Concern over load shedding effects on City network

QUESTIONS have been raised about the impact of load shedding on the City of Cape Town’s electricity infrastructure after it was revealed that parts of Zone 7 were being excluded.

City Bowl residents, who were previously excluded from load shedding finally had their lights switched off, like the rest of Zone 7, on September 24, but are now concerned about the effects that load shedding has on old transformers at substations.

A resident in Zone 7, speaking on condition of anonymity, confirmed that in previous years some homes in her street did not have load shedding due to the risk that old transformers at substations posed. But, following the replacement of transformers and servicing of substations, they began to have load shedding.

When asked about whether transformers at substations across Zone 7 needed to be replaced, the City of Cape Town offered no direct answer.

“This is not a maintenance-related matter. The City performs routine and unplanned maintenance work as required,” said Luthando Tyhalibongo, spokesperson for the City of Cape Town.

Over the past month there have been instances of areas in Green Point failing to be reconnected following load shedding. The City confirmed that on September 25, breaker springs needed to be changed at a Green Point substation, which resulted in a delay in the restoration of power.

When asked about when the affected substation was last serviced, the City did not share those details.

“It is not a maintenance matter. It is a load shedding matter,” emphasised Tyhalibongo.

The City also recommended that residents switch off all electrical appliances for the period during which they receive load shedding so that the system is not overloaded when the power is restored.

“The impact of load shedding on infrastructure cannot be discounted as the equipment is not designed for continued load shedding. It is meant to supply electricity,” said Tyhalibongo.

“Furthermore, some outages are as a result of what is called ‘cold’ load coming on after load-shedding. Secondary tripping is caused when all load in an area comes on at the same time, overloading the system and causing the outage.”

Another incident of power not being restored on time was reported in Bo-Kaap and De Waterkant yesterday. Weekend Argus was not able to confirm the reason for this outage.

This comes after complaints that De Waterkant had been excluded from load shedding, as had been the case for parts of Vredehoek, Oranjezicht and Gardens. The City did not offer a specific explanation as to why De Waterkant was excluded from load shedding.

“The City is guided by the national standards for load shedding,” said Tyhalibongo.

“The City does exclude major hospitals, major central business districts with high concentrations of people and vehicles and areas where there are major crowds gathered for specific events.”

De Waterkant, however, is not a major central business district. Areas with a much higher concentration of people and vehicles, such as Rondebosch, Claremont, Wynberg and Bellville, have not been excluded from load shedding. When asked about technical constraints at the substations in De Waterkant, the City did not respond.

Sandra Dickson, founder of Stop CoCT, commented that ageing infrastructure in the City of Cape Town is not new and appears to be the case with electrical substations that the City controls.

“If the City published its schedules of maintenance of substations in residential areas, it will go a long way to put the minds of residents at ease,” said Dickson.

Trevor Gaunt, an electrical engineer and emeritus professor of electrical engineering at the University of Cape Town, said the frequency of checking the condition of transformers depends on their size and history.

“Unless concern arises, it’s adequate to check and replace or refresh the content of the dehydrating filters … every three months and make a visual inspection of the transformer, mostly for leaks,” said Gaunt.

Gaunt said that small distribution transformers, like those in small substations, are sealed units that only need a visual inspection annually.

“Transformers are highly reliable provided they are not overloaded, exposed to system faults or subjected to other less obvious stresses,” said Gaunt. “They typically last 30 to 50 years, and I have known of even older units still being in service.”

The City did not confirm the number of transformers that are in need of replacement.

According to Gaunt, a transformer may be replaced with a larger transformer if the load in the area increases, and the older transformer can then be used elsewhere.

Gaunt added that if old transformers are in good condition, it would not be difficult or risky to restore power after blackouts and load shedding.

“The risk of damage by and beyond the transformer is small. A much greater risk lies in the damage to the system caused by thieves using the scheduled load shedding period, when feeders are de-energised, to steal the cables and conductors, creating really unsafe conditions for the public when the supply is switched on again,” said Gaunt.

“The impact on infrastructure cannot be discounted as the equipment is not designed for continued load shedding. It is meant to supply electricity.

LUTHANDO TYHALIBONGO City of Cape Town spokesperson

L FILE RESIDENTS in Cape Town are concerned about ageing electrical infrastructure.