CONCLUSIONS of IVth All-Russia Conference "Development and Reliability Improvement of Distribution Networks"
(July 3, 2018, Moscow)
The Conference has been held by "ELECTRIC POWER. Transmission and Distribution" journal with support of PJSC Rosseti and JSC "United Energy Company" (JSC UNECO) being the title sponsor.
The event has been dedicated to aspects of development and operation of MV (0,4...20 kV) distribution networks, which constitute the major part of the Russian power grid (96,7% by length) and cause lots of problems.
Participants: above 160 persons, including representatives of the Ministry of Energy of Russia, top managers and specialists of the Russian power grid (Rosseti Group, regional grid companies, public energy services), research and design institutes (including parts or affiliates of power companies), higher educational establishments, electromechanical equipment producers, representatives of foreign companies that operate distribution networks (according to the list).
Issues for discussion:
- Transition to digital process platform:
− Implementation of Russian Federation President May decrees "On national goals and strategic objectives of the Russian Federation development for the period until 2024" as related to transformation of key industrial sectors, including power infrastructure, and guaranteed power supply by introducing digital technologies and IT platform solutions.
− Development of electric networks as part of the program of power grid digitalization. Proposals and standards of Rosseti Company.
- Main issues of 20 kV network development:
− Improved technical solutions for structural development and advanced operation reliability of 20 kV networks in metropolitan cities.
− Technical solutions and recommendations on transition of existing 6-10 kV networks to 20 kV voltage level in rural areas.
− Optimal topology of a distribution network.
- Technologies and technical solutions for distribution networks:
− Advanced technologies for reliable and efficient operation of 20 kV networks in metropolitan cities.
− Improved reference documentation in respect of design and operation of a 20 kV network with resistive neutral grounding.
− 20 kV network equipment protection against commutation surges.
− Modern technologies of digital protection system design for a 20 kV network with resistive neutral grounding.
- Reliability and security of electric network operation. Sharing experience:
− Creation and introduction of cyber security system for a grid company.
− Practical experience of Rosseti Group related to provision of safety of emergency response and restoration works when eliminating large-scale power grid outages.
− Practical experience of Rosseti Group related to improvement of operational availability for elimination of large-scale power grid outages.
− Domestic and foreign experience of design and operation of 20 kV electric networks.
− Introduction of live work methods. Live work training of grid companies' personnel.
− Problems of fire safety of cable lines and wiring.
− Reliability management of external power supply of end consumers.
On completion of discussion the participants of the Conference have come to the following conclusions:
- The main goal of electric power digitalization is introduction of an IT-based risk-oriented management model aimed for minimization of the total cost of ownership to reduce the working cost of electricity with provision of the intended level of reliability and the acceptable level of rates.
- Main measures (scenarios) of electric power digitalization should be as follows:
− Creation and introduction of the unified field-specific digital environment to be used by power utilities for online process data transmission;
− Introduction of risk-oriented management;
− Creation of power supply reliability control and monitoring system;
− Development of client services for consumers;
− Creation of the system and formation of field-specific orders to encourage the Russian machinery building and microelectronics and to reduce logistics expense.
- The digital network is a combination of power grid facilities. The key factor of its effective management is digital data. Big data processing and making use of results of its study enable remarkable improvement of grid company activities, availability and quality of their services for consumers.
- Different scope of IT introduction is required depending on equipment of a network utility. PJSC Rosseti has developed "Technical requirements to digital network components" that define principles of digitalization and the optimal list of technical requirements to digital network components. Besides, Rosseti Group has developed and is introducing:
− new methodological base of risk-oriented management of production assets;
− online monitoring system that eliminates risks of accidental failure of equipment units and minimizes damage;
− new requirements to network attending personnel;
− renovation program of power grid utilities of subsidiaries and affiliates of PJSC Rosseti for the period 2018-2026 developed on the base of the risk-oriented management model.
