Purcell Lodge: a Priority Load-Controlled Hydro System Paul Craig & Robert Mathews c. 1992 Paul Craig & Robert Mathews The Canadian Rockies offer some of the world's most spectacular outdoor experiences: deep powder skiing, alpine hiking, and incredible glacier views. The Purcell Lodge is deep in these Canadian Rockies, near the town of Golden, British Columbia, four miles beyond the nearest (logging) road. Every piece of equipment, all supplies, and the guests are brought in by helicopter. Out here light, heat, and appliances made possible by the lodge's 12 kilowatt hydroelectric system are well appreciated. A Canadian Classic Hydro System The electricity generation system uses what has become in Canada a "classic" hydro set-up with a high head, small pipe, and Pelton wheel turbine. Turbine speed regulation is accomplished by electrically loading the generator to maintain frequency. The location was selected to provide year-round water. Fortunately an insulating cover layer of snow always arrives before ground-freezing weather. Even though the snow season can last six months, there have been no problems with frozen pipes. The intake weir (head pond, see photo) is a concrete wall in a largely bedrock location that provides a small impoundment basin. The pond stills the flow, allowing heavy debris to settle and light debris to float. The intake pipe is submerged at half- depth and screened. The pond also contains a submersible pump for domestic water. INSERT WEIR PHOTO The penstock is 1440 feet of 4 inch diameter solvent-welded PVC, with pressure rating increasing from 63 pounds per square inch (psi) at the intake to 160 psi at the turbine. Total head is 315 feet and maximum flow is 220 US gallons per minute. The penstock is buried to a depth of about 18 inches, and anchored with concrete and bolts at critical points. The 8 inch diameter pitch Pelton turbine was built by IPD of Montana. When spinning at 1800 rpm the wheel moves at 46% of the jet speed at the point of contact. (At 41% to 47% of jet speed, pelton wheels are most efficient.) The main nozzle is manually adjustable through a spear-type valve. Maximum nozzle diameter is 13/16 inches. The generator is a Fidelity brushless design rated at 12 kilowatts at 1800 rpm. Maximum power output was initially limited by the available flow to 7 kilowatts. During the fall of 1992 the water supply system was modified to provide the full 12 kilowatt output. This required relocating the weir to a region with higher water flow. The new weir is fed by 2700 feet of 6 inch aluminum irrigation tubing rated at 150 psi. The control system is unchanged. The added power allows more load at the lodge, and more electrical heat to offset propane use. Friction loss in the penstock is about 8% at maximum flow, and the turbine-generator converts the water energy reaching it with 56% efficiency. Output is 120/240 volt, 60 hertz single phase. The generator is direct-driven from the Pelton wheel. A flywheel maintains speed under high starting loads from induction motors, and provides general stabilization. To decrease energy loss and save wire costs, the voltage is transformed up to 600 volts for the 1750 foot run from the power house to the lodge. At the lodge a second transformer provides 120/240 volt output. Two #6 AWG (American Wire Gauge) RWU copper conductors are mechanically protected by a 1 inch poly pipe and placed under the 4 inch PVC penstock to provide further mechanical protection. Transmission power loss is 2.5% at the present 7 kilowatt output. [which strikes me as strange since they say they upgraded it to 12 kW...] Control by Prioritized Loads Primary load control in the Purcell system is perhaps the most interesting part of the system. The Lodge uses an Electronic Load Control Governor (ELCG) manufactured by Thomson and Howe Energy Systems. It's easiest to understand this regulator by contrasting it to more traditional control approaches. Solar systems are usually limited by energy. Design focuses on minimizing load, and on turning off loads when not needed. Hydro plants are traditionally controlled by regulating water flow as load varies. Not so in the Purcell environment. Here as in many modern microhydro situations, the water runs whether used for electricity generation or not. Since water is not trapped in a dam, the ecology of the stream is less impacted by this type of hydro system. But, if electricity is not generated, the energy in the falling water is lost. This makes possible a very different type of regulation, based on using all available water, while switching on and off priority loads to maintain a constant overall load. The more the electrical loading, the slower the turbine and generator run. Since the generator frequency is directly proportional to rotational speed, control of frequency automatically provides speed regulation. A rise in frequency means that more load is needed to slow down the generator. A drop in frequency means load must be shed. The lodge load is broken down into a number of circuits . The highest priority circuits, especially those that are safety