Carolina Power & Light Co. (CP&L), wanted to make a concerted effort to address customer interruption problems on its system. To do so, the utility first had to quantify the outages and determine where they were occurring. The only hard data available were counter readings collected semi-monthly from the majority of over 920 distribution feeder breakers, since fewer than 10% of CP&L's 285 transmission and distribution substations were equipped with distribution supervisory control and data acquisition (SCADA) systems. Not only were these statistics necessary for assessing system reliability, but the Distribution Dispatch Operations Unit (DDO) also needed to receive timely notification of customer outages and to distinguish between a full feeder lockout and an outage of lesser magnitude, such as a blown tap line fuse. In researching the problem, CP&L engineers found several products that met one or more of these requirements.
Product Availability Most of the products studied involved devices placed in customer locations that made telephone calls to a utility computer when certain predetermined criteria had been met, including outages, power restoration, low-voltage conditions, scheduled automated meter readings and periodic device health status. However, most of the devices could only make outgoing calls. Some of the systems required charges to the utility for every call or a different incoming phone line for each type of event reported and caller ID service on every line. One device, supplied by Design Concepts International (DCI), Boise, Idaho, U.S., could report momentary outages, which was important to us. That ability, along with the ease of implementation and cost, was sufficient for us to concentrate on using DCI's Sentry device.
Pilot Installation A pilot system of 10 Sentry2 devices was installed at several company employee residences in the Raleigh, North Carolina, U.S. area. A DOS-based master station PC was located at CP&L's Distribution Automation facility in Raleigh. After a short initial evaluation period, CP&L purchased an additional 200 devices and implemented a larger pilot installation by placing the devices at customer locations just downline of every automatic reclosing device on three of the five feeders out of the Zebulon 230-kV substation. With this configuration, it was possible to determine which section of the line was out for the purpose of dispatching personnel for service restoration. Additional devices were placed at about one per feeder in two of CP&L's business districts.
The original DOS-based Sentry program was a good tool that had some delinquencies with respect to call-taking speed, ease of use for the operator and data display. The since-discontinued Sentry2 device uses 1200 baud modem communications and takes up to 20 seconds to complete the data transfer after the PC answers the call. In addition, the DOS-based system could accommodate only one phone line. Display of outage data on the PC monitor was limited to one device at a time. Even with these limitations, the DOS-based system was extremely useful for dispatching and engineering functions. This pilot was successful enough to warrant wider application of the technology.
Implementation In early 1995, CP&L became a beta test site for WindowsTM version of DCI's Sentry Master Station and the Sentry4 series monitoring device. Some of the enhancements included faster call processing, multiple phone lines into the Master, better display of critical events and greater ease of use for the operator. Call-processing speed was increased approximately three-fold by using dual tone multiple frequency tones rather than modem communications for data transfer. Even though as of yet CP&L has used only one phone line into the Master, the system is expandable to 48 lines. The display of outages and other events were consolidated onto one main screen so that all of the "most recent events" and "current outages" could be seen together and be continuously updated. This enhancement allows the dispatchers to get the big picture when a feeder monitored by multiple Sentry devices is out.
In late 1995, CP&L committed to install at least one device on every non-distribution SCADA feeder and an additional device behind each three-phase line recloser. The model chosen for this project was the Sentry4.1, which supports over- and under-voltage detection but not contact-closure status. The total number of installed devices at CP&L was brought to about 1000. The devices were installed at homes near the substation where residents were home and granted permission. Most customers were happy to allow the installation when the system was explained to them. Although an occasional older home was not equipped with RJ11 jacks, requiring the installer to move on to the next customer, most installations were easy to make by simply finding an out-of-the-way 120-V outlet with a phone jack nearby (Fig. 1). Several three-phase devices, which come in a variety of standard three-phase secondary voltages, were placed in various commercial and industrial locations, requiring an electrician for installation.
To manage the outage data, Master Stations were installed at all five regional dispatching centers, which allowed the individual dispatcher to have total control over the Master Station and devices in his area. All devices use a single toll-free number, which is rerouted by the 1-800 provider based on the automatic number identification (ANI) of the incoming call (Fig. 3). By the end of the first quarter of 1997, all distribution dispatching functions at CP&L will reside in Raleigh at the recently completed Customer Service Center (Fig. 2). Sentry Master Station functions will be migrated into one PC in conjunction with the dispatching consolidation.
Interruption Reporting For several years, CP&L has had a Service Interruption Reporting System (SIRS), which is a key measure of the company's record with respect to continuity of service. To simplify and support the reporting of outage restoration data historically provided by line and service personnel for entry into SIRS, the Sentry System faxes interruption reports to the line and service facilities on a nightly basis. The reports are partly completed with outage data available from Sentry. The remainder of the data required for SIRS, but not available from the Sentry System, is completed the next morning by the restoring line worker and forwarded for engineering review and then on for entry into SIRS (Fig. 4). The need for this manual completion of these SIRS reports will no longer be necessary as CP&L brings on line its trouble call analysis (TCA) system, which is provided by a computer-aided distribution operation system (CADOPS) from ABB Power T&D Co., Jefferson City, Missouri, U.S. One of the many functions of the TCA system is to provide continuity-of-service data for the distribution system. Since the source of information for the system is customer outage calls, CP&L analysts have written a program that passes outage data from the Master Stations to CADOPS automatically.
