Plant Inspection

In December, Celeste and I inspected your cross flow turbine, power plant, with indirect supervision by our father. During the course of the inspection, we gathered information pertaining to your general equipment condition and the possible causes of a gradual diminution in power. We believe that multiple loss factors, attributable to equipment aging, combine to decrease your power output. We believe that losses in head and increases in skin friction are the primary culprits.

As you know the power output of your plant can be defined electrically, hydraulically and/or mechanically as the product of head times flow or volts times amps or torque times RPM. Hydraulic losses, either in diminution of pressure (head) or flow rate are often inter-related. These losses are a function of inner flow surfaces, skin friction, clearances between moving and stationary parts, maintenance of original blade angles, clogging of nozzle and blade passages by debris and backwater of both headrace and tailrace channels due to siltation and/or collapse of retaining walls. A reduction in static/dynamic head results directly in a reduction of flow through the machine. This double whammy, of both head and flow reductions, causes an exponential decay in the hydraulic power, a product of head times flow. These types of losses may result in excessive turbulence.

Mechanical losses, either diminution of rpm or torque are also interrelated. They can be a result of hydraulic losses but there are other factors. Roller and journal bearing deterioration, belt slippage, unintentional contact between rotating and stationary parts (scraping), wear in gears and improper lubrication can rob torque from it’s original value. Again this is interrelated with rpm. The loss in torque causes a loss in mechanical power. Please note that these types of losses usually create heat and accelerate the deteriorative process.

Electrical losses, either diminution of volts or amps are also interrelated. They also can be a result of hydraulic and mechanical losses but have distinctive additional losses that accompany them. These losses include deterioration of winding insulation, poor contact between carbon brushes and slip surfaces, poor cooling caused by dirty surfaces and plugged generator screens. Additionally, the instruments used to record the power can lose their accuracy with age. In particular, the kilowatt-hour meter should be calibrated every five years.

During the visit we spoke with your maintenance staff and made visual inspections of the equipment. Due to inordinately cold conditions, the head race could not be drained. As a result, important inspections of the runner blades, nozzle surfaces, runner passageways and tailrace tunnel were not made.

We were able to externally inspect the guide vane bell cranks and trunion shafts. The larger vane had alignment marks that matched the factory locations. This may indicate that the nozzle vane is properly aligned. The smaller nozzle did not have the marks.

Your staff indicated that the gearbox and turbine bearings had never been replaced. A statistical process, with a "B" number, rates roller bearings. It is recommended that bearings be replaced when a B-10 rating is exceeded. This is equivalent to 100,000 hours or 11.2 years. Your bearings are significantly over this statistical threshold.

We recommend that we return when conditions allow a thorough dewatering of the site. We need to pull the runner cover and pressure wash, the runner, the internal surface of the runner housing, the nozzle valves and the inside surfaces of the nozzle. This will remove the incrustation of hardened tubercles coating the flow surfaces. We should inspect the tailrace tunnel walls and floor for damage and debris accumulation. We need to perform a differential survey to determine the static and dynamic head losses. We need to record bearing temperature levels, acoustic noise levels and amperage levels. We need to determine system torque levels in the dewatered state and we need to determine nozzle and runner radial and side clearances.

We feel that a combination of small upgrades will significantly increase the power levels of your hydro plant.

We look forward to working with you and your maintenance staff to restore your system performance. Should you have any questions with regard to this report please do not hesitate to contact us.

Sincerely,

Celeste and Will Fay

French River Land Company Inc.

Send mail to: cfay@frenchriverland.com with questions or comments about this web site.
Last modified: 10/06/08