Cable Fault Locating

Although today’s power cable is designed for long life, failures can still be experienced. BET has taken cable fault locating from a hit or miss “art” to an exact “science.” The most common cause of failure is poor workmanship in the splicing and terminating of the cables. Even properly installed cables are subject to conditions such as overheating, excessive moisture, corrosive environments and aging of the insulation.

BET specializes in Cable Locating and Fault Location, using two methods of detection: The Terminal Measurement and the Tracer Method. These test procedures locate and identify short circuits, low resistance shunt faults, open circuits, high resistance series faults, wet sections, splices, transformers, cable transitions and concentric neutral corrosion. In addition, high resistance, intermittent, and flashover faults can be identified.

Our Terminal Measurement tests use a digital Time Domain Reflectometer (TDR) as a “cable radar” using a pulse-echo process to provide visual indications of cable faults. The TDR sends periodic pulses in the cable, as the pulse travel along the cable, a fraction of the pulse energy is reflected back from the fault to the test set. All reflections are displayed on the LCD. Any reflecting surfaces, cable start, joints, splices, transformers, faults, changes in cable type, as well as cable end, are shown in time sequence.

BET’s Tracer Method employs a capacitive discharge or “Thumper” technique used in conjunction with electro-magnetic and acoustical detection instruments. In this method an electrical impulse of sufficient voltage is transmitted along the cable to Arc over a break in the cable insulation. The arc can then be detected by sight or sound, or via the detection instruments. This helps permit the restoration of services with minimum labor and the least stress on customer and utility equipment.

In cases of lengthy cable runs it is beneficial to use both methods in order to reduce the time required to locate the exact point of cable failure. Once faults are identified, cable section replacement or fault repair can then be performed when scheduling permits.