Mobile Substations An additional function performed by the Sentry System is mobile substation alarming for the several fully functional substations that are mounted on tractor-trailer beds. These substations are used for planned and emergency outages of existing T&D substations. When not in use, they are stored at various sites across the CP&L system. When in storage, the batteries of these mobile subs are under constant trickle charge so they will be available at all times. Since batteries could drain and not be available in emergencies, mobile substation alarms were installed to alert dispatchers if power was lost to the battery chargers. The Mobile Substation Alarms, made by T&D Technologies of Raleigh, use the Sentry4.2 model, which has four contact closure inputs in addition to line voltage monitoring. These four additional alarm points can be used for fans, temperature monitoring and other parameters. Cellular technology is used for communications to the Master Station, as the mobile subs are monitored while in service, as well as in storage.
Power Quality Power quality monitoring is an important aspect of the system, which provides the data collected by the Master Station for engineers to analyze feeders that experience higher numbers of momentary interruptions than others. Sentry devices are also used as temporary voltage monitors for customers reporting excessive momentary interruptions, voltage sags or surges. The devices, installed at the customer premise for whatever time is necessary for the engineer to ascertain the characteristics of the problem, are programmed to call in when the parameters chosen by the local engineer are exceeded. The data are retrieved from the Master Station, eliminating the need to travel to the customer location except for device removal at the end of the data-collection period. Access to specific historical data by field engineers has traditionally been accomplished manually, but with the installation of a corporate-wide area network, access to historical and current data by remotely located field personnel was available in near real-time (seconds) in the first quarter of 1997.
Operation For outage detection purposes, three-phase inferences can be made with single-phase data, if the data are sufficient with regard to timing detail. CP&L has relied on the ability of distribution dispatchers to interpret the data so that only one single-phase Sentry per feeder is required to detect a feeder breaker lockout (Fig. 5). CP&L breaker trip and reclose timing is easily recognizable when it is reported by a Sentry device to the Master Station PC. Having set up the Master Response function of the software to sound an audible alarm when an "Off Continuing" event occurs, the dispatcher is alerted to these events. Upon finding a Sentry listed in the "Current Power Outages" box, the dispatcher scans the ""Most Recent Events" box for additional "Off, On, Off" events leading up to the present outage. If the characteristic pattern is found, line and service personnel are dispatched, often before the first customer has had time to call. If the preceding pattern is not found, the PC allows the dispatcher to retrieve additional information on the customer. The dispatcher calls the customer to investigate the problem and determine if line and service personnel need to be dispatched to the site. Sometimes, the customer can inadvertently cause the Sentry to call by turning off a breaker or by some other action (Fig. 6).
In early February 1996, an ice storm caused widespread damage and outages in CP&L's service territory in the Carolinas, resulting in many extended feeder outages. The volume of customer calls received during a storm of this magnitude made it difficult to determine which outages were due to feeder breaker lockouts and which were due to blown fuses. Once a downed line was repaired and restored, the feeder often held for only a limited time before more ice accumulated and took out the same feeder again, which compounded the problem of keeping track of which feeder breakers were out at any given time.
Most of the devices installed at that time were concentrated in the company's northern region surrounding Raleigh. The Master Station enabled the northern region distribution dispatch operations to know which feeders were out. The flexibility of the Master Station screens allowed the "Most Recent Events" and "Current Power Outages" boxes to be sized to fit the needs of the dispatcher (Fig. 5). The Master Response setup for most devices simply caused an audible alarm to sound when the device called in with an "Off Continuing" event. However, with the number of feeders on the outages list, the dispatchers needed a way to be alerted when a Sentry called back in to report that its power had been restored as well. Accomplishing this was nearly trivial with the flexibility of the Master Response setup screen. Devices are selected individually or collectively and the Master Station can be reprogrammed to respond in various ways depending upon which device calls, what type of event is reported and the day and time of the event. Dispatchers can enter this screen and select all devices for "Off Continuing" and "On" events, "any day/anytime" to beep until acknowledged (Fig. 7). Distribution Dispatch Operations recognized the value of the Sentry system during the ice storm, as did CP&L management. The system proved to be a valuable tool that significantly contributed to the fast restoration of the ice storm caused outages.
Conclusion The Sentry System has been an effective, inexpensive complement to CP&L's limited distribution SCADA system. With the functional flexibility offered by the monitors and the ease of use of the Windows-based Master Station, the system has met the needs CP&L set forth in the original 1994 project as well as meeting needs unknown at the start of the project.
David K. Lee was a senior engineer in CP&L's Distribution Engineering and Operations Department at the time he wrote this article. Since then, he has left the utility and is working for T&D Technologies. Lee received the BSEE degree from North Carolina State University in 1985. He is a registered professional engineer in North Carolina and is a member of the IEEE.