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40MODERNIZATION OF POWER DISTRIBUTION NETWORKS IN THE POWER SYSTEM OF UKRAINE
Kyryk V. V.
Doctors of engineering Tsyganenko B. V.
National Technical University "Kyiv Polytechnic Institute", Kyiv, Ukraine
Abstract. There was made an analysis of power distribution networks in the power system of Ukraine. There were grounded implementation of 20 kVpower networks and their benefit. And were highlighted Principles of 20 kV networks construction, conditions of their implementation and priority measures to implement 20 kV medium voltage class networks.
Keywords: power distribution network, 20 kV, 6 kV voltages
The implementation of modern approaches to management and process of transmission and distribution of electricity is impossible without significant modernization the whole power sector of Ukraine. Realization of principles of intelligent power systems (Smart Grids) should ensure world-class level of quality and reliability of power supply to consumers.
The National Commission of Ukraine, which performs state regulation in the power sector, is focused on indicators of quality of services of electricity transmission and distribution, which is characterized by indexes of the average outage duration (SAIDI) and the average number of interruptions (SAIFI) in the network. A number of power companies are planning to switch to stimulating regulation soon, were the quality target (SAIDI) for the urban area is set to 150 minutes, for the rural area - 300 minutes. The analysis of companies' quality across Ukraine shows that today SAIDI index is much higher than normalized indexes of European countries [1]. For companies that decided to switch to stimulating regulation, this means the necessity to reduce the average duration of power interruptions for 10 years, almost in 5 times.
One of the major factors influencing the power supply quality today is the status of 0.4 - 10 kV electricity networks. At present the length of electricity networks in Ukraine is: 0.4 kV - 449,832 km; 6 -10 kV - 332,568 km, and tends to increase annually. In 1st quarter of 2016 there were more than 30,000 technical breakdowns at units of electric networks organizations with voltage of 0.4 - 10 kV.
The non-supply of electricity to consumers is close to 8 million kW per year. A share of electricity of non-supply to consumers, due to technical breakdowns in 10(6) kV networks, is within 40.5 ^ 96 %. Significant percentage of non-supply of electricity is due to the fact that 10 kV overhead electrical networks are poorly equipped with automation devices. Devices for the damaged places recording at power lines are set only at 3 % of substations, and devices of double automatic recloser are almost completely missing. In 10(6) kV networks there are significant losses in electricity due to the low output of networks, especially on 6 kV networks, which exist in the power system.
In spite of significant development of 10 kV voltage networks of 10 kV in both rural and urban areas, Ukraine still has the 6 kV networks. They are used because this class was widely used in the middle of the last century in power systems of industrial enterprises, their substations were usually connected to consumers of urban and rural distribution networks. The use of voltage of 6 kV at industrial enterprises was determined by the absence of 10 kV electric motors at whole power range, and also by relatively small dimensions of enterprises territory, allowing acceptable system of power supply at voltage of 6 kV even with large electrical loads.
The privatization and unbundling of networks were also influenced by the technical conditions of the distribution networks. The development of some networks sections (financing, designing) often performed by different owners, which minimize investments.
Considering the present realities in the country and that the replacement of morally and physically worn electrical equipment in electrical networks, ranging from 40 to 70% by various estimates, are going slowly, and is even slower today, while density of load in cities is growing, which is already set up to 9 ^ 10 MW per km2 in the center of Kyiv (average for Kyiv is 2.4 MW / km2 and 3.6 MVAr / km2), and power losses are increasing as a result - there is a question of prospect of the development of distribution networks and their effectiveness .
It is possible to change the situation in the middle class of electrical networks only through their complete modernization. The best solution of increasing the capacity of existing networks from the economic point of view could be the increase of existing nominal voltage distribution networks in
rural areas, creation of power centers and construction of new power transmission lines of higher nominal voltage in large cities.
The main and most optimal way in this sense is replacement of exhausted 6 kV distribution networks by new 20 kV voltage networks with the following phased transfer of 10 kV networks to 20 kV voltage class. 20 kV voltage class is widely used in Western Europe and America. Gradation of power grids voltage in developed countries is presented in the table [2].
Advantages from transferring 10 (6) kV power networks to 20 kV are:
- More power transmission at the same sections of wires;
- reduction of technological losses;
- more efficient and economical electrical equipment at transformer substations (TS) and distribution points (DP) in dimensions of the old equipment;
- reduction of overall length of 0.4 kV networks and their losses by using masted complete transformer substations CTS 20 / 0,4 kV;
- preservation the 10-meters security zone of overhead power transmission lines;
- the opportunity to address the shortfalls in power supply centers in the electrical discharge 10 (6) kV on existing substations;
- creation of a reserve power to guarantee reliable power supply;
- opportunity to eliminate the power deficit in supply centers by unloading 10(6) kV electrical equipment of existing substations; creation of a power reserve to guarantee reliable power supply.
