High-tension heritage
2013-11-20 | Text: Lev Travin | Photo ©: | 8080

 

The plans of China for developing an energy bridge, designed to unite Europe and Asia, are based on technologies of DC transmission lines, resting on old Soviet developments. Head of Expert and Analyze Department of VEI Lev Travin has given us detailed information about these technologies and how they appeared.

 

The first developments in the field of high-tension converter equipment, power electronics and DC transmission lines (DC ETL) started in the Soviet Union during the 1930-s and continued after the Great Patriotic War – almost at the same time in several scientific-research institutes: Scientific-Research Institute for Direct Current in Leningrad (NII PT), All-Soviet Union Electrotechnical Institute n. a. V. I. Lenin (VEI) and Energy Institute of the USSR Academy of Science (ENIN).

These developments started with assimilation of new power and research equipment obtained as reparations from Germany. In 1941 In Germany a project was developed for a cable dc power line of 60 MWt, ± 200 kWt, 115 km with mercury arch valves for electric power supply of Berlin. By the end of the war a whole complex of electric equipment was developed for this power line, Siemens and AEG even started its consrtuction by the end of the Second World War, believing it to be the last chance for the power supply of Berlin. But the construction was not completed – Germany capitulated. The equipment was disassembled and trasnfered to the Soviet party. It was partially used for constructing an experimental indusrtial DC ETL Kashira-Moscow with the following parameters: transmitted power 30 MWt, voltage ±100 kV, current 150 A, cabel line length 120 km.

Kashira-Moscow DC ETL was constructed and adjusted during the difficult for the Soviet Union post-war period. Some types of German equipment were inoperable or broken on purpose and replaced by domestic ones. The cabel turned out to be inoperable and was replaced by the cable produced at “Moskabel” plant. Ground wires were missing. The Moscow department of NII PT developed new ground wires in coke filling which appeared to be so effective that were further on used in many DC ETL of the world.

The German control, regulatory and security systems were not operable as well and was developed in NII PT anew. Surge voltage protection system and surge arresters were developed in VEI. AEG high-tension mercury arc valves of HQNG-1/1 type were gradually replaced with VR-1 valves, developed in VEI. Kashira-Moscow DC ETL was put into pilot operation in 1950 and became the first large dc transmission line.

Intensive reasearch of creation principles, working schemes and regimes of DC ETL has been started in NII PT and VEI to form technical requirements for valves and other electrical equipment of coverter devices. At that time with no computer technics at hand mathematical descriptions of processes in converter devices was quite complicated and had to be solved with the help of complex systems of differential equations; so that is why VEI has developed a unique physical DC ETL model for studying working regimes of any DC ETL, including the present Kashira-Moscow DC ETL and designed Volgograd-Donbass line. Good results were obtained after comparing processes at the present Kashira-Moscow DC ETL and the physical model and thus the validity of such modelling was verified. The results of transient processes research using physical models showed that a simplified mathematical description of these processes can be used. Due to this fact the use of analogue continious mathematical machines became possible.

Even in the time of war the research was started in VEI, regarding designing, producing and applying of various converters of 10-30 kV based on mercury-arc valves of medium (ignitrons) and high tension. This research was accilerated and as a result a new high tension mercury-arc valve of VR-9 type 130kV, 900 A, was developed in VEI, and this development made it possible in late 50-s to start the Volgograd-Donbass DC ETL project. Three organizations took part in it: “Energosetproject”, NII PT and VEI under the general supervision of “Energosetproject”. Volgograd-Donbass DC ETL was designed and constructed using solely domestic electric equipment which major part was developed in VEI and produced at VEI Experimental plant. VEI analyzed the Volgograd-Donbass DC ETL working regimes using the physical model, but it was NII PT that developed technical requirements. NII PT also developed control, regulatory, security and automatic systems.

The project parameters of dc transmission line Volgograd-Donbass are as follows: voltage ±400 kV, transmitted power 720 MWt, inverted current 900 A, overhead line length 473 km. The line was set in operation in 1962-1965 and for several years it was the largest dc transmission line in the world.

After Volgograd-Donbass DC ETL was set in operation it arose interest of the whole world and VEI made annual reports over operating results using the methods of Conseil International des Grands Reseaux Electriques (CIGRE) and sent them to CIGRE Working group for DC ETL reliability rate. In 1969 CIGRE Research Commitee 14 “dc transmissions” was invited in Volgograd to hold a meeting dedicated to the demostration of this transmission in operation. Delegates from 40 countries attended this meeting. The meeting of CIGRE RC 14 and excursions to HPP and to Volzhskaya substation of a live-steam reheater were successful. The delegates remarked great achievments of the USSR in operating the largest DC ETL of the world.