related and those (such as lights) needed to maintain guest satisfaction, are wired directly to the generator service panel and are not under governor control at all. Lower priority services are connected to the ELCG. Eight circuits are currently in use. These are ranked by priority, with sewage aeration and water pumping followed by refrigerators, freezers, furnace fans, and the dish and clothes washers. Coarse & Fine Control Coarse regulation is provided by load shedding. For example, if the water system Ä a high priority function Ä turns on, a refrigerator or freezer might be temporarily shut off. Coarse control necessarily leads to large and fast changes in system loading. Without additional control this would lead to unacceptably large frequency (and hence turbine speed) swings. Here's where the ELCG proves its merit. Load swings are virtually eliminated by continuous, rapid control of resistive loads such as baseboard heaters and hot water tank heating elements. For this fine control the ELCG uses triac regulators to smoothly change the power delivered to resistive loads, increasing as other load drops, and decreasing as other load picks up. If the ELCG senses that the frequency is rising it knows that load is being shed (perhaps someone turned off a light), and increases power going to the resistive load. Conversely, if frequency drops, the ELCG smoothly sheds resistive load. In operation the system is almost unnoticeable. The only indication is occasional slight dimming of lights when a large motor starts up. (But of course this occurs with utility power too). If the load increase is too great to handle with the resistive load alone, the ELCG throws a relay to drop the lowest priority load connected. As load decreases again, the highest priority non-connected load is reconnected. There is a special circuit to keep track of and slowly correct for short-term excursions from 60 Hz due to extreme conditions, so that clocks will keep proper time. Maximum frequency correction is kept to 0.1 Hz. The wave form from the generator is excellent for all purposes. However, the switching triacs introduce considerable waveform distortion in the power going to their loads. Hence the resistive balancing loads used are hot water heaters and baseboard heaters, which are indifferent to waveform. It is important to assure that the system always has enough load available to maintain frequency. To accomplish this, priority loads and the resistive regulating loads must be connected at all times. Any regulation system based on the concept of loading is vulnerable to open circuits, which would lead to system runaway. Failsafe emergency protection is required. This is located adjacent to the generator. A mechanically interconnected water jet deflector safety system is actuated by a weighted lever. The turbine is shut down by a frequency guard sensor if frequency deviations become too wide (typically outside the range 53-67 Hz) for too long. The weighted control lever is held up by a normally energized solenoid which releases on power failure. Heat, Biodegradable Soap, and Solar Radios Although the building is heavily insulated, auxiliary heat is needed in winter. Since the available water flow doesn't provide enough energy to heat the building under extreme conditions, propane is used for back-up. Because the lodge is above timberline, firewood must be helicoptered in. The fireplace is mostly for aesthetics! Sewage is handled with a small biotreater plant, a miniature version of a commercial facility. Treated waste goes to a carefully monitored leach field. To minimize loads on the facility biodegradable products are used exclusively. Guests are asked to use the biodegradable soap and shampoo provided, rather than any they may have brought. In the Purcell Lodge environment, communications can be of life-or- death importance. Russ and Paul need high reliability communications between the lodge and the skiing and hiking parties, and with their base at the airport in Golden, BC. Complete coverage is provided by a radio repeater in a strategic location on a nearby mountain. The repeater is powered by a deep cycle battery and a solar charger. The Purcell Lodge system has operated without major problems since startup. The system provides pollution free, clean and reliable power in a location where commercial power is not an option. To the visitor, the years of careful planning and the extensive use of high technology are virtually invisible. Without them the rare combination of comfort and wilderness provided at Purcell Lodge would have been impossible. Access: Authors: Paul P. Craig, College of Engineering, University of California, Davis ù 916-752-1782 and Robert Mathews, Appropriate Energy Systems, Box 1270, Chase BC VOE1MO, Canada ù 604-679-8350 Purcell Lodge: Russ Younger and Paul Leeson ABC Wilderness Adventures Ltd., PO Box 1829 Golden, BC, Canada ù 604-344- 2639/FAX 604-344-6118 Hydro controllers: Thomson and Howe Energy Systems Site 17, Box 2, SSI, BC, VIA2YS, Canada. 604-427-4326 Fidelity Electric Co, Inc. 328 N Arch St, Lancaster PA 17604