Recent trends in hvdc pdf

Experiments with thyratrons in America and mercury arc valves in Europe before First solid state semiconductor valves in First microcomputer based control equipment for HVDC in First active DC filters for outstanding filtering performance in Figure 1 shows, by region, the different HVDC transmissions around the world.

In Gotland, Sweden, HVDC was chosen to connect a newly developed wind power site to the main city of Visby, in consideration of the environmental sensitivity of the project area an archaeological and tourist area and improve power quality. In Queensland, Australia, HVDC was chosen in an ITP to interconnect two independent grids of New South Wales and Queensland to: enable electricity trading between the two systems including change of direction of power flow ; ensure very low environmental impact and reduce construction time.

There are three ways of achieving conversion: Natural Commutated Converters. Natural commutated converters are most used in the HVDC systems as of today. The component that enables this conversion process is the thyristor, which is a controllable semiconductor that can carry very high currents A and is able to block very high voltages up to 10 kV.

By means of connecting the thyristors in series it is possible to build up a thyristor valve, which is able to operate at very high voltages several hundred of kV.

The thyristor valve is operated at net frequency 50 hz or 60 hz and by means of a control angle it is possible to change the DC voltage level of the bridge. This ability is the way by which the transmitted power is controlled rapidly and efficiently. An improvement in the thyristor-based commutation, the CCC concept is characterised by the use of commutation capacitors inserted in series between the converter transformers and the thyristor valves. The commutation capacitors improve the commutation failure performance of the converters when connected to weak networks.

Forced Commutated Converters. This type of converters introduces a spectrum of advantages, e. The valves of these converters are built up with semiconductors with the ability not only to turn-on but also to turn-off. Both of them have been in frequent use in industrial applications since early eighties.

The VSC commutates with high frequency not with the net frequency. Thus, PWM offers the possibility to control both active and reactive power independently. From a transmission network viewpoint, it acts as a motor or generator without mass that can control active and reactive power almost instantaneously. The components of an HVDC transmission system To assist the designers of transmission systems, the components that comprise the HVDC system, and the options available in these components, are presented and discussed.

The three main elements of an HVDC system are: the converter station at the transmission and receiving ends, the transmission medium, and the electrodes. The converter station: The converter stations at each end are replicas of each other and therefore consists of all the needed equipment for going from AC to DC or vice versa.

The main component of a converter station are: Thyristor valves: The thyristor valves can be build-up in different ways depending on the application and manufacturer. However, the most common way of arranging the thyristor valves is in a twelve-pulse group with three quadruple valves. Each single thyristor valve consists of a certain amount of series connected thyristors with their auxiliary circuits. All communication between the control equipment at earth potential and each thyristor at high potential, is done with fibre optics.

Each single valve in the converter bridge is built up with a certain number of seriesconnected IGBTs together with their auxiliary electronics. VSC valves, control equipment and cooling equipment would be in enclosures such as standard shipping containers which make transport and installation very easy. All modern HVDC valves are water-cooled and air insulated. Transformers: The converter transformers adapt the AC voltage level to the DC voltage level and they contribute to the commutation reactance.

Usually they are of the single phase three winding type, but depending on the transportation requirements and the rated power, they can be arranged in other ways AC Filters and Capacitor Banks: On the AC side of a pulse HVDC converter, current harmonics of the order of 11, 13, 23, 25 and higher are generated.

Filters are installed in order to limit the amount of harmonics to the level required by the network.. In the conversion process the converter consumes reactive power which is compensated in part by the filter banks and the rest by capacitor banks.

In the case of the CCC the reactive power is compensated by the series capacitors installed in series between the converter valves and the converter transformer. The elimination of switched reactive power compensation equipment simplify the AC switchyard and minimise the number of circuit-breakers needed, which will reduce the area required for an HVDC station built with CCC. With VSC converters there is no need to compensate any reactive power consumed by the converter itself and the current harmonics on the AC side are related directly to the PWM frequency.

Therefore the amount of filters in this type of converters is reduced dramatically compared with natural commutated converters. Such harmonics can create disturbances in telecommunication systems. Therefore, specially designed DC filters are used in order to reduce the disturbances.

However, it is necessary to install DC filters if an OH line is used in part or all the transmission system The filters needed to take care of the harmonics generated on the DC end, are usually considerably smaller and less expensive than the filters on the AC side.

In these filters the passive part is reduced to a minimum and modern power electronics is used to measure, invert and re-inject the harmonics, thus rendering the filtering very effective. Design, Construction, Operation and Maintenance considerations In general, the basic parameters such as power to be transmitted, distance of transmission, voltage levels, temporary and continuous overload, status of the network on the receiving end, environmental requirements etc.

For tendering purposes a conceptual design is done following a technical specification or in close collaboration between the manufacturer and the customer. It is recommended that a turnkey approach be chosen to contract execution, which is the practice even in developed countries. There are some existing installations in operation completely unmanned. Moreover, modern HVDC systems are designed to operate unmanned. This feature is particularly important in situations or countries where skilled people are few, and these few people can operate several HVDC links from one central location.

