Coal, Gas, Renewables

CAD measuring boasts hydro blade efficiency benefits

Issue 10 and Volume 100.

CAD measuring boasts hydro blade efficiency benefits

Hydroelectric utilities and their turbine suppliers put significant engineering effort into attaining the highest possible efficiencies with their turbine wheels. The design calculations and their optimization are done on a computer. Then the design file is translated through computer-aided design (CAD) software into engineering drawings. The last stage–confirming the turbine blades, as manufactured, conform to the optimized computer design–has been a tedious, entirely manual process. It doesn`t have to be any more.

Shape recovery, comparing the actual measurements to the CAD design, can be worthwhile for hydroelectric utilities because even small dimensional discrepancies between the product and the original design can impair the ability of the runner to absorb the water`s energy, and lost efficiency means lost revenue. Losing only 0.1 percent efficiency would mean losing 1 kWh for every MWh of rated output. Over the 8,760 hours in a year, the facility could then lose 8,760 kWh annually for every MWh of rated output. Assuming a 100 MW unit and power valued at $0.065/kWh, annual revenue loss could equal $56,940.

A typical hydroelectric turbine wheel, also called a runner, has between five and 15 blades, stands about 8 feet tall, about 20 feet in diameter and weighs close to 12 tons.

Experience

In the past, field measurements at a generating station were taken along hand-placed templates and then digitized by referring to a table of digital equivalents.

Using templates tends to be awkward, especially in the restricted-flow passages between the casing and turbine hub. The total time for a technician to position and trace the flow-passage sections for just one blade is about 210 hours, including 80 hours for the CAD shape-recovery.

In January, Ontario Hydro engaged AD3R Technologies Inc., an engineering services firm from Montreal, to use an improved technique for measuring the runner at Ontario Hydro`s Kapuskasing, Ontario, generating station, using a FaroArm, a portable coordinate measuring machine made by Faro Technology Inc., Lake Mary, Fla., and Faro`s AnthroCam software loaded onto a laptop PC. To measure a turbine blade in the field, the FaroArm is first bolted to a plate that`s welded to the casing or some point on the blade itself.

The mounting plate is later cut off and the joint ground smooth. The FaroArm has a 6-foot reach over 600 degrees of rotation, and with two degrees of freedom at its base, its elbow and its wrist, it can easily reach over and behind blade edges.

Raw data is sent to the computer and as the arm is moved, its position and orientation are presented continuously on the computer`s screen to ensure sufficient points are taken, even in sectors of rapidly changing curvature. The data is saved on the computer`s hard drive, then translated into a file that`s compared directly with the design data.

With only about four hours of preparation time and a total of 80 man-hours, the new technique saved about 130 man-hours, allowing the utility to receive test results about one month faster. Precision is also one order of magnitude better than the template method, bringing greater assurance of conformity to the optimized CAD model.

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