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Introduction

Hydroelectric turbines comprise approximately17% of the total number of power generatingunits in the United States and Canada.

According to a North American ElectricReliability Council (NERC) Generating

Availability Report, failures of the wicket gatemechanism, turbine governor, generator

bearings and lube oil system are among thetop 25 causes of forced and scheduled outagesand deratings of hydroelectric turbines. This

represents a tremendous opportunity to applystate-of-the-art filtration to improve reliabilityand availability of hydroelectric turbines.

How They WorkHydroelectric Turbines

There are a number of different hydroelectricturbine designs, but they all incorporate thesimple principle of converting the potentialenergy stored in water to mechanical energy byusing a portion of it to rotate a paddle-wheel orpropeller-type runner on the turbine.Thisrotating mechanical energy is used to turn an

electric generator to produce electrical energy.

There are two categories of hydroelectricturbines:Impulse and Reaction. Impulseturbines are driven by one or more water jetsdirected tangentially into buckets or paddlesof a wheel-shaped runner turning in air.Reaction turbines are completely immersed in

water, and are driven by the difference in waterpressure between the pressure side and thedischarge side of the runner blade much likea windmill propeller is driven by the wind.

Hydroelectric turbines can have either avertical or horizontal shaft orientation. Mostreaction turbines have shafts that are verticallyoriented. These account for the majority of allhydroelectric turbines in service.

Pumped Storage Hydropower Plants

Power plants produce electricity moreeconomically by maintaining a constant ratherthan a varying output. However, since thedemand for electricity fluctuates, these powerplants have a surplus of electricity during off

peak periods. This surplus dump power is

Maximizing Hydroelectric Turbine Performance and Reliability

A hydroelectric dam

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often sold by the facility to pumped storagehydropower plants at low cost. The pumpedstorage plant uses this inexpensive energy topump water from a lower reservoir to a higherreservoir, where it is stored.During peakdemand periods, the water is released from thehigher reservoir and flows through a turbineto generate electricity that can be sold at apremium price.

Some designs use a separate pump andpenstock system for the pumping portionof the operation, and a separate turbine andpenstock for the generating portion of theoperation.The more modern designs use areversible turbine and a motor/generator to

both pump and generate power. They aresimilar to standard reaction turbines in theirfunction and design and typically have a

vertical shaft.

Contamination Control

There are a number of hydroelectricapplications that can benefit from Total FluidManagementSM, Palls unique equipment &services integration program designed to yieldthe highest efficiency at the lowest cost.

Among these are inlet valve hydraulic powerunits (HPUs), turbine bearing lube systems, andthe turbine governor system. Of these three, the

turbine governor system is by far the mostcritical application in terms of hydraulic oilcleanliness because of its importance inmaintaining the proper rotational speed ofthe turbine.

Turbine Governor

The governor uses either mechanical orelectronic feedback to sense the speed of theturbine. Proportional or directional valvescontrolled by the governor operate cylindersthat open and close wicket gates or needle

valves to adjust the flow of water to the

turbine in order to maintain a constantturbine speed. Hydroelectric turbines rotateat relatively low speeds compared to steamturbines, with larger hydroelectric turbinesrotating at 35-75 rpm, and smaller ones asfast as 150 rpm. The large turbine diametercombined with the massive inertia of the

water flowing through it makes precisecontrol of rotational speed a critical concern.

If governor proportional or directional valvesdo not respond instantly and accurately tofluctuating generator loads, there is a lagging

behind of the wicket or needle valve position.This results in an oscillating conditionwhereby the turbine is constantly speedingup and slowing down. This inefficient powerproduction, although difficult to quantify,leads to loss in revenue for the utility.Furthermore, if this oscillation exceeds themaximum allowable frequency, then theturbine must be shut down, resulting intemporary loss of generating production.

Also, in the event of a sudden loss of load,it is important that the governor actinstantly to shut down the turbine toprevent a runaway speed condition.Runaway speed is the speed at which theturbine exceeds its designed maximumrotational speed. When this occurs it ispossible for the turbine to disintegrate dueto massive centrifugal forces.

