Within budget and on time: Substation strengthens city’s distribution network

February 28th, 2019, Published in Articles: EE Publishers, Articles: Energize, Featured: Energize

Sebenza substation, the city of Johannesburg’s biggest electrical project in a decade, was officially opened by the city’s mayor, Herman Mashaba, recently. In his speech, Mashaba said he was proud to announce that this substation, which will strengthen City Power’s distribution network had been built within budget and on time.

This new substation, which is located immediately behind the Kelvin power station near Kempton Park, Ekurhuleni, is rated at 1000 MVA, 400/275/132 kV. As one of the main intake substations in the north-eastern region of Johannesburg, it provides a reliable supply of electricity to the businesses and residents of the city.

The new substation was built by Consolidated Power Projects (Conco), an engineering procurement and construction (EPC) contractor, with consulting engineers from PSW and Nyeleti. The substation has been fitted with three 315 MVA, 275/88/22 kV autotransformers which were specially designed and manufactured locally for the project.

Covering a land area of 260 x 440 m, the substation is situated on land which was previously used by the Kelvin coal-fired power station to dump coal ash from its furnaces. This project is expected to stimulate much needed economic growth for the city of Johannesburg and will relieve load from the Prospect substation.

Conco says this substation has been built to dramatically improve reliability and stability of the grid.  Part of the Sebenza project involved Conco having to upgrade and make additions to both Prospect and Kelvin substations, which included installing four sets of reactors and new switchgear on some of the main feeders at Kelvin.

This substation incorporates a number of special features and not a few “firsts”.

Firstly, it uses specially designed transformers which use high-impedance coils to match the 40 kA circuit breakers installed at the old Kelvin power station. These transformers incorporate a specially customised three-stage cooling system designed to provide high efficiency cooling at various temperatures, while at the same time minimising energy use.

It also incorporates the largest 132 kV high voltage gas insulated switchgear (GIS) board ever delivered in Africa. The gear consists of 132 kV GIS, circuit breakers 88 kV surge arresters and point-of-wave relays. The 132 kV GIS board comprises 38 bays.

Evacuating power from the substation is done by means of heavy-duty high-voltage cables. These cables run from under the power transformers, out of the substation building underground in special trenches, to new overhead lines. New towers carry new lines out of the substation to transmit the power to the city via the transmission grid at 88 kV.

The lines are however built for 132 kV duty. The connection between Prospect and Sebenza is via a double circuit 275 kV line which was totally refurbished during this contract. This installation is also equipped with a state-of-the-art SCADA communication system which allows central control to operate this installation remotely.

Mario Prasti, Conco’s special projects director, says the company is proud of this project and pleased to report that although the lifetime of the project required over 1-million man-hours of work, it incurred no lost-time incidents.

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