RESULTS of the IInd All-Russian Conference "Technical-Economical Aspects of 20 kV Network Development"
(July 12, 2016, Moscow)
Organizer: JSC UNECO, "ELECTRIC POWER. Transmission and Distribution" journal.
Moderator: S.A. Shumakher, leading expert of "ELECTRIC POWER. Transmission and Distribution" journal.
Participants: 90 persons, including representatives of the Ministry of Energy of Russia, the headquarters, subsidiaries and affiliates of Rosseti, JSC UNECO, engineering companies, operation, design and research companies, equipment developers and suppliers (according to the list).
Issues for discussion:
- What was the reasoning behind the intention of grid companies to construct and operate 20 kV electric networks? What new technical and economic-ecological requirements are imposed to next generation networks?
- How many new 20 kV networks have been constructed in Russia to the moment and how many 10 kV networks have been transferred to 20 kV voltage level, in what regions? What investment projects these activities are (were) part of? What state-of-the-art equipment is (was) used?
- What does experience of construction and operation of 20 kV networks show? What difficulties occur when transferring the existing 10 kV networks to 20 kV voltage level? What causes 20 kV network failures?
- What is the economics of construction and operation of 20 kV networks? How do these costs align with those of construction and operation of 10 and 35 kV networks? How will distribution network operation efficiency and electricity tariffs improve?
- What are the most effective distribution network diagrams including 20 kV voltage level in actual conditions? What network components can be used to improve its reliability? What automatic load transfer, circuit-breakers with relay protection should be used, in what sections of a 20 kV network they should be installed and who should do this? Do they need booster transformers, what are pros and cons?
- What is peculiar about operating modes of a 20 kV network? What neutral operation modes are available and preferable? How much do they need to invest to get the neutral grounding via a low-value resistor?
- The main objective of grid companies is to provide reliable and uninterruptible power supply. How should the term "uninterruptable power supply" (UPS) be understood? Is there any market for UPS today?
- How soon will definition of electric network reliability be revised in Russia (not by one parameter - outage duration, but two, as is common in foreign practice - outage duration and rate?)
- What is the market situation with regard to equipment for 20 kV voltage level, availability (absence) of domestic raw materials for 20 kV XLPE cable production?
- What is cost estimation for a XLPE cable with sector-shaped conductors? What are design (technical) advantages of new sector-shaped XLPE cables? Are they reliable and safe? How many Russian factories can undertake their production? Can ordinary stranded circular conductor cables be deemed an alternative to cables with new (triangular) sector-shaped conductors?
- Are there any producers of cable armature, joints and terminations in Russia? What measures should be taken to solve the problem of import phase out for these products?
- What new materials and equipment are recommended for application in production of 20 kV cables and 20 kV network construction?
- Is there any real problem of power-loss-in-cable-shields impact in a 20 kV network on their operating modes?
- What is the way to overcome divergence in law enforcement related to selection of power consumer categories (i.e. when Electric Inspection Service ignores and the Government resolution No. 861 does not oblige)?
- Who will be the mastermind and supervisor of a new trend - construction and operation of 20 kV electric networks?
- When will the specific standards on construction and operation of 20 kV networks be developed?
On completion of discussion the participants of the Conference have come to the following conclusions:
- The experience of Moscow Region companies in design, construction and operation of 20 kV networks, especially of PJSC Rosseti Moscow Region and JSC UNECO, is significant.
- There exists a positive trend to construct and develop 20 kV power utilities in other regions of Russia, including Saint-Petersburg, Yekaterinburg, the Khanty-Mansiisk autonomous district, the Moscow region.
- At present, the application area of 20 kV networks includes regions with high load density and remote consumer power supply diagrams. However, there are still more grounds to consider a historical mistake of the USSR to eliminate common usage of 20 kV voltage level, but to develop 6-10 kV voltage level instead. The reason was underestimation of the electric network load and the sole intention "to light a lamp in every house".
- Construction of new 20 kV networks is a sufficiently less problematic objective than transfer of existing 6-10 kV networks to 20 kV voltage level. For instance, consumers do not always understand their favor in rated voltage increase, and, therefore, don't want to invest into reconstruction of their electrical facilities. This is the point where a grid company has to establish good and mutually beneficial cooperation with consumers. This work should be carried out in advance.
- During construction of 6-10 kV overhead lines they widely use 20 kV isolators with increased impulse strength in conditions of lightning surges. This practice should be continued as it helps to avoid replacement of line armature during transfer of 6-10 kV lines to 20 kV voltage level.
- It is possible to increase voltage in busbars of remote 6-10 kV consumers by installing boosters of different design. However, this should be considered as a temporary solution, and its alternative is transfer of the network to 20 kV voltage level.
- In 20 kV networks it is recommended to use the resistive neutral grounding with protection adjustment to fast tripping in conditions of a phase-to-ground fault. This solution helps to avoid sustained arcing in the point of insulation fault and to minimize other phase faults.
- In 20 kV networks it is recommended to use three-phase groups of single-phase XLPE cables. Closed triangle laying is preferable for three single-phase cables. To accelerate the process of cable laying, it would be good to perform triangular stranding in the factory.
- Application of three-phase XLPE cables, including sector-shaped conductors, in 20 kV networks is possible but subject to thorough substantiation with regard to wiring ease, careful removal of semi-conductive insulation layer, applicability of typical assembly tools, etc.
- In 20 kV networks with the resistive neutral grounding it is reasonable to use single-phase cables with minimum shield sections (25-35 mm2), thus, enabling easy double-end grounding of copper shields in closed triangle laying of single-phase cables. No need to perform one-end grounding or transposition of shields.
- When laying 20 kV cables in polymeric tubes in ground, they should be non-flammable. It is especially important in arrangement of a 20 kV block draining system.
- To provide reliability of 20 kV networks it is desirable to establish cooperation with manufacturers of dry transformers to find out true reasons of their high fault rate and to develop the action plan including improvement of insulation strength of such transformers.
- To acknowledge importance of results of the work of the Conference on 20 kV networks for domestic power industry and to meet next year again to exchange opinions and to adjust the technical policy.
- To thank you the participants of the Conference for their contribution to development of 20 kV networks and to ask them to pay special attention to defining economic parameters of 20 kV network operation compared with 6-10 kV networks. Such systematic work will help all parties concerned to enhance the 20 kV voltage application area in Russia.
- To mark the significant role of PJSC Rosseti and the field-specific journal "ELECTRIC POWER. Transmission and Distribution" in 20 kV topic coordination and to ask them to continue this work.