Hydroelectricity is a cornerstone of power generation in the United States. Since the 1880s, engineers have harnessed the power of rushing water to generate electricity, from the iconic Hoover Dam to much smaller hydroelectric projects.
But in the last few decades, the same people who benefit from hydroelectric power have realized the environmental impact of dams – especially on local fish populations.
Species, such as salmon and herring, migrate from the ocean and into rivers to their spawning grounds. Once hatched, juvenile fish migrate back down rivers to live in the ocean. Traditional dams have disrupted this life cycle by blocking the free flow of rivers to the sea.
Federal and state regulators have taken steps to restore these populations by requiring utilities to find innovative ways to help fish circumnavigate dams. Tacoma Power in Washington state is one of these utilities. Owned by the city of Tacoma, the utility provides electricity to over 50 percent of city residents. Ninety percent of that energy is generated by hydroelectric powerhouses on rivers in western Washington.
When Tacoma Power's license to produce power for the city was up for renewal, the city needed to create a fish passage around two of its dams to help preserve the local population of endangered steelhead, sockeye and salmon in order to renew its license.
At the time, Tacoma Power's Cushman No. 2 Dam upstream of the North Fork Skokomish River was not equipped with hydroelectric generation capabilities on the North Fork of the river. The dam had been in place since 1929 as part of the system keeping water within Lake Cushman, a man-made reservoir.
The power company added two river outlet valves to the base of the dam in 1992, allowing water to flow from the lake into the riverbed. However, the flow of water through the valves was too strong for fish migration. To provide a gentler passage for the fish, Tacoma Power needed to build a fish-collection facility for both the adult fish headed upstream and the juvenile fish swimming toward the ocean.
The utility needed to diffuse the water current and saw an opportunity to capture the force of the flow and turn it into hydroelectric power by building a new powerhouse at the base of the dam.
The powerhouse would need to simulate the natural flow of the river to keep the surrounding area safe from flooding and make fish migration manageable. Similar to other powerhouses Tacoma Power owns and operates, the new Cushman Northfork Powerhouse needed to be completely automated to eliminate the need for on-site staff. Staff would remotely access the dam from the operations center at the Tacoma office.
Customers would also benefit, because the powerhouse would generate enough renewable energy for 1,700 homes.
Tacoma Power had been using Allen-Bradley® ControlLogix® programmable automation controllers (PACs) to automate its other seven powerhouses.
“Our experience with Allen-Bradley controls convinced us to use the same solution for this new project,” said Ozan Ferrin, generation automation supervisor for Tacoma Power.
Ferrin and other Tacoma Power controls engineers designed a completely automated system using four ControlLogix PACs. Two PACs each control one of two 1.8 MW generator units, a third controls the balance of the plant including operation of an existing river outlet valve for flow continuation in the event of a unit trip, and a fourth controls the fish collection equipment and fish hoist system at the base of the dam located just outside of the powerhouse.
With the new system, the operator controls the powerhouse using a single flow control setpoint for the plant. The balance of plant PAC receives the control set point and automatically issues flow instructions to each of the generator units and the river outlet valve to ramp flow at a regulated rate, mimicking seasonal river flows. DNP cards and Modbus® cards from ProSoft Technology, a Rockwell Automation Encompass™ Product Partner and a member of the Rockwell Automation PartnerNetwork™ program, interface with sensors, equipment and other systems at the Northfork Powerhouse. They provide seamless Ethernet communication across multiple platforms.
If one or both of the generators goes offline, the balance of plant controller will immediately open the river outlet valve to make up for the lost flow, keeping water flowing at a uniform rate.
For the fish collection facility, the Tacoma Power engineering team needed to design a hoist that could move adult fish over the dam and smolt down the side of the dam smoothly. This required drives with precise control.
That control begins at the base of the dam. As fish swim toward the dam, fully grown fish are captured in a hopper at the fish collection facility and automatically hoisted up the side of the dam on a tram operated by an Allen-Bradley PowerFlex® 700 AC drive. The drive's Allen-Bradley TorqProve™ functionality helps manage control of the hopper when transferring control between the drive and the tram's mechanical brake.
The hopper lifts the fish to the top of the dam, where they are separated, counted and transported via trucks to Lake Cushman. PowerFlex 70 drives and combination starters are used to operate the fish collection equipment.
On the other end of the fish lifecycle, juvenile fish swimming toward the ocean are placed into the hopper at the top of the dam and are carried down onto a smolt release cart to release the fish downstream toward the ocean.
Tacoma Power control engineers programmed the PowerFlex drives with Allen-Bradley DriveTools™ SP software and Rockwell Software® Studio 5000 Logix Designer™ programming software. The engineers were able to add the drives directly to the Studio 5000 Logix Designer program as an add-on profile, which helped save programming time by automatically integrating drive parameters into the Studio 5000 Logix Designer application – the same software used to program the ControlLogix controllers.
“We've tried other control software, and none that met all our controls needs were as easy to use as the Studio 5000 Logix Designer software,” Ferrin said. “And since we can use the same software that we used to program our controllers to also program and store our drive parameters, we save on commissioning time and are able to store our drive parameters and controller program in a single file location.”
The Tacoma Power team also uses I/O cards from Rockwell Automation to remotely monitor temperature, equipment status and to control equipment from the Tacoma office.
The collection facility has restored the fish migration route, and the company is now licensed to generate electricity for the city of Tacoma until 2048.
Tacoma Power also met its operation goal for the new powerhouse – generating 3.6 additional megawatts of hydropower.
Because the powerhouse is completely automated, the company avoided incurring additional operator costs. “With one push of a button from our control center, we can ramp flow up or down – which is more accurate than doing it manually and saves us the costs of on-site staffing,” Ferrin said.
The system also reduces the risk of violating flow requirements set by the Federal Energy Regulatory Commission (FERC). The ability to automatically open the backup river outlet valve in case a unit trips helps the utility company meet those compliance standards more effectively.
Another plus: Because the company added more renewable energy to its portfolio, it now receives renewable energy credits from the state.
To further boost the fish population, Tacoma Power is building two new hatcheries at the Cushman River Project. The first will raise 2 million sockeye each year, and a second will raise 425,000 young salmon and steelheads. All will be released into Lake Cushman.
The results mentioned above are specific to Tacoma Power's use of Rockwell Automation products and services in conjunction with other products. Specific results may vary for other customers.