Digital substations

Enabling a digital grid

A major theme of ABB’s current product planning is its focus on ‘enabling a digital grid’ and a major component of this offering is the digital substation.

As well as key features such as safety, flexibility and availability, cost, risk and environmental impact the concept implies the deployment of intelligent electronic devices (IED) with integrated information and communication technologies, enabling monitoring and diagnostics, as well as data and asset management.

At the component level this includes disconnecting circuit breakers with fibre optic current sensors (FOCS), hybrid high- voltage switchgear with a digitally compatible motor drive, sensing and monitoring devices for transformers, ‘Relion’ protection and control IEDs, the Fox family of communications devices, and the MicroSCADA Promonitoring system and asset health centre.

At the heart of its offering is a series of primary equipment solutions and IT, of which the following are some.

Transformer intelligence ‘Transformer Intelligence’ extracts and analyses relevant transformer data, to enable smarter decision making to optimise transformer performance, through the combination of sensors, monitoring platforms, transformer monitoring software solutions and expert assessments.

Plug and switch system with motor drive PASS is a compact hybrid switchgear assembled and high-voltage tested in the factory, for rapid installation and energisation. It encloses all functions of a complete switchgear bay in a single module. This switchgear can be equipped with Motor Drive, NCIT (non-conventional instrument transformers) and an intelligent local control cabinet for monitoring diagnostic and control purposes.

Live tank circuit breaker An AIS solution for digital substations with integrated fibre optic current sensor under the IEC 61850 9-2LE protocol is available for the LTB and the disconnecting circuit breaker (DCB). The DCB provides the functions of a circuit breaker and a disconnector combined.

Fibre-optic current sensor for HV applications This FOCS is a non- conventional current transformer, enabling digital substations and smart grids. Having an optical IEC 61850-9-2LE Ethernet output, it is based on the Faraday effect principle, meaning the design is inherently free of magnetic saturation.

FOXMAN-UN is a network management system that can be used in combination with various ABB communication devices. It provides supervision features, such as graphical representation of the communication network, a view of the synchronization status of FOX615 network elements and performance monitoring. In addition, it allows certain tasks, such as firmware distribution and activation, to be automated and scheduled. 

GE to enable Britain’s pilot of a multi-vendor digital substation

Scottish Power Energy Networks has selected GE to be the supplier of the digital control system for its Future Intelligent NEtwork SubStation (FITNESS) project. FITNESS is intended to pave the way for a smarter electricity grid as part of UK’s energy security initiatives to transition to a low carbon economy and is part of the RIIO Network Innovation Scheme (NIC). GE will deliver an intelligent digital substation with a full suite of interoperable solutions to SPEN.

A smarter electricity grid is a critical enabler for Britain’s aim to reduce CO2 emissions by 80% in 2050. Through RIIO NIC, the UK is investing over £500 million to support smart grid trials. This project should provide an intelligent digital substation solution that enables faster deployment, greater availability, improved safety and greater controllability with a reduced footprint and cost.

It will be the first live project in the UK to demonstrate multi-vendor interoperability through the IEC 618501 standard. Multi- vendor interoperability will endow customers with the freedom to ‘plug and play’ the best solutions to fit their needs, irrespective of vendor.

Colin Taylor, director of Engineering Services at SPEN, commented “[following] a successful demonstration it will change the way we maintain and build new substations ... we see huge potential for benefits to our customers through minimising use of copper and reducing substation footprint.”

GE will provide SP Energy Networks with a digital substation architecture that will connect GE equipment with a selection of third party vendors. These vendors will be interfaced to GE’s IEC 61850 compliant process and station buses based on GE’s DS Agile. The project solution consists of a substation digital control system encompassing fast and reliable data exchange across the whole substation. Integrated with a ‘grid stability package’, this control system enhances grid controllability and improves asset efficiency through monitoring, managing and analysing the grid dynamics.

The substation is said to be a compact and light solution with reduced equipment size and replacement of copper wiring, with digital communications over optical fibre.

It is equipped with Compact Sensor Intelligence (COSI) digital instrument transformers that digitise signals at the source, and is said to be capable of delivering enhanced functionality, made possible through the qualities of optical sensors and greatly improved access to dynamic measurements, including new options for fault and harmonic information management to assist engineers in the transition to a low carbon grid. It will also enable more rapid connection of renewable generation, through the standardised integration of new and flexible wide area control capability in a digital substation environment, enabling the employment of transmission assets at levels closer to their physical limits. 

