Innovation in Global Power - Parsons Brinckerhoff

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Distributing Power to Users http://www.pbworld.com/news_events/publications/network/ Upside Down! How Innovation in Distribution is Challenging Tradition... By Alex Neumann, Newcastle, UK, 44 91 226 2460, neumannA@pbworld.com Towards the end of 2007 PB’s power specialists in the UK undertook a review of innovation in distribution networks. Northern Ireland Electricity (NIE) was looking to prioritise its internally funded research investment spending, and tasked us to advise on the current innovation work across international distribution networks. This article provides a brief summary of some of the work that we identified as part of this project. Acronyms/Abbreviations DFIG: Doubly fed injection generators DG: Distributed generation DNO: Distributed network operator FCL: Fault current limiter IFI: Innovative funding initiative LV: Low voltage OfGEM: Office of Gas and Electricity Markets RPZ: Registered power zone SCFCL: Superconducting fault current limiter 1 PB is leading a collaboration project to develop a generator controller that regulates output based on the thermal ratings of the distribution system. To read more about this project, which is investigating the potential headroom that may be exploited on distribution overhead lines, cables and transformers, please see the preceding article, “Thermal Controller Project Innovation in UK Distribution Networks” also by Alex Neumann. With distributed generation (DG) offering a relatively clean and green source of power generation, development and deployment of these smaller and dispersed generation technologies is being incentivised around the world. Distribution systems of the future must be flexible and responsive components. This is a far cry from the traditional design specifications that assumed one way power flows to “dumb” loads. In 2005 OfGEM, Great Britain’s energy regulator, introduced the Innovation Funding Initiative (IFI) and registered power zones (RPZ) as part of its distribution price control aimed at stimulating research and development on the UK’s distribution networks. British distribution network operators (DNOs) have embraced these schemes, with more than 150 IFI projects and three RPZs being registered. A recent extension by OfGEM has confirmed that IFI funding will continue up to 2015 to allow projects with timescales greater than five years to maintain their momentum. Several of the innovations covered in our review are discussed below. Operational Innovations Several UK DNOs have reported actual cases where constraint management techniques could be applied to their distribution networks to avoid network reinforcements and thereby facilitate more efficient generator connections. On-line Control. Greece’s Hellenic Transmission System Operator introduced a novel type of interruptible contract for wind generators in congested areas of its network. An on-line control scheme is used to regulate the output of wind farms and allow increased penetration of wind generation, while maintaining network security levels by using a control scheme to monitor system bottlenecks. This system can take action by applying either preventative or corrective control modes, depending on the desired level of system security. Dynamic Thermal Ratings. Dynamic thermal ratings of power network equipment are being investigated in R&D projects in Great Britain and Northern Ireland. This active management of constrained connections has the potential to unlock additional power transmission capacity at times when DG is operating at peak output. 1 Central Networks, the electricity distribution company serving central England, has developed an RPZ that applies an active rating to a 132 kV overhead line based on real time measurements of ambient temperature and wind speed. Fault Current Limiting Devices. Increased levels of DG will result in increased local distribution system fault levels. When the network fault level approaches the rating of its switchgear, the connection of more generation may result in costly asset replacement or connection at higher voltages. Active fault current limiting devices, such as I s limiters and fuses, have been developed for low voltage and high voltage distribution applications up to 36 kV. These devices are not considered to be failsafe however! We concluded that their installation leads to difficulties complying with UK Health and Safety legislation, which is unlikely to change in the near-term. As such, it is unlikely that these devices will offer a practical solution to increased network fault levels. Newer technologies, such as solid state circuit breakers and superconducting fault current limiters (SCFCLs), do offer superior performance, however, when compared with existing commercially available FCL devices. The most significant advantage is their automatic recovery property, which allows continuous operation of the device on the power system. Some SCFCLs are considered fail safe and can be built to exhibit negligible impedance during normal system operation. One disadvantage is a power loss under normal operating conditions caused by the current leads passing from room temperature to cryogenic temperature. Research associated with SCFCL technology is focusing on 110 kV voltage levels and above, positioning the devices PB Network #68 / August 2008 72