Scientists and engineers, employees of VEI, NIIPT, ENIN and other organisations researching and developing DC ETLs and corresponding equipment had high authority among their foreign collegues. From the foundation of CIGRE RC 14 to the latest time, for instance, VEI employees were permanent CIGRE members from the side of the USSR (further Russian) National Committee. Foreign specialists considered the regularly published works of VEI and NIIPT employees, articles in domestic techincal magazines to be textbooks on DC ETL theory and application.

In 1970 a Technical Subcommittee 22F “Converters for high-tension dc transmission lines” (SC 22F) was formed in the International Electrotechnical Commission (IEC) which main purpose is developing international standards in the fields of elecrtotechnics, electric power and electronics. As credit to the Soviet specialists for improving this part of electric power industry the Soviet National IEC Committee was given the right to take chair of the SC 22F Secretariat which was VEI’s responsibility. At that time the Soviet National IEC Committee had the right to take chair of 9 IEC Technical committees out of 100 in operation. Since that time and till now the SC 22F secretary is a VEI employee, though the number if IEC secretariats in Russia has decreased to two.

 

In 1995 the SC 22F field of work was essentially expanded, it was renamed to “Power electronics for electric transmission and distribution systems”.

The interest of the whole world to DC ETLs could be explained throgh the fact, that in many cases they possess essential technical and economical advantages over equivalent in power ac power transmissions.

 DC ETL substations are more complicated and expensive than those of ac ETL, as they demand additional equipment (powerful converting complexes with separate regulatory, security, alarm, cooling and other systems; synchronous capacitors and powerful condenser batteries for compensating reactive power consumed by converters; bridge harmonic filters on ac and dc sides; smoothing inductors, etc.). On the other hand overhead nad cable dc lines are simplier and cheaper than ac lines: unlike three ac phases dc lines usually have two poles, so much fewer wires and cables should be provided for a DC ETL, their supports are simplier and lighter, materials consume is reduced, the line route is narrower, construction costs are lower, so the cost of a whole DC ETL is much lower. If you compare equivalent ac and dc lines, you will see that with some certain (critical) line length their full costs (substation and the line) are almost same, but if the line is longer than critical DC ETL becomes more cost-effective. At the present time the critical length of an overhead line is 600-800 km, of a cable one – 30-50 km. But even with a zero length of the line the so-called back-to-back stations (BBS, when a rectifier and an inverter stations are installed in one building) can solve problems which can not be overcome with the help of ac ETL at all – for instance, to connect two ac systems that operate asynchronously or have different frequencies (50 and 60 Hz systmes like in Japan, for instance).

The power and the length of a DC ETL is limited only by parameters of converting and transforming equipment, while those ofn ac ETL are limited by static and dynamic stability. The power transmitted over DC ETL can be easily regulated almost from zero to maximum, while it is much harder to regulate an ac ETL power. DC ETLs are safer than ac ETLs – if one phase wire is damaged, the whole ac ETL is balcked out, while if the wire of one of the DC ETL poles is damaged 50%-power can be transmitted via the second pole wire.

Using classic DC ETLs (with high-tension line commutated mercury-arc or thyristor converters) can solve the problems of electirs power systems which are impossible or very hard and expensive to solve using traditional facilities:

1. It becomes possible to ensure a safe, cost-efficient and fully controlled transmission of high power (thousands of MW) for long distances (thousands of kilometers) from remote powerful HPPs or TPPs, which are located right near coalmines, oil fields, etc., next to load centers or for export. It was especially important for the USSR, where the main energy ressources were located to the East from Ural and load centers – in the European part of the country.

2. It becomes possible to provide a safe, cost-efficient and fully controlled cable transmission for distances longer than 30 km (for undrewater cable lines – up to 500 km) – load centers in large cities; for places where it is irrational to construst overhead ETLs.

3. It becomes possible to connect power systems which work asynchronously or with different frequences (50 and 60 Hz). In this case rates of short-circuit current do not increase, no equipment must be replaced (circuit-breakers, disconnecting devices, etc.), unlike the case when power systmes are connected with ac ETLs. Static and dynamic stability of the power systems increases, as well as electric reliability. There is no risk of system break-downs or power system collapses, the number of which keeps growing in well-developed countries due to increasing power of power systems. This causes enormous economic damage.

