The reclosers communicate back to the host by a 900-MHz spread-spectrum radio. PPL selected Microwave Data Systems (MDS; Rochester, New York, U.S.) as the radio supplier and radio survey consultant. The radio network uses repeaters to get to each device. The host polls each recloser for its status about every five seconds. If a fault occurs, the fault flag is set and passed back to the host at the next poll.

When a fault condition exists, SISRS gathers the fault flag from each switch and determines which section of the line has the fault. It then isolates the fault by opening the switch on each side of the fault. After fault isolation, it attempts an upstream restoration if possible. Upstream is done first since the circuit was supplying that portion of line before the fault. Then it attempts downstream restoration after checking to see if the adjacent circuit can accept the load. This can be done using real-time load information from the adjacent sub or with load curves that simulate it.

If the receiving circuit can accept the load, SISRS will close the normally open recloser to finish the downstream restoration. The reclosers switch to alternate settings and protect in the backfeed condition. Tests show a total restoration time of 2 to 3 minutes.

The results are communicated back to the main SCADA computers by a digital cellular link through a firewall and ModBus interpreter. PPL uses a Telemetric (Boise, Idaho, U.S.) modem to communicate back to its SCADA system. The operator has complete control of every switch in the system through the SCADA link. There are one-lines that the operator can view to determine what has happened. Load data is also available to display on the operator's screen. The load data is transmitted hourly. The operator can query SISRS for the latest load information on each device. The system can be disabled locally at the host computer cabinet or remotely through SCADA.

Once data is transmitted to the SCADA system, it can be passed on to the outage management system as a confirmed outage to aid the dispatcher in sending crews to the proper location.

THE RADIO NETWORK

It is easy to try and shortcut the radio network. Each repeater costs money and takes more time to design and build. PPL has learned that the radio network is not the place to try and cut costs. The utility was on a tight schedule and rather than installing several high antennas as repeaters, it decided to try and use the store-and-forward method to get communication to the normally open point. This involved each device passing the message on to the next device serially until the message got to the proper device.

PPL did the radio survey in November, when there were no leaves on the trees, and installed the system in April, when there were still no leaves on the trees. The system was communicating quite nicely. Then May came and so did the leaves. The line-of-sight 900-MHz radios didn't like the leaves. SISRS lost contact with one or more devices on a regular basis and started sending loss-of-communication messages frequently. It was particularly bad when communication was lost with the first device, which resulted in lost communication with all the devices. The system was corrected and this lesson learned.

USER EDUCATION

Change is difficult. Although installing a system as complex as SISRS was technologically possible, every department had to be onboard to make it work. PPL could have done a better job educating all of our operators and linemen.

One mistake was commissioning the system before the SCADA one-lines were complete. When the system operated, the operator had to go to a website consisting entirely of text messages. These messages were mixed in with dozens of other remotely controlled devices and were cryptic in nature. The operators were not familiar with the nomenclature they saw, because it was not the standard nomenclature they were used to seeing on SCADA. This could only lead to confusion in a time of crisis.

PPL learned that thorough operating instructions for SISRS should be issued before the systems are commissioned. The operators need the knowledge to understand how the system works.

The utility needs to do a better job of communicating the use of reclosers as simple switches and as fault-interrupting devices. The linemen as well as the operators are used to seeing reclosers work as reclosers. When the recloser, acting as a switch, failed to isolate a fault, it was confusing to them, even though it was operating as designed.

Another lesson learned is that there is a lot of work required to design, build and install the systems, and a dedicated team of engineers, technicians, operators, IT personnel and linemen is necessary. Coordinating all of them requires a full-time project manager or engineer. This person also needs to keep up with the pace of evolving technology to make sure the investment that has been made can continue to work with the newer technology.

THE NEXT IMPLEMENTATION

PPL's next step will be to take what it has learned from the two independent circuits that are already installed and apply it to a fully integrated system. This system will have four substations with six circuits and 24 switching devices. All of this will be controlled with one host computer at one of the substations. The radio network will contain several main repeaters that can see all the devices.

PPL wants to build a lab with a working SISRS installation that has actual recloser controls in series with lights that simulate actual load. Flat-panel displays will show what is happening both graphically and with text alarm messages. Users will be able to apply any kind of fault they can think of and watch how the system reacts. Instructors will answer any questions about how the system works. Operators, engineers and technicians will be able to spend time there to become acquainted with the system.

The radio network has been designed, the SCADA displays are in progress, the reclosers are being installed and the operating instructions are being developed.

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Howard Slugocki is a supervising engineer in the distribution planning department of PPL Electric Utilities. He has more than 25 years of experience in engineering, distribution planning, customer service and information technology at PPL. He has developed planning tools and techniques to help PPL make informed decisions regarding capital improvements and maximizing system utilization. Slugocki is a system storm director during storm restoration. He has spent the last two years developing and implementing a distribution automation program for PPL. He is a licensed professional electrical engineer in Pennsylvania and has a bachelor's degree in civil engineering from Michigan Technological University.
hsslugocki@pplweb.com