By Ed Sullivan, Contributing Author
Advancements in products that leverage converging technologies have created significant opportunities throughout the power systems industry. Advancements in communications solutions means that with the right choice, return on investment (ROI) can be extended via expanded power system benefits. Such has been the case at Dairyland Power Cooperative (DPC) in La Crosse, Wis.
DPC, a 1,000-MW generation and transmission cooperative, was experiencing diminished service within its analog cellular-based data communications system, with the possibility of no further service beyond February 2008.
A Touchstone Energy affiliate, DPC’s service area encompasses 62 counties in four states (Wisconsin, Minnesota, Iowa and Illinois). It provides power for 25 member cooperatives and 20 municipalities that serve more than 500,000 customers. The cooperative owns and operates some 3,100 miles of transmission lines and 348 substations. DPC produces electricity from a variety of sources, including hydro and coal-fired plants plus renewable resources such as landfill methane recovery and animal waste-to-energy.
“With the imminent need to replace the old cell phone system, there was an opportunity to install a new automated telecommunications system that would provide secure collection of meter readings from all of our substations,” said Ed West, DPC director of telecommunications and control. “At the same time, we wanted the same system to provide real-time meter data, local alarms and a secure communications path for our AMR members.”
DPC’s staff identified a list of required capabilities for a secure communications path including:
- Substation automation information from the substation to the DPC office,
- Real-time meter data for display on a security system operations (SSO) Web site,
- Substation kilowatt hour meter readings every 15 minutes for billing purposes,
- AMR data from the substation to the distribution cooperative office, and
- One system that could support the needs of the member utilities and DPC for secure, robust, wide-area communications.
To simplify new equipment installation in each distribution substation and minimize the amount of training required, DPC staff made decisions early in the design process.
- Each distribution substation would have a standard set of equipment.
- The communications cabinet would have a custom-designed enclosure.
- The communications cabinet components would be assembled in the DPC facility.
- The spread-spectrum radio, router, communications, protocol interface device and high-end multifunction meter would be tested and verified by the DPC meter lab.
- Remote facility monitoring would be provided with physical security and cybersecurity.
- A 48-Vdc battery-backed power supply would be included for all equipment.
- The cabinet design would allow for modular expansion to meet each substation’s requirements.
- Each completed cabinet would be taken to the substation to be installed and field verified.
To accomplish these goals, a comprehensive plan was approved for the installation of an upgraded distribution automation/telecommunications system. The project included the existing digital microwave network’s expansion, point-to-point, IP-capable spread-spectrum radio installation and a custom-designed metering and communications cabinet installation to provide secure serial and IP connections for real-time billing metering data, historical data, distribution SCADA, load management and AMR traffic.
This metering and communications cabinet provides secure serial and IP connections for real-time metering data, distribution SCADA, load management and other data.
Because metering was one of the project’s primary goals, Dairyland Power evaluated a Schweitzer Engineering Laboratories Inc. (SEL) multifunctional digital meter, the SEL-734 Revenue Metering System for the project.
“From a metering perspective, DPC wanted to do daily load profile and interval-by-interval metering of their delivery points for billing purposes,” said Dick Martin, SEL Meter Systems Division product manager. “They also wanted to provide real-time monitoring of energy—the amount of power being delivered—for both generation and transmission purposes and to make that information available on a distribution SCADA system to their members. As a multifunction device, the SEL-734 Revenue Meter is well suited to meet those needs.”
Billing data are collected from the meters by a master station system running Itron’s latest MV-90xi meter-reading software, which can query devices over a wide-area network (WAN). At the same time, via the meter’s DNP3 protocol capability, DPC is using its distribution SCADA system to poll the meters for real-time operational data. Otherwise, this remote function would be done typically by remote terminal units (RTUs) costing $3,000 to $5,000 (for models suitable for this application).
“Historically, the sensors on RTUs required dc input,” Martin said. “That usually meant incorporating ac-to-dc transducers that require annual calibration, which can be a maintenance nightmare.”
Because the SEL-734 Revenue Meter communicates via DNP3 protocol, however, it is compatible with SCADA just as if it were an RTU—without the maintenance costs and headaches, he said.
“Another factor that drove the scheme was that the meters DPC was using before had room for improvement,” said Ken Graves, the utility’s manager of telecommunications services. “We felt confident that the SEL-734 revenue meter would provide us with a good, workable solution.
The back of this DPC revenue metering system shows the current, voltage, serial communications, output contact and optoisolated input connections.
“For our transmission environment, the SEL-734 met our requirements nicely, rather than the standard round, socket-based meter. So there was interest in the SEL-734 from the transmission side of our business. Plus, using a high-end, panel-mounted meter allowed us to use the same meter to meet our distribution metering needs.”
The SEL-734 Revenue Meter’s power quality monitoring capability was another significant feature to DPC. The utility wanted to make certain that the power it delivers to customers is within its high-quality parameters. If there were issues, it needs to have quick access to information.
“Dairyland Power selected the SEL-734 because it provides high-accuracy energy metering, load profile data collection, instantaneous power measurements, power quality monitoring and communicates simultaneously over a modem, serial ports and wide-area networks,” Martin said.
Ed Sullivan is a freelance writer in Hermosa Beach, Calif. He has researched and written about power systems, industrial process equipment and other technologies for more than 25 years.