Electricity + Control July 2017

round up

DRIVES, MOTORS + SWITCHGEAR

Miniature, integrated circuit transducers for ac and dc isolated current measurement LEM has expanded its miniature, integrated circuit transducers range for ac and dc iso- lated current measurement up to 300 kHz with the introduction of the GO series. These new components offer full isola- tion, despite their small size, by integrating the primary conductor for nominal current measurements of 4 A, 6 A, 8 A, 10 A, 12 A, 16 A, 20 A or 30 A with a measurement span of 2,5 times the nominal current . Products in the GO series are able to support high overload currents up to 200 A peak for short durations (1 ms). onto a printed circuit board as SO8 or SO16 SMD devices, reducing manufacturing costs and providing much needed space saving for space-constrained applications. GO models are simple to use as they in- tegrate low resistance primary conductors (minimising power losses) within a propri- etary ASIC to allow direct current meas- urement and consistent insulation perfor- mance, while still providing high creepage and clearance distances. sions and 500 MV @ IPN for 3,3 V versions. Ratiometric output is also an option though dedicated models. Enquiries:Tel. +27 (0) 11 626 2023 or email denvertech@pixie.co.za

Standard models provide an analogue voltage output with different sensitivity lev- els according to the models to achieve an output voltage of 800 MV @ IPN for 5 V ver-

Available from Denver Technical Prod- ucts , the transducers are mounted directly

Africa’s largest rotor pole refurbishment

subjected to insulation resistance and inter-turn insulation tests, comprising both impulse and power frequency inter-turn insulation tests. Extensive visual inspections were also conducted. The test results were analysed, resulting in the decision to refurbish 11 of the 14 poles; two coils were accepted as healthy and the station owned a spare universal coil. To facilitate the grinding procedure necessary to remove the support side brackets from the main rotor poles, a customised heavy duty jig was manufactured. After the severity of the dam- age was determined, various techniques and repair concepts were tabled and discussed in great detail. It was finally agreed that the coils be stripped of their existing inter-turn insulation layers and the coils be reinsulated, heat cured using 2 500 Amps, including press- ing at up to 1 000 tons, and reassembled to the main poles. To fast track the process, Marthinusen & Coutts prepared custom parallel operations at their two facilities; separating the dirty and clean pro- cesses with full clean conditions areas for the critical pressing and heat curing processes. Enquiries: Richard Botton. Tel. +27 (0) 11 607 1700 or email richardb@mandc.co.za

In probably the largest repair of this nature in Africa, Marthinusen & Coutts , a division of ACTOM , recently refurbished 11 of the full set of 14 rotor poles of Motor Generator Unit 3 at Eskom’s Ingula Pumped Storage Scheme on South Africa’s Drakensberg escarp- ment. The rotor poles were extensively damaged during a fault con- dition at the station, and the return to service of the unit was of na- tional importance. Working closely with stakeholders, an extensive local programme of testing, dismantling, inspection and repair was conducted by Marthinusen & Coutts within extremely tight time frames to accommodate the criticality of the project. A technical audit confirmed that facilities at both Marthinusen & Coutts’ 8 000 m² main workshop at Cleveland, Johannesburg, and its 12 000 m² Benoni Power Generation division were indeed up to the daunting task. All 14 main rotor poles were then collected from Ingula Pumped Storage Scheme and dispatched to the Benoni works using Marthinusen & Coutts’ in-house transport. Each pole weighed 12 tons with the coil alone weighing in at over two and a half tons. It was vital that Marthinusen & Coutts determined not just the electrical status of the windings, but the health and physical integ- rity of each entire rotor pole (body and coil). They were therefore

18 Electricity + Control

JULY 2017