Figure 1. Schematic drawing of a pumped storagehydropower plant

Figure 2. Hydraulic turbine governor utilizing mechanicalfeedback to sense turbine speed

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Neyrpic and Woodward Governor Company are twomajor manufacturers of hydroelectric turbinegoverning systems. The Neyrpic governor usesproportional valves to control wicket gates or needle

valves, while the Woodward governor uses directionalvalves. Both of these systems operate at relatively lowpressures (approx. 200 psi).

Silt size particles can cause sluggish response,

jamming, or wear of valves. This can lead to turbineoscillation or a potentially dangerous runaway speedcondition. Because of the small clearances inproportional and directional valves (1-8m) they areinherently sensitive to contamination. For this reasonthe turbine governor system hydraulic fluid should bemaintained at ISO 16/14/12 or better. To accomplishthis the following is suggested: Install a Pall non-bypass filter assembly with 5m

(5(c)1000) Dirt Fuse elements in-line just upstreamof each proportional or directional valve to providelast chance protection.

Install a Pall filter assembly with a 5m (5(c)1000)

element on the pressure line of the HPU to protectvalves, pumps, and cylinders.

Replace the reservoir fill cap with a Pall ReservoirVent Filter to eliminate the introduction of airborneparticles into the HPU reservoir.

Bearing Lube Oil System

Currently most hydroelectric turbine bearings areinspected and, if necessary, reworked/replaced duringregularly scheduled outages. Downtime, reworking orreplacing bearings, and labor can be a significant cost toa hydroelectric power producer. The frequency with

which these bearings are replaced/reworked can begreatly reduced if proper attention is given to turbinelube oil contamination levels.

Particulate contamination is a major cause of wear andpremature failure of bearings. By maintainingcleanliness levels at ISO 16/14/12 or better, journal

bearing life can be extended. For turbines that use rollerbearings, cleanliness levels should be ISO 15/13/12 orbetter. Sometimes there are separate lubrication systemsfor each bearing in the hydroelectric turbine.

These reservoirs vary in size from 45 to 100 gallons,while large central lubrication systems may have 1000gallon reservoirs. To achieve the required cleanlinesslevel each lubrication system should have a Pall filter

assembly either inline (preferred) or in a kidney loop.Turbines with journal bearings or roller bearingsrequire 7m (7(c)1000) filtration. It is alsorecommended that fill caps be replaced with PallReservoir Vent Filters to eliminate the introduction ofairborne particles into the reservoir(s).

Typical horizontallyoriented hydroelectric

turbine

Continued on back panel.

Trash Rack WicketGate

Shaft

Generator

Runner ThrustBearing

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System Components

Though there are different

types of hydroelectric turbine and

pumped storage designs,

they almost always incorporate

the following components:

Penstock

The penstock is a conduit used to carry waterfrom the dam or reservoir to the turbine.

Runner

There are a number of different kinds ofrunners. They translate the linear motion ofthe water into rotational motion by the use

of blades or buckets. Many designs look verymuch like large propellers, while others aremodern versions of the paddle wheel. Somepropeller-type runners have the capability of

varying their pitch blade for optimumperformance in varying flows and headpressures.

Governor

This is the system that automatically monitorsand maintains the speed of the hydraulic unit.It is also used to synchronize the generator tothe system frequency (Hz) for connection to

the power grid, and to shut down the unit inthe event of a sudden loss of load. As withsteam turbines, malfunctioning of the governorcould result in a dangerous runaway(overspeed) condition.

Wicket Gate

These are angularly adjustable, streamlinedcomponents that direct and control (throttle)

water flow to the runner in reaction-typehydroelectric turbines. They are regulated bythe governor via mechanical-hydraulic orelectro-hydraulic controls.

Needle Valve

The needle valve is used to regulate theflow of water to the runner in impulse-typehydroelectric turbines, and is regulated bythe governor via mechanical-hydraulic orelectro-hydraulic controls.

Inlet Valve

The inlet valve is located upstream of theturbine and is used to cut off the flow of

water in the event of an emergency or formaintenance. These valves are often sphericalor butterfly valves, and are usually operated

by hydraulic power units.

Main Guide Bearing

This bearing is located closest to the turbinerunner and radially supports the rotatingrunner and shaft assembly. Many designsincorporate an upper and lower guide bearing.