Distributing Power to Users initially at the more capital intensive power networks where the potential financial benefits are more substantial than those at lower distribution levels. AREVA has developed a prototype magnetic FCL (MFCL) for 400 V application. Central Network’s IFI report indicates that part of its network will be used to trial the MFCL, which it expects is more promising (than SCFCLs) as it uses permanent magnet material and is easier to handle. The Electricity Networks Association in England has a research project underway to develop a “fault level instrument” that will provide real time estimation of network fault levels taking into account all connected elements (e.g. motors, DG, etc.). Scottish Power is participating in this project and estimates that this prototype instrument is at least three years from adoption. Voltage Control. The installation of high voltage/ 400 V transformers with on-load tap changers (OLTC) would improve voltage control of the low voltage networks. AREVA is currently developing a two-position tap changer for such applications and there are plans to trial this on the United Utilities network in Great Britain. Series connected power electronic single phase LV voltage regulators are currently being trialled by United Utilities and Scottish Power to solve customer under and over-voltage complaints on their networks. Although the regulators used were designed initially for single phase operation, they have been used also to solve threephase voltage complaints on the Scottish Power networks. GenAVC is being trialled by EDF Energy and United Utilities to optimise network capacity and generation export. The GenAVC system uses state estimation techniques to feedback nodal voltage level into the substation voltage control scheme to reduce or increase the primary busbar volts accordingly. This solution is currently being trialled on 33/11 kV transformers to control 11 kV system voltages. Reactive Power Compensation. Reactive power compensation can be used to control voltage and increase capacity by injecting or absorbing reactive power at the point of connection. Dynamic reactive compensation can enhance system stability and quality of power supply, providing fast reaction to voltage fluctuations and controlled damping of oscillations on the networks. The D-VAR is a type of static compensator that detects and instantaneously compensates for voltage disturbances by injecting leading or lagging reactive power at key points on the network using power electronic converters. This device can connect to network voltages up to 35kV and can inject up to +/- 8MVAr. Widespread DG may lead to the formation of power islands http://www.pbworld.com/news_events/publications/network/ on power systems following network disconnections. This is not permitted in many countries as these islands can give rise to safety, power quality and operational problems. The UNIFLEX-PM consortium project is aiming to develop and experimentally verify new and innovative power conversion architectures for universal applications in power networks. The converters will be capable of running a standalone power system both coupled with the wider distribution network or in island mode using islanding detection algorithms, voltage and frequency control and energy management using storage. A graphical depiction of a future power network utilising the UNIFLEX converters is shown in Figure 1. Figure 1: Future Active Network with UNIFLEX-PM system. Source: J. Clare and F. Iov, F’s UNIFLEX - PM. CIRED 2007, Workshop on Power Converters for the Future European Electricity Network presented on 25 May, 2007, (Slide 13). Energy Storage Technologies. The need to continually balance supply and demand for electricity, coupled with the intermittency of DG output and peaky demand curves, makes electricity storage a tasty proposition on future electricity networks. Energy storage technologies offer a local solution by regulating power flows by either employing peak load shaving or regulation of power sent out from DG installations (e.g., wind farms). Energy storage devices must be capable of fast operation to allow participation in fast acting energy management schemes of the future. Commercially available energy storage technologies are presented in Figure 2, categorised by output capacity and supply capability. Demand Side Innovations: Smart Meters Involving the consumer in the electricity market is a sure way of increasing awareness and provides opportunities to increase consumer efficiency and incentivise adoption of small scale DG technologies. Today, widespread smart meter installation is more commonly driven by the cost savings associated with the elimination of meter readers as well as more timely 73 PB Network #68 / August 2008
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