MechChem Africa January-February 2025

ACTOM’s local MV-switchgear solution MCA talks to Rhett Kelly, ACTOM’s design and development manager for MV-Switchgear, and technology development specialist, Johan Jordaan, about the new locally developed and manufactured GELPAG 12 kV SIS metal-enclosed MV-switchgear panel, which was on display at Electra mining last year.

T ypically used on mines and in industrial plants using electrical equipment such as motors and other electrical machinery, medium voltage (MV) switchgear is primarily used to isolate sections of the electrical network and to interrupt current to downstream equip ment in the event of a fault, so as to ensure the safety of people and to protect electrical assets and infrastructure. “MV switchgear panels are used in substations to interrupt the electrical supply feeding into a mine, plant or factory, either automatically in the event of a fault, or manually when any electrical work on the system needs to be done,“ begins ACTOM’s Rhett Kelly. A medium voltage network is gener ally in the range from 3.3 kV up to 33 kV, he says. Connecting and disconnecting at these voltages and currents involves controlled arcing between the contacts of the interrupting device used in the switch gear, which erodes the contact material. When an uncontrolled arc occurs due an insulation failure within the switchgear, this can cause the air or gas pressure to rapidly increase, potentially resulting in a high energy explosion. By using inter nal arc-tested and classified switchgear, the hot gases and plasma produced in the switchgear during such a fault can be safely released in a manner that ensures the safety of people. Key to preventing arcing from happen ing is the integrity and type of internal insulation used. Describing the insulation options typically used to insulate the live conductors inside the switchgear, Kelly says that there are three traditional op tions for switchgear, oil-insulated switch gear (OIS), air-insulated switchgear (AIS), and gas-insulated switchgear (GIS). These systems are used to provide the required dielectric insulation between the ener gised conductors and the sheet metal of the earthed enclosure. “Our new GELPAG metal-enclosed MV-switchgear solution uses a fourth insulation medium, namely solid dielec tric insulation, which encapsulates the live conductors of the main circuit with an epoxy resin. Switchgear using such insulation is referred to as solid dielectric

insulated switchgear (SIS). In the case of ACTOM’s GELPAG product, a conductive screen layer is added to the outside of the epoxy resin, which is earthed during normal operations, making the function ing of the switchgear immune to harsh environmental effects such as moisture and pollution, since none of the insulation surfaces within the switchgear is exposed to ambient air. “The main current interrupting device is still a vacuum interrupter, embedded inside the epoxy resin,” he points out. “Since we are not filling the whole of the enclosed area inside the panel with a gas such as SF6 – which has a very high global warming potential – or any other insulating fluid, there is no requirement for having gas or fluid monitoring devices fitted to the switchgear. In addition, the earthed screen layer on the epoxy resin eliminates the electrical stress in the air between phases, which allows the overall footprint of the switchgear to be reduced. This enables the overall volume of the whole substation building to be signifi cantly reduced. “We can typically achieve the same level of compactness as GIS, potentially even more, because the dielectric strength of epoxy is very high and independent of pressure,” Kelly explains. MV Switchgear designed and manufac tured in accordance with SANS 1885, the South African front end standard for the IEC 62271 MV switchgear standard, has to be metal enclosed by design, he explains, “In the case of GIS, the whole ‘tank’ enclos ing the high voltage components of the switchgear is sealed for life, with the gas at a positive pressure above atmosphere. The GELPAG SIS solution is manufac tured and supplied in accordance with SANS 1885 does not require a sealed pressure system and associated monitor ing systems to maintain the insulation integrity. GELPAG also falls under the cat egory of metal enclosed switchgear, which means all the high voltage components are housed within a metal enclosed panel rather than a gas compartment,” he says. “One of the big advantages of the earth screening system is that it maintains the

integrity of the epoxy resin insulation without the need for a sealed pressure system, because moisture and pollution settling on the insulation surfaces will not result in any leakage currents, which typically give rise to erosion or tracking phenomena on the insulating surfaces. Unless the pollution deposits are periodi cally cleaned, tracking and/or erosion on unscreened systems degrades the quality of the insulation over time and are often the root cause of an internal arc fault as described above,” he adds. “By screening our insulation system, we have effectively taken out the effects of environmental factors,” Kelly points out. “This panel has actually been tested underwater for 96 hours, and while it is obviously not intended to be operated underwater, this clearly shows that in flooded conditions in a mine or when underground dusty or humid conditions are high, the insulation system is well protected,” Kelly tells MCA. According to technology development specialist, Johan Jordaan, these features make ACTOM’s new GELPAG 12 kV SIS metal-enclosed MV-switchgear panel ideal for mining or even coastal environ ments. The safety features are arguably at a level above traditional switchgear. With no exposed conductive or live surfaces, it reduces the risk to personnel operating and maintaining the equipment – par ticularly when operating procedures are not correctly followed. Furthermore, the switchgear has an extremely low probabil ACTOM’s compact GELPAG metal-enclosed MV-switchgear solution uses solid dielectric epoxy resin insulation to encapsulate the live conductors of the 12 kV main circuit.

34 ¦ MechChem Africa • January-February 2025