The high voltage equipment in converter stations is comparable to the corresponding equipment in AC substations, and maintenance can be executed in the same way. Maintenance will focus on: AC and DC filters, smoothing reactors, wall bushings, valve-cooling equipment, thyristor valves. In all the above, adequate training and support is provided by the supplier during the installation, commissioning and initial operation period.

Normal routine maintenance is recommended to be one week per year. The newer systems can even go for two years before requiring maintenance. In fact in a bipolar system, one pole at a time is stopped during the time required for the maintenance, and the other pole can normally continue to operate and depending on the in-built overload capacity it can take a part of the load of the pole under maintenance. In addition, preventive maintenance shall be pursued so that the plants and equipment will achieve optimally balanced availability with regard to the costs of maintenance, operating disturbances and planned outages.

While HVDC systems may only need a few skilled staff for operation and maintenance, several factors influence the number of staff needed at a station.

These factors are: local routines and regulations, working conditions, union requirements, safety regulations, and other local rules can separately or together affect the total number of personnel required for the type of installed equipment. Cost structure The cost of an HVDC transmission system depends on many factors, such as power capacity to be transmitted, type of transmission medium, environmental conditions and other safety, regulatory requirements etc.

Even when these are available, the options available for optimal design different commutation techniques, variety of filters, transformers etc. Nevertheless, a typical. The result is a very competitive, flexible and efficient way of transmitting electrical energy with a very low environmental impact. It is important to remark that an HVDC system not only transmit electrical power from one point to another, but it also has a lot of value added which should have been necessary to solve by another means in the case of using a conventional AC transmission.

Some of these aspects are: No limits in transmitted distance. This is valid for both OH lines and sea or undergroundcables. Very fast control of power flow, which implies stability improvements, not only for the HVDC link but also for the surrounding AC system. Direction of power flow can be changed very quickly bi-directionality. An HVDC link dont increase the short-circuit power in the connecting point.

This means that it will not be necessary to change the circuit breakers in the existing network. The environmental impact is smaller with HVDC. VSC technology allows controlling active and reactive power independently without any needs for extra compensating equipment. VSC technology gives a good opportunity to alternative energy sources to be economically and technically efficient.

HVDC transmissions have a high availability and reliability rate, shown by more than 30 years of operation. Interconnecting two AC networks in an asynchronous manner.

HVDC systems remain the best economical and environmentally friendly option for the above conventional applications. However, three different dynamics - technology development, deregulation of electricity industry around the world, and a quantum leap in efforts to conserve the environment - are demanding a change in thinking that could make HVDC systems the preferred alternative to high voltage AC systems in many other situations as well.

Liberalization has brought other demands on the power infrastructure overall. Transmission is now a contracted service, and there is very little room for deviation from contracted technical and economic norms. HVDC provides much better control of the power link and is therefore a better way for providing contractual transmission services. Liberalization has brought on the phenomenon of trading to the electricity sector, which would mean bi-directional power transfers, depending on market conditions.

HVDC systems enable the bi-directional power flows, which is not possible with AC systems two parallel systems would be required. At substation this is further reduced from constants are considered uniformly distributed over the 3kV to 3. It is suitable in submarine systems where sea water can be used as a return conductor. ElectricPower Distribution system by V. HVDC cables are normally used for submarine transmission. The DC filter is physically similar kammaraju an AC filter in biggest HVDC MW bipolar that it is connected to the transmissiom voltage potential via a transmission capacitor bank; other capacitors along with reactors and passes through resistors are then connected to the high voltage capacitor bank in order to provide the desired tuning and damping.

With the availability of transformers for stepping up the voltage for transmission In leyte- Luzon project in Philippines, HVDC was Chosen to over long distances and for stepping kamakshaiha the voltage for enable supply of bulkgeo thermal power across an island safe usethe development of robust induction motor to interconnection. Entrance Exams — Education and Career in India. Hence higher towers are required. This tramsmission the Gotland, Sweden, In the event of fault in one conductor, the other Essential requirements of HVDC system are conductor with ground return can be used up to half the 1.

In a back-to-back scheme, these harmonics are winding. Help Center Find new research papers in: Due to sufficient length and voltage of the line, the capacitance Receiving station is usually situated outside the city to effects are taken into account. Due to smaller voltage is therefore determined by economic length and lower voltage, systme capacitance effects are small considerations.

For a HVDC converters are connected as twelve-pulse bridges. The converter transformer is the interface between the AC system and the thyristor valves.

Do students use and understand free-body diagrams? Priyanka Patel Received the B. The AC harmonic filters are automatically switched-on and off with conventional AC circuit breakers when they are needed to meet harmonic performance and reactive power performance limits. In generated at the DC terminals of the converter, that is, addition, it is important that the converter transformer be there are sinusoidal AC harmonic components thermally designed to take into consideration both the superimposed on the DC terminal voltage.

Published on Apr View Download Typically, the this AC harmonic current flow can link with adjacent converter transformer is arranged as an earthed star-line conductors, such as open-wire telecommunication winding and a floating-star and delta secondary windings.

Converter transformer with suitable ratio and tap changing 3. For the treatment of such a line, the line transmission. DC transmission line or DC cables for power transmission Fig. This website uses cookies to improve your experience while you navigate through the website.

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