The energy transmission and distribution industry is evolving. For switchgear customers, distribution automation and environmental responsibility are now high on the agenda, alongside the traditional requirements of performance, reliability, safety and cost. However, as the lifetime of switchgear is often 20 years or more, technology R&D must be both innovative and pragmatic – meeting demands for automation and load-related growth, while allowing for the refurbishment of, and integration with, existing assets. Sundeep Singh, product marketing manager at Lucy Switchgear, explains
The smart grid distribution network is a critical goal for utilities in helping to manage our electricity needs – now and in the future. Utilities have an increasing need to understand the load on their network and improve their ability to share the load in real time between different networks in order to minimise the disruption of power supply. The ultimate aim is to improve reliability, to increase efficiency and capacity, to help reduce energy wastage. Our job, as a specialist in secondary distribution solutions, is to develop the next generation technology that will help utilities to meet this goal.
Just 15 years ago switchgear could only be manually managed on-site. Now, utilities with Scada systems have extensive control over transmission, and increasing control over distribution equipment from remote locations.
The goal of distribution automation is real-time adjustment to changing loads, generation, and failure conditions of the distribution system, without operator intervention. By providing a better understanding of network loading and an opportunity to manage the varying load quickly, by controlling field devices remotely, distribution automation technology is becoming increasing attractive to utilities and network operators beginning major smart grid deployments.
Indeed, global spending on intelligent electricity distribution systems rose 7% last year to reach $13.9bn. Further steady 10% growth is expected to see the market worth $25.2bn by 2018.
Despite this potential, utilities’ number one challenge remains justifying the business case; the scope, complexity and costs of the IT investments necessary means each step of deployment requires careful cost-benefit analysis. It is critical, therefore, switchgear being developed and deployed today is automation ready, ensuring easy integration with existing networks, while not compromising future smart grid developments.
Furthermore, as switchgear has long life cycles, many utilities currently have a significant installed base of ring main units (RMUs) designed in late 1980’s. Most of these RMUs were not designed for automation and could not be motorised for remote automation and control. As such, utilities have two options: either to replace the old equipment with new at high capital cost, or extend the life of current equipment by automating it.
Lucy Switchgear has designed a solution to upgrade installed switchgear with actuators and Gemini Remote Terminal Units (RTU) to enable remote operation and control, thereby creating significant savings for utilities and network operators. This is universally recognised as a more financially viable option than completely updating the infrastructure with brand new technology, without compromising the quality and safety of the public or the operator, or lowering delivery efficiency.
Environmentally responsible RMUs
Albeit high up the priority list, enabling smart grids isn’t the only concern of utilities and network operators at the moment – environmental responsibility is also rising up the agenda. In switchgear technology, SF6 (Sulphur Hexafluoride) gas has replaced oil and air for electrical insulation and arc interruption in most new and retrofit RMU installations due to its excellent electrical insulation and non-corrosive properties.
SF6 is a greenhouse gas, and there are some environmental concerns around using it in switchgear. Specifically, during arc extinction, SF6 gas is incinerated, producing toxic by-products which require special precaution while dismantling and recycling the switchgear. However, if SF6 gas is used in conjunction with vacuum bottles then the arc breaking is done by a vacuum breaker and SF6 is therefore only used as an insulating medium. This method of arc breaking offers a clean solution with no by-products.
Plus, if the gas tank is designed in such a way that it is resistant to corrosion and can keep the SF6 gas pressurised throughout the whole lifecycle of the switchgear, then the SF6 gas can be recovered and recycled for reuse. This reduces the impact of SF6 on environment, while utilising the inherent insulating properties of the gas.
Some manufacturers have started to use solid insulation techniques (epoxy resins) in distribution switchgear because it is regarded to have a lower environmental impact than SF6 gas. However, the use of epoxy resins significantly increases the risk of fire and the incineration of polymers will also produce greenhouse, as well as potentially hazardous, gases into the atmosphere.
For more than 40 years Lucy Switchgear has successfully designed and marketed a wide range RMUs using vacuum interruption technology alongside SF6 gas, capitalising on its excellent benefits.
RMUs are generally used in distribution substations, which are often close to, or sometimes located within, populated areas. Therefore, the safety of local communities and the RMU operators should always be the top priority. All live switching functions are hermetically sealed for life in an SF6 gas insulated, earthed metal tank, providing protection against electric shock and minimising the risk of accidents caused by human error. For example, the Lucy Switchgear Sabre range is designed to protect the operator from the front, sides and back of the unit in the event of internal arc.
SF6 gas is non-toxic, non-flammable and non-corrosive, which means:
• No oxidation (corrosion) of the contacts and screwed joints, meaning there is no gradual reduction in the carrying capacity of the equipment over time
• No synthetic material inside tank (cast resin insulation) reducing the fire risk
• No reduction in insulation capacity of unit due to external factors
• No risk of internal failure due to partial discharge
Hermitically sealed SF6 insulation means that the unit is completely independent from harsh environmental conditions, including: high humidity; flooding; creepage; pollution – dust and smoke; and saline deposits in coastal areas. Also, the excellent thermal conductivity and high heat transfer permits a higher operating efficiency despite ambient temperatures, meaning that switchgear utilising SF6 gas can be manufactured and deployed in almost any region in the world.
Ease of installation
The dielectric strength of SF6 gas is twice that of air, which means the physical units can be smaller and lighter than traditional RMUs. This has the obvious benefits of easier transportation and installation, as well as allowing for better use of space.
Evolution rather than revolution
The evolution in switching, protection and automation solutions for electrical distribution has been led by the evolving needs of utilities and network operators, as demand for energy that is safe, reliable and sustainable increases. Investment in technological innovation is key in helping our customers meet this need, but given the cost-implications of replacing old equipment with new, R&D should also focus on how to upgrade existing assets and make them fit-for-purpose.
The development of SF6 gas as an insulator used in conjunction with a vacuum breaker in RMUs is a great example of how retrofitting existing equipment can lead to improvements in performance, and should not be downplayed. As the UK moves closer to smart grid deployment, taking a future proof approach to our energy infrastructure and management needs will be critical.