10 Sep-2026

Power cables, as the primary carriers of electrical energy transmission, are widely used in urban distribution networks, industrial and mining enterprises, and rail transit systems. Because cables are typically buried underground or laid in cable trenches and trays, quickly and accurately locating a fault point during operation remains one of the most challenging tasks in field O&M.

The KD-212X cable fault tester, independently developed by Wuhan Kedia Zhongwei Electric Co., Ltd. (hereinafter referred to as "Kedia Zhongwei"), integrates three core functions—ranging, path tracing, and pinpointing—and can precisely determine fault locations without excavating the ground or damaging the cable outer sheath. This article systematically introduces the complete technical solution for cable fault testing, from fault causes and detection principles to field operation procedures.

I. Typical Classification of Cable Faults

Before conducting fault detection, the fault type must first be clarified. Based on differences in electrical characteristics at the fault point, faults are generally divided into three categories:

Open-circuit fault: One or more core wires of the cable are broken, but the insulation resistance between cores and between cores and ground remains within the normal range. Such faults are mostly caused by external construction damage or corrosion-induced disconnection at joints.

Low-resistance fault: A short-circuit channel forms between cable cores or between a core and ground, and the DC resistance at the fault point is lower than the characteristic impedance of the cable. Main causes include water ingress and moisture, insulation aging, or mechanical compression leading to phase-to-phase short circuits.

High-resistance fault: The DC resistance at the fault point is higher than the characteristic impedance of the cable, and no reflected signal is detected when using the low-voltage pulse method. The cable appearance is intact, but the insulation performance has severely deteriorated, requiring a higher voltage to make the fault point exhibit breakdown characteristics. High-resistance faults can be further divided into leakage-type high-resistance faults (stable but low insulation resistance) and flashover-type high-resistance faults (good insulation under normal conditions, but breakdown discharge occurs after high voltage is applied).

The Kedia Zhongwei KD-212X cable fault tester covers all fault types for power cables up to 35kV—open-circuit, short-circuit, low-resistance, high-resistance leakage, and high-resistance flashover faults can all be detected. At the same time, the device is also suitable for fault locating on railway signal control cables, street lighting cables, and airport navigation signal cables. Accurately identifying the fault type is a key prerequisite for selecting the correct detection method.

II. Core Technical Principles and Implementation

The basic principle of cable fault testing is the pulse reflection method, whose working mechanism is similar to radar ranging—an electrical pulse signal is sent into the cable under test, and the fault location is determined based on the reflected echo generated at the impedance change point. There are two main implementation methods:

Low-voltage pulse method: The tester transmits a low-voltage pulse signal into the cable, and the pulse propagates along the cable. When it encounters an impedance discontinuity such as an open circuit, short circuit, or ground fault, a reflected echo is generated. By calculating the time interval Δt between the transmitted pulse and the reflected pulse, and combining it with the propagation velocity V of the pulse in the cable, the fault distance can be calculated (L = V × Δt / 2). This method is convenient to operate and highly safe, and is suitable for rapid ranging of open-circuit faults and low-resistance short-circuit faults, as well as for measuring the total length of a cable.

High-voltage flashover method: For high-resistance faults, the low-voltage pulse cannot penetrate the fault point to form an effective reflection, so a high-voltage generator is required to apply DC high voltage or impulse high voltage to the cable, forcing the fault point to break down and discharge. At the instant of breakdown, the high-resistance fault transforms into a transient short-circuit state, generating a strong reflected signal. The instrument captures this signal and calculates the fault distance. The high-voltage flashover method is the primary technical means for handling high-resistance and flashover faults.

The KD-212X has achieved multiple performance improvements based on the above technologies: the main unit adopts a highly integrated communication architecture and provides six sampling frequency options from 6.25 MHz to 200 MHz for automatic selection—the higher the sampling rate, the richer the waveform details and the higher the positioning accuracy, with a resolution of up to 1 meter at a 200 MHz sampling rate. The device supports both the low-voltage pulse method and the surge current method, and adopts an innovative design that can obtain multiple effective waveforms from a single discharge, effectively suppressing the impact of oscillation interference on test results.

III. Standard Field Operation Procedure

Cable fault field testing strictly follows a three-stage procedure: "ranging – path tracing – pinpointing".

