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Analysis of line voltage helps utility monitor

Growth is good, but for an electric utility servicing a rapidly growing suburban population, it is also a challenge – especially managing power quality across an expanding distribution network.

Wright-Hennepin Cooperative Electric Association, based in Rockford, MN, is a perfect example. Currently serving about 45,000 customers in the western suburbs of Minneapolis, the utility has added one-third of its total customer base in the last seven years.

Power quality analysis was one of the factors the utility weighed before choosing an advanced metering infrastructure (AMI) system. Wright-Hennepin began deploying the TS2 system from Landis+Gyr in 2005. This two-way power line carrier-based system provides daily usage and engineering data to support interruption reporting, line loss analysis, outage detection and load management. And with the TS2 FOCUS endpoint, it also can provide service and average voltage readings on a daily basis.

“For major projects, engineering is able to provide better basis for their recommendations because the Landis+Gyr system offers real data instead of modeled theories,” said Lance Hovland, vice president of energy distribution at Wright-Hennepin. “On an individual basis, we can make sure that each customer at the end of a line is receiving the same industry-leading power quality that everyone should expect from their electric utility.”

Voltage analysis

Wright-Hennepin’s customer base is largely residential. Since 2000, when the utility’s service territory really began to expand, it has averaged about 1,700 new customers a year. To manage the growth, the utility has added substations and aggressively managed other crucial infrastructure.

Customer feedback is one of the methods Wright-Hennepin has used for pinpointing power quality issues. In one case, the utility discovered an overloaded transformer was causing occasional voltage sags at a residence.

“The customer had added a boiler in his shop and reported that whenever he turned that on, the lights would dim. With the Landis+Gyr system, we’ll be able to identify these situations ahead of the phone call,” said Tony Nelson, manager of substation engineering at Wright-Hennepin.

The TS2 system allows the utility to isolate potential issues before they become a problem. For its AMI deployment, Wright-Hennepin is using a mix of retrofitted electromechanical and solid-state meters. As part of this mix, the utility is strategically placing 2,500 TS2 FOCUS endpoints on certain end of line taps to monitor voltage.

The FOCUS™ meter from Landis+Gyr offers features, such as voltage readings, that are unique for a single-phase residential meter. In the TS2 FOCUS endpoint, the TS2 module reads the meter register to capture and transmit a variety of data values, including service voltage and average voltage readings accurate to better or less than 1 percent.

The utility can choose to return a variety of voltage readings and remotely program the endpoint to change the voltage data that’s requested. These include average voltage over a specified period of time, maximum and minimum voltages with date and time stamp, and instantaneous voltage.

Using Command Center™, the data management software for Landis+Gyr advanced metering systems, the utility selects the voltage information it wants the meter to report. Because it is most concerned with voltage sags, Wright-Hennepin retrieves minimum daily voltage data from the meter, and then exports it for analysis. In the future, the utility hopes to map this data in its engineering software to speed analysis when trying to isolate voltage issues by location.

“We’re placing the FOCUS endpoints at the end of longer feeds and other locations where we suspect voltage may be an issue,” Hovland said. “Then we look for readings that fall out of our expected bandwidth. Ultimately, this data along with peak load information will be used to plan new substation locations and major capital improvements.”

Load analysis

In addition to voltage analysis, the TS2 FOCUS provides a number of two-way communication functions, such as:

  • Outage detection and restoration notification
  • Peak demand and time-of-use data
  • Remote programming
  • Tamper detection

Wright-Hennepin is taking advantage of these features to monitor loads and record peak usage. The utility is a summer peaking system, but also needs to monitor peak consumption during extreme cold spells during winter months. The TS2 system allows the utility to schedule four time-of-use periods from each meter per day. Using this feature to capture demand data for its average peak from 6 p.m. to 7 p.m., the utility can analyze transformer loading, protective device sizing and identify load management receiver failures.

With about 40 percent of their system deployed with AMI, Wright-Hennepin has already been able to identify a handful of transformer change-outs and fuse replacements. “We expect to find more in the summer months and hopefully proactively prevent outages,” Hovland said.

Considering the utility’s rapid growth rate and ambitious power quality management objectives, Wright-Hennepin is pleased overall with the value an AMI system adds to engineering and operations departments.

“We can say so far that we are achieving nearly all of our power quality objectives,” Hovland said. “The project has been a huge success in preventing overloads and detecting low voltages.”

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