Electric utilities are seeking to improve the reliability of service to their customers, often well in advance of regulatory changes.
Florida Power & Light (FPL, Juno Beach, Florida, U.S.) anticipated the need to meet the expectations of its customers and to maintain their trust by providing reliable power. The installation of programmable power transducers at more than 100 substations since 1997 improved FPL's reliability by providing real-time feeder-telemetry data through a custom-designed protocol translator.
Program Cuts Outage Time in Half
As Florida's largest utility, FPL serves 7.3 million people (Fig. 1) — nearly half the state's population — and operates about 3.9 million accounts. In terms of kilowatt-hour energy sales in 2000, FPL's residential customers represented 50.4% of the total; commercial, 40.2%; and industrial/other, 9.4%. From 1990 to 2000, FPL's number of customers grew by 22%, including a 2.5% increase in new accounts from 1999 to 2000. The utility's seasonal peak loads are similar in its total magnitude (about 17,800 MW in the summer and 18,200 MW in winter), but markedly contrasting in character. Temporary or part-time residents who flock to Florida during the winter create a very different load shape from summertime peaks characterized by fewer residential consumers.
|Average time customer is without power (minutes)||70.3||75.2||100.2||136.8|
|Average restoration time (minutes)||58.3||60.6||64.9||80.9|
|Average number of outages per customer||1.2||1.2||1.5||1.7|
|Average number of momentary interruptions per customer||10.8||11.1||11.7||N/A|
In 1997, to accommodate further growth while improving reliability, FPL launched its “Reliability 2000” program and began a major upgrade of its electricity-delivery system. FPL has replaced or upgraded more than 3.4 million ft (1 million m) of underground electrical cable and has built 245 main distribution power lines. Installation of an additional 2.4 million ft (0.73 million m) of underground cable is planned for the near future.
Since 1997, the Reliability 2000 program slashed the average outage time by nearly 50%, from 137 minutes per year to 70 minutes (Table 1). The program decreased the number of interruptions per year to an average of 1.2 (a 29% improvement) and reduced the time to restore service to an average of 58 minutes, down from 81 minutes in 1997 (a 28% improvement). In terms of service and reliability, the Edison Electric Institute ranks FPL among the top 20% of U.S. utilities.
Throughout this program, FPL's strategy employs new technology and improved processes for preventive maintenance and service restoration. FPL uses programmable power transducers manufactured by Second Wind Inc. (Somerville, Massachusetts, U.S.) to provide three-phase or per-phase feeder-line monitoring (Table 2). The feeder-telemetry devices, called phasers (Fig. 2), integrate with FPL's substation-communication systems through vendor, custom-designed, legacy protocol translators.
|Parameters monitored by FPL|
|Current, amps, per phase|
|Current total harmonic distortion (THD), mean|
|Power factor, percent, per phase|
|Reactive power, mega-VAR, total per feeder|
|Real power, megawatts, total per feeder|
|Voltage, volts, line-neutral (l-n), per phase|
|Voltage THD, l-n mean|
|Phaser signal-processing capabilities|
|Per-Phase and Three-Phase|
|RMS current and voltage (l-n, line-to-line [l-l])|
|Current and voltage (l-n, l-l) THD|
|Real, reactive and apparent power|
|Real and reactive power at F0*|
|Phase angle at F0|
|Compensated real and reactive power|
|Loss real and reactive power|
|Line frequency (F0)|
|Current hours (per-phase and three-phase)|
|Voltage hours (per-phase and three-phase, l-n, l-l)|
|Delivered & received (D&R) data, three-phase:|
|Real energy at F0|
|Compensated real energy|
|Reactive energy at F0|
|Compensated reactive energy|
|Four-quadrant reactive energy|
|* F0 = normal frequency, 60 Hz.|
The primary goal of FPL's feeder-telemetry program was to obtain a true representation of regulated voltage to the customer, specifically by collecting real-time information from individual phases. In FPL's system, most feeder lines possess voltage regulators (or tap-changing transformers). This allows interfacing the feeder-telemetry equipment to the voltage-regulation device and providing per-phase current to each transducer.
The first step in implementing the program was to test the various devices that were commercially available at the time. During 1997 to 1998, FPL initiated a testing program that included the installation of several pilot sites. After a successful testing, FPL selected the Second Wind phaser device based on performance, cost, reliability and installation characteristics (ability to interface to a vast number of different regulators).
FPL began the program in the densely populated Miami-Dade and Broward counties. The higher the density of population and load on the feeder lines, the more likely that if a problem does occur, it would occur there. Feeder interruptions were the largest contributor to customers' minutes of interruption. Improvements to the overall system would be demonstrated more quickly and thoroughly by avoiding problems in the high-density areas.
Solution Meets Requirements
FPL's existing substation equipment and communication systems presented three challenges to the installation and operation of feeder-telemetry equipment:
- Legacy protocol conversion
The substation's legacy-communications protocol was bit-oriented Control Data Corp. (CDC) language. Essentially, the new phaser devices would have to “look” like a remote thermal unit (RTU) to FPL's supervisory control and data acquisition (SCADA) system, so that the utility could avoid additional programming, wiring modifications and other changes to the existing communications setup. Another obstacle was integrating the large amount of new data into the SCADA system; existing RTUs had little or no capacity left. FPL chose to have a uniform solution for all configurations, regardless of age or manufacturer. A host protocol converter (HPC) was developed that communicates via Modbus with phasers distributed around the switchyard and reformats the data into FPL's RTU data structure. Each HPC poses as one, two or three RTUs. The HPC prioritizes commands (such as block vs. reduce) via a specific algorithm dictated by FPL and allows the utility to view the status of each feeder line.