The experience of producing electric equipment for powerful DC ETLs, gained during the 60-s in the USSR, along with succefull operation of Volgograd-Donbass DC ETL, at that time the most powerful in the world, became a basis for further development of high-tension converter technics. In 1966 Council of Ministers of the USSR enacted a R&D for producing DC ETLs for extremely long distances. VEI became the head instution for developing complex electrotechnical equipment for a 1500 kV DC ETL. VEI headmaster was nominated as Chief Designer. Being a very well educated specialist he immediately defined the key problem – converters. VEI had the leading position in the country and in the whole world in the field of powerful mercury-arc valves and electronic vacuum devices.

However, development of semiconductor power devices (SPD) was not left unattended as well, though this field could not be thouroghly researched at that stage.

In the middle 60-s the USSR developed a State programm, which final objective was to consrtuct an extremely powerful Ekibastuz-Center DC ETL, tension 1500 kV (±750 kV), power 6000 MW, length 2400 km. According to the project, powerful mercury-arc valves were to be used for converters at the first stage. But in 1970 due to the rapid development of semiconductor converters the works over new powerful mercury-arc valves were cancelled and further development was to be connected with high-tension thyristor valves (HTV).

To speed up the work and to get better performance characteristics the USSR made a decision to use three competing R&D associations led by VEI, NIIPT and ENIN.

In VEI the HTV-development was initially based on final-objective-oriented principles, i. g. producing extremely powerful HTV. These principles included in the first place indoor valves installation, valve module structure, wide usage of optoelectronic channels for controlling and monitoring, cooling heat-producing elements by DI water. Many of these techincal solutions were realized for the first time in the world practise. All these innovations helped VEI win the competition with other institutions and take the leading position in developing this new type of high-tension equipment.

In 1970-s after the decision was made to construct the 1500 kV Ekibastuz-Center dc substation on high-tension thyristor valves, VEI formed a deparment for high-tension converter technics.

Innovative scientific and technological solutions, developed in this collective, made it possible to produce HTV exceeding international standards.

Ministry of Electrical and Tool Engineering alloted a branch factory for organizing HTV production – Uralelectrotyazhmash (Ural factory of electrical engineering, UETM) in Sverdlovsk, a huge factory-town with more than 10 thousand workers.

 

Due to the hard work a new section was formed in UETM and the first HTV-samples were produced, two of which were delivered to VEI Volgograd Engineering Research Centre (VEI branch in the city of Istra near Moscow). An experimental Scheme #5 was constructed in Istra Centre, where at first high-tension mercury-arc valves passed tests and later – thyristor valves for Ekibastuz-Center dc substation.

According to the State programm in 1969 an inverter bridge with HTV was set in operation on Kasjira-Moscow DC ETL. In 1974 a test output of the inverter bridge with HTV began on Volgograd Donbass DC ETL. Bridge parameters: voltage 100 kV, inverted current 900 A. A high-tension Thyristor bridge was at the maximum potential i. r. t. the ground in the stage circuit of converters connection on Volzhskaya converting substation (400 kV). High-tension thyristor valves for these DC ETLs were developed in VEI and produced at Uraltyazhmash plant (UETM) in the city of Sverdlovsk (today Ekaterinburg).

Complex research done in VEI while developing and testing HTVs for Kashira-Moscow and Volgorgad-Donbass ETLs dc substations served as basis for developing extremely powerful HTVs. Production of all following HTVs was organized at mid-Volga production association (MVPA) “Transformator” in the city of Tolyatti.

Further HTV production in Sverdlovsk was admitted counter-productive, as geographically it is too far even from Tambov substation. So they decided to move thyristor HTV production to “Transformator” MVPA in the city of Tolyatti (“Trasnformator” PA). Due to the hard work “Trasnformator” PA organized a perfect production using all modern technologies and test-results of thyristor power cells, light controll systems based on semiconductor lasers, fiber optics and water cooling systems.

The most important and significant works in the period of 1970-1980 were developments of electric equipment complexes for ultrahigh-tension 1150 kV ac ETL and 1500 kV ((±750 kV) dc ETLs. The implementation of ultrahigh-tension 1150 kV ac ETL and 1500 kV ((±750 kV) dc ETLs projects began with the resolution of CPSU Central Committee and USSR Cabinet of 30.04.1981 #412.