Table 1. Rated voltage classes in various countries
Country Rated voltage of distribution networks with three phase alternating current, kV
Ukraine 6 10 - - 35 110
Russia 6 10 - 20 35 110
France 5,5 10 15 20 30 110
Germany 6 10 15 20 30 110
USA 4,8 (7,8) 12 14,4 23 31,5 115 (138)
Belgium 6 10 15 20 30 100
Austria 5(6) 10 15 20 (25) 30 (35) 110
Czech Republic 6 10 15 20 (22) 30 (35) 100
Hungary 5,4 9 13,5 18 31,5 125
Finland - 10 - 20 - 110
20 kV voltage has some principled advantages over 10 and 35 kV. It's better to use 20 kV electric equipment inside buildings and in city networks with significant density loads. Compared to voltage of 35 kV, 20 kV transformer substations are complete with fully prefabrication. Electrical devices and cables of this class are less material intensive, therefore they are lighter and cheaper than 35 kV. The use of 20 kV voltages will reduce annual costs in comparison to 10 kV by the reduction of energy losses in networks, transformers and other electrical equipment, short-circuit current will be reduced, power supply of some remote consumers is easier. Concerning XLPE cable lines, in the 20 kV networks, these usually operate as grounded neutral through a resistor, there is no need to use the reinforced cable screens.
The main concept of construction of 20 kV networks should be based on the following principles:
- 20 kV distribution network is based on two-beam scheme, were supply of each TS is carried out by two inter-reserving lines;
- 20 kV supply line scheme is performed from two-piece DP with the double automatic recloser on sectional switch. DP supply goes from two independent, geographically separated 110/20 kV substations to two independent (inter-reserving) lines;
- 20 kV electrical network is implemented on the basis of a backbone (from two lines);
- TS is sectioned into two sections of 20 kV buses with installation of section and linear load switches;
- use of automatic points of 20 kV transmission line (reclosers) sectioning, to implement automatic switching networks capabilities, implementation of automatic disconnection (exudation) of damaged area, double automatic recloser of line, automatical collection of information about the networks' operating modes;
- it is preferable to carry out small-sized new 20 kV distribution or connecting points, of
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block type (in cells of 20 kV DP the loading switches can be used). Gas insulation should be used to reduce the size;
- XLPE cables should be used for laying 20 kV cable lines;
- construction of modern DP with 20 MVA capacity will enable to transport required power directly to consumers, as analogue substations of deep input. This will not only reduce electricity losses during transmission, but will allow more quickly and flexible development of new high power substations on existing land sites, especially in cities.
To convert electrical distribution networks on voltage of 20 kV a number of mandatory conditions should be done:
- preparation of regulatory framework with development of new national standards and technical regulations;
- concept of 20 kV networks development and execution of technical and economic assessment of networks construction;
- provision of reserve power at 20 kV level at 110 kV power centers;
- organization of equipment and cables market with voltage of 20 kV.
Nowadays an electrical market of 20 kV in Ukraine is almost missing. But this problem could be solved and as example is advanced European countries.
The result from transition of some countries on 20 kV voltage class, was transition of all major manufacturers of electrical equipment for the European market to 20 kV equipment with gradual outlet of previous generation of equipment from the production lines. Reorientation of Ukrainian manufacturers of electrical equipment on output of other voltage classes will increase or at least save workplaces at enterprises. Also it will attract big foreign manufacturers of modern electrical equipment and their experience with possible joint ventures. During the production of transformer products there will not be any problems with introduction of 20 kV voltage on the low voltage side, as production of 20 kV windings were done by Zaporizhia transformer plant PJSC under certain orders. Implementation of this approach will attract a large number of organizations for construction and installation works, including design.
Conclusions. At today's stage of urban distribution networks operation in terms of formation of numerous owners of network objects, there is a pressing problem of absence of centralized networks management system, that would ensure their efficient operation, and would exclude department interests.
Development of electrical distribution networks is slowed due to a number of objective factors - lack of investments, density of existing buildings and long approval procedures of design solutions on electrical network units (DP, TS) and line routes, saturation of underground utilities and necessity for coordination of engineering utilities.
Applying 20 kV voltages in existing 6-10 kV distribution networks will switch to higher level of power supply in Ukraine, increase bandwidth in comparison with existing networks within an allocated land, reduce technical losses; improve quality of electricity, energy security and reliability of electricity transmission systems.
We urgently need to implement mechanisms of construction of electrical networks and development of 20 kV networks concept on the territory of a particular city or district on the basis of complex schemes with implementation of new elements of distribution network for guaranteed connection of consumers with minimum technological losses.
An investment attractiveness of territories under infrastructure development of city or district should determine a vector of development of complex schemes of electrical networks, in relation to territorial plans.
REFERENCES
1. "IEEE trial-use guide for electric power distribution reliability indices," IEEE Std 13662012 (Revision of IEEE Std 1366-2003).- 2012.
2. "Standard voltages", IEC 60038 - 2002-07, (Edition 6.2). - International Electrotechnical Commission, 2002.
