George was flabbergasted by what he uncovered while inspecting a new 1.2-mw hydro facility. The Municipal Commission a government department that manages bankrupt municipalities requested that he inspect the plant, which was built by a remote village to replace expensive diesel power. After spending a year unsuccessfully attempting to commission the plant, the village defaulted on bonds issued to build the plant and declared bankruptcy.
The hydro scheme was simple. At a nearby river, the village built a low concrete weir to divert the flow of water into a short canal that bypassed some rapids. The water flowed to a concrete powerhouse that contained a single vertical axis propeller turbine, in an open flume setting, operating at about 6 meters of head.
The civil work was fine, but the equipment was a disaster. The village had hired Joss, an elderly retired engineer with little experience in the hydro industry, to procure equipment. With instructions to keep costs to a minimum, Joss had purchased used equipment from a recently renovated plant. In the new plant, he installed a mid-1920s turbine-generator, a Woodward HR model governor, and open switchgear panels.
Unfortunately, Joss passed away just before commissioning work started. A local electrician and car mechanic attempted, unsuccessfully, to complete work on the project. The village declared bankruptcy, and the Municipal Commission called George to help determine the cause of the problem and, hopefully, discover how to get the plant running.
George arrived at the village in early winter and stayed at the local inn. Upon learning that George was there to inspect the hydro facility, the landlady asked him to look at her freezer. George discovered that the motor was burnt out. He asked the landlady if the lights had been unusually bright before the freezer stopped working, and she said they were. She also said this was her second freezer; the first also had failed but was replaced under a guarantee. Based on this information, George knew that the hydro plant had frequency and voltage control problems.
The next day, George performed a quick inspection of the site and equipment. He then asked the operator to start the turbine-generating unit. To do this, the operator manually opened the wicket gates at the governor servomotor wheel. When the unit reached near-synchronous speed, as indicated by the revolutions per minute (rpm) dial gauge, the operator closed a large switch and attached a 20-kilogram weight to the switch handle. When George asked about the weight, the operator said it prevented the switch from flying open. The operator then opened the wicket gates to about 50 percent, and the powerhouse lights came on.
George thought the plant was now supplying electricity to the village. However, the operator said all the electricity being generated was being used to light and heat the powerhouse! Connection to the village system required shutting down the diesel and was prohibited because the last two attempts had burnt out all the lights!
George noticed that the operator continually made small adjustments to the wicket gate opening, while watching the rpm gauge. He realized that the governor was not operational, hence the frequency deviations. A visual inspection indicated that the kilowatt meter also was not functioning.
George asked the operator to shut down the unit and open the concrete casing so that he could inspect the turbine. The operator accomplished this task by closing the wicket gates; lifting the weight off the switch; and placing a 20-centimeter-square, 5-meter-long timber in the generator pit, with one end wedged against an air vent. The operator then used a come-along on the opposite end to force the timber against the generator shaft, to act as a brake! The operator used the rack-and-pinion gears to close the two timber headgates, then opened a manhole in the powerhouse floor. The operator descended into the concrete casing carrying a long forked shaft, which he used as a probe to locate a valve handwheel. He used this handwheel to open the turbine casing drain.
After checking that there was no pressure in the governor, George entered the turbine casing and looked at the four-blade runner. He discovered that it was loose on the shaft. He also saw a 2-centimeter gap between the runner blades and throat ring. The gap existed because the conical draft tube, which had been fabricated locally, was slightly oversized.
Deciding he had seen enough, George asked the operator to close up. George noted the alacrity with which the operator ascended the ladder out of the casing. This was necessary because of the rapidly rising water level arising from significant gate leakage.
The generator casing of the unit still bore the old turbine nameplate. It indicated a design based on net head of 9.15 meters, a speed of 150 rpm, and a runner diameter of 2.54 meters. Turbine horsepower was 3,500 (2.6 mw). From this information, George estimated the old design flow at about 33 cubic meters per second. Down-rating to 6 meters of head should have produced an output of about 1 mw at the generator. However, power production was less than anticipated because of losses around the runner and operation at off-design head. The low power output at 50 percent gate confirmed this situation.
In his report to the Municipal Commission, George recommended replacing the equipment at this facility with a modern Kaplan turbine with a gear-driven high-speed generator and electronic controls. However, the commission determined that it would be more economical to build a transmission line from the nearest utility substation. So the project was abandoned.
This case is disastrous. A village had taken the initiative to construct a small hydro plant but had received poor advice. An adequate feasibility study was not undertaken, and the consultant was inexperienced. Always look for an experienced consultant. As added security, ask engineers with extensive hydro experience to review the feasibility report.
In addition, try to avoid using old equipment. Definitely avoid equipment older than about 50 years. If suitable older equipment is used, install modern switchgear and controls. Old switchgear cannot pass modern safety codes, and old controls cannot maintain the steady frequency now required by electronic equipment.
Finally, never use a single propeller turbine on an isolated system. The turbine would be difficult to control and very inefficient at part load.
By James L. Gordon, B.Sc., hydropower consultant; (1) 514-695-2884; E-mail: jim-gordonsympatico.ca.