This resolution contained the task for the USSR Power and Electrification Ministry (Minenergo) to construct and during 1981-1990 set the following 1150 kV ac ETLs in operation: Ekibastuz-Kokchetav-Kustanai-Chelyabinsk (1272 km), Surgut-Ural (500 km), Itat-Novokuznetsk (272 km), Novokuznetsk-Zapadno-Sibirskaya-Ekibastuz (950 km), along with the 1500 kV Ekibastuz-Centre DC ETL (power 6000 MWt), length 2414 km). Moreover they planned to construct 500 kV ac ETLs (with substations) with overall length of about 2 thousand km, connected to electric energy distribution from 1150 kV and 1500 kV substations.

To realize 1150 kV and 1500 kV ETLs construction and to produce required equipment the following institutions united their efforts: State Planning Committee of the USSR, the USSR State Logistics Committee, the USSR Academy of Science, USSR State committee for science and technology, factories of almost all the USSR Ministries. Almost the whole huge industry of the USSR was working to produce the first ultrahigh-tension dc and ac ETLs in the world.

The VEI administration decided, that for an adequate design of future ETLs and the corresponding equipment development it is necessary to attract experienced designers. So in the mid 70-s a Department for complex developments of electric equipment (ORKRO) was formed in VEI out of former employees of Energosetprojekt and Hydroprojekt, who now came to work in VEI. Their further work in developing technical requirements for produced equipment of new ETLs and DC links was very esssential and helped to differently organize ORKRO based on the laborotory team, where the working regimes of DC ETLs had been researched and their influence on HTVs and other equipment of converting substations had been defined.

The major works done in ORKRO are approving technical requirements and developing performance specifications for power equipment of Ekibastuz-Centre DC ETL and USSR-Finland DC link in Vyborg, along with testing this equipment on a testbench in Tolyatti. This unique Powerful test centre (MIS) for full-scale long-term tests of all major electric equipment types for 1150 and 1500 kV ETLs was built in 1979. Even today no other country in the world possesses such a test centre.

MIS consisted of outdoor switсhgears, where all basic equipment types of an outdoor facility were installed for the 1150 kV ac substations and ±750 kV DC ETLs converting substations. Using MIS it was possible to undertake any high-tension tests as well as mains-operated stability tests during short cirsuits. Testing facilities of this centre in transformers short cirsuit stability tests remain unrivaled: during the 80-s the tests of 320 MVA single-phase transformer and 666 MVA three-phase transformer were held there.

The development of Ekibastuz-Centre DC ETL project began in 1970 and three organisations were responsible for it: Energosetprojekt (chief designer), VEI (electric equipment developer) and NII PT (developer of technical requirements for the equipment). The Ekibastuz-Centre DC ETL was to become the biggest in the world. ETL’s specifications: poles tension ±750 kV, transmitted power 6000 MWt, pole current 4000 A, pole wires 5 x ASO – 1200, length of the single-circuit overhead line 2400 km.

A rectifier substation was located in Ekibastuz, an inverter one – in Tambov. Objective – power transmission from Ekibastuz regional power stations to the Central power system to cover power deficit in this region.

For Ekibastuz-Centre 1500 kV DC ETL they developed, produced, tested and partially set in first order of converting substations (one branch of 1500 MWt power) unique high-tension thyristor valves BVMP-800/470-III, single-phase double-winding converting 320 MVA tranformers for ±400 and ±750 kV voltage types, feeder reactors 4G, 1000A for ±750 kV voltage type, universal surge arrestors RL, RG-400 and RG-800, equipment for control, regulatory, security and automation systems of ETLs and other electric equipment (70 titles).

It was planned to set this DC ETL in operation in 1992-1995. The first equipment was installed at converting substations, an overhead ETL of almost 1000 km was constructed, but when the USSR collapsed all works were stopped, the equipment installed at converting substations was destroyed, the ETL was demounted and sold for scrap.

 

The 1500 kV DC ETL equipment, produced in the USSR was twenty five years ahead of the international technical standard. The first ETL of such class (1600 kV or ±800 kV) was cnostructed in China only in 2010.

The Ekibastuz-Centre substation experience was used for quick development and production of equipment for the Vyborg DC link. Vyborg DC links (VPT), providing asynchrone connection between 330 kV mains of the Russian North-West and 400 kV mains in Finland, was set in operation block-by-block in 1981-1984. By the end of this period, according to the project it consisted of three blocks with converting packages of nameplate power of 335 MWt (nameplate direct current 2100 A, nameplate fixed voltage 170 kV). According to the agreements made before the project was designed the basic power of the DC link was 600MWt.

In1981 the first converting package was set in operation and in 1983 – the last third one. In 1989 the chief designer of high-tension thyristor valves and other VEI employees were rewarded with the State Prize for this development.