- Based on practical experience of operation and development of distribution networks of metropolitan cities, to acknowledge most efficient the following ways of 20 kV network development:
− provision of optimal reliability and efficiency based on complete observability, remote control engineering of switching apparatuses;
− improvement of network controllability;
− provision of the normalized level of consumer power supply reliability by N-1 principle;
− digital protection introduction;
− establishment of communication channels and joining of all distribution and switching nodes into the united system of surveillance, monitoring and control of a metropolitan city network;
− improvement and development of reference documentation with respect to design and operation of 20 kV networks with resistive neutral grounding.
- To take into account that transfer of existing 10 kV networks to 20 kV voltage level does not require significant capital investments as 10 kV and 20 kV overhead lines have same overall dimensions, the majority of operating 10 kV lines are equipped with 20 kV insulators as demanded by latest edition of the Installation Code. Thus, transfer of 10 kV overhead lines to 20 kV voltage level costs practically nothing. Self-supporting insulated conductors for a 10 kV overhead line are designed for 20 kV rated voltage. The cost of a 20/0,4 kV transformer substation (TS) is about 25% higher than that of a 10(6)/0,4 kV TS. What's more, after a slight change it is possible to use available designs of pole- and master-type TS. All above-mentioned facts provide for practically common feasibility of 20 kV rated voltage application in overhead networks.
- On completion of 10(6) kV overhead line transfer to 20 kV voltage level the latter's efficiency grows still higher as each component kept from the "out-of-fashion" infrastructure makes the initial capital investments less.
- Construction of 20 kV overhead networks is a great challenge as it makes their transmission capacity doubled with nearly same costs for ownership and reduces process-related power consumption. This is a critical point for provision of new process connections of consumers in conditions when existing 10(6) kV networks have no transmission capacity left.
- To use low-resistive neutral grounding with single phase-to-ground fault current of 200 A (60 Ohm resistor) in design of 20 kV networks. This will improve reliability and security of electric installations, minimize risks of electric shock hazard. Single phase-to-ground fault current of 200 A is a compromise solution with regard to provision of required relay protection and automation sensitivity and acceptable resistances of grounding devices (safety requirements to them are more severe).
- The low-resistive neutral grounding mode requires specific operation logic of relay protection, automation and autoreclosing devices in conditions of single phase-to-ground faults. To make requirements to grounding devices less strict, it is necessary to provide the minimum possible fault clearing time.
- To deem actual the following trends of 20 kV network protection and automation development:
− To speed-up fault clearance;
− To increase the number of independent selective zones in the supply part of the network;
− To improve network observability;
− To keep in operation the most of consumers supplied via transformer substations with no power circuit-breakers and relay protection devices available in the distribution network;
− To develop technical solutions that support the multi-end supply mode;
− To speed-up restoration of power supply after network failures.
- To deem mandatory the following amendments and supplements to the valid reference documentation:
− Installation Code, Chapter 1.7 "Grounding and protective measures for electrical safety". To add the procedure of grounding device parameter calculation based on permissible touch voltage values for a network with resistive neutral grounding.
− Installation Code, Chapter 3.2 "Relay protection". To review the partition on protection of overhead and cable lines in 20 kV networks with resistive neutral grounding and of the neutral grounding resistor. The protection set should be defined by 20 kV network operation conditions. Besides, it is essential to define the minimum possible sensitivity factors for main and backup protections of a 20 kV network with resistive neutral grounding.
− Guideline document RD 34.20.185-94 "Instruction on design of municipal electric networks". To review this Instruction with respect to available 20 kV network operation practice, revised feasibility study and practical reasons of 20 kV voltage level application in Moscow.
− Guideline document RD 34.45-51.300-97 "Scope and norms of electric equipment testing". To be supplemented with requirements to the scope and norms of testing the resistor - the essential electric device for a network with resistive neutral grounding which provides its operation reliability.
