A renewable energy revolution is being witnessed across the world. In India, the renewable energy capacity is set to increase to 175 GW by 2022. Of this, 60 GW will be from wind. This poses several challenges for distribution and transmission utilities. A look at some of the challenges, solutions and technology deployments to facilitate renewable energy integration…
Transmission perspective
From the perspective of transmission com-panies, a key challenge is that renewable power generation is difficult to predict. Moreover, generation sites are often located far from the load centres (offshore or in desert areas), implying the need for transmission of power across long distances on lines with limited capacity. This is a challenge as long transmission lines and high load have stability problems. This also results in a need for increasing the inter-area energy exchange.
One of the solutions to these challenges could be adding a renewable energy management package (REMP) to the traditional supervisory control and data acquisition (SCADA)/energy management system (EMS). This allows for forecasts of the system state such as load forecast, renewable generation forecast, switching forecast, etc., and combining this information to know how the system will evolve over the next few hours or days. Optimal generation despatch has to be carried out, making sure enough conventional energy reserves are available. Power flow analysis can also be done to check for any congestion or voltage problems and respond accordingly. One of the possible responses is curtailing renewable generation.
At present, conventional means of checking the load flow situation in the grid include a state estimator, contingency analysis and power flow. These existing components are in a steady state and what is new is the necessity to carry out dynamic stability analysis, which is a part of the traditional SCADA EMS. In particular, this package has been added as a renewable energy management component. It is applied to determine whether the system can survive several worst-case short circuit scenarios without losing more renewable generation than there are reserves from conventional generation. If this is not the case, the system must determine how much renewable generation must be curtailed to restore the system to a secure state. This procedure/algorithm, which is a combination of a state estimator and dynamic security assessment, has been implemented in Turkey (in the Turkish Electricity Transmission Corporation) where 55 wind parks are being connected to the grid.
Another aspect of renewable integration is related to the fact that power is usually fed into the transmission grid whenever possible because it entails no cost and one would not shut it out unless there is a substantial reason. However, if there is a problem in the transmission grid, the system operator has the right to curtail renewable generation. However, this has to follow certain precisely described procedures, which may need an interaction with the providers of renewable generation and integration with the concerned authorities. Siemens is automating the whole process of defining remedial action, that is, what is to be done, and how generation is to be curtailed and where. This also includes the process of announcing these actions and carrying them out, as well as monitoring, finalising and documenting it. This sequence is automated, which in this case involves the integration of the SCADA EMS environment with a lot of other players in the renewable generation market, making the task of the transmission operator much easier. This is being implemented in a German utility, 50Hertz.
Distribution perspective
On the distribution front, problems have arisen due to the advent of renewable energy generation. The complexity of the grid is increasing due to the integration of distri-buted energy resources and storage. For example, there may be a redirection of power flows, wherein the power flow direction may be altered to the opposite direction. There are also excessive voltage profiles, which may have to be brought under control. At the same time, there are other issues pertaining to ageing infrastructure, growing regulatory and customer pressure to provide reliable supply, and climate change causing both extreme weather conditions and outages in the distribution grid. Therefore, with more renewable generation being fed into the grid, the distribution grid has to fulfil tasks such as managing outages, reducing outage duration, automating fault localisation and ensuring supply restoration, in order to benefit from the information gathered from smart meters. While outage management is one aspect, there is also a need to analyse the grid and the power flow, and to try to optimise it, as well as to minimise grid losses and maximise grid utilisation, without investing in new equipment.
Increased renewable generation for the distribution grid necessitates the bringing together of three areas – distribution SCADA, advanced fault and network analysis, and outage management. These need to be integrated and operated on one technology platform with one common user interface. These three areas have to be combined into a single system, which is called the advanced distribution management system (ADMS).
On the analysis and optimisation front, the technologies that can be implemented in the field to increase renewable generation include controllable loads, energy storage, voltage control devices, transformers, controllable generation, controllable loads, and real-time thermal rating. The steps to be followed include first getting to the network state from the SCADA system, then identifying a problem, followed by making a decision regarding how to resolve it and finally, implementing the set point commands or if necessary, manual switching action. This process is combined into a package called Active Network Management based on real-time state estimation.
Such a system has been implemented by Siemens in the UK for the Northern Power Grid with the aim of addressing issues related to voltage violations and thermal overload. The equipment deployed includes 1,200 secondary substations, 15 autonomous substation controllers, seven batteries, two line voltage regulators, six controllable transformers, one capacitor bank and 10 demand-response contracts. The solution implemented is a multilevel, hierarchical one, which incorporates a central application system with a data warehouse and an autonomous substation controller using a wide area communications system. The Grand Unified Scheme brings together battery storage (6×5 MVA), enhanced voltage control, demand response and real-time thermal rating in closed loop for optimal grid operation. The integrated multilevel hierarchical solution entails benefits in the form of cost reduction and accelerated delivery by using a combin-ation of network technologies and flexible customer response.
Outage management
When it comes to outage management, there can be benefits from integrating it with IT by making use of the data from the meter data management system (MDMS). The data from the MDMS, for instance, can be used for out-of-service notifications, that is, meter events are mapped to customers and/or distribution substations. There is a visualisation on a map using coordinates and processing in outage management system (OMS) fault location. The ADMS operator or application pings specific meters to verify power outage – visualise “no power” status on the map process in the OMS fault location. The ADMS operator or application pings specific meters for verification after service restoration. In terms of solutions and technologies, there is the traditional SCADA, in this case the DMS environment controlling the field resources, and now, an additional range of market-driven applications is emerging. For instance, on the EnergyIP Platform, applications like the outage event service can be found as a part of the meter data management system.
One example where these systems have been implemented is Spain’s distribution company Iberdrola, which supplies power to one-third of the country’s consumers. The equipment implemented includes two data collection devices, a traditional remote terminal unit interacting with the SCADA system, a smart meter, and a data concentrator that collects information from the lower level (the substation in this case) and takes it to the energy business platform. From this platform, select information, like outage information, goes back into the SCADA system through web services and database adapters. Another example is from the city of Prague. It has also implemented an interface to meter information, though not for outage management. This is aimed at improving the calculation of the grid by enhancing the quality of load profiles of the transformers.
Given the current scenario, there is an integration of OT and IT, and the next step that is expected is the advent of cloud applications, whereby some of the applications will not be installed on the customer side but somewhere on the cloud.
Summing up
Large-scale integration of wind power generation is a reality today in many countries including Spain, Germany and Turkey; India is also growing fast in this regard. While wind power is the forerunner, solar photovoltaic is also coming up. On the transmission side, REMP is being added to the conventional SCADA/EMS and dynamic stability analysis is being carried out in real time, in order to address the challenges faced by transmission consumers. On the distribution front, ADMS, which is a single integrated software solution enabling optimised workflows and simplified operations with one common user interface, is available. Meanwhile, integration with the MDMS helps reduce the outage duration and increases the accuracy of network analysis and optimisation. SCADA, DMS and EMS are being integrated with energy business-driven platforms like EnergyIP, applying Common Information Model (CIM IEC 61970) and software-oriented architecture technologies. The upcoming innovations in the market include cloud-resident applications and big data analytics.
Based on a presentation by Dr Roland Eichler, Head, Technical Sales, Smart Grid Solutions, Siemens AG, Germany, at Smart Utilities’ 14th Annual Conference on IT & OT in Power
