The fast-paced internet age has inspired ABB to create a programme that enables customers to design and plan their substations on-line. This method, claims the company, can reduce planning and design time from months to minutes.
BB believes that real-time applications on the internet are the future of engineering in power technology projects. The advantages are clear, speed and efficiency in design and a shorter lead-time to commissioning, especially when emergency replacements are needed urgently to get a substation back in operation. There is also the capability to explore an almost limitless variety of equipment options and layout variations to determine the optimum specification.
Figure 1. A comparison between conventional and compact substation layouts
But in order for this to happen, high voltage equipment must be suitable for on-line configuration. Carl Ohlen of ABB’s Power Technology Products division describes how the old blueprint for substation equipment is being replaced by a new generation of Compact modular switchgear which has been designed with e-business in mind.
High voltage substations are used in the power system to interconnect transmission lines, cables, transformers and other primary equipment. The design is influenced by many factors such as rated voltage, current, size, location, climate and environmental aspects. The main objective is to ensure reliable supply of power throughout the system that means the substation always has to be available without interrupting the power flow.
There are two basics factors which can prevent a substation from being fully available. Firstly, a failure or routine maintenance of one essential component, which requires a circuit to be opened. So a high value of MTBF (Mean Time Between Failure) and MTBM (Mean Time Between Maintenance) is therefore important. Secondly, if a failure has occurred or maintenance is needed there is the time taken to carry this out. Ideally, we want to minimize this stand still time. A low value of MTTR (Mean Time To Repair) and MTTM (Mean Time To Maintain) is therefore equally important. The unavailability of a substation can be indicated numerically as MTTR/MTBF + MTTM/MTBM; ideally this interruption time should be zero.
There are two principal types of substation: AIS, Air Insulated Substations and GIS, Gas Insulated Substations. GIS is mainly used for specific applications subject to severe atmospheric pollution, for cable connections and where space is restricted. The majority of the substations are AIS installations, which means they are exposed to weather and wind as well as lightning strikes. They consequently have to be designed to withstand all types of severe conditions to ensure reliable performance without interruptions.
High voltage functions
The main high voltage functions in a substation are:
- Surge arresters to protect the substation against switching or lightning voltage transients.
- Instrument transformers to measure current and voltage for energy metering, but also to feed the control and protection system so it can monitor and protect the substation against short circuit currents and other abnormal conditions.
- Circuit breakers to switch load and short circuit current when necessary.
Figure 2. ABB has supplied the Compact solution to several installations around the world, including this switchgear facility in China
Surge arresters, instrument transformers and circuit breakers have all been substantially improved during the last ten to 20 years utilising new and improved technology as well as automated high quality production. This has been documented as providing lower failure rate and consequently higher MTBF. Maintenance requirements have also been reduced drastically, especially for breakers, giving significantly higher MTBM. Today, ABB can supply all high voltage products with porcelain as well as composite material with the additional possibility to improve reliability and safety.
Conventional AIS substations have used the same basic design blue print for more than 100 years. This incorporates a large number of discrete high voltage devices that have to be installed, connected and maintained separately, including a large number of disconnecting switches with open contacts to allow the circuit breaker to be isolated for maintenance. That was a good design principle 20 years ago when the air blast or oil circuit breakers required a lot of maintenance. But today, the disconnecting switch requires maintenance more often than the circuit breaker.
Naturally, all of the different devices are tested according to IEC or ANSI standards for the stipulated voltage and current level. However, the voltage and current withstand capability of the substation depends on the weakest link, which can be one connection. Similarly, the total availability of, for example, a line bay depends on all the devices connected in series, which is also determined by the weakest link. But the calculated withstand level for the complete substation is based on certain assumptions. No one has actually tested the complete substation. You could say that the industry has been building substations for more than 100 years without knowing the actual voltage and current levels and without knowing the availability.
The old blueprint often stipulated more than one busbar that resulted in a complex scheme of disconnectors and interlocking. Today, the most critical component in a conventional substation is the disconnector, both as a primary component with exposed contacts and for the interlocking and protection system if the auxiliary contacts of the disconnector fail. The main question is why continue to use a 100-year-old blueprint, which is no longer appropriate and is also more expensive and does not improve availability?
Reliability and maintenance
When analysing the substation of today it is easy to show that the disconnector is the critical component if we apply the simplified formula of unavailability = MTTR/MTBF + MTTM/MTBM. If we take a reliability centred approach to the substation design it is equally easy to see that the most reliable substation is achieved if we have maximum values of MTBF and MTTM and low values of MTTR and MTTM. So to obtain the minimum value possible for the disconnector you have to eliminate the disconnectors.
ABB has applied this approach to the design of the Compact and Combined switchgear modules. So the main functions with surge arresters, instrument transformers and circuit breakers are integrated together with the busbar within a single type tested and pre-designed module. This means that the basic insulation level for voltage and the withstand level for current is type tested for the integrated module and is not calculated as in a conventional bay.
