Enabling works- how do we facilitate connections?
As we see an increase in connections to our high voltage electricity systems- work is needed to ensure our networks can continue to handle the increased demand- delivering power safely and efficiently.
Our electricity networks in England and Wales are made up of largely interconnected circuits formed of overhead lines, usually carrying voltages of 275kV and 400kV. The individual equipment in a circuit is rated to a certain capacity to carry electricity- which cannot be exceeded without increasing the risk of fault. So, when more connections wish to export or import extra energy to or from the grid, certain necessary upgrades to existing circuits may be required to accommodate this.
This process and the tasks arising from it are called Enabling Works. The large number of connections currently entering and already within the pipeline is driving up the number of enabling works triggered to accommodate this capacity. This in turn means other projects are then scheduled for delivery behind increasing amounts of these works.
But what are some of the types of work to increase capacity on a circuit?
Increasing thermal rating- reconductoring overhead line circuits (OHL)
Each OHL is strung with a set of conductors- which commonly consist of strands of metal woven together. A conductor type is rated for a particular power throughput- which also comes with a specific thermal rating. If the power load increases- the heat begins to rise, and the thermal operating rating could be exceeded. Heat causes the metal to expand, and sag, potentially breaching required safety distances, or hitting trees or other objects.
To avoid this, we can restring the circuit with larger conductors or new technology. A simple conductor is generally a mix of metals- but an increased capacity can be achieved using different materials. Some types have an air gap in the middle between the strands of metal- which can allow for more effective cooling of the conductor, or a carbon rod may be used as support in the centre of the woven strands, which means it will not sag when the metal expands.
To install new conductors which may have increased weight, towers (commonly known as pylons) may also need to be updated. Each tower is designed to consider the weight of the conductors combined with the forces operating upon it, including the soil types in which the foundations stand and weather conditions. Towers can be strengthened using steel reinforcements and repainted to prevent corrosion. Older routes might require full design re-assessment to support greater weights. Equipment in substations must also be uprated to ensure they can also handle the increased capacity- for example by changing transformers to newer or more efficient models and increasing the cooling capacity.
Reactive power compensation
There are many different types of reactive power compensation. Some examples include shunt reactors, series reactors or synchronous compensators. Different types have different functions- some can mitigate for over voltages to protect equipment; others can boost voltages to decrease current- or support voltages during drops. Installation of reactive power compensation can mean that the overall capacity of the circuit can operate more safely under a varied load. Varied loads present their own challenges. Older, more centralised generators like fossil fuel plant provided a steady base load, with the ability to flexibly ramp up or down depending on the required power output in times of fluctuating demand. Renewable generators can have very high and very low output- but this is dependent on environmental factors and cannot always be relied upon. Therefore, some power compensation measures are needed in areas of high renewable penetration, to ensure the system can compensate for fluctuations in demand. These can be activated when the voltage drops or increases beyond a certain point, ensuring that a reliable supply of power is maintained.
Protection upgrades
Another key area of upgrades are protection upgrades. These measures are there to ensure the system can prevent more serious fault on the networks by cutting off supply where issues are detected. Computer systems at the end of each circuit (usually located within substations) monitor the flow of power. If voltage or current were suddenly to rapidly increase or decrease, protection equipment such as circuit breakers and isolators would be activated to prevent further damage to any systems. Some circuits may have special protections, meaning if one area is affected, it is able to be isolated- thereby ensuring that no other parts of the system are impacted. Reconnection may also be attempted- for example, a falling tree branch might strike a conductor and cause a temporary fault, and the protection systems may attempt to reconnect after a certain amount of time. However- if this reconnection fails- the fault is likely more significant, and notice will be sent for an engineer to attend.
New circuits or substation assets
If upgrades have been assessed and are not adequate, or if the number of connections and the increase in demand is too great to be carried via the existing system- a new circuit or new substation asset could be triggered. This would then require further assessment, and full siting studies. For more information on how we determine location and our internal processes, read our article on siting studies here.
