I. Core Definitions and Resistance Value Ranges
Low-Resistance Cable Fault (Low-Resistance Fault):
Definition: The insulation resistance at the fault point drops to a very low level, or even becomes a direct short circuit with the conductor. Under DC high voltage, voltage cannot be established at the fault point; it breaks down instantly, forming a low-resistance path.
Resistance Range: Typically refers to a resistance to ground (or between phases) of less than 100-200 Ohms (a conventional industry value, not an absolute standard; sometimes the boundary is set at 10 times the cable's characteristic impedance).
High-Resistance Cable Fault (High-Resistance Fault):
Definition: The insulation resistance at the fault point has decreased but remains relatively high. When DC high voltage is applied, the fault point can withstand a certain voltage until the voltage rises high enough to cause breakdown.
Resistance Range: Typically refers to a resistance to ground (or between phases) greater than 200-300 Ohms, and can even reach Megaohm levels. High-resistance faults are more common, accounting for about 80-90% of all cable faults.
II. Comparison Table of Main Differences
| Feature Dimension | Low-Resistance Cable Fault | High-Resistance Cable Fault |
|---|---|---|
| Core Definition | Very low fault point resistance, DC high voltage cannot be established | High fault point resistance, DC high voltage can be established and eventually causes breakdown |
| Resistance Value | Low (Usually < 100-200 Ω) | High (Usually > 200-300 Ω, can be up to MΩ level) |
| Common Causes | Mechanical damage, short-circuit burn-through, water ingress causing short circuit at joints | Dampness, aging, treeing, partial discharge, local defects, poor joint craftsmanship |
| Detection Difficulty | Relatively Simple | Relatively Complex |
| Preferred Detection Method | Low-Voltage Pulse Method, Bridge Method | High-Voltage Flashover Method (Direct Flash/Impulse Flash Method) |
| Detection Principle | Send a low-voltage pulse into the cable and locate by observing the open circuit/short circuit reflection waveform | Use high-voltage equipment to force the high-resistance fault point to break down and discharge, and locate by recording the waveform of the discharge pulse |
| Waveform Characteristics | Clear waveform, easy to identify | Requires experienced interpretation, waveform can be complex (e.g., discharge delay) |
| High Voltage Required? | Usually not (except for the Bridge Method) | Absolutely necessary (HV generator, pulse capacitor, etc.) |
| Fault Point Phenomenon | May be a permanent short circuit or low-resistance path | May be a flashover type (breaks down at high voltage, recovers at low voltage) or a fixed high resistance |