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Eskom grid collapse concerns well overdone – Kela Securities
According to a research report from Kela Securities, the risk of a complete grid collapse and a nationwide blackout lasting two weeks or more in South Africa is extremely low. The country’s electricity frequency of 50Hz is crucial for operation, and deviations from this frequency can cause blackouts. However, South Africa has automated load shedding and alternative measures in place to manage frequency and prevent blackouts. In the event of a blackout, power plants can be restarted within minutes using hydro plants and gas turbines, and the majority of the country can be back online within hours. The main challenge lies in repairing distribution infrastructure and coordinating supply and demand to restore power to all regions. The current situation is attributed to political interference and insufficient plant maintenance, which can only be resolved through proper maintenance and short-term load shedding. Here’s the full report below.
By Lesedi Kelatwang and Kudakwashe Kadungure of Kela Securities
After having conducted on-the-ground research as well as consulting several experienced engineers with technical knowledge of Eskom’s power generation operations, we at Kela believe that the risk of a complete grid collapse, leading to a blackout that will last two weeks or more, is extremely low. In fact, we understand that should the grid collapse, electricity would be back up and running within hours at the majority of the country’s large economic hubs.
For a nationwide blackout to occur in South Africa, the country is essentially not producing any electricity at all and or Eskom’s highly skilled managers have forgotten how to maintain the grid frequency 50Hz. Given that peak demand this year in May was c.33GW, and Eskom implemented stage 6 to get through it, a nationwide blackout is akin to Eskom implementing a further 27 stages of loadshedding above stage 6. This is naturally on the basis that each stage of load shedding is 1Giga Watt (GW).
Below we unpack how, at a basic level, this could potentially happen. Accordingly, we will also outline the reasons why we think it will not happen at all. We will limit our discussion to a single common parameter through electrical components, that of Frequency.
Electricity in South Africa is generated at a frequency of 50Hz. Using a dynamo to power the lamp on a bicycle as an example, where it is assumed to be rotating at the same speed of a power station of 3000RPMs (revolutions per minutes), it would consequently be generating electricity at 50Hz. As 1Hz is defined as being equal to 1 cycle per second, the dynamo operating at 3000RPMs would be achieving 50 cycles per second.
For South Africa, and in fact almost all grids across the world, it is sacrosanct that frequency is always maintained at 50Hz. As South Africans, our electrical devices/equipment are designed to operate using electricity generated at this frequency. A material deviation from 50Hz essentially means that anything connected to the grid would not work, or for the lack of a better word, break.
Power plants, together with household appliances can accommodate a small variation of frequency changes without any reaction. However, this is limited to a 1% frequency deviation in most cases, or 0.5Hz. This is known as the dead band, where frequency changes can be accommodated without any change in plant output. Any changes to the frequency of more than 1% will cause the plant to produce more or less power to bring the frequency back. And if the frequency cannot be brought back to within the dead band it will switch itself off. This is a safety feature that is built into the actual design of the plant.
Read more: Reserve Bank preparing financial contingency plan in case of total power grid collapse
What would cause a powerplant or grid to struggle maintaining 50Hz?
This can happen if there is an internal breakdown within the plant or if there is a material imbalance between the generation and utilization (supply/demand) of electricity. The former is pretty straight forward to understand hence we turn our attention to the latter. Every gigawatt (GW) generated must have an associated consumer (load).
Loosely speaking, if our theoretical grid of 5 power plants, with each producing 1GW generate 5GW, then you need 5GW worth of demand. In the instance of demand dropping to 3GW while supply stays at 5GW, this would have the effect of increasing the frequency of the grid. As mentioned, 50Hz must be maintained no matter what. The power utility would respond by reducing the power generated at all 5 power plants to be equal to 3GW, or switching off 2 plants, in order to reduce supply by 2GW. Alternatively the utility could look for means to increase demand by selling more electricity to neighbouring countries via the Southern African Power Pool (SAPP).
Conversely, in the instance of demand exceeding supply, this would have the effect of reducing the frequency of the grid. The utility can respond by increasing supply or by reducing demand. The former is not immediately possible for South Africa, and given that SAPP neighbours have relatively small installed capacity for South Africa to import from, this leaves loadshedding as the only option we have, which has the effect of reducing demand.
Assuming that all our plants are in perfect condition, what could possibly cause a black out?
In instances where supply exceeds demand the utility would need to switch off or throttle excess supply or export more to the SAPP. If, for whatever reason, this is not achieved then we would have several power plants taking themselves off the grid due to over-frequency protection, which would subsequently lead to a black out.
Logically, this is highly improbable given that Eskom has the control to switch off supply. In instances where there is a spike in demand that outstrips supply, the only way a blackout happens is when Eskom somehow fails to shed demand accordingly. While this is equally highly improbable, this has actually materialized in certain African countries. The underlying cause was that they struggled to cut off demand in time and the plants tripped, switching themselves off due to under-frequency protection as they are designed to do.
The reason these incidents occurred is due to there being a high degree of manual intervention in those countries in order to implement loadshedding. South Africa’s grid is much more sophisticated in that there is a high degree of automation. South Africa has automated load shedding that is embedded in the system, over and above the normal manual load shedding we are all accustomed to, that is based on frequency to manage frequency decays and power plant generation can also be controlled centrally to reduce load or increase it, purely based on frequency values.
Over and above this, there is a wide array of alternative measures in place. For instance, Eskom can switch off some of the large industrial consumers for a few minutes. This is already accounted for in their contracts and can happen automatically when the frequency drops off sharply and the automated switching off of plants, based purely on frequency, occurs. In those few minutes Eskom can then fire up their reserves, namely their open-cycle gas turbines (OCGT), the pumped storage schemes and/or implement loadshedding in order to prevent more plants from tripping and allow for the frequency to normalise.
source:Eskom grid collapse concerns well overdone – Kela Securities (biznews.com)
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