modelling resilient distribution networks
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The electricity supply industry is under pressure to accommodate the increase in renewables share on the grid. However, it is a welcome challenge. New technologies, including solar and wind, support decarbonisation efforts and increase electrification rates.

Still, it is a concern for distribution engineers and planners responsible for keeping the network stable and resilient who must now consider factors such as reverse power flow, fluctuations, and integrations.

At their disposal are years of tacit knowledge, home-grown calculation tools, cloud-based digital modelling software, and outsourcing the task to consultants. But which solution is best suited to tackle the challenges associated with maintaining high reliability of supply while increasing integrated distributed energy resources (DERs) on the network?

Demand for power in Africa set to expand

Though the 2019 Electricity Access in Sub-Saharan Africa report by Agence Française de Développement (AFD) and the World Bank states that the electrification rate in Africa is estimated at 43.5%, there are factors underway motivating a splurge of new connections and consumer demand.

One such element is the advent of the African Continental Free Trade Area (AfCFTA) on 1 January 2021, which comprises a market of 1.2 billion people and a $3 trillion combined GDP. The initiative sets out to boost trade across the continent, and it is here that the need for grid expansion and reliable electricity supply will take centre stage.

To address this need, several government-led high-value generation, transmission and distribution projects are underway across the continent. Highlighting a few, Botswana, Namibia and the United States have concluded and signed a historic memorandum of intent (MOI) to create a Mega Solar project in the two southern African countries. And in Nigeria, the Federal Government plans to spend $3 billion on the energy sector in the next 24 months. It anticipates increasing power wheeled by the Transmission Company of Nigeria from the current 4,900MW to at least 7,000MW.

Accuracy in grid expansion and distribution planning

Many utility companies use outdated tools to achieve results in Africa’s evolving electricity landscape. However, these are homegrown solutions to manage and operate the network, which may no longer meet the industry needs or require manual effort for data maintenance and affecting grid reliability. With the added responsibility to maximise grid utilisation, expand the network and integrate alternative energy resources, distribution planners require tools to streamline modelling and analysis of the continuously changing power grid using time series from actual data.

Engineers along the distribution value chain must investigate digitalisation in grid operations, such as those offering power system simulation (PSS®). In this scope, the PSS®SINCAL Platform has for over 30 years enabled engineers to tackle different challenges of the changing distribution grid, including maintaining high reliability of supply and efficiently integrating DERs. Continuous improvements to this digital application provide distribution engineers with the current simulation tools they need to plan, design, and operate their power distribution networks.

This solution applies to balanced, unbalanced, radial and meshed networks – from low to high voltage. For example, the modular platform of PSS®SINCAL supports the entire workflow from the initial data import and network modelling (considering past, current and future conditions) to primary and extended calculations, all the way to extensive protection simulations and analysis as well as other methods in time and frequency domains.

A Moroccan case study using PSS®

Decentralisation and renewable energy are an integral part of Morocco’s policy agendas, including reaching 10GW of renewables or 53% in its energy mix by 2030. A step toward this goal was a 2017 research paper, Steady State and Dynamic Analysis of Renewable Energy Integration into the grid using PSS®E Software. The paper outlines that the challenges to the Moroccan grid system operators are that areas with high renewable energy potential are highly concentrated and unevenly distributed. They are mainly located in areas of low consumption, and the integration of intermittent renewable energy sources into the grid creates new challenges.

To examine the power system’s stability and define the potential integration of distributed generation into the grid, steady-state and dynamic simulations were conducted. The steady-state analysis is based on the calculation of load flow on the voltage profiles of system bus bars, transmission lines and transformers. This analysis was an integral approach to investigating power system planning and design of power plants’ connections to the transmission grid.

Also, dynamic stability analysis involves investigating and predicting network behaviour when faced with sudden disturbances – especially three-phase faults created by tripping of transmission lines, transformers or bus bars connected to generators. Therefore, the objective of this work was to analyse the Moroccan southern transmission network with large-scale integration of renewable energy by the year 2020 through performing steady-state and dynamic simulations.

Using the PSS®E software simulation tool from Siemens PTI, the authors analysed the transmission network consisting of two central fossil fuel power stations, two concentrating solar power plants, one hydro plant and four wind farms. With a focus on the impact induced by any power unit added to the power system through power flow calculation and transient stability, the study revealed that the critical fault clearing time (CFCT) was 200ms.

