MechChem Africa January-February 2025

⎪ Local manufacturing and food processing ⎪

ity of an internal arc developing due to the earth screen layer on the epoxy resin. This solution poses far less risk for operators than traditional switchgear designs,” he continues, adding that switchgear could rupture explosively in the event of an internal arc due to the high energy, tem perature and pressure that develops due to the vaporising the conductors. Kelly adds that ACTOM’s SIS system has nevertheless been fully tested and classified on all sides for internal arcing up to 40 kA for 1.0 s. “Even though we know we are unlikely to ever get an internal arc, we still had to do the internal arc clas sification test to meet the requirements of the South African and International standards.” “By using earth-screened epoxy resin insulation along with vacuum interrupter technology, we have practically elimi nated the chance of an internal arc ever occurring,” he assures, before going on to demonstrating the gas venting pathways included for this very unlikely event. “The device that interrupts the load or fault current we call the vacuum inter rupter. A vacuum interrupter is a hermiti cally sealed system that keeps the area around the main switching contacts under vacuum, so that the interruption of any arc current is assisted by the dielectric properties of a vacuum,” Kelly explains. “Because vacuum is such a brilliant insulator and arc quenching medium, when the contacts separate, the arc is extinguished after the first zero crossing, within a half cycle of the 50 Hz ac current wave. And an open gap of just six to eight millimetres is all that is needed between

the contacts to maintain an open circuit voltage at 12 kV,” he says, adding that the unit’s electrical insulation capacity passed withstand-level tests for a 95 kV lightning impulse. The switchgear has a three-position switch, with a closed position, an open position and an earth position. “The mechanism that drives this and the circuit breaker vacuum interrupters incorporate a proprietary designed system using bel lows to keep the contacts of the three-po sition switch and the circuit-breaker drive insulator hermetically sealed at all times. “Another feature that is really notewor thy is that, because this is a fixed-pattern switchgear solution in terms of the open (isolated), closed and earth positions, we have included a mirror-based system to enable an operator to visually check the exact position of the moving contact at any time, therefore confirming its safety status,” he adds. As is the case of most MV switchgear, the operating mechanism used to open and close the current interrupting device is a mechanical device that has been tested for extended mechanical endurance in accordance with the relevant IEC stan dards. To break the circuit, a conventional circuit breaker mechanism is used, with the energy stored in a system of springs, because at any time, the switchgear must be ready and able to rapidly open the breaker. “The energy is derived from the main closing spring, which is automatically charged using a small motor. On closing and latching the contacts, some of the closing spring’s energy is transferred to charge the contact pressure and opening

springs,” says Kelly. If there is a fault such as an electrical short circuit, a protection relay, used in conjunction with current transformers, will automatically trigger an electromagnetic coil to release the stored mechanical energy in the mechanism to open the breaker. Alternatively, a simple push switch can be used to do the same thing manually. To complete the picture, he says that earthing the circuit– e.g. the connected cables – is achieved by moving the three position switch into the earth position and closing the circuit breaker. In terms of successes in the field for ACTOM’s 12 kV SIS MV-switchgear, Johan Jordaan says that ACTOM has sold some 160 of these units to a copper mine in the DRC for underground applications where there is extreme humidity. “We have also recently coupled a three-panel switchboard fitted inside an outdoor enclosure to a battery energy storage system (BESS) for a shopping centre. The compact nature of our GELPAG switch gear makes them ideal for use in e-house applications,” he says, adding that a 36 (40.5) kV version of the same product is planned for launching in 2025.” Concluding, Rhett Kelly says: “The de velopment of the new ACTOM GELPAG SIS solution adds to our local capability to develop, engineer and manufacture switchgear for African and the global markets, be it for indoor switchgear, containerised switchgear, compact substations, renewable energy applica tions, minisubs, outdoor kiosks or bulk metering units.” www.actomswitchgear.co.za

The new GELPAG SIS solution adds to ACTOM’s local capability to develop, engineer and manufacture switchgear for African and the global markets.

January-February 2025 • MechChem Africa ¦ 35