Tracking Underground Cable Failures Using AM/FM
By Gary C. Kirkland, JEA
Jacksonville Electric Authority (JEA) serves the greater Jacksonville, Fla., metropolitan area–a service area of more than 900 square miles and a population of more than 1 million. JEA first began development of an AM/FM system in 1988, in conjunction with installation of a mainframe-based distribution service restoration (DSR) application. Intergraph`s facility rulebased application model management environment (FRAMME) software was selected to provide circuit connectivity tracing capabilities to meet the needs of DSR, as well as providing generic utility mapping and facility modeling capabilities. Conversion of paper map records included aerial photography, ground monumentation and global positioning system (GPS) surveying methods in order to establish an accurate digital land base.
JEA`s AM/FM database is fully populated with facility information for the entire utility distribution system (except for the downtown secondary-network area). The model contains more than 1 million facility features, including more than 300,000 meters, 120,000 poles, 65,000 transformers and more than 4,500 circuit miles of distribution primary (ranging from 4 to 26 kV) lines. All major distribution components, such as reclosers, lateral fuses and other devices which affect customer connectivity to serving circuits are included. JEA is currently adding street lights and considering the addition of transmission substation and other facility elements to the system.
As the AM/FM system has matured, its scope has been expanded to include transformer load management and interfaces to provide information for external distribution analysis and circuit reliability applications. Electronic interfaces have been established with all external applications in order to interchange information efficiently and reliably. A significant amount of data validation processing is integrally performed by interface software to help ensure that the user applications receive reliable information.
Several platform changes have occurred as technology has evolved over the years, beginning with MicroVMS minicomputers and UNIX workstations culminating to the client/server technology used today. Each transition has offered increased levels of processing power and speed, which usually translates into additional application functionality and performance. JEA`s standard FRAMME workstation platform is now on Windows 95, with master graphics and database files stored on a Windows NT server.
Users can access AM/FM graphical information in two distinct ways: (1) FRAMME client software in the office desktop environment and (2) Field View (Intergraph software) package in both office and field environments. The Field View product utilizes a user-defined subset of the complete FRAMME model, which can reside either on a file server for common office use or local disk/CD-ROM for field access. Donald Bishop, JEA transmission and distribution foreman, finds the package particularly useful in arranging outages with customers since he is able to obtain the required information to contact customers by phone from field construction sites.
Integration options for melding the functionality of AM/FM with other facility-related applications such as SCADA, customer isolation system and distribution service restoration are currently being considered. In addition, an automated design environment for distribution engineering is under development to provide faster, more accurate updates of facility model information.
Cable Failure Tracking Application
As is true of many electric utilities, JEA has a tremendous amount of underground distribution circuitry, much of which was direct-buried in the soil. Most of these installations consist of single-phase lateral loops in underground residential and apartment developments. As failures became more frequent on the older cables (due to concentric-neutral corrosion and other factors), JEA needed a way to minimize unplanned interruptions of service to its customers.
JEA distribution engineering and construction personnel developed threshold parameters to guide designers in making systematic decisions for replacing failed cables. These factors are defined in terms of percentages of cable spans in each lateral which have had one or more failures. For example, if 40 percent of the spans in a lateral have failed at least once, JEA`s policy is to pre-emptively replace the entire lateral. The threshold is lowered to 20 percent if the spans involved have experienced multiple failures. Individual spans are replaced if two or more failures have occurred. Other factors are also taken into consideration, such as the age of the cables and the number of customers affected.
Textual databases and other record-keeping systems were initially used to track failures, but these proved less than ideal due to the nature of the information involved. It was difficult to adequately address failure locations to ensure that all failures were included, but not duplicated. In contrast, AM/FM systems, with both textual and graphic views of the actual facilities, offered a better solution for tracking this information. This illustrates the inherent value of the “AM” aspect of these systems. Accordingly, a decision was made to implement an AM/FM-based solution to meet this need.
AM/FM Provides a Solution
JEA`s AM/FM system model contains detailed records of all distribution circuits, including primary conductors–both overhead and underground. Primary conductor database records contain all pertinent information needed for the user applications for which the system was designed. The addition of the “cable failure tracking” application required that JEA capture and maintain additional information about those conductors which fail. The JEA project team designed a method for capturing the information, such as failure date and failure phase, and storing it in the database. Once stored there, this information can be routinely reviewed by engineering personnel to determine when and where failures are occurring throughout the service area.
As cable failures occur, maintenance personnel create a sketch of the failure location using the FIELD VIEW software. Certain required information about each failure, such as the date and phase, are “redlined” onto the electronic map which is then printed and sent to engineering for entry into the master AM/FM database.
Failure information is entered by interactively locating and editing the particular cable facility database records; there is no change to the graphical records. For future enhancement, JEA is investigating the feasibility of direct entry of this information by maintenance personnel in the field. Once entered, failure information is retained not only for the life of the individual cable, but until such time as the entire lateral may be replaced. When recabling jobs are completed, entries are made in the cable database records showing the date of replacement
A circuit tracing process is performed regularly for the entire electric distribution system, which summarizes the number (both single and multiple failures) of failed spans and stores the results in the serving lateral fuse records. The tracing process follows all connectivity paths for each complete circuit and is done on a phase-by-phase basis. This information is routinely analyzed by a standardized database query process to provide reports to engineering personnel of lateral fuse locations which have exceeded the predefined failure thresholds. These locations are then investigated in detail for possible complete lateral replacement, including installation of new conductors in conduit. Reports are also produced to show the complete list of all active failures–that is, those in laterals which have not been replaced.
Results and Conclusions
According to R.T. (Mac) McCauley, JEA network/commercial construction manager, nighttime call outs due to failed cables have been reduced by 50 to 60 percent as a direct result of failure tracking and JEA`s pre-emptive replacement policy. McCauley indicated that the worst problems have been experienced on cable installations more than 20 years of age where faults have further weakened the cables, thereby contributing to additional failures. He also stated that improved cable technology and installation techniques which prevent water intrusion will help reduce the incidence of cable failure on newer facilities.
By means of using AM/FM technology, JEA is now better able to monitor failures of underground direct-buried cable throughout the service area and systematically decide which cable segments should be replaced with new cables in conduit. This practice will continue to have a significant effect in improving the quality of service customers receive.
Donald Bishop, JEA T&D foreman, uses a portable computer with data on CD-ROM.
Gary C. Kirkland is manager of geo-facility applications at JEA. He has worked for 27 years in the electric distribution field in both engineering and information systems roles.
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