Siemens has launched a new HVDC control and protection system which uses cutting edge technology.

The package is designed to bolster redundancy and simplify fault-finding.

Gero Di Piazza

When talking about the bread and butter of High Voltage Direct Current (HVDC), many factors come to mind. But how often is the control and protection aspect of HVDC at the forefront of thought? Not as often as it should be, so does that make it any less important? Actually, it is one of the most important aspects in ensuring that transmission flow operates without major disturbances. In simpler words, a very big deal indeed.

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Siemens Power Transmission and Distribution (PTD) of Germany has taken two years to design and launch what it believes to be the ultimate control and protection system for HVDC systems that enables it to fault-find at a faster pace than competitors as well as reinforce its redundancy system.

The new hardware and software system, dubbed Win-TDC, which will be used for the first time in the Basslink project in Australia in 2005, will be able to replace equipment used in existing HVDC systems while taking up half the space.

Michael Festor, engineer at Siemens in Erlangen, Germany says: “To achieve the very high reliability and dynamic performance of Win-TDC we’ve tested a fully redundant monopolar HVDC scheme. Only after complete successful conclusion of all functional and dynamic performance tests are we able to offer our new technology to our customers.


Figure 1. Six of the most recent Siemens HVDC projects around the world
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“The Basslink project in Australia is the first HVDC system that we will install after the completion of our tests and it will therefore be the first project to benefit from our new Win-TDC technology.”

Functions

The HVDC-related protection functions are referred to as DC protection. The DC protection system has the task of protecting equipment and personnel on a per pole basis. The protection systems can be divided into two areas. These include the classic DC protection functionality consisting of convertor protection as well as the AC filter protection and converter transformer protection.

The AC protection scheme consists mainly of the AC busbar, the AC line and the AC grid transformer protection. The task of the AC protection equipment is to prevent damage to individual components caused by faults or overstresses.

Each protection zone is covered by at least two independent protective units – the primary and secondary (back-up). Some control actions are initiated by the protection scheme via signals to the control systems. With this monitoring system, a false trip due to a fault in the protection hardware itself is almost impossible.

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The required functions of the various protection relays are executed reliably for all operating conditions. The selected protection systems ensure that all possible faults are detected, selectively cleared and annunciated. The continuously active self monitoring systems take care that defects of the DC protection hardware will be detected.

All the protective equipment in the HVDC convertor station is realized either with the digital multi-microprocessor system or with digital Siemens standard protection relays.

Product cycle

“Our new control and protection system, Win-TDC, is based on standard products which are used worldwide in various applications,” said Festor. “We introduced the new control and protection system to be able to offer a system with a very long product life cycle and to take advantage of the latest software and hardware developments.”

Two aspects of the system that engineers believe are real selling points are that it has a lifespan of 25 years and that it takes less time to process faults within the HVDC system: in the past it has taken several minutes but now it takes just ten seconds. As an optional feature, the control system can be accessed from remote locations via the internet. This allows plant monitoring and detection of faults to be carried out from remote locations. Siemens is marketing the product towards retrofitting existing HVDC.links rather than just focusing on new HVDC transmission projects.


Figure 2. Principle of redundancy management
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The main objectives for the implementation of the HVDC control system are reliable energy transmission which operates highly efficient and flexible energy flow that responds to sudden changes in demand thus contributing to network stability. The package, which configures exclusively to any Siemens system, can link up to 85 training centres using a single programme language thus making it highly accessible to operating personnel and engineers globally.

Redundancy

The Win-TDC system is designed to be highly redundant. To simplify the principle of redundancy, the model works like a pair of braces and a belt at the same time. The belt is the main force holding up the trousers, but if the belt snapped then the redundant braces would hold the trousers up. All control and protection systems are equipped with self-diagnostic features that allow the operator to quickly identify and replace the defective part to recover redundancy as quickly as possible.

The pole and station control systems are designed as redundant schemes, with the redundancy management system which is also redundant. Both redundant systems remain on-line and run in the identical operational state but only one of the controllers actively controls the process at any one time. This operational mode is referred to as Hot Standby and is ideal for fast changeovers.

The changeover logic is responsible for the selection of the active control system and two changeover logic modules are required for each redundant system. The first is assigned to control system 1 and the second to control system 2. If one changeover logic module fails, the control system with the healthy changeover logic will automatically become active. If the standby system is also faulty, the converter pole is tripped by the changeover logic. The active system can be selected with a push button on each module. It is also possible to activate a manual mode which also enables maintenance to be carried out on the inactive system.

The use of a digital system also saves manpower by reducing the need for routine maintenance. If a replacement of a single module is needed, then the package design means that there is no operational impact on the HVDC system. This is achieved by designing all major components as redundant systems, where one channel can be switched off without impact on the other channel.

The whole package will be an eye opener for plant operators since the bulk and size that they are used to seeing for such systems is almost halved with the new product. Previous control and protection cubicles for a bipole HVDC was 20.4 m whereas Win-TDC is just 10.5 m. This could send a subtle message to plant operators thinking of retrofitting their existing system.

