7 Step: How Find Cable Fault Location

How to Find Underground Electrical Energy Transmission Lines Cable Faults?

Finding the faulty point of an underground cable doesn't have to be like finding a lost item on the street. There are many fault locating methods depending on who finds the fault, and how they want to find it. Detection technologies are now much easier to find the cable fault; also important is the technique applied, which makes the task much easier and less time-consuming. However, we can say that there is no single method or combination of methods that is universal. Skilled technique and proper tool selection are the key points to finding the cable fault more easily and within a minimum time.

Types of Cable Faults

When electrical energy is generated in the generation stations or power stations, it is distributed to different loads like cities, towns, and villages for the consumption of electricity. The cables are mainly used to distribute the electrical energy; the cables may be either insulated or uninsulated. The choice of underground cables mostly comes into play when energy is to be transferred in the underground installation process.

Commonly found types of Cable Faults in the underground cable transmission line system are as below.

1.   Open-Circuit Fault means there will be no flow of electrical current at all as the conductor is broken. An open circuit fault is a kind of fault that occurs as a result of the conductor breaking or the conductor being pulled out of its joint

2.   Short-circuit or cross-fault means the current will flow directly from one cable to another or from one core or multi-core cable to the others.  This kind of fault occurs when the cable insulation between two cables or between two multi-core cables gets damaged.

      Ground or earth faults mean current will not flow through the load, but rather ground or earth. This kind of fault occurs when the insulation of the cable gets damaged.

There are two basic methods of locating an underground cable fault.

Sectionalizing means cutting and splicing the cable, dividing the cable into successively smaller sections that will enable finding the faulty point.

Thumping means supplying a high voltage to a faulty cable whose high-current arc makes a noise loud enough for you to hear above ground.

General methods to find the cable fault step by step are as below:

Step 1 - Cable Isolation & Safety Procedures: During a cable fault, it is always a permanent fault, which means the protection devices either at both ends or one end tripped and isolate the faulty part from the live part of the transmission network. But the faulty cable is still not safe to work on until it is isolated from the system by earthing or grounding both ends, or at least one end. Only after the appropriate procedures have been carried out can any testing personnel be allowed to approach the cable and prepare for testing. 

Step 2 - Cable Identification: There are multiple cables exiting either outside the substation or inside the substation. Cable identification testing will identify the correct cable to work on; otherwise, it may cause much longer outages for the connected customers due to fatal mistakes.

Step 3 - Cable tracing: Cable tracking is important before starting the cable fault finding. Generally, underground cable laying is brought in a straight line, but rather meanders in depth and direction. Cable tracing is done to determine that the route of the cable follows the expected path. 

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Step 4 - Fault identification: First need to identify the faulty phase from multiple cables and then find the resistance of the fault. Typically, if the fault is found to be below 100 Ohms, a low voltage pulse (e.g., 40 V) from a TDR (time domain reflectometer) can be used. If the fault is a higher resistance (> 100 Ohm), a low voltage pulse will likely not see it, and needs an Impulse generator (shock discharge).

Step 5 – Fault pre-location: A reliable and precise pre-location method is necessary to locate a cable fault quickly and efficiently.

a)   If it is a low resistance fault, pre-location was likely to be the only means necessary for location.

b)   For high resistance faults, ARM (arc reflection) or ICE (impulse current) techniques on an SWG (surge wave generator) need to be used.

Step 6 - Pinpointing:  In most cases, shock discharge generators are used for pinpointing in conjunction with acoustic methods. The discharge creates a loud noise, which is pinpointed precisely using an acoustic pinpointing device.

Step 7 - Re-energization of the cable: After completing the fault finding and all testing and repairs have been successfully completed, the cable is then handed back to the appropriate operators to reinstate the cable and re-energize the loads on the newly repaired cable. 

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Causes of Cable Faults

Faults in cables are mostly caused by dampness in the paper insulation of cables. Lead or Aluminum sheathed XLPE cable can be damaged in many ways. Most of the faults may be due to the chemical action of soil on the lead when buried, mechanical damage, and crystallization of the sheath through vibration. 

Power Cable Fault-finding Tools and Their Uses

Power cable fault‑finding relies on specialized diagnostic tools such as cable fault locators, insulation resistance testers, time domain reflectometers (TDRs), and earth fault indicators. Each tool has a distinct role—from pinpointing underground breaks to measuring insulation health—making them essential for safe and efficient troubleshooting.

🔧 Key Power Cable Fault-Finding Tools and Their Uses

Tool	Primary Use	How It Works	Typical Applications
Cable Fault Locator (Thumper)	Locates faults in underground or concealed cables	Sends high-voltage pulses into the cable; fault location is identified by acoustic/vibration signals	Underground power distribution, telecom cables
Time Domain Reflectometer (TDR)	Detects distance to fault	Sends electrical pulses and measures reflections caused by impedance changes	Pinpointing cable breaks, shorts, or open circuits
Insulation Resistance Tester (Megger)	Measures insulation health	Applies DC voltage to cable insulation and measures resistance	Detects moisture ingress, insulation breakdown
Continuity Tester / Multimeter	Checks basic connectivity	Measures resistance or continuity across conductors	Quick checks for open circuits or short circuits
Clamp Meter	Detects leakage currents or load	Measures current without breaking the circuit	Identifying earth leakage or overload conditions
Earth Fault Indicator	Identifies ground faults	Detects imbalance between phases and the Earth	Used in substations and distribution networks
High Voltage Bridge Method	Locates high-resistance faults	Uses bridge circuits to measure resistance differences	Long-distance cable fault location

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⚡ Common Fault Types These Tools Detect

• Open circuit faults → Broken conductor, detected by continuity tester or TDR.

• Short circuit faults → Conductors touching, identified by multimeter or fault locator.

• Earth faults → Insulation failure causing leakage to ground, detected by earth fault indicators and insulation testers.

• High resistance faults → Partial breakdowns, located using bridge methods or TDR.

• Intermittent faults → Often due to moisture ingress, detected by insulation resistance testers.

✅ Practical Considerations

• Safety first: High-voltage thumpers and insulation testers require trained personnel.

• Cost efficiency: Digging up cables is expensive (up to £4 million per mile in urban areas), so precise fault location tools save significant money.

• Combination approach: Engineers often use multiple tools together (e.g., TDR + thumper) for accuracy.

• Preventive use: Insulation testers and clamp meters are also used for routine maintenance to avoid unexpected outages.

⚠️ Risks & Limitations

• Misdiagnosis risk: Using only one tool may give incomplete results; cross-verification is essential.

• Environmental factors: Moisture, soil conditions, and cable age can affect readings.

• Training required: Tools like TDRs and thumpers need skilled operators to interpret results correctly.

👉 If you’re working in Dhaka or similar urban areas, underground cable fault locators and TDRs are especially valuable because excavation costs are high and faults must be pinpointed before digging. Would you like me to create a step-by-step troubleshooting workflow showing how these tools are used together in practice?