− "Guideline instructions on design of grounding devices for 6-750 kV substations" (Company standard of JSC FGC UES 56947007-188.8.131.52-2012). To make amendments with regard to calculation requirements for grounding devices of a 20 kV network with resistive neutral grounding.
− Technical Maintenance Rules for electric stations and networks of the Russian Federation (PTE). To introduce changes and amendments to enlarge the scope of application of the resistive neutral grounding operation mode.
− Research and technical documentation in regards to ferro resonance overvoltages. To add description of capabilities and conditions of ferro resonance origination in a 20 kV network with resistive neutral grounding and to develop the related technical requirement to 20 kV voltage transformer parameters for a network with resistive neutral grounding.
- To deem advisable development of "Norms of technological design of a 20 kV network in a metropolitan city" with observation of requirements stipulated in PJSC Rosseti Company standard "0,4-110 kV Distribution networks. Requirements to technological design".
- In some cases the intensive transients that originate in switching and lead to failures are caused by the resonance due to similar length of the cable and the transformer winding and in some cases - due to large capacitance of a cable line connected to busbars. High capacitance of modern XLPE cables is typical in cases when they have the increased length and/or there are several cables provided per phase. A way to solve this problem could be application of special RC-circuits in transformer terminals, that are more efficient compared with surge arresters.
- In conditions of creating an advanced IT-based power grid, cyber security system becomes the absolute must-have for:
− protection of data resources of the automated remote control system against external and internal threats;
− fulfillment of applicable cyber security requirements;
− provision of operation reliability of main and auxiliary equipment of the automated remote control system;
− online monitoring of the current cyber security level of the automated remote control system.
- To deem expedient the use of similar international practice in development of IT-based solutions for reliability and efficiency improvement of operation of metropolitan electric networks that include 20 kV networks.
- To recommend regional grid companies make use of practical experience of Rosseti Group with respect to safe emergency response and restoration works during elimination of large-scale outages for maintenance of attending personnel health and life during emergency response and restoration works.
- To reduce the number of process disturbances in electric networks, to improve the average rate of consumer supply interruptions and average duration of supply interruptions during large-scale outages, to recommend regional grid companies make use of Rosseti Group practical experience in regard to operational availability for elimination of large-scale outages.
- To acknowledge inefficient (in many cases) the traditional electric network diagram in inhabited and rural areas with regard to the scope and the expense of its maintenance and actual transportation losses. It is reasonable to calculate the 'ideal' diagram based on actual loads, to compare it with the existing diagram and to define the measures required for its improvement.
- To consider main pros of arranging live work (6-10 kV above all) in networks:
− improved client-oriented approach due to reduced number of disconnections for repair;
− improved safety of the live working personnel;
− less human mistakes in commutations and their consequences, keeping commutation life of equipment;
− less non-productive labor costs, time lags for request clearance, expenditures related to disconnection (and re-connection) of network sections;
− high qualification of the personnel and advanced production practices;
− maintenance of the normal operating mode and the power supply diagram;
− technological method of reliability improvement (SAIDI, SAIFI).
- Technical managers of grid companies are recommended to consider development of 6-10 kV live work procedures, live work (different voltage levels) training of the personnel .
- Recommend to use cables with improved fire safety properties (НГ, нг(А)-LS, нг (…)-НF, нг (…)-FR, нг(…)-LTx) and to carry out routine thermal imaging diagnosis of electric equipment of residential and public buildings to provide fire safety of cable lines and wiring.
- To take into account the report of O.A. Tereshko on possible establishment of contractual economic responsibility of individual grid companies in different regions for reliability of external power supply of end consumers.
- Review of the IVth All-Russian Conference "Development and Reliability Improvement of Distribution Networks" from the "ELECTRIC POWER. Transmission and distribution" journal
- Program of the IVth All-Russian Conference "Development and Reliability Improvement of Distribution Networks"
- Photo report: IVth All-Russian Conference "Development and Reliability Improvement of Distribution Networks"