Existing projects

Siemens’ existing control and protection system is already in place in a number of other HVDC projects yet to be put on line. For example, the Guizhou Guangdong (Gui Guang) HVDC project in China is currently being constructed but will not use the latest Win-TDC equipment.

Siemens is currently simulating and testing the HVDC equipment for China’s 940 km long Gui Guang interconnector project. Testing is performed using the original hardware. Two converter stations have been simulated at the Siemens PTD headquarters in Germany, replicating exactly the 3000 MW Gui Guang project. The process involves real time, digital simulation of the overhead transmission line, complete with all HVDC equipment including converter valves, converter transformers, smoothing reactors and high voltage switchgear and the associated AC power systems, connected to the original control and protection system. The testing was completed in mid August, and the testing cabinets were shipped to China where they will be reassembled in exactly the same configuration.

Georg Wild, director of HVDC control and protection at Siemens, explains: “With the Gui Guang project in China, the protection and control system that was used for the Basslink project in Australia will not be implemented since the technology, when working on the project last year, was unavailable at that time.” The market for this technology, says Wild, is promising.

This could be seen as an ideal situation for Siemens to implement the Win-TDC programme to existing HVDC clients around the world, since the target market is to retrofit and not just implement on new projects.

The HVDC portfolio that the German outfit has assembled over the year is boastful. An insight to the six most recent projects consists of the Moyle interconnector project in 2001 that connects Northern Ireland and Scotland. This link is a 2×250 MW, dual monopole transmission system. The link is 55 km long plus 8 km on land (3 km NI and 5 km in Scotland). Siemens also supplied the Celilo converter station in North America, Dallas in 2002. The 3100 MW bipolar plant has a 1200 km long transmission line.

India’s East-South interconnector has a transmission line 1450 km long and has a power output of 2000 MW, bipolar. In 2004, the Nelson River project will be the next HVDC installation to be completed. It consists of a 900 km long distance line. The next two projects include Basslink (see below) and Gui Guang. These will be installed in 2005.


Basslink: a ‘green’ link down under

In 2000, National Grid Transco of the UK was contracted by the Tasmanian government in Australia to build, own and operate the

360 km long Basslink electricity interconnector between Loy Yang in Victoria state and George Town in Tasmania. National Grid Transco created Basslink Pty Ltd., (BPL) a special purpose subsidiary, to implement the project, which will connect the Victoria and Tasmanian electricity grids for the first time.


Figure 3. The Basslink project in Australia will be the first HVDC link in the world to use Siemens’ new Win-TDC control and protection system
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The project will consist of two converter stations, 66 km of overhead DC line, two transition stations, 8 km of land cables and a 295 km-long submarine DC cable. The two converter stations will convert AC electricity from the Tasmanian or Victorian grid into DC electricity for transmission across the Bass Straight (see Figure 3). The transition stations are the point where overhead lines are transferred to underground cables. The Basslink interconnector will run from Loy Yang in Gippsland, Victoria across Bass Strait to Bell Bay in northern Tasmania. When implemented the 295 km undersea cable component for Basslink will be among the longest of its type in the world.

Basslink will have the capacity to operate at 480 MW continuously or up to 600 MW capacity for some hours to provide for peak export demand. It will also include a fibre optic telecommunications cable link between Tasmania and mainland Australia.

Basslink Pty awarded the engineering, procurement and construction (EPC) contract for constructing the link to the Tas-Vic Interconnector consortium, consisting of Siemens Power Transmission and Distribution (the consortium leader) and Pirelli. Pirelli will manufacture and install the submarine and land cable sections of the project. The turnkey EPC contract is worth g300 million, according to Siemens.

The project will allow Tasmania to participate in Australia’s National Electricity Market for the first time and is of strategic significance to both Tasmania and Victoria. The link has been planned for more than ten years and approval for it was received from the Tasmanian state in August 2002 and the Victorian and federal Australian governments the following month. Extensive environmental assessments were carried out during the planning stages to address environmental risks, cultural heritage issues, visual impact and Aboriginal issues.

The construction contract became effective in November 2002 and is scheduled for completion in 2005. When operational, Basslink will allow Tasmania to export cheap hydropower-derived electricity to Victoria during peak periods. During off-peak periods, Victoria will export baseload electricity to Tasmania, allowing Tasmania to conserve its hydro resources.

Basslink will therefore provide Tasmania with a cost-effective means of protecting itself from periods of low rainfall and will increase security of supply in Victoria. It will also allow Tasmania to develop its abundant wind power resources by providing it with a large export market for this ‘green’ energy. The development of wind power in Tasmania will also help Australia meet its targets for renewable energy and greenhouse gas emission reductions.

In addition, the link will help to maintain competitive pressure on electricity prices in the southern states of the National Electricity Market by introducing capacity for the two-way exchange of competitively priced power. And by including a fibre optic telecommunications link, Basslink also will open the way for greater competition and capacity in Australia’s telecommunications sector.