By Richard R. King, P.E., Jersey Central Power & Light
In 2005, Jersey Central Power & Light (JCP&L), a subsidiary of Akron, Ohio-based FirstEnergy Corp., initiated a project to identify protection system improvements that could be made to proactively combat sustained power outages resulting from wind- and lightning-related weather events. JCP&L determined these improvements had the potential to improve the System Average Interruption Duration Index (SAIDI) reliability metric by as much as 45 minutes annually.
Like many utilities, JCP&L operates a large installed base of electromechanical and microprocessor-based protection relays in its substations, complemented by line reclosers on its distribution system. JCP&L’s 3,200-square-mile territory, with 1,100 circuits, services 1.1 million customers.
Customer research indicated that reducing the number of momentary outages on blue-sky days drove higher levels of customer satisfaction, while momentary outages during storms, generated minimal customer dissatisfaction. With that information, JCP&L set out to devise a protection scheme that limited the number of sustained outages resulting from temporary faults during storms.
One of the first obstacles noted was the current system’s inflexibility, specifically the limitations of the electromechanical relays installed in JCP&L substations. It was recognized that while each was equipped with two timing curves–delay and instantaneous–these timing options were only selectable locally through dedicated cut-off switches wired to the units.
New System Concept
Based on the satisfaction data and recognition of the significant investment of installed electromechanical relays, JCP&L’s challenge was to develop a system able to change relay timing settings proactively in response to real-time weather information. A solution was prototyped in early 2006 utilizing a series of relays and intricate wiring tied into the SCADA system. From a schematic perspective, the solution was simple (see Figure 1), and the concept proved to be viable with a projected reduction in SAIDI of 25.1 minutes annually if deployed system wide.
The next phase of the project involved finding a commercially available product supported with engineering expertise to meet the application requirements. The relay product needs were summarized to include: field-tested reliability, SCADA compatibility and feedback capability to confirm operation, a local target display, models available for operation at 48 or 125 VDC, and the ability to expand to control more than one breaker installation. Finally, there was the desire for a model that could not only interface to the electromechanical relays, but also to the several different manufacturers’ microprocessor-based relays in use on the system–and do it in a cost-effective manner. Electroswitch, of Weymouth, Mass., was contacted and, after an initial concept meeting, provided a solution: a variation of a two-position Series 31 Tagging Relay (TR).
How the System Works
JCP&L’s northern and central regions, each with its own regional dispatch office, operate 13 independent districts. Each district has one substation outfitted with SCADA-interfaced wind speed and lightning detection equipment. These systems report to the regional dispatch office by exception when measured wind speeds cross a 25-mile-per-hour threshold or the presence of lighting is detected. Based on these inputs, each regional dispatch office has the ability to set the protection-timing scheme of each substation individually or by group. The simple actuation of the Electroswitch Series 31 TR via SCADA closes in the instantaneous relay, changing their relay-timing scheme to a fuse-saving mode.
Fuse-saving mode is a protection scheme where a feeder circuit breaker is set to operate in its instantaneous mode, allowing it to operate first, faster than the lateral tap fuses. Data supports that approximately 70 percent of faults are temporary, and having the ability to open the circuit first on a breaker’s instantaneous setting and then close back on a slower time-delayed setting allows most of these types of faults to clear themselves. If the fault is still present after the breaker closes back in on its time-delayed setting, the fuse on the affected lateral will blow requiring a line-crew to replace. But because most faults are temporary, this fuse-saving scheme prevents a large number of unnecessary fuse operations. When a system is operated in a fuse sacrifice mode, the instantaneous relay trip is disabled, and the fuse is always allowed to operate first.
When a regional dispatch office operator makes the decision to change relay protection timing in response to inclement weather, a SCADA signal is sent and each selected TR reports back confirming the operation. Locally at the substation, each Electroswitch TR latches in its orange mode target to signal that the protection scheme is in storm fuse savings mode. Additionally, the dispatch office sends a system-wide page to appropriate managers and operations personnel alerting them of the system timing change.
During five storm mode periods, 100 percent of the 275 adaptive relay sites confirmed proper operation, 64 breaker operations were recorded, and an estimated 7,546 customers were saved from sustained outages.
Once the weather alert has subsided, the dispatch office sends another SCADA command to the selected TRs to command each back to their normal operate mode. An acknowledgment of operation is received, the TR’s local mode tag changes from orange (storm fuse savings mode) to green (normal time delay mode), and the dispatch office reissues a system-wide page alerting all that the protection timing is back to its normal, blue sky, fuse sacrifice mode.
JCP&L started the system-wide project implementation in July 2007. It was completed and fully functional in December 2007. Installations were completed at 275 locations, which are able to control all 1,100 circuits in JCP&L’s 13 districts. The installations included the Electroswitch Series 31 TRs, wiring, testing, upgrading of the regional dispatch office SCADA software, commissioning, and training of management and operations personnel on the adaptive relay solution.
Over the first 46 days of operation from Dec. 16, 2007, to Jan. 30, 2008, there were five wind-related instances where the system was operated proactively switching to prepare for inclement weather. During these five storm mode periods, 100 percent of the 275 adaptive relay sites confirmed proper operation, 64 breaker operations were recorded, and an estimated 7,546 customers were saved from sustained outages.
The conservatively calculated savings over this period were 2.695 SAIDI minutes, an annualized run rate of 21.4 SAIDI minutes. Results through March 2008 also exceeded the annual SAIDI savings forecast of 25.1 minutes.
JCP&L anticipates additional benefits from this protection timing strategy. Operating in instantaneous mode during storm periods will limit the system’s exposure to extended fault current, improve the life of station transformers, in-line equipment and distribution lines, and reduce exposure to conductor burn down.
With one SAIDI minute saved per $30,000 invested, the six-month project is recognized by JCP&L as a most cost-effective SAIDI improvement project.
Richard R. King is supervisor of engineering for Jersey Central Power & Light. He is responsible for leadership and direction of system reliability for JCP&L’s central region. A licensed professional engineer in New Jersey, New York, and Pennsylvania, King has been at JCP&L since 2003. He holds a Master of Science degree in engineering from the New Jersey Institute of Technology and a Bachelor of Science degree in engineering from the City College of the University of New York.