Inside the belly of the beast

11 February 2015 - 02:20 By Penwell Dlamini
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SHORT CIRCUIT: Engineers at the National Control Centre in Germiston monitor a map of the country's power grid. The giant screen can display all generating units in the grid, the distribution network and electricity coming from renewables like wind and solar. This is where load-shedding begins and the balancing act between demand and supply plays out
SHORT CIRCUIT: Engineers at the National Control Centre in Germiston monitor a map of the country's power grid. The giant screen can display all generating units in the grid, the distribution network and electricity coming from renewables like wind and solar. This is where load-shedding begins and the balancing act between demand and supply plays out
Image: ESKOM

Technicians and engineers watch an overhead screen inside Eskom's National Control Centre.

The cinema-sized screen at the front of the room holds key information that will determine whether or not the lights stay on.

This is where Al'louise van Deventer spends her working hours. She manages the control centre and all the engineers turn to her when the illuminated lines and dots on the screen above start indicating the national electricity grid is under severe strain.

Eskom operates 27 power stations with a total nominal capacity of 41995MW.

This is made up of 35726MW of coal-fired stations, 1860MW of nuclear power, 2409MW of gas-fired, 2000MW hydro and pumped-storage stations and a 3MW wind farm.

Electricity is moved from generator to metros and municipalities and ultimately to homes along 359337km of power lines and substations with a cumulative capacity of 232179MVA. All this is represented on the circuit board-like screen - an image of the national grid representing every unit of electricity produced and the entire distribution network.

Given the strain the grid has been under recently, one would expect Van Deventer and her team to be scurrying around, plugging holes and flipping switches.

Instead it is a sea of calm.

Cellphones and any recording equipment are not allowed inside the control room. Visitors are kept out but can view the scene from behind a glass screen.

After about 18 years at Eskom, Van Deventer knows the grid intimately. Reading the screen, she can tell the impact of a veld fire on the pylons in Mpumalanga. She can tell which power stations have lost generating capacity.

Most importantly, she can tell when to shed the load to save the national grid.

Under normal circumstances, Van Deventer and her team need a 2000MW operational reserve margin. But things are no longer normal at Eskom. Maintenance has not been done sufficiently for years and the company now needs 5000MW to have the "head room" to conduct maintenance at its plants.

The priority is to keep the 50Hz frequency at the right top corner. This represents the balance between supply and demand at any given second .

Van Deventer's job with her engineers is to keep the frequency between the 49.8 and 50Hz bands.

If demand is equal to generating capacity, the frequency stands at 50Hz. If demand increases beyond supply, the frequency drops below 50Hz.

But load-shedding is not based just on the frequency.

"We shed not based on frequency but generation capacity," she says.

As generating units come in and out of the system, supply changes and when it reaches a point where demand puts pressure on the constrained supply, an alert is issued to the six regional control rooms in the country. This is then cascaded to municipalities.

The stage of load-shedding is determined by the number of megawatts required to ease pressure on the grid.

If Van Deventer sees she needs more room, she has discretion to request that big customers like manufacturing and mining reduce their load. This depends on the required capacity to stabilise the system.

After receiving relief from load-shedding, engineers then monitor the system to see if the "headroom" required was achieved.

"Managing the grid is not an easy task. It is a complex process which requires each desk in the centre to monitor every part of the national grid. That is why the staff in this place is trained thoroughly and they spend time at the power station to get first-hand experience of power generation," Van Deventer said.

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