Electricity and Control June 2023

TRANSFORMERS, SUBSTATIONS + CABLES

drocarbon oil is usually the standard medium used for cooling transformers, there has been growing interest in ester oil, which is made from sources that are not hazardous to the environment. “Ester oil is considerably more expensive, but it does not car ry the risk of contaminating land or water if it is spilt,” he says. “It also has the significant advantage of being able to withstand higher temperatures without breaking down.” A further benefit is that it is not generally flammable, so there is little chance of it contributing to an explosion or fire in or around the transformer. Ester oil also retains heat better than normal oil, he adds. This is a plus factor as it moderates the temperature of the windings in an inverter transformer, so they are closer to operating temperature when they are reactivated at the start of the day. Managing harmonics “When dealing with electricity from PV cells on a solar plant, another important element to consider in the transformer design is the harmonics of the incoming current,” Potgieter notes. “Harmonics are generated when the current is converted from dc to ac – and the transformer must filter the harmonics so that the current going to the substation is clean.” This requires an analysis of the harmonics that are likely to come through the system. He cites examples where high har monics have not been adequately factored into the design, lead ing transformers to overheat and fail. Collaborative design He says the design of the WEG transformers is conducted col laboratively between the South African specialists and the WEG design office in Brazil. The company’s sophisticated design soft ware allows various specifications to be prioritised, funnelling down the design options for the engineers. “Our design engineers can then sit around a table with the information from the customer, to identify the best solution for the specific site conditions and the customer’s requirements,” he says. “We then work further with the customer to focus the options – to achieve a technically compliant design that is cost effective within the project budget.” Following the international collaboration between Zest WEG and its Brazilian counterparts, the design can be taken forward and implemented by the expert South African team. The final de sign is checked again by engineers in the WEG head office to make certain that all parameters have been met. After that, it

The WEG photovoltaic solution: the company supplied 10 x 5 MVA, 11 000/600-600 V transformers with ester oil as the coolant.

The LV termination side of WEG transformers is designed for maximum safety and reliability. moves into the manufacturing phase at one of Zest WEG’s South African transformer facilities. “This process of collaborative design development to WEG’s global standards and our local manufacturing expertise give us the confidence to offer a standard three-year warranty on our transformers, including those for solar PV applications,” Potgieter says. □

For more information visit: www.zestweg.com

JUNE 2023 Electricity + Control

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