Henning Oetjen, product manager, cable test
Locating faults on underground power cables is a task that’s usually considered difficult, complicated, potentially dangerous and, in short, best left to the experts. However it is becoming more and more common to employ all available field personnel – essentially, whoever happens to be available on a given shift – to perform cable fault location. This approach means that fault location is now often carried out by field personnel who perform the task only a few times each year.
This change means that test equipment suppliers must now provide equipment that, in as many situations as possible, will allow users to locate faults successfully even if they are not fault location experts. Until recently, this challenge had never been fully addressed, but this situation has changed with Megger’s introduction of a new generation of intelligent cable fault locators, based on the E-TRAY platform.
Just like conventional instruments, the new units incorporate a “thumper” that injects a surge current at high voltage into the faulty cable, and in combination with a time-domain reflectometer (TDR), they measure the distance to the fault. The difference with the new E-TRAY platform is that the units are not only much easier to use, they also feature an automate test sequence for the fault location process and, crucially, provide interpretation of the test results.
The E-TRAY user interface is operated by a turn-and-click rotary pushbutton that allows the user to automatically proof-test, pre-locate and pinpoint faults. No adjustments or settings are required and, at every stage, the unit suggests the next logical step in the testing sequence. The test set adjusts the surge voltage automatically to minimise the stress on the cable and, before the testing starts, it carries out safety checks to protect the user from the risks that could result from incorrect or faulty earth connections.
Even the interpretation of the TDR results – a task that’s often considered to require a large amount of experience and expertise – is eliminated in many situations through the use of the smart software being an integral part of the E-TRAY platform. After the initial test sequence has been completed, the smart software analyses the TDR results and presents them to the user in a clear and readily understandable form. It is, however, worth noting that the user can, at any time, overwrite the automatic setting of test parameters, the automatic sequence of the process and/or the automatic interpretation of the test results.
This high level of automation makes the new intelligent cable fault location test sets, of which the new Megger Smart Thump ST16 is a leading example, an ideal choice for use by users who are experienced in high-voltage systems, but are not specialists in cable fault location. That doesn’t mean, however, that these test sets are of limited use to more experienced operators, as they offer the full complement of typical fault locating features and options.
The new E-TRAY intelligent test sets have a wide range of capabilities and are suitable for use on low and medium-voltage distribution networks with system voltages up to 35 kV. They are capable of working with circuit lengths from typically 100 m to 5,000 m, and are intended for use with cables having solid dielectric insulation like EPR or XLPE. Typical users who will find them of interest include power utility companies, street lighting maintenance providers, private network operators, airports, ports, military bases, large industrial organisations and high-voltage electrical contractors.