After all three converting packages were set in operation and the short (less than a year) early-failure period was over, the average power transmission via the DC link was about 4500 GWh a year (designed value – 4000 GWh a year).

In 1991 existing economical connections of all levels collapsed, development and production plans were cancelled, the majority of industry stopped production, there was a surplus of generating capacities in power energy and lack of demand for new electric equipment for power energy, defence and the majority of other economy branches. Some of the leading industries, NII and design engineering departments of power industry appeared to be abroad. Such resession in economy had led to decrease of R&D financing from the state budget of the Russian Federation, reduction in the number of orders for developing new electric equipment by commercial agreements. The fees for heat and power energy consume, water, connection services, transport and other overhead costs increased rapidly. The salary, on the contrary, decreased essentially, which made many scientific employees, especially young ones, resign.

But from mid 90-s another working stage began, which included not only recostruction, but also development of Vyborgskaya dc link. The basic objective of this stage was to increase the basic power of the dc link at least up to 1000 MWt and the maximum power – up to 1400 MWt. Both receiving and initial systems were interested in it: the first one required additional energy, the second one possessed it.

In 2000 mounting and adjustment works at the new converting nlock of Vyborgskaya dc link (converting package-4) were completed. This block was arranged by the same scheme as the three previous ones, but it also had control, regulatory, security and automation systems of the new generation (KURB). In 2002-2005 all other blocks of Vyborgskaya dc link also got new controlling equipment.

Due to the installation of a power readjustment channel (to the extent of 10%) in the regulatory system depending on frequency Vyborgskaya dc link nowadays not only provides the scheduled power transmission, but also has a function of a regulated energy source, that provides frequency maintenance in the Finnish energy system.

In 2000-2002 a stable power transmission of more than 1000 MWt to Finnland was provided. The difficulty in this work is, that according to the standards of the receiving system it can not receive such power out of one source (common node).

The Master plan of electricity generating facilities location up to 2020 was widely discussed in Russia in 2006-2007 and approved by the Government of the Russian Federation in 2008. This plan included construction of three ±500 and five ±750 kV DC ETLs in Ural and Siberia along with six 500 MWt dc links.

In 2010, however, the Master plan realization was monitored and based on the results it was decided to correct the plan, relying on such factors as increase in potential growth of power consume due to the growing EE in economy, financial problems of private energy enterprises, growth ratio decrease of generating capacities, etc. Another Mater plan of electricity generating facilities location up to 2030 was developed, in which the construction volume of power stations and ETLs were decreased (the most powerful Evenkiyskaya HPP was also excluded from the plan). This Master project upto 2030 is now discussed but not yet approved. In the period of 1991-2012 there was no new dc transmission line or dc link built in Russia.

In 2010-2011 there were plans for constructing a dc link operating with fully controlled equipment (IGBT, IGCT) of 200MWt power at Mogocha substation, in Chita power system of Siberia. Front end engineering design was done for constructing a ±600 kV dc substation in 2010-2015 for power transmission to China (the inter-governmental agreement was signed of transmitting up to 16,5 GWh to China), as well as a cable ±400 kV dc substation for transmitting power to Japan. There were also plans for further reconstruction of Vyborgskaya dc link and constructing a 1000 MWt, ±300 kV DC ETL of Leningradskaya APS-Vyborgskaya dc link.

At the moment a 200 MWt dc link is constructed at Mogocha substation in Chita power system of Siberia at the stage of delivering and mounting electric equipment developed and produced in Russia. The dc links is located between two non-connected power systems of the Far East and Eastern Siberia and consists of two parallel non-connected circuits, each of which can transmit the actve power of 100 MWt in both directions. There are four voltage converters (VC) at the dc linkm arranged by three-level scheme with fixed capacity of 102 MWt, Ud=68 kV, Id=1500 A, which are connected with the ac mains via 220.35 kV transformers. At the ac side of each VC there are facilities for regulating reactive power in the extent of ±66 MVAr. According to the schedule Mogocha dc link should have been set in operation in 2012.

There is a decision to construct a 1000 MWt, ±300 kV Leningradskaya APS-Vyborgskaya dc link substation (underwater cable and overhead bipolar ETL) and probably to increase the power of Vyborgskaya dc link. The active part of the project should start in the current 2013.

A construction of Kalinigradskaya ASP (1 GWt in 2017 plus 1 GWt in 2020) is planned, the major part of its power is set for export. One 220 kV ac line to Lithuanina is planned along with the project of constructing two dc links of 500-600 MWt at Mamonovo substation, one of which will be used for exporting power to Poland and the other one, probably, to Germany.

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