A 34-kV distribution automation project provides a learning experience while reducing SAIDI by half.
Improving the reliability of the 34-kV circuits in its mostly rural south district was both an economic and a technical challenge for Kansas City Power & Light (KCP&L). A distribution engineering team was formed to create a plan that would cut the average outage time in half on the 14 circuits — stretching 337 circuit miles (542 circuit km) — by deploying automated reclosers. This distribution automation (DA) solution was cost-effective, improved safety and provided increased supervisory control and data acquisition (SCADA) operating data. The 34-kV recloser project consisted of three phases:
Phase I: Install solid dielectric reclosers with electronic, communication-ready controls as sectionalizing devices.
Put the Smart Switch in a Smart Place
Phase II: Add communication to enable remote control for reconfiguration.
Phase III: Automate circuit restoration.
KCP&L spent considerable time selecting optimal sites for the new automated reclosers. Engineers looked at the number of customers served by each substation, the actual circuit load and the miles of overhead line, and then they developed a new criterion called customer load miles (CLM) that combines the data from the other three criteria. Engineers compared CLM with prior trended performance and known issues of each circuit and each line section.
Early Communication Challenges
KCP&L vetted and reviewed this information to select the final recloser sites. Lines serving significant loads were given additional consideration. For example, some lines serve significant single delivery points such as power supplies to rural cities or rural electric cooperatives. A total of 35 automated reclosers were installed in KCP&L's south district. The optimal recloser location selection using CLM and other criteria required a diligent and detailed review of each circuit.
Nearly all of the normally open 34-kV circuit ties were equipped with automated reclosers. Substations that served larger numbers of customers and were fed by a 34-kV line with greater overhead exposure had reclosers installed on both the incoming and outgoing source to a 34/12-kV substation in order to isolate and restore service more quickly.
When KCP&L began its automated recloser project in May 2006, digital cellular general packet radio service (GPRS) coverage from public carriers was sparse in the south district. Sensus-Telemetric, the communications supplier chosen for the project, supplied the GPRS digital cellular technology within its remote telemetry module (RTM). Early implementations in this rural area were difficult because coverage was sparse and signal strength weak.
The digital RTM cellular radio automatically switches between the preferred carrier (AT&T) and the roaming partners in an ordered list programmed on the AT&T subscriber identity module (SIM) card. Available networks in the KCP&L south district included AT&T and four roaming partners. The default radio option seeks the AT&T signal even if a stronger roaming network is available.
Although automatic roaming technology is normally beneficial, KCP&L found that the radio would sometimes excessively reconnect between available carriers or attempt to find an AT&T signal that proved to be too weak. Sensus-Telemetric addressed this concern by introducing configurable radio software with the option to force the RTM to remain on AT&T or one of the alternate carriers.
Subsequent RTM software enabled robust troubleshooting features that provided valuable field support to KCP&L relay technicians. In collaboration with Sensus-Telemetric, KCP&L developed the following radio antenna procedures:
Early Field Technical Issue
Use an omnidirectional antenna (360-degree coverage) normally having a 3.0-dB signal gain.
Otherwise, use a high-gain active antenna with 10-dB signal strength gain to retain 360-degree coverage.
Consider using a directional antenna with an 8.5-dB to 10-dB gain and a 90-degree coverage range to force the RTM to seek a tower in a given quadrant, rather than attempting to lock onto towers in other quadrants.
KCP&L now works with Sensus-Telemetric to perform radio propagation studies prior to commissioning reclosers. Site towers are digitally mapped in relation to the given recloser location. Technicians go to the site with a game plan to optimize radio performance. Then they use the hardware and software options to deliver the best solution at each site. To date, all KCP&L-installed GPRS RTMs work at each of the utility's automated recloser locations, even in very remote areas.
Early in the implementation, some users reported that control operations were not functioning as expected. It was discovered that some Amphenol connectors' terminals on the cable between the recloser and control were corroded. Simply cleaning the connectors resolved the problem. However, additional research showed the corrosion resulted from unanticipated shipping and handling conditions.
Dispatcher Training and Comfort
Reclosers were shipped from the factory with plastic covers banded around the connectors. KCP&L removed these covers to perform acceptance and calibration testing. In some cases, the covers were not replaced before being shipped to the service centers. When shipped during wintertime, the recloser and cable connections may have been exposed to chemicals used to reduce roadway ice. Corrosion of the connectors was the result of these events.
KCP&L and Cooper collaborated to develop a solution. Cooper now supplies the utility's reclosers and cabinets with threaded Amphenol protective caps, and KCP&L places all cables in a sealed tub that is added to the recloser pallet. Such practical solutions are essential to the success of any (DA) project.
As more was learned about the Cooper recloser, KCP&L worked with Cooper to target, develop and test additional desired recloser features. Some of this new functionality was obtained by configuring the control program options and some was through basic logic added by KCP&L relay engineers. In other cases, the changes needed were made by programming code supplied by Cooper. The recloser control refinements were as follows:
- Automatic protection profile change
Automation Does Not Replace Linemen
This allows the recloser to automatically sense forward and reverse power directions. Then, after a delay interval, protection settings are automatically changed to match the power-delivery direction. This works well for planned switching and is a popular feature for the dispatchers.
