Electricity supply systems of the future



 

The purpose of modern power systems is to supply electric energy while satisfying the potentially conflicting requirements of an economical solution with high reliability which offers the best environmental protection. This article discusses international views on the subject of future supply systems.

Electricity utilities and operators need to be aware of the impact of future technologies and make preparations to enable them to adapt to a changing environment where the involvement of the customer in the operation, reliability and use of the grid, will continue to increase. Electricity utilities and operators need to be aware of the impact of future technologies and make preparations to enable them to adapt to a changing environment where the involvement of the customer in the operation, reliability and use of the grid, will continue to increase.

Cigré, the Council on Large Electric Systems, which was founded in 1921, is an international non-profit association for promoting collaboration with experts from all around the world by sharing knowledge and joining forces to improve electric power systems.

Fig. 1: Relative comparison of reliability contributions of resource groups (EPRI).

Regarding the electricity supply systems of the future, Cigré has identified the following challenges:

  • Policies for lower carbon, renewable energy sources (RES), efficient energy use.
  • Integration of RES and distributed generation (DG) into the grids.
  • Increased customer participation and new needs for distribution grids.
  • Progress in technology including ICT.
  • End-of-life grid renewal (aging assets).
  • Methods to connect remote areas with no electricity.
  • Market design and regulatory mechanisms for an equitable, cost-effective transformation.
  • Environmental compliance and sustainability.

With respect to the first two points, in order to operate an electricity supply grid reliably, there is a need for the full component of services to be provided by generators. This list as well as the ability of different generation (resources) to provide these services is shown in Fig. 1.

In Fig. 1, zero indicates no ability to contribute to a reliability function, and five indicates full capability. In order to operate the grid, resources with capability of at least four should ideally be constantly available.

With the increased deployment of inverter based resources, the synchronous resources are required to contribute a higher level of ancillary service than originally anticipated. This often comes at a cost to the synchronous resource either in terms of life of plant or cost of operation. These costs need to be recovered (e.g. by an ancillary service market) to ensure continued supply of these services.

Non-synchronous ancillary service can be provided via flywheels (inertia) but these are limited in the service provision and duration. Batteries provide more potential services and show promise for larger deployment in future.

In costing the resource it is important to include full cost of supply including additional ancillary service support if required. This will ensure maximum possible penetration of inverter based resources (if cost effective) with the ability to operate the grid reliably. In meeting the challenges listed above, it is necessary to focus on ten areas of technology which are covered in the following sections.

Grid model

With the advent of distributed renewable generation, it was initially assumed that bulk transmission would not be required. This has proved not to be the case as the location of renewable resources are often in areas remote from the load.

There are two likely models that will coexist in future:

  • Increasing importance of large networks for bulk transmission
  • The emergence of clusters of small, largely self-contained distribution networks

The role of transmission will become much more diverse covering bulk transmission, balancing resources across wider synchronous areas and providing a very different set of services to those it was originally developed for. Transmission has to evolve, and evolve quickly.

Ten issues of consideration to transform to the modern grid

The following ten points have been identified by Cigré as being necessary to take into account when moving to the modern grid. It is suggested that these points be considered in research, investment and development of standards by operators and utilities when moving to incorporate all types of resources in the modern grid. It is critical that all ten areas are addressed simultaneously. If one is omitted it will affect the purpose as described in the introduction.

Active distribution networks

This includes massive rollout of smart meters, determining network architectures as well as micro-grid and remote area connections.

  • Distribution level needs more “smartness”: This includes analytics, monitoring and feedback of grid parameters.
  • Massive penetration of smaller units: This imposes the need for their control and coordination and applies to operation and maintenance as well as fault management.
  • Smart metering implementation: The challenge is to enable open source technology to reduce the required maintenance and refurbishment burden on utilities.
  • Evolution of markets and regulation: These should include ancillary services provided via customers.
  • Novel distribution network architectures: The power and telecommunication/computer architecture needs to be developed and planned upfront.
  • Connection of remote areas with no access to electricity: These include innovative metering and revenue collection, low cost low density technologies. Communication to enable faults to be reported and repaired in reasonable time.
  • Micro-grids and virtual power plants
  • Solutions for remote micro-grid connections

Massive exchange of information

With the installation of large amounts of smart meters as well as smart generation and inverters, there will be large amounts of data available. It is important that this information is converted into usable information and does not lead to lower productivity. Data recovery and cyber security as well as management of big data is key.

  • New architecture of the whole system for system operation, protection, etc.
  • It needs to be established what data must be exchanged and with what kind of requirements (volume, frequency, availability, security, etc.).
  • Big data: massive amounts of data exchange/storage.
  • Disaster recovery and restoration plans.
  • Cyber security and access control.

Integration of HVDC power electronics

With the advent of large scale inverter base resources (many hundreds of thousands), there is a need to understand the integration of power electronics into the system as well as the impact “dumb” inverters may have on the waveform.

