Selection and Application of Power Cable Fault Detection Technologies Under Multiple Operating Conditions--PartII

A 10 kV buried distribution cable under urban roads tripped and lost power. Maintenance staff conducted two exploratory excavations along the general direction but found no faults. The fault point (a damp intermediate joint) was finally found 20 meters away from the second pit on the third day.

The whole process involved three power outage days, three excavation pits and two sections of pavement restoration. The actual cable repair took less than half a day. Most time and cost were spent on fault searching, not repair.

Cable fault testers are professional tools specially designed to solve the problem of fault searching.

It is not a single instrument, but a complete fault positioning system composed of multiple functional devices, completing three core tasks:

1. Judge the type of cable fault
2. Measure the approximate position of the fault point (accuracy within ±5 meters)
3. Locate the exact excavation position on the ground (accuracy less than 1 meter)

Accurate positioning enables targeted excavation instead of blind exploration by experience.

Important Reminder: Many purchasers only buy the main unit without a positioner. The main unit can measure "fault at about 150 meters", while the positioner can confirm "fault under this floor tile". Both are indispensable.

Cables are buried more than 50 cm underground or laid in cable trenches/pipelines, completely invisible. Traditional methods rely on experience and blind excavation.

Solution: Inject electrical pulses into cables, calculate electrical length of fault points based on signal reflection characteristics, and confirm ground coordinates with path finder.

Urban distribution cables and factory cables are usually hundreds of meters long. It is impossible to determine the excavation position without testing instruments.

Solution: Complete ranging within 1 to 3 hours for cables of any length, narrowing the troubleshooting range to within 5 meters.

High-resistance faults feature degraded insulation. The cable can still operate under rated voltage until complete breakdown and power outage. No obvious physical damage can be found by visual inspection.

Solution: Apply high-voltage impulse via high-voltage generator to induce discharge at high-resistance fault points, and locate faults by analyzing discharge waveforms.

Sonar transmits sound waves underwater; the waves reflect when hitting obstacles, and the distance is calculated according to the round-trip time difference.

The low-voltage pulse method (TDR) of cable testers works in the same principle:

1. The tester transmits electrical pulses to the cable
2. Pulses propagate along the cable
3. Pulses reflect at fault points with impedance mutation
4. Reflected pulses return to the tester
5. The instrument measures the round-trip time differenceΔtFormula: Fault distance = Wave velocity * Δt ÷ 2(Divided by 2 because the pulse travels a round trip)

Misunderstanding: Fault positioning and excavation completion mean the end of work.

Standard Complete Workflow:

1. Fault ranging & positioning → 2. Excavation & repair → 3. Re-test & acceptance after repair → 4. Power restoration

The acceptance test (Step 3) must include insulation resistance test, continuity test and voltage withstand test (according to cable voltage level).

Acceptance Standard Basis: GB/T 50150-2016 Standard for Electrical Equipment Handover Tests of Electrical Installation Engineering.

A cable fault tester is a professional system to quickly and accurately locate underground cable faults without large-scale blind excavation. It changes "unknown fault position" to "clear position", and changes "blind excavation" to "one-time accurate excavation".

Repair acceptance test is mandatory to confirm the cable is fully qualified for re-operation.

Safety Notice: High-voltage tests shall be performed only by professionally trained and qualified personnel. Comply with DL/T 474-2018 and relevant safety regulations.