T&D World Magazine

Testing Cable Sheaths and Locating Cable Faults With a Mobile Device

BAUR Prüf- und Messtechnik GmbH has designed “shirla,” a lightweight device weighing less than 20 kg, for cable/cable sheath testing and cable fault location and pinpointing. Powered via the mains supply or via a built-in accumulator, shirla enables cable and cable sheath testing up to 10 kV DC.

Preliminary location of low ohmic faults, e.g. sheath faults, works with direct current and is based on the Wheatstone measuring bridge. Hereby, a measuring bridge is balanced with a variable resistance. In shirla, the measuring bridge is used according to Murray (bridge circuit with one auxiliary return) and Glaser (bridge with two auxiliary returns). When measurement is completed, shirla displays the distance to the fault location, either in percentage of the measured cable line or in meters. For distance calculating, the device considers inputs for length, conductor cross-section and conductor material of the cable and its segments to increase the accuracy of the result.

As length and position of the cable are usually known for in-house infrastructures, the fault can be detected within a few meters using a line measuring device (running wheel). Then exact pinpointing only takes a short time. The search receiver KMF 1 or the universal receiver UL 30 can be used for pinpointing. The step voltage method can be applied with both receivers and the sheath fault is often located within a few minutes. shirla delivers the required voltage (e.g. rectangular shape). Depending on cable type, the operator can adjust this pulsed voltage continuously between 100 V and 10 kV.

Shirla - the cable sheath testing and fault location system - has proven to be a universal tool for finding cable sheath faults in low voltage structures, such as the lighting network, and also within medium voltage networking, e.g. of wind power plants. Operators and makers of solar parks use shirla regularly for testing and fault location, even on 1 kV DC cables. Apart from faults in the sheath (earth-sensitive faults), low and high ohmic faults can be located with the BAUR device.

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