A 202T modem was built into the HPC and can connect to a standard telephone interface. The modem was designed to be field-exchangeable with an isolated RS232 port to accommodate later improvements to the substation communication systems. The new HPCs installed at FPL substations are modemless and communicate via direct serial connections.
- Fiber-optic communications
Phasers in the switchyard connect serially and interface to the HPC using fiber-optic cable, in part because of Florida's propensity towards lightning. Just as important, however, was the potential for any power surge to disrupt the substation communication system and destroy equipment. The fiber-optic sensor connections improve the reliability of communications within the substation.
- Current transformers
FPL's existing tap-changing voltage regulators used a full-scale line capacity rating of just 0.2 A. With the vendor's modification, the phasers are able to accommodate the 0.2-A output. The device was designed to accept multiple current-transformer (CT) and potential-transformer (PT) ratios, allowing it to interface to existing and new technologies.
As of year-end 2000, FPL had equipped 136 of its existing substations with HPCs and three-phase feeder-telemetry devices measuring 13 system parameters. By year-end 2001, FPL had installed Phasers and HPCs at an additional 127 existing substations, bringing the total to 263 substations with feeder telemetry by year-end 2001. In 2002 and 2003, FPL will complete installations in areas to the north and west. Meanwhile, all new substations built are equipped with the most recent phasers and modemless HPCs. As of early 2001, more than 1900 phasers and 280 HPCs had been installed, shipped or ordered.
FPL expects that the phaser's ability to measure total harmonic-distortion voltage and current will become more important as nonlinear loads on the system increase.
To satisfy Florida's growing demand for electricity, FPL invests approximately US$100 million per year on system expansion and upgrades, including energizing more than 100 feeder lines during 2000. The investment in feeder telemetry is already paying off. Accurate, real-time data is one of the most important tools in supplying customers with high-quality power and demonstrating a commitment to reliability of service. The data feeder telemetry provides has proven useful in reducing outage times, number of interruptions and the time required to restore service.
Gregory Johnston, a senior distribution planning and reliability engineer, joined FPL in 1980. He received the BSEE degree from the University of Tennessee. Johnston plans the economic expansion of the distribution system and performs systems analysis for the West Palm Beach area.
Robert J. Miller is a senior engineer at FPL, Relay and Communications Component Team. He received the BSEE degree from the University of Wisconsin-Madison, before joining FPL in 1984.
Top Reasons to Invest in Feeder Telemetry
Feeder-telemetry data is used in several ways to improve overall distribution system reliability:
- Avoid interruptions
The telemetry system transmits real-time data enabling employees to prevent interruptions by providing an alarm before an overload occurs. This alarm, especially during peak-demand periods, means the difference between maintaining service and an outage.
- Accelerate restoration of service
In the event of a feeder outage, FPL uses the telemetry system to determine whether the problem is inside or outside the substation. With feeder-telemetry data, problem diagnosis happens more efficiently and effectively, contributing to faster power restoration. Also, feeder telemetry provides load readings on other feeder lines that are operating, as well as the load on the troubled feeder before it tripped. This knowledge allows the utility to decide much more quickly how to switch the working feeders to pick up the interrupted load. This sometimes saves hours (depending on the time of day, traffic and local conditions) that would have been spent switching loads around. The availability of real-time information contributed to complementary improvements in FPL's customer care-center operations.
- Improve system load balance
Using feeder-telemetry data, FPL improves the balance of loads on its system. For example, if one of the three feeder-line phases is operating at 300 A and the other two are at 150 A, the whole feeder line is limited by the 300-A phase. If that phase goes up to the trip rating, the whole feeder line goes out. In contrast, if the three phases are balanced (say at 200 A each), the feeder line's overall capacity increases, providing an extra margin of reliability. Also, obtaining real-time data allows seasonal trending of load characteristics.
- Target investment in system expansion
Feeder-telemetry data enables FPL to analyze real-time customer load shapes, which facilitates planning, calculation of returns and justification of capital investment. Previously, FPL used monthly peak-demand readings to make decisions on system improvements. With feeder-telemetry data, information is more recent and decisions can be made with improved response time, allowing FPL to stay aligned with customer demands. With a better picture of exactly how the system is operating — when and where problems are occurring, especially during peaks — planners can target their system-expansion investments more accurately, and the utility can spend its money in the right place to get the most impact from the investment. The ability to analyze real-time load shapes is especially important in characterizing FPL's distinctly different summer and winter peaks and the daily or even hourly changes in residential and commercial loads.
- Improve voltage control
The feeder-telemetry system provides an interface to voltage reduction and regulator blocking. This could allow FPL employees to block individual feeders, rather than blocking the entire substation. Feeder telemetry also facilitates voltage reduction during peak-demand periods.