- Open conductor trip and alarm
The control senses the condition that one of the three 34-kV circuit conductors is physically open. The recloser then opens and sends out a unique alarm for this condition.
- Trip and lockout due to fault
This is a specific alarm indicating the recloser tripped to lockout due to a fault.
- Automatic fault trip targets reset
Current Project Status and Future Plans
SCADA receives and processes fault trip targets. The targets and alarms are automatically reset when the recloser closes and stays closed for 20 seconds. This gives dispatchers assurance the fault target is valid and not stale.
- Fault current values
Planning and relay engineers have access to stored actual fault values to validate their models. Protection engineers use this data to compare engineered settings against actual recloser protection performance.
- Enhanced sync-check algorithms
This feature was added by Cooper software engineers with input from KCP&L relay engineers.
- Automatic daily peak current reset
This information helps dispatchers make proper and prompt system capacity decisions to support planned or emergency switching.
- Customized faceplate alarms
Linemen are able to view all important alarms (such as battery alarms and control power availability) on the control faceplate.
The key use of the Cooper reclosers in this automation application is to identify and isolate the faulted line section rather than opening the entire circuit from the source substation breaker. Remote-control commands are then used to restore non-faulted line sections through normally open ties.
DA engineers provided recloser and control training on the Sensus-Telemetric website. Initially, only e-mail and pager alarms were provided to dispatchers. This worked for routine issues, but was not practical during storms when the system would generate many alarms that could overwhelm the operators. Therefore, KCP&L integrated basic open and close alarms from its automated reclosers into its energy management system (EMS) to provide important visibility of the alarms at all times.
Dispatchers went through a learning curve before reaching a comfort level with the new technology. Early technical challenges were identified and resolved, and KCP&L has provided periodic refresher and reinforcement training to capture the full benefits of this remote-control switching. The system average interruption duration index (SAIDI) for this south district 34-kV circuitry has been reduced from 172 minutes to 78 minutes, and using remote control instead of dispatching linemen also has relieved daily work load.
The south district 34-kV automated recloser project has helped improve customer reliability performance indices while providing a remote-controlled recloser that is safer to use and operate. However, KCP&L realized the limitations of automation after a devastating 100-mph (161-kmph) windstorm on July 8, 2009.
In the same storm, 300 south district poles were broken and various sections of 34-kV lines were lost. Dispatchers used information from the automated reclosers to identify faulted portions of the 34-kV lines. In most cases, there were multiple faults on numerous occasions on the various circuits. Where possible, dispatchers used automated reclosers to reconfigure the circuitry to restore line sections or verify line sections with faults.
However, many line sections were without any source feeds because of the extent of line damage. Crews were dispatched to install new poles, repair broken crossarms and replace damaged conductors throughout the service territory, with high priority given to the 34-kV circuitry. The experience from this storm highlighted the value of linemen, who physically rebuilt the grid to optimal performance, and reinforced the benefits of the automation program.
In July 2008, KCP&L merged with a neighboring utility, expanding its service territory from 4800 sq miles to 18,000 sq miles (12,432 sq km to 46,620 sq km) and from 2300 to 3200 employees. The acquisition necessitated a revision to the project deployment strategy.
Several utility and division-wide process improvements have been or will be implemented to unite the operations, improve efficiency and capture all the possible synergies.
KCP&L managers and DA project leaders recognized the value of deploying 34-kV automated reclosers and other DA projects in the newly acquired territory. For the time being, the focus is on deployments in new areas, in addition to the original project goals for automatic circuit restoration.
Over the past four years, KCP&L has installed a total of 89 34-kV automated reclosers that provide regional customers, dispatchers, engineers and relay technicians with improved, more cost-effective service. The recloser project has enabled the utility to cut its 34-kV circuit outage durations in half, with additional improvements and refinements still being implemented.
User requests drove the need to integrate the new technology into proven processes, such as bringing automated recloser alarms into the KCP&L EMS for greater visibility. Ongoing training and feedback continue to benefit all users of the automated equipment and processes.
Recloser automation now economically facilitates everyday operation and remote switching reduces maintenance costs. Electrical operating data is routinely reported through the radio. Engineers use this information for system planning and modeling. Data from the battery alarms and other controls help the utility maintain and manage the automated devices.
Carl R. Goeckeler (Carl.Goeckeler@kcpl.com) is the lead distribution automation engineer at KCP&L. He received his BSEE degree in power systems from the Missouri University of Science and Technology in 1975. Under Goeckeler's direction, KCP&L has won five national awards for its distribution automation projects, including the T&D Automation Project of the Year (DistribuTECH 2004). In 2007, KCP&L received the Edison Electric Institute Utility of the Year Award and also the 2007 PA Consulting Group's National Reliability Excellence Award. Goeckeler is a registered professional engineer.
Kansas City Power & Light www.kcpl.com