  • High voltage direct current (HVDC) systems employing power electronics (PE) may create harmonic distortion which has to be managed with filtering.
  • Fault behaviour: The fault level may vary drastically in short periods of time.
  • Network performance needs to be carefully studied, with appropriate models of the HVDC and PE systems.
  • HVDC grids LV DC grids.
  • The penetration of power electronics at medium and low voltage levels needs to be integrated. This may alter the load type from constant current/resistance to a constant power load for example with the use of electronic voltage regulators.

Massive installation of storage

In order to provide ancillary service and continuous source of energy massive storage is required for frequency, voltage control and reduction of peaks.

  • Modeling for steady state and dynamic simulations
  • Management for storage
  • Sizing of storage devices
  • Co-operation with RES for hybrid systems
  • Management in autonomous power systems
  • Ability to reduce peaks
  • Co-operation with DSM
  • Frequency control

System operations and control

The ability to control the system with large scale inverter resources requires different measurement parameters (displays of inertia and rate of change of frequency (ROCOF) levels in control rooms) as well as different analysis models and operator skills.

  • Power balancing, congestion and risk management.
  • New software to quickly determine system status over wide areas, automated configuration adjustment, automated service restoration.
  • Inertia, synthetic inertia, rate of change of frequency and the consequence of rapid changes of generation sources with different inertias and reliability needs to be taken into account.
  • Training of system operators.

Protection schemes

This includes wide area schemes, ability to deal with low fault levels, rapid and reliable ROCOF protection as well as home energy management and electric vehicle integration.

  • New wide-area protection systems.
  • Impact on the protection system of new generation (variable fault levels, multiple in-feeds to faults) – this may require dynamic protection setting.
  • Technologies (decreasing short circuit power).
  • Capabilities for fault-ride-through.
  • Coordination between protection and new generators capabilities.
  • Inadvertent Islanding detection.
  • Intentional islanded operation.
  • Rapid under frequency operation.
  • Data management and architecture of the future.
  • Metering as information collectors for distribution.
  • Networks automation, home energy management.
  • Electric vehicles.

New concepts in planning

Includes risk based planning, understanding full cost and capabilities of new technologies, integration of micro-grids and integration of HVDC grids and AC networks.

  • Risk-based planning to manage uncertainties and changes in nature of supply and demand and role of the power system.
  • Interaction of transmission and distribution expansion investment needs, to plan best for demand response, distributed generation.
  • Understand cost, capabilities and lead times of each new technology.
  • Keep learning about pros, cons and combinations of central planning vs. market solutions under changing market and regulatory environments.
  • Single phase analysis, integration of micro-grids, load and voltage determination.
  • Integration of HVDC grids and AC networks.

New tools for technical performance

This includes advanced numerical techniques and numerical methods for the solution of multiphase load-flow problems, and time domain simulation. Analysis of dynamic behaviour, islanding and power quality effects is also required as well as models simulating HVDC grid, converter stations, and FACTS (flexible AC transmission system) devices.

It should be noted that FACTS also applies to distribution voltages, but that the simplified tools used in the design of LV networks are no longer applicable. It is necessary to perform dynamic studies on LV networks with inverter based resources, which will drastically increase the workload of planners unless the correct tools, training and systems are in place.

  • Advanced numerical techniques and numerical methods for the solution of multiphase load-flow problems, steady-state initialisation of network studies and time-domain simulation.
  • Bridging the gap between 3-phase and positive sequence modeling – single phase.
  • Geographical Information System (GIS) based tools.
  • Advanced tools and techniques for power balancing and reserve requirement evaluation.
  • Operational tools allowing a probabilistic and risk based planning.
  • New tools for development and operation of active networks, especially their dynamic behavior, islanding and power quality effects.
  • Models for assessing the interaction between the AC system and HVDC converter stations, HVDC grids and for FACTS devices.

Increased use of existing corridors

Includes uprating of lines, use of high temperature conductors, conversion of AC lines to DC and development of new insulated AC and DC submarine and underground cables.

  • There is a need to determine which technologies are appropriate and can be used for uprating existing lines in each case. These include probabilistic ratings, real time ratings, re-templating of lines and possible use of high temperature conductors.
  • Conversion AC to DC lines as well as towers with combined AC and DC circuits.
  • Develop new insulated AC or DC submarine and underground cables.
  • Investigate the ability of all components to withstand transients and over voltages.
  • Increased use of interconnections and their implications on planning, operation and control and the establishment of electricity markets.

Stakeholder awareness

The production consumer or prosumer needs to be aware of different products, ability to sell services into the grid as well as receive different services from the grid. Community involvement is critical for rollout of any new home based generation, storage, appliance control or smart metering device.

In the planning phase:

  • To demonstrate the usefulness and the benefits given by the network.
  • To guarantee that sustainable development principles and issues are being incorporated during this stage.
  • To take into account public views and needs already in the design steps (e.g. the choice of alternatives).

Community involvement in the construction and operation phases:

  • To demonstrate the compliance with environmental standards, to obtain a support to the necessary actions (e.g. maintenance).
  • Community involvement – especially in the employment of residents for installation of infrastructure in areas of low employment.

Conclusion

Utilities and operators need to be aware of the impact of future technologies and make preparations in each of the ten areas mentioned above.

Contact Rob Stephen, Cigré, Tel 031 563-0063, rob.stephen@eskom.co.za

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