Medium voltage substations are marvellous inventions, but they don’t come without their problems. Thomas Naul, utilities director for power systems, UK & Ireland at Schneider Electric, gives us six ways to mitigate some of the challenges.
The energy sector is shifting to a decarbonised, decentralised and digitised model, and the utilities industry needs to adapt alongside this change, or it will struggle to keep up with end-user expectations for green and clean renewable power.
Ofgem’s recently announced five-year investment programme to deliver greener energy networks has made it clear that minimal costs should be passed onto consumers to prevent enthusiasm for green energy from waning.
One of the great challenges utilities face is how to manage the increased integration of distributed energy resources (DER) into the grid and the growing pressure to keep down costs and optimise assets, while at the same time improving and maintaining power quality and service continuity.
Smart technologies are being introduced to medium voltage (MV) and low voltage (LV) substations to combat these challenges. Substations are prime candidates for the innovative smart capabilities that are becoming a crucial element of a digital national grid, because substations play a central role in electrical power distribution systems. They hold the switches, capacitors, transformers, and other assets utilities need to keep grid power flowing, balanced, and routed appropriately.
So, what are the ways in which smart grid technology can solve medium voltage substation challenges?
Managing and optimising assets remotely
Utilities are under constant pressure to reduce their capital and operational expenditures as the industry shifts to more cost saving technologies. This means they must optimise assets and manage them more efficiently in order to extend their life span and reduce operation and management costs. Once the sector has all their ducks in a row with the basics, then they can look at how to juggle both keeping costs low and getting the most out of their strengths whilst maintaining the high-quality power and service.
Smart investment in smart meters
Smart meters are an enormous investment for utilities, in fact it is estimated that there will be 800 million smart meters deployed worldwide by 2020. A key benefit of deploying these smart meters is their ability to both empower consumers and improve their energy usage. However, investing in them may also result in numerous costs.
For example, some utilities have not been able to reap the financial benefits from the billing perspective as of yet. In the UK, the rollout is expected to be completed by 2024, although a ‘false start’ with the digital limitations of SMETS1 models initially held up adoption among consumers.
For utilities to reap the benefits, they should leverage smart meter data to optimise their distribution networks. They can do this with smart meters that communicate through power line carrier (PLC) technology. Through this method, utilities can add value to their assets that are currently in place. All connected smart meters communicate through the substation they are attached to, making medium or low voltage substations a critical point of a PLC-based smart meter measurement aggregation.
Providing a quality service
Another way utilities can solve substation challenges is by improving their quality of service. One of the most critical elements of quality of service is minimising customers’ interruption time. Even short interruptions are inconvenient, disruptive, costly, and potentially damaging and dangerous.
A key factor when improving the quality of the service is the location of the distribution grid. Underground distribution grids typically have fewer interruptions and better performance than overhead grids, which are vulnerable to vegetation and storms.
As it is not always technically or economically feasible to move overhead lines underground, utilities can focus on smart technologies that reduce the difference in performance between overhead and underground grids. This can be achieved by adding smart reclosers in distribution network feeders where transient self-clearing faults frequently occur so they can reduce outages, allow for rapid recovery, decrease the number of end-users affected by an outage, and reduce the amount of non-produced energy and non-distributed energy.
Smart fault passage indicators (FPI) offer ways for the utilities to increase quality of service for a maximum of grid users, especially when switches are remote controllable. It also enables grid operators to optimise maintenance activities if it is necessary for field crews to fix assets on the site. The FPI also allows for faster diagnoses of issues and can warn connected distributed generation sources of the feeder status to avoid islanding the grid.
Monitoring and managing voltage fluctuations
Voltage fluctuations are a major pain point for utilities and a key challenge they need to overcome. They can be costly, inconvenient and affect power quality, safety, and reliability, which can damage customers’ facilities and equipment. The task of managing fluctuations has become more difficult as an influx of distributed energy resources (DER) have been integrated into the grid. Further to this, the supply of weather-dependent sources of energy like solar and wind power cannot be predicted with complete accuracy or turned on at the push of a button, which forces utilities to monitor and adjust power levels more actively.
To combat these fluctuations and mitigate the risk of under supply, utilities can harness an array of technologies. One way is with smart transformers that can meet dynamic voltage regulation needs, and are an appealing option for utilities that are planning for how they’ll meet their future distribution network challenges.
These smart transformers include actuators that can help manage voltage, as well as active and reactive power. They automatically regulate the medium voltage to increase or decrease the low voltage and ensure it keeps within the contractually allowed limits. Alternatively, utilities can use feeder switches that have intelligent local controls which can constantly monitor the system to identify and react quickly to fluctuations and faults.
Balancing LV feeder loads
Another obstacle smart grid technology can solve in the substation is when the feeder load is unbalanced. This can happen when low voltage ends of the distribution networks are unbalanced between transformers, between low voltage feeders within a transformer, or between the three phases of a particular transformer. Finding this feeder load balance is becoming more difficult as utilities cope with the growing addition of DERs, which range from supply-side to demand-side resources, and can magnify the imbalance because of an unsteady power influx.
If utilities can better balance LV feeder loads, they can achieve optimal performance and reduce energy loss, which, in turn, cuts costs. Smart technology can improve the feeder load balance by equipping LV readers with energy meters that connect to the remote terminal unit (RMU) in the substation and can calculate imbalances in real-time, as well as rebalancing loads using repartition units.
Steer clear of unwanted islanding
Intentional islanding is when a distributed generator continues to supply power to a portion of the grid when the main public electrical power grid is no longer present. This is a useful tool for utilities in an emergency when the grid is showing signs of impending failure.
However, unwanted islanding is a safety hazard and can lead to damage to the distributed generator unit, network components, and customers’ equipment. It most commonly occurs when protection devices located at the DER site don’t properly detect the occurrence and therefore don’t trip, or when the incorrect operation of a switch or breaker creates islanding conditions.
Unwanted islanding is becoming a more common occurrence because of the injection of DER, along with the rise of microgrids connected to the distribution network, which can disrupt system stability. Anti-islanding protection based on communications with the MV/LV substation creates a more flexible, localised option.
For example, smart fault passage indicators may be able to warn connected, distributed generation sources of feeder issues and by doing so help avoid islanding part of the grid. Smart technology can be used to force a disconnection by asking the feeder components to communicate with all attached DER.
Moving forward and thinking smart
Utilities today face ever higher expectations to maintain power quality and achieve greater service continuity. With the widespread integration of distributed energy resources all along the network, more smart grid capabilities are being introduced into MV/LV substations to meet these expectations.
MV/LV substations lie at the heart of the needed evolution of the electrical distribution network. Now is the time for utilities to formalise their roadmap for MV/LV substation and grid transformation. Smart technologies are now available to enable such a transformation affordably. Utilities companies that have begun looking ahead to a greener future and are investing in smart technologies will be able to equip the skills to build a healthier, more resilient energy network that drives sustainable economic prosperity and aligns to the national goal of net zero by 2050.
