The global positioning satellite (GPS) emergency repair system in service at Shanghai Municipal Electric Power Co. (SMEPC; Shanghai, China) offers a management capability that can bring significant improvements to SMEPC's customer service.

The system applies several technologies — such as geographic information system (GIS), GPS and a computer network — that provide a real-time positioning monitor for managing the utility's electric power emergency repair vehicles. The system is capable of working with two public communications networks — the cellular digital packet data (CDPD) network and a global system for mobile communications (GSM) network — as well as with the existing trouble-call system and electric power GIS information system to share information resources and monitor emergency repair vehicles. The system identifies the position of emergency repair vehicles; dispatches the nearest repair vehicle to the fault position; and reduces response time to fault calls, replying to any enquiry and eliminating faults much faster.

SMEPC

The SMEPC power network has a maximum system demand of 12,500 MW, which supplies six million consumers via a network of underground cables and overhead lines operating at various voltage levels. For example:

• Voltages used include: 220 V, 380/400 V, 10 kV, 35 kV, 110 kV, 220 kV and 500 kV.

• Length of underground cable (over 35 kV): 3700 km (2300 miles).

• Length of overhead line (over 35 kV): 6000 km (3730 miles).

In 1996, SMEPC published a consumer service guarantee that states the fault repair teams would be on-site at the fault position on all 200-V to 35-kV networks within 45 minutes of receiving a customer no-supply call. The range of faults allocated to these repair teams include all faults associated with third-party damage, underground cable mains and service cable faults, overhead line mains and service faults, substation and consumer fuse failures, and consumer metering faults. To satisfy this service guarantee, SMEPC invested 3 million RMB on a GPS emergency repair system for use on the distribution network, which operates at voltages up to and including 35 kV.

GPS Emergency Repair System

The GPS emergency repair system comprises the satellite positioning system, the traffic GIS and digital radio communications technology. With the aid of the integration of GPS, an electronic map of the city and radio data communications technology, the emergency repair system can realize the position, dispatch, give commands and communicate with the patrol repair vehicles. The mobile part of this emergency repair system includes 600 repair vehicles linked to the system. The receivers installed in the mobile repair vehicles receive information from the satellite, calculate the vehicle's position and transmit real-time data to the control or monitoring center of the emergency repair system.

The monitoring center is equipped with several networked computers that constitute the multifunction system with facilities to collect information to manage mobile vehicles. The visual displays an aid in the decision-making process that includes a wall-screen presentation with a vector electronic map background, and real-time displays that record and replay the disposition of the patrol repair vehicles. The main functions of the emergency repair system are to:

• Transmit real-time data between the monitoring center and move repair vehicles to keep track of the vehicles position.

• Display and continuously update the electronic map of the districts in the city.

• Display and update the important management targets.

• Provide a real-time display in the control center showing the position of all mobile fault repair vehicles.

• Communicate between the control center and the tracked vehicles.

• Record and analyze the vehicle driving routes.

• Receive automatic alarm in the control center when contact with a vehicle receiver is lost (beyond the communications range or receiver failure).

System's Main Technologies

The GPS system technology was purchased and installed by the manufacturers. The GPS comprises ground control station, space equipment and GPS customer receivers. The GPS system continuously positions any customer receiver on the surface of the earth via the 24 positioning satellites that travel in six orbits surrounding the earth. The accuracy of the real-time positioning system enables each receiver to be identified with an error of less that 20 m (65 ft).

Data communications technology forms an important basis for all modern information technology systems, and the development of space information technology depends on data communications technology. In the course of developing GPS, GIS and general packet radio service (GPRS) technologies, it was absolutely necessary to develop the high-speed, large-capacity and high-reliability data communications. Several data communications modes — including GSM, code division multiple access (CDMA) and CDPD — can be applied to the system to position, dispatch and monitor the patrol repair vehicles.

The main features and advantages of GSM technology (short-message communications) are: the ability to offer nationwide coverage; high reliability and ease of application to both data and voice communications; low investment for construction; and moderate operational costs. The GSM short-message communications system does not require a voice communications line or dialing, but GSM does take a relatively long time to send and receive messages, so the system has a low real-time performance characteristic.

CDPD technology offers similar advantages and features to GSM. Although the operational cost of CDPD is slightly higher, this is compensated for by the superior real-time performance (sending and receiving messages almost simultaneously) and higher capability of anti-interference (which is more suitable for positioning moving targets).

SMEPC's System

SMEPC's GPS-aided emergency repair system can use both CDPD and GSM communications modes. CDPD, with its strong capability of anti-interference and high real-time performance, is applied to the urban zone of Shanghai; GSM is applied to the spacious Shanghai suburb zone where CDPD has blind areas. The monthly rental charges associated with CDPD could be reduced, but the resulting area of coverage would be too narrow. The coverage area of GSM is much wider though its real-time performance is relatively lower. CDPD is used by the moving repair vehicles in the urban area of Shanghai where CDPD coverage benefits from the higher rate of refreshing GPS data, as well as vehicles in some suburb areas where the CDPD coverage is inadequate use GSM. The main characteristic of the hardware configuration for SMEPC's the emergency repair system is that the two communications modes can be applied simultaneously by one set of monitor systems.

GIS is absolutely necessary in the service system provided for the mobile teams. GIS can display the position information collected by the GPS terminal on the digital electronic map and describe the information of objects such as streets, blocks, borderlines between administrative divisions, main architectures, rivers, railway and other important features of the locality. By employing some compiling and viewing software such as Mapinfo and Arcinfo, every object is solely expressed by a group of numerals on the vector digital electronic map. These numerals can be amended or recompiled as required.

Operational Experience

The GPS satellite positioning-aided emergency repair system in SMEPC was commissioned in December 2001. It soon reached the predicted performance requirements and system targets after a period during which minor improvements were necessary to speed up the processing of fault information and accurately dispatch the mobile fault repair teams. Currently, SMEPC has a fleet of 300 fault repair vehicles equipped with GPS receivers able to operate within the area supplied by the Shanghai electric power network, of which some 86% of vehicles are scheduled to operate in non-attended substations or to repair system faults.

Following the commissioning tests, the GSM and CDPD operated satisfactorily and the Integrated Services Digital Network (ISDN) special line connection was stable. The system now positions vehicles, sends short messages from the control center to vehicle receivers and receives feedback information. It also has made the GIS identify fault position through intermediate databases. The GPS's ability to find and mobilize the position of the fault repair vehicles nearest to the fault position intelligently has improved the real-time and reliability performance of the distribution system.

System Benefits

The promised standards on “Power Supply Services” states that repair workers should arrive at the fault position within 45 minutes in the Shanghai urban area within the inner-circle route (a famous overhead circular road system around Shanghai's downtown) and within 90 minutes in the area outside the inner-circle route. Since the GPS-aided emergency repair system was commissioned, SMEPC has satisfied the promised standards and now handles about 500,000 faults annually.

Recent performance statistics show that, on average, it takes the fault repair teams 22 minutes to arrive at the fault position in the area within the circle route and about 80 minutes in the area outside the circle route. These figures confirm that by replacing the time-expired radio intercom and phone communications equipment with new technology, SMEPC is now able to dispatch fault repair and operational teams to the fault position with far greater efficiency.

Sheng Ming received bachelors degrees in power system engineering and business administration from Shanghai JiaoTong University prior to joining SMEPC in 1994. His currently is responsible for power system management. He has published several articles on communications and power systems in the Chinese Society for Electrical Engineering and Shanghai Electric Power magazines
shengm@smepc.com