by John Graminski, Southwestern Electric Cooperative Inc.
As an independent, member-owned co-op that has consistently lowered rates and returned earnings to members, Southwestern Electric Cooperative Inc. is always looking for ways to cut costs and operate more efficiently. The Greenville, Ill.,-based cooperative maintains nearly 3,500 miles of power lines and serves more than 22,000 residential, commercial, agricultural and industrial members in 10 counties.
Improving the systems for determining the extent and location of outages in the distribution system is essential to serving Southwestern Electric’s members. The co-op’s outage management system (OMS) works with its supervisory control and data acquisition (SCADA), automated meter reading (AMR) and advanced metering infrastructure (AMI) solutions. Information security staff consistently seeks new methods for proactively discovering and identifying outages.
Southwestern Electric’s system allows for quick response when members notify the cooperative of lost power. The co-op’s OMS from National Information Solutions Cooperative (NISC) automatically responds once several calls indicate a possible outage. The OMS prompts the Aclara TWACS technology AMI system to ping affected meters and those around them to identify the outage’s extent. The collected data is fed into a geographic information system (GIS) that maps the outage. The OMS uses this model to build a graphical display that, when combined with crew location information, allows IT staff to visualize the outage and the cooperative’s response.
Figure 1: A system map will display meter outages once the meters are tied to the SCADA system.
The next step for Southwestern Electric is to make outage identification more proactive. The co-op is implementing AMR Visualization from its SCADA vendor, C3-ilex. The application will allow the cooperative to proactively investigate potential consumer outages based on reports by the SCADA system (such as a relay event). SCADA systems report a lot of information back to utilities, but the data alone does not indicate what the event signifies.
When the SCADA senses a change in distribution system conditions, it could mean many things. Sometimes the event signals the start of an outage; other times it might indicate an overcurrent that resolves itself before an outage. At Southwestern Electric, AMR Visualization responds to a SCADA event by prompting the AMI system to ping a series of so-called bellwether meters at critical junctures on each feeder. Bellwether unit status is reported back to the SCADA system within a minute, confirming a probable outage or that the fault has cleared.
Verifying the Outage
Once AMR Visualization identifies a potential outage, the utility verifies the extent by pinging revenue meters along affected sections of the distribution system to identify meters that are not operating properly. Just like Southwestern Electric’s system, pinging results are used to visualize the outage in the OMS.
This two-step process of pinging independent bellwether units before checking revenue meters is necessary. The bellwether transceivers can be signaled any time without interfering with messaging related to meter reading and will respond immediately. The units can be pinged repeatedly without exceeding their thermal limits as defined in the AMI system. Most residential meters are designed to be read several times a day and pinged once in a while. The pings create a short inside the meter, communicating a signal to the utility. Each ping also creates heat, and too much heat can destroy a meter. Thermal limits are set in AMI systems to prevent meters from being pinged too often. Bellwether units have no limitations and can be replaced if thermal limits are exceeded.
The Role of MultiSpeak
The AMR Visualization software employs MultiSpeak Web services to make the connection between the AMI and SCADA system. The MultiSpeak Initiative is a collaboration of the National Rural Electric Cooperative Association (NRECA), leading software vendors supplying the utility market and rural-electric cooperatives. The initiative has produced a specification that provides standard messaging formats for software applications commonly used by electric utilities, making it easier for them to integrate data from diverse applications and streamline business processes. Software that conforms to the MultiSpeak specification helps vendors and utilities connect various systems without extensive custom interfaces.
The MultiSpeak-compliant Web services interface that connects the AMI system to the SCADA system is Aclara’s Twacs Optimum. The application supports MutliSpeak methods and allows utilities to link multiple software platforms to make it easier to manage time-critical operating scenarios such as power outages and restorations. It also is useful in bringing data into customer billing, supervisory control, data acquisition and engineering analysis systems.
Southwestern Electric’s SCADA vendor plans to bring voltage readings back from the system into AMR Visualization eventually, and the cooperative would like to use this function to improve its ability to monitor its distribution system. The co-op would do this by reading voltages from a single, logical point defined in the SCADA system. This logical point would comprise clusters of meters at the ends of specific lines. The system would retrieve voltages from meters in the clusters using a round-robin approach, rather than constantly interrogating a single meter, eliminating potential difficulties with thermal overload.
End-of-line voltages are an important data element in overall system voltage monitoring. The ability to monitor voltages at the ends of lines would make it easier to maintain the system, giving Southwestern Electric information that would help identify and replace potentially faulty equipment between the substation and the end of the line. The cooperative aims to go beyond voltage monitoring and developing methods to help proactively control voltage related events on its system.
John Graminski is director of information technology at Southwestern Electric Cooperative Inc.