Thrust BearingThe thrust bearing carries the weight of theturbine and the generators rotating parts for

vertical turbine designs. It can be locateddirectly above or beneath the generator rotor.Horizontal designs may have two thrust

bearings, or a double-acting thrust bearing tocarry the axial thrust in both directions.

Lift Pump

Some large hydroelectric turbines areequipped with lift pumps (sometimes called

jacking oil pumps) that are used to pump lowflow, high pressure oil to the bearings duringthe process of increasing the rotor speed fromminimum speed up to maximum design-ratedspeed. The turbine bearing journals arehydrostatically lifted off the bearing race inorder to reduce metal-to-metal contact atlower rotational velocities.

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Schematic of a

Hydroelectric Facility

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Two Types ofVertical Runner Designs

Reservoir

Trash Rack

Dam

Penstock

Powerhouse

Generator

TurbineMainGuideBearing

Inlet Valve

Thrust Bearing

Runner

FrancisTurbine

Propeller(Kaplan) Turbin

Generator

Generator

5

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25 Harbor Park DrivePort Washington, NY 11050

1.888.873.7255 toll free516.484.3600 phone516.484.0364 fax

Visit us on the Web at www.pall.com

Pall Corporation has offices and plants throughout the world in locations including:Argentina,Australia, Austria, Belgium, Brazil, Canada, China, France, Germany, India, Indonesia, Ireland, Italy,Japan, Korea, Malaysia, Mexico, the Netherlands, New Zealand, Norway, Poland, Puerto Rico,Russia, Singapore, South Africa, Spain, Sweden, Switzerland, Taiwan, Thailand, United Kingdom,United States, and Venezuela. Distributors are located in all major industrial areas of the world.

Copyright 2006, Pall Corporation. Pall, , Pall Aria and Dirt Fuse are trademarks of Pall Corporation.

Indicates a Pall trademark registered in the USA. is a service mark of

Pall Corporation.

Lift Pump

Large hydroelectric turbines may use a liftpump prior to start-up or shutdown to preventmetal-to-metal contact of bearings. By forcingpressurized oil into turbine bearings, the

journal is lifted from the race until, in the caseof the turbine start-up, sufficient hydrodynamicforces are generated by the rotation of the

bearing to achieve operating clearances.

Because the clearances in the turbine bearingare minimal during start-up and shutdown, it isimportant to maintain lift pump oil cleanlinessat ISO 15/13/12 or better. To achieve thiscleanliness level it is recommended that aPall filter assembly with a 7m (7(c)1000)element be installed either in the lift pumppressure line (preferred) or in a kidney loopoff the turbine lube oil reservoir.

Water Removal

Because of their proximity to water,

hydroelectric turbine lube oils often haveunacceptably high water content. This canresult in a variety of problems ranging from

bacterial/fungal growth and premature oildegradation to component wear and failure.Bearing journal scoring can occur as a result ofinsufficient oil film thickness caused by watercontamination. Water can also cause therusting of pipes and other componentsproducing particles that promote wear of

bearings and performance degradation inproportional and directional valves.

For these reasons it is recommended that aPall vacuum dehydration purifier be used toreduce the water concentration well below thesaturation level of the oil. A major turbinemanufacturer recommends the use of vacuumdehydration purifiers in continuous operationto remove water contamination. The Pallpurifiers integral, high-efficiencyx(c)1000filtration will remove damaging rust and wear

particles already in the system, while its waterremoval capabilities will help prevent otherproblems associated with water contamination.

Drinking Water

Due to the remote location of many hydroplants and the lack of municipal water supply,each location is required to produce theirown potable water. Older technology hastraditionally been used, but as local regulationsregarding how potable water is produced

become more stringent, plants are forced tolook at equipment upgrades to meet the

tighter requirements.

Pall Ariawater treatment systems arespecifically designed to produce drinking

water that meets todays stringent standards.Pall Aria systems are uniquely designedfiltration modules in a hollow fiberconfiguration to remove the following fromground and surface waters and secondary

wastewater effluent: Turbidity Bacteria Cysts and Oocysts

Iron and Manganese

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