Figure 3. Enmax’s 145 kV substation in Calgary, Canada, is equipped with the latest switchgear technology
Although the individual disconnectors have been eliminated the disconnecting function is integrated in a maintenance free withdrawable breaker (Compact) or as a ‘disconnecting breaker’ (Combined). The Compact design has a unique advantage for high voltage applications since it can be rapidly withdrawn and replaced without disturbing the rest of the substation. This offers a further improvement for the availability of the station.
Modular substation design
The ABB modular concept not only provides high availability but also the capability for the rapid design and installation of a typical substation in minimum space. Utilising this concept means it is not necessary to ‘reinvent the wheel’ every time a new substation is built. Pre-designed and type tested modules eliminate detailed calculations since connections at site and all necessary drawings and documentation are already available.
The ‘plug and play’ philosophy of the integrated Compact module is ideally suited for use within on-line design tools such as ABB’s ‘Compact Configurator’ application presented in 3D virtual reality and streaming video on the ABB website. Using the Compact Configurator customers can design a substation on-line according to their own specific functional requirements. There is basically no restriction in the number of bays or the number of busbars.
A variety of different potential solutions can be evaluated for availability, environmental impact and total cost in order to establish ‘the right solution for the right application’. The Compact concept combines the advantage of pre-engineered and type tested modules with the free choice of a customized solution. The user can view the different options on streaming video and 3D virtual reality interactive models, then rapidly design different substation alternatives directly on the internet, compare the alternatives, decide on ‘the best solution’, and request a formal proposal; all while seated in front of their own computer screen.
ABB has structured the Compact Configurator to offer a number of different levels of information from product descriptions to on-line design:
- General information on the ABB website includes power point presentations, streaming video clips and 3D virtual reality interactive models of modules and stations.
- A selection guide for solutions between 88-300 kV for maximum eight bays is available on the dedicated microsite. This selection guide offers pre-designed examples of modular substations using Compact switching modules. The user simply specifies number of modules, area required and estimated cost.
- An alternative ‘free configuration’ is also available. Here the user can design any type of substation with conventional, combined or compact modules. The layout is viewed directly on the screen with all basic data. Local cost levels for labour and land etc can be inserted. It is even possible to estimate and compare the total cost and availability for the station. An e-mail form is used to communicate with the appropriate ABB department.
- At the highest level a detailed configurator for each module is available. This enables drawings and circuit diagrams to be downloaded. An e-mail form will send a direct ‘Request for Proposal’ to the ABB sales team.
Potentially, this on-line approach can enable the total planning and design time for a substation to be reduced from several months to a few minutes. It is important to note that this modularized concept does not reduce the freedom of choice or possibility to adopt for different environments. ABB standard components for all different ratings can be integrated. The concept also allows different sizes and configurations of the substation with one bus, duplicated buses, ring bus or breaker and a half. What is common, is that the substation will improve availability and be significantly smaller and can even be installed indoors.
To date, ABB has supplied the Compact solution for applications between 72 and 550 kV to a number of different countries such as Argentina, Canada, China, Brazil, Germany, Norway, Spain and Sweden.ATCO in Canada installed the first
300 kV Compact substation in northern Alberta at the start of 2001, and this was soon followed by several other Compact substations delivered to other Canadian customers.
In August 2001, the Canadian Enmax Power Corporation started operating a new 145 kV substation to meet the increasing energy needs of the area around Calgary. During the plant’s opening ceremony, Sneh Seetal, spokesperson for Enmax, said: “Enmax Power is the first municipal utility in Canada to use this more efficient, state-of-the-art switchgear technology at one of its substations.”
Figure 4. Norway’s Hydro Aluminium Sunndalsöra has installed several Compact switchgear modules
Rob McLeod, senior transmission engineer at Enmax added: “The technology requires a smaller footprint and is far easier to maintain than a typical substation. Since the new technology is much smaller than conventional gear, we could use it in areas where the cost of land is higher or the visual impact is greater.”
At around the same time, Hydro Aluminium Sunndalsöra, one of Europe’s largest aluminium plants, located in Norway, placed a repeat order with ABB for 24 Compact switchgear modules. ABB supplied combined disconnecting breakers, instrument transformers and surge arresters all in polymer to withstand salt and pollution. ABB also supplied filter units controlled by ‘SwitchSync’ point-of-wave operation to minimize transients when switching the capacitive filters. These units ensure the power supply and quality for the expanding production facilities of Hydro. In February 2001, the company decided to furnish a Compact switching station of 132 kV, and five months later the modules were energized.
With new e-business tools such as the Compact Configurator the way electrical infrastructure companies do business is beginning to change dramatically. ABB forecasts a drastic shortening of the business process from months to weeks and from weeks to days.