In many African countries, generation shortfall is being addressed through investment in large-scale renewable energy sources plus significant growth in distributed energy resources and other low carbon technologies. Across the region, there is great potential for high volumes of photovoltaic, wind or geothermal energy generation, depending upon the location. [quote]
However, this growth in distributed energy resources (DER) presents a number of challenges in terms of grid management. Traditionally, the design of distribution networks accommodated power flow from grid supply points to the electrical consumers through the medium and low voltage (LV) networks. These networks’ design met the needs of normal operation, fault conditions and the abnormal operations (when the network is re-configured for maintenance purposes). As such, the design limits of the network were calculated based on the connected generation and other rotating plants, so that it remained within fault current levels.
In the past, the changes in fault levels could be planned and predicted but in today’s networks, embedded generation and other forms of DER are providing an additional contribution to fault current. The embedded and intermittent nature of this is not only making fault calculations more complex, but the combination of operational switching is adding to that complexity. To further complicate matters the growth in embedded generation is being determined largely by customer takeup rather than central planning and is increasingly occurring at low as well as medium voltage level.
As a result, utilities are having to address this either temporarily or permanently by increasing the ‘electrical headroom’ of the network to take into account the voltage fluctuations this brings. Furthermore, active network management at medium and low voltage distribution levels is becoming ever more important to maintain quality of service to customers.
According to Dr Willie de Beer, a former executive of EDI Holdings, distribution-linked power disruptions are rising, but this is being masked by the generation shortfall. This suggests it is more important than ever before that utilities are able to manage networks efficiently and proactively to reduce fault-related interruptions and guarantee quality of supply to the end customer.
This is driving increasing investment in automation and smart grid projects to provide the network intelligence companies need to realise efficiencies across networks, improve network capacity and quality of supply and help future proof the infrastructure.
However, utilities generally have very little knowledge or visibility of the ‘last mile’ of the distribution network, where much of the embedded generation is being installed, and the stresses this introduces to an already stretched network. In fact, when customers are disconnected due to power system faults, utilities often have to rely on them reporting the problem to identify where the fault has occurred.
A low voltage measurement system, which allows utilities to dynamically understand their LV networks and provides actionable information for protection and control systems, can deliver the vital piece to complete the gap in information needed to actively manage the whole network.
Low voltage monitoring
Historically, distribution challenges have been focused on improving quality of supply to customers and operational efficiency of the networks. This was achieved through power flow monitoring and fault passage measurement on the MV network. However, the new challenge will be in enabling and managing DER such as embedded generation and energy storage (ES), improving energy efficiency and increasing flexibility through access to daily energy profiles.
When considering the constraints due to fault limitations, utilities will need to consider what electrical headroom there is for increased fault levels. A fault on an LV network is largely determined by the LV feeder transformer short circuit impedance. With the introduction of large amounts of small-scale embedded generation, fault levels will rise, but the biggest effect will be on voltage profiles. Given that the rising peak demand may need to be met without major reinforcement, it will be important to prevent overload of the network through integration of DER and other forms of LCT. Active network management control systems (ANM) will manage this electrical headroom; however, fault current levels may be reduced Having the ability to predict where faults are likely to happen, detecting when they happen and providing information that will allow the fault to be fixed more quickly will allow network distribution operators to better plan for these additional fluctuations on the low voltage network.
This is where effective low voltage monitoring can help. Lucy Electric’s GridKey range is a world leading low voltage continuous monitoring system, which measures, communicates and stores real-time data and, through analysis tools, translates this into actionable information.
GridKey increases the visibility of the LV network and allows distribution companies to rapidly identify and accurately locate faults so they can be quickly resolved. By improving fault response and resolution time, utilities can drive improvements in service quality and increase customer satisfaction. Analytics currently in development will allow a level of fault prediction, which will provide the ability to use planned maintenance to prevent faults happening in the first place.
Using information provided by the system network operators can identify areas of stress on the network and manage these fluctuations through active network management. The information also allows companies to plan for replacement and reinforcement of assets.
By giving utilities clear visibility of power quality across the LV distribution network, the system can help to identify issues and plan for changing conditions on the network. This allows companies to safeguard power quality levels and ensure statutory voltage levels are maintained. Technical and non-technical losses can also be clearly identified so issues can be quickly managed. As a consequence losses are minimised, lowering the overall financial impact and reducing costs for the consumers.
The system also has the potential to provide wider benefits in conjunction with other network management tools. Linking the low voltage network information with geographic network views through a distribution management system will provide fast and user-friendly identification of issues and improve the operation of the network. Where possible, customer data can be linked to MV and LV circuits for improved network management and to improve the load modelling and load profiles for customer segments or large customers. The Lucy Electric DMS combines information from several customers’ points and can identify and alarm for conditions including blown fuses, broken conductors, under- and over-voltage alerts and the location of LV faults.
With the growth in DER and renewable resources set to continue as part of the response to the energy generation shortfall across the region, utilities will need to develop more tools for the proactive management of networks to ensure that quality of service is maintained. Dynamic measurement and monitoring of the network will be ever more important to help companies manage the challenge of intermittent generation and bi-directional power flows.
This vital information will form the foundation for companies to actively manage distribution networks from centralised control points down to low voltage level, and with the growth in microgrids or off-grid applications it will also be key in ensuring visibility and management at more localised control points. ESI