MV Switchgear Divisional News – MV Switchgear develops gas-insulated ring main unit for local market

MV Switchgear develops gas-insulated ring main unit for local market


MV Switchgear recently introduced a medium voltage gas-insulated ring main unit range it has developed for the local market in collaboration with an international manufacturer and supplier of electrical equipment.

The new product, referred to as RMV, comprises a range of extensible and non-extensible secondary distribution medium voltage switchgear for use in miniature substations, outdoor kiosks and indoor substations.

It is MV Switchgear’s first own-developed gas-insulated ring main unit on offer in the local market. It is designed and tested in full compliance with the latest SANS 1874 and SANS 62271-200 standards.

It was introduced at the African Utility Week trade exhibition in Cape Town in May this year. Available up to 24kV, the product was developed over the past three years by the business unit in conjunction with LSIS, the industrial division of the South Korea-based multinational company LG Corporation.

The range includes three primary switching devices available in various combinations for the ring main and tee-off functions and include a switch-disconnector, switch-fuse combination and circuit-breaker. Metering and bus-section units are currently being developed and will be added to the extensible range of switchgear.

“The gas-insulated ring main unit in this voltage range already on offer by LSIS into the global market required certain important modifications to meet the specifications applicable for use in the local market, the main one being inclusion of an integral cable test facility on all switch-disconnector functions,” explained Greg Whyte, MV Switchgear’s Design & Development Manager.

“In our consultations with LSIS it was arranged that we would provide the design concept for this component, based on the successful integrated cable test facility incorporated in our existing oil-insulated ring main unit, the K3AF. The design was then type tested and LSIS has subsequently begun manufacturing the product in accordance with local requirements.”

The additional type tests carried out to verify the new designs and compliance with local requirements in accordance with SANS 1874 included internal arc, mechanical interlock verification, dielectric, single- and three-phase short-time current withstand, earthing switch short-circuit making and the verification of the proper functioning of the position indicating devices.

Noteworthy type tests that were successfully performed in South Korea in July this year were the dielectric tests on the cable testing circuits in accordance with clause 6.2.101 of SANS/IEC 62271-200, which is the IEC standard applicable to metal-enclosed medium voltage switchgear.

“The dielectric type tests were carried out using the on-site test voltages specified in the SANS 10198-13 code of practice applicable to the on-site testing, commissioning, maintenance, diagnostics and fault location of cables,” remarked Rhett Kelly, MV Switchgear’s Technology Development Specialist.

The RMV is arguably the first medium voltage gas-insulated ring main unit currently on offer in the local market that has been fully type-tested in accordance with the most recent editions of these standards. The latest edition of SANS 10198-13, which was published in 2016, incorporates more onerous on-site cable test voltage levels than previously.

“The ratings achieved for the ring main unit with the cable test facilities, which include both a.c. and d.c. cable test voltages, are stated on the name plate of each unit supplied into the market. This is important because the technician on site performing a cable test needs to have the confidence that the insulation levels of the ring main unit are capable of withstanding the test voltage applied to the cable while the busbars remain alive without posing a safety risk,” Greg commented.

Rhett, who is Chairman of the South African IEC committee for high voltage switchgear, participated in the formulation of the revised SANS 10198-13 standard in his capacity as a member of the SA Bureau of Standards’ TC66 technical committee for electric cables, under which SANS 10198-13 falls.

Caption: Linky Mdaka, MV Switchgear’s Technical Sales Consultant, and Mphumuzi Khoza, a power engineering trainee at the business unit, with one of the first RMV ring main units produced for the market.