The Valley power plant in Milwaukee, which Wisconsin Electric Power (WEPCO) wants to switch from coal to gas for clean-air reasons, is needed for grid support in the area and should not be shut outright.
Ronald Snead, employed by ATC Management, the corporate manager of American Transmission Co. LLC as the Vice President of System Planning, outlined the need for the plant in Aug. 20 testimony filed at the Wisconsin Public Service Commission.
If the Valley plant is retired without significant changes to the transmission system, Snead said he expects transmission reliability issues to arise in the following three areas:
- during 90% of peak load conditions or greater, certain contingencies would cause thermal line overloads;
- during light load, system intact conditions, the loss of generators to absorb reactive power (VARs) generated by the extensive 138 kV underground cable system in the Milwaukee Metro area would cause high voltage conditions; and
- following widespread outage conditions, restoring the transmission system of southeastern Wisconsin with designated black start units would be technically difficult and take considerably longer to execute compared with the current system restoration plan which utilizes Valley generation early in the process.
“The Valley Power Plant’s particular physical location is important because of the configuration of the transmission system serving the Milwaukee area, combined with the large amount of load in the area,” Snead noted. “In general, power tends to flow into the Milwaukee load area over the available transmission paths. Essentially, the Milwaukee area is a load pocket, that is, a concentrated area of load, that relies on a combination of the Valley Power Plant and the transmission lines that connect the area to the remainder of the system. The Valley Power Plant helps maintain reliability by reducing the power flows through the transmission system that supplies Milwaukee, and can eliminate thermal line overloads under certain outage conditions.”
The Valley plant can also be used to control voltages in the area by generating or absorbing reactive power, Snead pointed out. Reactive power is necessary to supply magnetizing currents required in equipment such as transformers. Without enough reactive power, voltages can decline so much that customer electrical devices become unusable. Reactive power output (MVAR) of Valley varies between -50 MVAR and +50 MVAR for each unit. This means that Valley functions to maintain voltages within planned limits by supporting or reducing voltages when needed.
Testimony was also filed Aug. 20 from Robert Greco, employed by WEPCO as Manager–Air Quality. He explained how the conversion is needed to comply with air rules, including the Mercury and Air Toxics Standards (MATS).
The Aug. 20 filings were made in two companion dockets where WEPCO is asking for approval of the Valley plant conversion, and also asking that Wisconsin Gas LLC be allowed to install necessary equipment to get the needed gas to the plant.
The Wisconsin Department of Natural Resources, in the meantime, is taking comment until Sept. 14 on a draft permit allowing WEPCO to convert four coal-fired boilers at Valley to fire natural gas. The DNR has made a preliminary determination that the application meets state and federal air pollution control requirements and that the permit should be approved.
Valley is a cogeneration facility that has an electric capacity of about 280 MW and is the sole source of steam for the Downtown Milwaukee Steam System. The facility has two generating units of about 140 MW apiece. Steam for each unit is provided by two boilers. These are four identical Riley dry bottom wall-fired boilers. The company hopes to have the entire conversion project completed by the fourth quarter of 2015.