These CFCT results showed that the integration of renewable energy does not affect the Moroccan transmission power system stability. The terminal voltage and frequency behaviour and the active and reactive power outputs did not fall under allowed values. Reset to their initial conditions was found soon after the fault clearing. This research shows that using a digital solution, such as the PSS, is a valuable tool for transmission and distribution grid planners and operators in making timely, forward-thinking decisions.

First steps to adopting digital solutions

The increase of wind energy, solar power, electric vehicles, and battery storage do cause stability and resilience issues for the distribution network. However, having a clear view of the challenges is the first step to managing the risk. Therefore, with solutions such as the PSS®SINCAL, which offer modelling and simulation capabilities, distribution planning departments can refocus time to where it is most needed – ensuring network reliability. Even so, investing in a simulation tool requires investigation into its viability for your utility or company. Not all solutions are equal or attuned to the specific needs of Africa’s many utilities’ unique network conditions.

Therefore, as with any innovation and advanced technology, utilities must raise questions such as what training is provided and can the tool be integrated with existing software? Other queries involve extra cost for additional users, what expertise the service provider holds, and is there long-term training and after-sales support?

Network operators can also acquire insight from a utility similar to their own already using the solution. Another is to take up any free trials available; however, beware of short-term trials as your unique circumstances may require more time to evaluate whether this tool meets your goals.

The biggest hurdle, and most important to overcome, will be earlystage training for system operators, planners, and engineers on the new system, followed by long-term support.

Design and protect your network model

The proliferating deployment of DER on distribution networks is adding to the pressure requiring grid operators and planners to increase the number of grid interconnection studies; however, with limited resources and time. Therefore, utilities and DER investors will benefit from tools that can help them automatically assess the viability of various interconnection proposals.

As an example, the Maximum Hosting Capacity (ICA) module within PSS®SINCAL automates different calculation functions (such as load flow, short circuit analysis, protection checks with network adoptions, voltage fluctuations due to DER coming online and offline, etc.). Additional PSS®SINCAL features for DER integration include timeseries load flow with grid controllers (voltage, power), short circuit with defined contributions of generators and converters, harmonic distortion limits according to standards, unbalanced RMS grid current and Electromagnetic Transients (EMT) simulation.

Distribution planners can intuitively design their network model in PSS®SINCAL, either by drawing it within GUI or automatically through interfaces with other systems. Multidimensional networks can be visualised in schematic, geographic, or multilayer diagrams. The visual representations are interactive, and network elements can be auto-populated, created, edited, and formatted directly within the network graphic.

To build up or strengthen the network model, data can be easily imported, through various standard interfaces and adapters for data formats of other network calculation programs (for example, PSS®E which was used in the Moroccan research), for standardised data formats (for example, CIM), for data sets using the supplied standard Excel import, and PSS®SINCAL specific datasets. Network models can also be generated by an external interface from the data set of a network calculation software, a geographic information system (GIS) or the network model management of a control system.

The evolution of the energy market is changing how utilities optimise, protect and expand their networks. While end-users expect quicker response times to medium and low voltage outages, distribution system operators can implement feasible tools to reduce manual efforts and ensure network reliability and protection significantly. ESI

Empower your distribution planning engineers
Learn how PSS®SINCAL can address your distribution planning needs. Visit the PSS®SINCAL website to watch the introduction webinar: Streamline distribution network planning and renewable integrations.
Sign up for the free trial programme including exclusive hands-on training and more. Siemens.com/pss-sincal-africa

References
• African Union, 29 March 2021. The AfCFTA Secretariat and UNDP sign a strategic partnership agreement to promote trade in Africa
• ESI Africa, 24 May 2021. Nigeria: Federal Government to spend $3b in power sector
• ESI Africa, 29 April 2021. Botswana, Namibia and the US sign MOI for mega solar project
• Ameur, Arechkik & Loudiyi, Khalid & Aggour, Mohammed. (2017). Steady State and Dynamic Analysis of Renewable Energy Integration into the Grid using PSS/E Software. Energy Procedia. 141. 119-125. 10.1016/j.egypro.2017.11.023.
• ESI Africa, 29 April 2021. Micro-grids: A solution to Africa’s electrification challenges?