Protection equipment will prevent a blackout

November 19th, 2014, Published in Articles: Energize


Robbie van Heerden, the general manager of Eskom’s transmission system, says that, to assist in preventing a system collapse due to the integration of the new power stations, ageing infrastructure must be replaced with newer equipment which will operate more reliably as a result of better communication techniques and faster protection responses.

Robbie van Heerden - 2

Robbie van Heerden

Delivering the keynote address at the recent Southern African Power Protection Conference in Midrand, Van Heerden said that the system is currently constrained because the utility has limited generation capacity to meet demand, with very little in reserve. The utility must constantly maintain a balance between supply and demand. On a daily basis, it forecasts the demand and the operating reserve requirement. Generation is scheduled to meet the anticipated load demand, with emergency generation in reserve if required. This constrained situation can only be addressed by either providing more generation, or by reducing demand. Eskom uses its open cycle gas turbines (OCGTs) to generate power when existing generation is insufficient to meet demand, and reduces demand (via load shedding) when necessary.

OCGTs are expensive to run, but load reduction impact on the country’s economy more severely. The utility has to keep these two factors in mind, while ensuring that the network is never overloaded to the point where the system shuts itself down, resulting in a blackout. A blackout, Van Heerden said, would require a total “black start” process which could take as long as two weeks before the network would be stable again. This would have a devastating effect on business and result in major financial losses to the country’s economy. For this reason, the utility will do everything it can to prevent a blackout from ever occurring.

Van Heerden said that the summer load profile is “flatter” than the winter profile, and that peaking plant is needed for more hours during the day in summer than in winter. In addition, power stations are usually taken off line for maintenance in summer, resulting in less electricity being available to meet demand. Sometimes, the utility has to use its OCGTs throughout the day, and shed load during peak times. Managing the winter profile is easier because although the profile has short, sharp peaks, the rest of the day is more manageable.

Not every outage is as a result of load shedding, he said. Referring to the recent interruption experienced by a number of areas in Johannesburg, he said that many outages result from technical faults such as the one which affected supply to the Prospect substation. The utility is building additional power stations and refurbishing and upgrading its infrastructure with modern equipment. However, it faces the challenge of doing this in a constrained system with diminishing stability margins.


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