Since 1996, the 10-kV distribution system in the urban area in Yancheng has been reconstructed, interconnected and equipped with additional in-line section switches to provide a level of automation required for remote surveillance and control. Power-supply reliability has improved year by year, from 99.7% in 1996 to 99.98% in 2000, and Yancheng now has one of the most advanced distribution management systems (DMS) in China, which contributes to the social and economic prosperity of the city.
With the planned reformation and upgrade of the distribution system, the Yancheng Power Bureau's (YPB) goal is to improve supply reliability and voltage regulation to 99.99%, a level of performance that will make YPB a top-ranking power enterprise in China as well as internationally.
Yancheng's urban area is supplied by the Yancheng Power Plant and the 110-kV transmission system that supports five unmanned 110/10-kV substations. The 110-kV installed transformer capacity is 350 MVA that, to date, has a recorded peak demand of 160 MW. The 10-kV distribution network, comprising 42 10-kV circuits, has a total length of 334 km (208 miles), a transformer capacity of 296 MVA that has supplied a 100-MW peak demand. The YPB consumer base includes 1013 high-voltage consumers.
In 1996, YPB, supported by the Nanjing Southeast University and Beijing Creative Distribution Automation Co., launched a long-term distribution automation system (DAS) project to create a fully automated system offering consumers a high-quality, reliable electricity supply.
Automatic Management/Facility Management (AM/FM) Bsed on Geographic Information System (GIS). The system includes four parts: subgraph drawing, graphics management, data management and integrated inquiry subsystems. The distribution data management includes the following components:
Basic drawing tools and graphics information to be written and maintained in layers.
Documents and maintenance records.
Graphic management subsystem, including 10-kV distribution network and geographic connection diagrams.
Geographic and schematic diagrams that can be displayed independently and viewed in various formats.
Real-time operational displays of the distribution network.
Supervisory Control and Data Acquisition (SCADA). The DAS collects and processes real-time data from remote terminal units (RTUs), in addition to links with management systems, including automated dispatch and the load control system. Currently, data are collected from distribution switches, fault indicators, substation switches and some consumer transformers.
Selection of Automatic Switch. All 10-kV substation switches are vacuum units with microcomputer protection. The distribution management system (DMS) achieves remote control of substation switches by linking with the energy management system (EMS) through the network communications interface. The loop scheme of the vacuum recloser/circuit breaker is rated at 630 A and equipped with intelligent control to provide overhead line automation. These switches can be operated in the field or remotely controlled.
A padmounted switchgear (PMS) loop scheme is used for cable network automation. The PMS load switch (in-feed) and the circuit breaker (out-feed) are also vacuum units with three operating modes: hand operation in the field, electromotive operation and remote operation.
Switch Control Device. Recloser/circuit breakers and PMS are equipped with the “four-remote” function, RDCU-1, that can realize protection, reclosing, fault isolation and power supply transfer. The RDCU-3 unit provides “four-remote” to more than four load switches, CBs and PMS simultaneously. The RDCU controls made by Creative Distribution Automation Co. offer the following SCADA functions:
Metering function: The RDCU can be used to measure phase and zero sequence currents, phase zero sequence voltages, power factor, active and reactive power, harmonic components of current and voltage, and system frequency.
Data logging: Daily load current values are recorded every 15 minutes and switch operating times.
Communication. RDCU is equipped with a standard RS-232 port that connects to all communications devices. In this way, telemetry, telecommunications, remote control and remote setting are realized for SCADA applications. Radio communication is used between each substation and the distribution base station with a polling protocol at a frequency of 228.550 MHz, which is within the bandwidth for electrical load control. The imported radio station has a power output of 10 W, which is sufficient to transmit more than 20 km (12.5 miles) with a communications speed of 9600 bps.
The cable automation system adopts a master-slave configuration, optic-fiber loop communications scheme with the base station being located in the YPB office.
The distribution base station is key to the distribution SCADA with the following functions:
Collects and processes running data and status information from all RDCUs and other devices.
Displays statistical and event data in real-time.
Remote control, enables/disables some functions and modifies field switch protection settings.
Provides a network model for other application software of DMS.
Fault Automatic Isolation
All switches on cables/overhead lines analyze and transmit fault information and receive and implement remote-control operation. The overhead line network is not complex, so YPB uses the distributed intelligence mode, whereby the recloser automatically isolates the fault and transfers supply without base station intervention. For cable networks, optic fiber is used, which offers high speed and reliability. In the event of a fault, the fault restoration software in the distribution dispatch base station undertakes a topology analysis, and the fault isolation and supply transfer is executed by SCADA.
Fault Isolation Scheme in Overhead Line Automation
The overhead line network adopts a three-recloser/circuit breaker-loop scheme. For example, consider a fault on L1. The Jianxi 186# switch will trip and fail to reclose, then Radio Station 5301# switch will automatically trip after a power loss for three seconds. Then the Nurse School 5801# recloser will close after a five-second power loss from the supply side. Thus, segment L1 is isolated and segment L2 is transferred for supply to the Huanxi line at the Chengzhong Substation.1 Operations take less than 10 seconds. Similarly, when there is a fault on L2 or inside the substation, the field switches that have protection and loop function will isolate the fault in optimizing mode.
