Electricity supply to Joburg's north-east suburbs has stabilised: City Power

City Power says it has been able to stabilise electricity supply after the problems at the Sebenza sub-station in Kempton Park which resulted in load rotation in the north-eastern suburbs over the past few days.

Residents in the north-eastern suburbs of the city have been experiencing frequent power outages over the past few days which has raised questions as to whether the City Power system is able to meet the high winter demand.

City Power briefed the media in Braamfontein on Monday‚ saying the load rotation was implemented due to problems at the Sebenza sub-station.

“We have stabilised the network. The new transformer has been tested. It will be put on load tonight. That will give us continuity of supply from that transformer. If anything else happens elsewhere on the network‚ it might have implications but that will be communicated and tested at that time.

“But from the transformer that we’ve just done at Sebenza‚ we are confident we’ll have continuity of supply. The issue is fixed‚ there will be continuity of supply‚ if something else happens‚ then it would have been unforeseen‚” said Tefo Khama‚ City Power project manager.

On June 29‚ there was a problem with a gasket‚ a seal on one of the transformers‚ at the Sebenza sub-station.

A transformer has pipes which are used to circulate oil used to cool it down. The oil must move to the tank which is at the top of the transformer. When the load peaked and the pressure on the pipes peaked‚ the pressure became too much for the seal gasket and it began to leak. The transformer automatically switched off as a built-in safety measure‚ hence there was an unplanned outage.

Engineers had to replace the gasket and refill it with 3‚000 litres of oil. After all the testing of the process and the oil was concluded‚ the transformer was fixed on Sunday.

But the transformer could not immediately transfer the load and had to be warmed up. The warm-up process takes between 24 hours and 30 hours after the refill.

“Yesterday we tested it‚ put pressure on the transformer to make sure that there are no other leaks that are not detectable… We switched it on yesterday and by midnight we would have done 30 hours‚ which is fine. Then we will be able to transfer the customers to it and move the constraint and the risk that we have currently‚” said Khama.

Khama said another transformer would come online at the end of July‚ which would give the sub-station more capacity to deliver to customers. However‚ the process would at some stage require some load rotation as the engineers would interface the new system to the old system at the sub-station.

The new transformers would bring a new voltage level which would be higher than what the current system was handling.

Another transformer would also come online later in the year which would provide room for the system to have backup load capacity.

Johannesburg MMC for environment and infrastructure services Nico de Jager said that load rotation was the same as load shedding but City Power could not use the latter as the outages had nothing to do with Eskom.

Power outages were experienced in a number of areas as the Sebenza sub-station is closer to the city‘s Eskom connection point.