Fault Location in Gas Insultated Conductors Using Magnetic Sensors

A new technique is described for fault location within gas insulated conductors which are commonly used in above-ground compact substations. When a fault occurs between an enclosed conductor and the outer sheath, locally strong magnetic fields develop on the outside at the flashover point. To exploit-this phenomenon, small permanent magnet sensors are mounted on flexible fiberglass tapes at regular intervals and demagnetized with a "degaussing" coil. The tapes are attached to the outside surface of the outer conductor prior to the occurrence of a fault. The external field magnetizes the sensors, leaving behind a permanent record of the fault location. At a later time, the magnetic sensors can be removed from the conductor and "read" to determine the fault position. A primary advantage of this technique is that the method can be implemented on existing equipment without cutting or drilling into the pressurized enclosure. In the text, a complete instrumentation system is described which results in the measurement and retention of a local magnetic flux density as low as 0.5 mT. The paper also contains data from successful laboratory demonstration. tests using actual flashovers in SF6 insulated conductors.