The Isolation Scheme for Cable Automation
Faults on the cable system should be interrupted instantaneously. Therefore, in the cable loop, the main loop is equipped with load switches (without protection function). The feeders with circuit breakers have a protection function. A feeder fault is isolated by the circuit breaker in the PMS. In the event of a fault on the main loop, the substation switch trips. On receipt of information from the RCDU, the base station will initiate fault isolation and supply restoration. In semiautomatic mode, the remote control is routed to the load dispatcher for confirmation, but restoration is accomplished within one minute. Important consumers are supplied via four circuits to enhance supply reliability.
The distribution network is sufficiently complex enough to provide the additional information required for fault location, and a fault location system (FLS) has been developed for some overhead and cable lines. The FLS includes fault detector (FD), submitter (ST), base station (BS) and offers:
Fault Detector is a mini fault-detecting device that is hung on the 10-kV distribution line. A short circuit changes the color of the FD and simultaneously sends fault information to local ST by a high-frequency communications channel (for overhead lines) or audio cable channel (for cable).
Submitters monitor the FD's collecting and transmitting to the base station and address the data of the FD subject to short-circuit current. For overhead lines, a special ST that monitors 12 FDs is installed.
Detect Base Station is the application software for the distribution station. The software demodulates and decodes the address information from STs, recovers the address of FDs and after verification and analysis, displays the fault on a geographic map.
Integration of Automation System
Hardware Configuration of the Base Station. The configuration of a DMS computer system includes an HP Server P II 350/128M/8G, which serves as the administer core of the whole DMS; two IBM P II 350/64M/4G computers, which serve as a dispatching platform and a distribution management platform; and two Yanhua P II 350/128M/4G industrial computers as the front terminals that provide the required level of redundancy.
Software Configuration of the Base Station. The software system adopts an open and standard configuration, a unified operating system, a unified database and a unified DMS. The operating system of the server is Windows NT. The operating system of the man-machine interface is Windows NT Workstation, and the programming language is VC, Vb and Delphi. The database is DB2.
System Integration. The system uses radio, optic fiber, audio cable and other communication channels for remote control of 70 switches and 100 groups of FDs on 18 overhead lines and four cable circuits. At the same time, it integrates feeder automation (FA) and offline DMS. By connecting to YPB's management information system (MIS) it provides inquiry functions on display terminals in the bureau and information intercommunication with dispatching automation, utilization business and load control system.
Distribution automation improves power-supply reliability and can identify and isolate faulty sections of network, transferring the disconnected load to healthy sections of the system with minimal delay. From 1996 to 2000, there were more than 200 occasions when DAS reduced outage times to within one to three minutes. This compares to 35 minutes previously.
A further 46 instances of load transfer or fault isolation occurred where the outage time was reduced by an average of 60 minutes. The DAS has added 130 MWh and 70,000 RMB (US$10,000) to annual revenue and more than 130 million RMB (US$18 million) of social production value. The DAS is expected to achieve financial payback within five years.
Real-time SCADA functions of the DAS decrease manpower and time involved in field data measurement and in computer drafting. Equipment management and defect management based on GIS can reduce repetitive work and labor costs. Computer automation addressed the error and random manual searching problems, the global sharing of data has improved security, and the level of service has improved the enterprise efficiency. The indirect benefits are substantial as well.
DAS has optimized the use of the existing distribution system, reducing local peak demands and thereby deferring capital investment in system reinforcement. YPB plan to further develop the DAS to optimize reactive power, reduce system electrical losses, and improve voltage quality and regulation.
Yancheng DAS started with proven technology. With advanced functions, high reliability and the GIS/AM/FM system, it is possible to store a mass of data that can be accessed and analyzed in the format required by the YPB's distribution management and professional staff. This has contributed to marked improvements in safety and service levels.
Installing a sophisticated DAS requires a huge capital investment but the overall benefits are substantial. The distribution network is the link between the power system and the customer, so system reliability and electric quality are directly related with state policy and people's lives. Reconstructing the distribution network and implementing distribution automation will improve the management of the distribution network. In addition, it will produce economic and social benefits, such as improving power-supply reliability, reducing system electrical losses, reforming power quality and reducing the peak load.
Zhang Huailian is the former director general of Yancheng Power Bureau Jiangsu Province, a senior engineer, director of Yancheng Society of Electrical Engineering, and decision-maker of the Distribution Automation Project. Huailian was recently appointed director of presidents at Jiangsu Provincial Electric Power Company.
Cai Guilong is chief engineer of Yancheng Power Bureau, Jiangsu Province, and senior engineer, responsible for the design of the Distribution Automation Project.