable under supervision, and visually confirm the fault point (such as presence of ablation marks, external damage, etc.).
After repair, DC withstand voltage test with leakage current measurement or AC withstand voltage test must be conducted in accordance with regulations to ensure repair quality and the overall insulation strength of the cable.
Prevention is better than emergency repair: Regular preventive tests such as insulation resistance, DC withstand voltage/leakage current, and even partial discharge tests are core means to detect potential defects and avoid faults. Establishing a sound detection and maintenance system is key to ensuring the long-term healthy operation of cables. For related preventive test equipment and services, please contact sales@celestep.com.
Professional high-voltage cable fault detection is a high integration of safety regulations, solid theories, rich experience, and advanced instruments. Only by following scientific procedures and proficiently applying various methods can we quickly locate the "lesions" in the complex power network, providing a solid guarantee for the robust and efficient operation of the power grid.