Grid support

Siemens pushes vacuum interrupters to 145 kV 

While millions of vacuum interrupter units are used in medium voltage switchgear worldwide, until now they have come up against their limitations in the high voltage sector above 72.5 kV. At higher voltages, SG6 is generally used.

But following intensive research and development in this area, Siemens has developed a high voltage interrupter and gas-insulated switchgear, using vacuum technology and what is called ‘clean-air’ technology, up to a voltage of 145 kV.

With this technology, a vacuum interrupter unit performs the switching and arc extinguishing activities. Technically processed and purified air with a mixing ratio of 80 % nitrogen to 20 % oxygen – so- called clean air – provides the insulation for the current-carrying conductors inside the housing of the metal-encapsulated, gas- insulated switchgear (GIS).

The resulting outdoor circuit-breaker 3AV1 and new switchgear 8VN1 Blue GIS (photo, right) with vacuum switching technology and clean-air insulation are scheduled to be launched commercially in 2018. They are further developments of the circuit breakers and switchgear that use sulphur hexafluoride (SF6) as insulating, switching and arc extinguishing gas and which will continue in the product range.

With the combination of vacuum switching technology for switching and arc extinction and clean air as high voltage insulating medium, Siemens has further developed existing insulation and arc extinction technology to meet climate neutrality requirements. “With this technology, we are expanding our high voltage portfolio and offering our customers an alternative solution without SF6 for higher voltage levels as well. The use of technical switching and insulating gases with high global warming potential can be reduced or even avoided completely in many application areas with the help of vacuum switching technology,” commented Karlheinz Kronen, CEO of the Business Unit High Voltage Products within the Siemens Energy Management Division.

How it works

With vacuum switching technology, when the contacts are opened the switching arc is contained in a metal-vapour plasma between the contacts inside the vacuum extinction chamber. The metal vapour condenses back onto the contacts after the arc is extinguished. No decomposition products occur and the arc does not affect the surrounding insulation. This means that natural insulating gases such as dry air, nitrogen or carbon dioxide that only have poor arc extinction properties, if any at all, can be used for high-voltage insulation of current-carrying conductors. The use of technical insulating gases that have to be able to insulate live parts as well as extinguish arcs effectively can be reduced or even completely avoided by means of vacuum switching technology. The combination of vacuum interrupter units up to 145 kV for arc extinction and dry air (clean air) as high voltage insulating medium offers an additional alternative to sulphur hexafluoride to supplement the existing insulating and arc extinction technology.

Capabilities

Siemens has used vacuum switching technology for more than 40 years in its medium voltage switchgear as well as in high-voltage circuit-breakers up to 72.5 kV.

The new technology will extend the application of vacuum switching technology to a rated voltage of 145 kV, a rated short- circuit breaking current up to 40 kA, a rated current of up to 3150 A and operating temperatures from -55°C up to +55°C.

This wide service spectrum makes the new CBs and switchgear suitable for many applications in both outdoor as well as indoor installations. The lower insulating capability of natural gases results in slightly larger dimensions compared with gas-insulated switchgear with SF6, but power transmission efficiency in practice remains as high as before. Vacuum switching technology provides advantages for the operator including, for example, easier handling during transport and installation and in operation as well as during maintenance and when recycling. The operator is also relieved of the task of reporting the volumes of gas used. 

‘Green’ gas gets first substation outing

Deployment of the g3 gas mixture as a replacement for SF6 has taken a major step forward: Alstom’s (new GE’s) F35-145 kV gas-insulated substation may now be SF6-free. It has the same physical footprint as its SF6-based GIS predecessor and can operate at ambient temperatures as low as -25 °C.

Two years ago GE announced a breakthrough in developing a substitute for SF6 in gas-insulated equipment. Such a substitute had become necessary because SF6, despite its undeniable qualities – its arc-quenching and dielectric capabilities – has a global warming potential (GWP) 23 500 times that of carbon dioxide, with a lifetime in the atmosphere of over 3000 years. With g3, a fluoronitrile and CO gas mixture, GE was able to develop a suitable operational 2 alternative with a GWP brought down by 98% compared with SF6. Now the product is to get its first outing in a commercial application.

At a site in Switzerland, GE will provide Axpo Holding, the Swiss energy utility, with a F35-45kV gas insulated substation. Here, instead of SF6, g3 will be used in all components including circuit breakers. Located close to Zurich, this substation will be the first in the world using g3. The installation is in line with Axpo’s stated aim of reducing net greenhouse gas emissions.