Stage 1: Rough ranging of fault distance

Connect the test main unit to one end of the cable, select the low-voltage pulse method or high-voltage flashover method according to the fault category, and obtain the approximate distance from the fault point to the test end. The error in the rough ranging stage is generally controlled within 1%, narrowing the fault range to tens of meters.

Precision assurance of the KD-212X in the rough ranging stage: The software system supports automatic identification and search of low-voltage pulse and multiple pulse wavefronts, automatic locking of waveform inflection points, and direct reading and display of fault distance. The screen can simultaneously display waveform information in three areas and provide multiple measured waveforms for comparison and selection. The dual-cursor fine adjustment accuracy reaches 0.15 meters. The instrument's maximum ranging capability is no less than 50 km, the blind zone is only 5 meters, and the inherent system error is less than ±1%.

Stage 2: Cable path tracing

For directly buried or concealed cables, a path tracer is needed to determine the exact route of the cable underground. Distance data alone cannot determine the direction—it is necessary to clarify which direction the fault point lies in before proceeding to the subsequent precise pinpointing stage.

The supporting path tracer of the KD-212X has a detection distance of no less than 15 km, an effective detection depth of ≥3 m, and a route positioning error of less than 20 cm. The transmitter output power is 5 W, and both the receiver and transmitter are equipped with rechargeable lithium batteries, providing up to 8 hours of continuous operation.

Stage 3: Precise pinpointing of the fault point

Carry the pinpointing instrument to the vicinity of the rough ranging position and use acoustic-magnetic synchronization technology for precise pinpointing. The high-voltage impulse generator causes the fault point to break down and discharge, and the fault point simultaneously radiates electromagnetic waves and sound signals. The pinpointing instrument synchronously receives both types of signals—electromagnetic waves travel extremely fast and arrive first, while the sound signal arrives later. Based on the time difference between their arrivals, the instrument gradually approaches the fault point and finally locks its precise position.

The supporting pinpointing instrument of the KD-212X is equipped with a high-brightness color display, suitable for outdoor strong-light environments. The dynamic range of the sound channel is greater than 104 dB, and the impulse discharge sound gain is higher than 90 dB. The precise positioning deviation can be controlled within ±0.2 m. The pinpointing instrument can also digitally display the distance change between the test point and the fault point in real time. While pinpointing, it can assist in detecting the cable path direction. The noise suppression filtering technology further enhances on-site anti-interference capability.

IV. Product Features and Field Adaptability

The KD-212X is designed with full consideration of the usage requirements in complex field environments. The main unit is equipped with a 12.1-inch industrial-grade touch screen, and the high-brightness LCD panel ensures clear visibility under outdoor strong light. The engineering plastic enclosure is shockproof and moisture-proof, and the lithium battery power supply allows continuous operation for approximately 6 hours. The main unit weighs only 6 kg, making it easy to carry and set up on site. The software system has a built-in library of typical waveforms and wiring reference diagrams, facilitating on-site comparative analysis and daily skills training. It also supports automatic generation and printing of test reports, which can be retained as cable O&M records.

V. Conclusion

Cable fault testing is a highly specialized field operation. Mastering the core principle of pulse reflection, familiarizing oneself with the standard "ranging–path tracing–pinpointing" workflow, and understanding the detection strategies corresponding to different fault types are the fundamental guarantees for rapid fault location and shortened repair time.

Wuhan Kedia Zhongwei Electric Co., Ltd. (referred to as "Kedia Zhongwei") was established in 2012 and is a high-tech enterprise integrating R&D, production, and sales of power testing equipment, instrumentation, and online power monitoring systems. The company has obtained certifications including the "High-Tech Enterprise Certificate" and "ISO9001:2000 Quality Management System Certification." Its product portfolio encompasses more than 300 models across 15 major categories, such as series resonance test systems, high-voltage test equipment, transformer testing instruments, relay protection testers, and cable fault detectors. These products are widely applied in power, water conservancy, petroleum, railway, mining, chemical, and other industries. The market covers all provinces and regions in China and exports to Australia, Russia, India, Pakistan, Vietnam, and other countries. The company boasts a team of professionals—including doctors, masters, and professor-level senior engineers—specialising in high voltage, computer science, and electronics. With the purpose of "technology-oriented, quality-first, customer-supreme, win-win cooperation," it is dedicated to providing high-quality products and services that support the development of China's power industry and the safe operation of power systems.