Switchgear and substations – Meeting the system demands of the future

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The Government projects the UK will go significantly beyond its commitment under the Kyoto Protocol and reduce its greenhouse gas emissions by almost 20 per cent below 1990 levels by 2010. With such emphasis being placed on renewable energy sources the energy industry needs to look ahead in order to identify what the effects of the system changes will be, as a consequence of the changing power sources. Masoud Bazargan at Areva T&D explains the importance of suppliers within the industry working with their clients’ systems departments.

In order to work more effectively, suppliers and users need to make sure transmission equipment is designed to incorporate current and future system requirements taking into account the changes in generating methodology needed to support the rigorous climate change programme the UK is undertaking.
Transmission and distribution plants have always been subject to continuous research and development in order to maximise reliability, safety, and wherever possible reduce capital and operating costs for the network operator. There are a large number of areas where development has provided benefits. Examples for transmission switchgear, have been the move from hydraulic to spring operated mechanisms; reduced energy mechanisms; more sophisticated interruptive technology; design improvements, modelling technology, arc physics; compact solutions; hybrid GIS solutions; end of life disposal; environmental considerations; reduced power to weight ratio; less site assembly times and lower volumes (i.e. space-saving).
However, one key area where development effort is being focused has been driven by more pressing external forces. Indeed, concerns about damage to the ozone layer and associated climatic effects caused by carbon emissions has accelerated the decline in the popularity of traditional fossil fuels and in turn driven the ascent of renewable energy sources. Generally this shift which has been welcomed, despite some opposition concerning local issues, is set to have wide ranging impact on transmission and distribution networks. Fundamental differences associated with renewable energy include fluctuating outputs and often remote geographical location of suitable power sources. Existing networks were designed for ‘traditional’ fossil fuel based generation in centralised locations and the change in generation mode and location to embedded generation from renewable sources in remote locations will inevitably impact on the specification for switchgear and other equipment.
In order to provide products that will fulfil the needs of network operators today and in the future, it is important to ensure that equipment is designed in line with the DNO’s development strategy. In order to achieve this, Areva T&D has developed close working links with system designers, using partnerships wherever possible in order to ensure that product design and development is aligned to the needs of the market, especially as what was an extremely stable market is about to go through one of the biggest changes since its inception. For these partnerships to succeed, they need to be a two way process with transfer of information of value, to and from both parties. The fact that continuity of specification ensures that substation components from different suppliers are in some cases very similar, makes this type of value add extremely important.
One of the most effective and favoured forms of renewable energy is wind-power. However due to public objections and land availability constraints, we are looking more and more to utilise the renewable energy available in the marine environment through construction of offshore wind farms. By its very nature, the offshore wind farm creates huge challenges for the transmission and distribution sector. The challenge facing the industry is not only to capture and convert the natural energies of the wind and the ocean but also how to transmit this power to the shore considering the difficult environment. These considerations can range from ecological impacts on the environment, e.g. effects on marine life and by the environment, such as marine growth on the installation, through to shipping lanes, oil and gas pipelines, geological and seabed consideration, access, weather condition, foundation, corrosion and cost.
One proven way of addressing the transmission issue is to connect the wind farm turbines via an inter array network of cables which link at offshore transformer substations located within the wind farm. Electricity from all the individual wind turbines is collected and the voltage stepped up to 132kV to make it more easily transported to shore via high voltage cables reducing the power losses.
The concept of an offshore substation, close to the turbines, does help resolve transmission issues, however, it also introduces problems of a different kind as the module will need to resist highly aggressive marine conditions, alien to its land-based cousins. Seawater induced corrosion can be minimised by locating the module out of the splash zone, around 10m above the high water mark, but a specialised external paint finish should be utilised to protect the structure and reduce the need for maintenance. The location of equipment types within the substation and its surface profile can also influence corrosion rates and must be carefully planned. Mechanical elements such as diesel generators must also be protected from water and salt ingress and suitable arrangements made for the substation to be self sustaining for say seven days in case of power loss. The transformer itself should also be reviewed in terms of layout, corrosion resistance and long term maintenance with particular reference to radiators, tank, fan and pump. Ventilation also needs to be considered, employing special filters to prevent salt ingress that could cause contamination and corrosion. In addition, handles and all other external fittings need to be re-specified for a marine environment to prevent corrosion.
Another consideration for offshore substations is the mounting arrangements and weight distribution. While a traditional land based substation will usually be mounted on a reinforced concrete plinth, an offshore module may be mounted on a large diameter steel monopile. The very nature of the support structure dictates that loadings must be minimised by managing the centre of gravity to the module and ensuring even weight distribution. Consideration must also be given to both dynamic and static loading in temporary as well as service conditions. Finally but no less importantly, the installation, commissioning, and any subsequent maintenance will have to be carried out in an alien, hostile environment far from overland access.
These changes are fundamental enough to require a paradigm shift in mind-set and an evolution of the current skill set. But we believe the whole industry will rise to the challenge and ensure that energy can be generated from renewable sources and distributed to where it is needed, consistently, cleanly, efficiently and safely ensuring that we all play our part in providing the electricity we need while combating global warming.