03 Jan Success Story: The Cable Fault Locator from SCOPE accurately located a long pending critical fault in an LT Cable
One of the major thermal power plants from Northern India was living with the problem of an undetected cable fault for over two years on their LT Cable. Since this cable was used for Street lighting and had a backup line which used to power up the street lights, this faulty cable went into the background. The officials did their best to clear this fault, for which they took the help of local vendors, but all 3 vendors failed to detect the fault and clear the line. These local vendors used the conventional set-up of the Surge Generator & Pin-Pointer to locate the fault but failed to pinpoint the fault. Determination of the type of fault with proper diagnosis and measurement of fault distance before pinpointing plays an important role. It avoids the unnecessary stress the cable has to go through because of High Voltage surging or thumping on the Cable Under Test (CUT).After two years of fault occurrence, SCOPE T&M supplied a Surge Generator, Prelocator, Audio Frequency Generator (Route Tracer), and Pinpointer to the thermal power plant. SCOPE Team was challenged to locate the above-mentioned long pending fault during the commissioning of the products. SCOPE Team came out with flying colours.
Cable Under Test (CUT) details
| Cable Insulation Type | PVC |
| Cable Rating | 1.1 kV |
| Cable Length | Approx 100m |
| Other Information | 4 core, 95 mm2 |
Diagnosis from End 1 (R, Y, B: Three phases, N-Neutral, A-Armour)
| Sequence | Continuity | Ohmmeter | IR Tester = 5kV | TDR Results | |
| R | A | Ok | Infinite | 600GΩ | 120m Open, 89m Partial Open |
| Y | A | Ok | Infinite | 1kΩ | 120m Open, 89m Partial Short |
| B | A | Ok | Infinite | 510GΩ | 120m Open, 89m Partial Open |
| N | A | Ok | Infinite | 2kΩ | 120m Open, 89m Partial Short |
| R | N | Short | 0 Ω | 0 kΩ | 89m Short |
| Y | N | Short | 0 Ω | 0 kΩ | 89m Short |
| B | N | Short | 0 Ω | 0 kΩ | 89m Short |
| R | Y | Short | 0 Ω | 0 kΩ | 89m Short |
| Y | B | Short | 0 Ω | 0 kΩ | 89m Short |
| B | R | Short | 0 Ω | 0 kΩ | 89m Short |
Now we will discuss the actual fault location steps carried out by the SCOPE Team and their respective results.
Prelocation Summary (R-N)
| VOP (V/2) | 79m/µs | Total Cable length | 120m |
| Moisture | Not Found | T Branch | Not Found |
| Open Ckt Fault | Not Found | Short Ckt | 89m |
| Joint Location | Not Found | ICM Reading | No Reflection |
| SIM/ARM Reading | No Reflection | Voltage Decay Reading | No Reflection |
Actual Cable Length = Distance L shown on Prelocator – Prelocator’s Test Lead Length
= 91.68 – 2.00
= 89.68m
Route Tracing
Pinpointing of the Fault
Conclusion
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