EPCOR needed a new solution to discharge residual voltage in switched off, high voltage lines. They had deemed that the practice of shorting the lines by throwing a grounding wire caused too much stress on the equipment.
In search of a more controlled process, EPCOR requested that Magna IV Engineering develop a discharge stick suitable for 80kV to 240kV lines, with the ability to indicate when safe to attach a safety ground to the line.
The task was to find bleeding resistors and a suitable casing that would keep them manageable and isolated for the requested voltages. Next, we had to identify and incorporate an indication circuit.
The resistors needed to be small enough to fit the casing, and yet rated for high voltage and able to tolerate significant wattage. A collection of resistors rated for 40W used in parallel and in series would fit neatly into the space available inside the glastic casing we selected.
At the time, the client required just 5 units, 2 for 80kV lines and 3 for 240kV lines. To keep cost down and the solution practical, we worked to minimize the variety of components that would make up the discharge sticks.
We employed a modular solution, breaking the discharge stick into segments: the indication circuit, two extensions to increase the resistance factor, and the top section for attachment to the line at a safe limit of approach. This design increased the quantity of specially made components, but reduced manufacturing time as well as cost per component. The extensible set accommodates 80kV, 160kV and 240kV lines.
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