Wouldn’t it be nice if there was an

Automatic Index Test Box for Kaplan Turbines By Douglas J. Albright

Abstract

This article describes how index testing and then optimization, or tuning of Kaplan

turbine variable geometries achieves higher efficiency over a wide range of power

levels. Kaplan turbines can be index tested 3 ways:

1. fixed-blades, swept-gates

2. fixed-gates, swept-blades

3. Constant-power, swept-gates-and-blades.

The Actuation Test Equipment Company (ATECo) Index Test Box (ITB) is

presented with a description of how it can conduct the Constant Power test.

The new Hybrid Index Testing method allows a Kaplan turbine to be index-tested

without requiring the test engineers going to the dam.

All on-site work is performed by the normal powerplant personnel from setting up

and calibrating the instrumentation to exercising the machine while streaming data

into a datalogger.

The data files are emailed to ATECo and reduced by the Index Test Box to

produce efficiency profile data for a Joint Load control system and a new

optimized 3-D Cam surface profiles.

Background

Index testing has been available as a means to improve Kaplan turbine

performance for many years1,2&3 but due to the expensive, tedious and time-

consuming requirements of collecting the field data index testing the majority of

Kaplan turbines never get this tune-up. Industry organizations (ASME & IEEE)

have created measurement procedures and standards for turbine control system

performance6 and index testing5 to optimize Kaplan blade to gate relationships by

absolute and relative efficiency measurements. Many articles have been written to

present methods to determine the optimum blade to head and gate relationships of

Kaplan turbines using traditional methods1,2,3&4, many of which have been posted

on the ATECo website: Click for Reference Materials

Introduction

In this time of heightened global concern over energy availability and carbon

emissions, an instrument that can automatically perform an index-test, or “tune-up”

on Kaplan hydroelectric turbines to improve efficiency up to 5% to make more

power with no carbon emissions and minimized environmental impact has great

appeal to the power industry. Index testing refines head and gate to blade

relationships for Kaplan turbines to get peak efficiency at a given water flow rate.

This profile is then programmed into the turbine blade control system to realize

this improved efficiency performance.

The “Constant Power” method is best suited for Run of the River powerplants

where flowrate must remain constant.

The ITB is intended only for use in index testing and optimization in order to get

maximum return on investment from Kaplan turbines.

It is not intended for acceptance tests to verify that contract guarantees are met.

The Constant Power method has three primary benefits over traditional index

testing methods:

1. Power level remains constant during the automatic testing sequence; the

traditional index testing method requires changing power level every 5

minutes or so. These power changes must then be coordinated with the

control room and dispatcher.

2. Flow level remains constant within a few percent during the automatic

testing sequence; the traditional index testing method requires wide swings

in flow and power and then waiting for water levels to stabilize after

each flow and power level change. In most instances the waiting interval is

too short which makes the collected data much noisier.

3. The new test instrument and methods presented herein allow unattended,

automatic index testing, thereby alleviating the expense and tedium of this

task and avoiding the problems of both #1 and #2 above.

Kaplan Turbine variable geometry

Kaplan turbine variable-pitch blades are adjustable to achieve maximum operating

efficiency across a wide power range. In early designs, the blade angle tracked the

gate stroke along a 2-Dimensional cam profile; whenever the gates moved, the

blades would follow as defined by the two dimensional cam response; but no

automatic correction was made for head changes, Whenever water level changed

enough to warrant it, the 2-D cams were swapped manually by the operator to one

for the new existing head. This was time consuming and often didn’t get done -

and even when it did the head-tracking resolution of this old system was still not

very good.

Even greater efficiencies were made possible by the development of computer-

based Kaplan 3-D cams that trim runner blade angle for minute changes in water

level automatically – with up to 16 bit resolution. This provides precise, automatic

high-resolution trimming of the blade to gate relationship as head varies, but in

order to achieve these gains the turbines must be individually index tested and

setup properly in order to achieve the highest possible operating efficiencies.

Figure 1 Kaplan runner on display outside Bonneville Dam

Figure 2 Cutaway view of wicket gates and runner section of Kaplan turbine

This cross section shows the arrangement of the wicket gates and the runner

blades. At lower flow rates, the gates are mostly closed; water flow squirts through

the gates into the runner section with a significant whirl imparted on it. The

optimum blade angle is a function of both the volume of water flowing through the

unit and the vector angle that is caused by the velocity of the whirling. When

turbine efficiency is maximized, the whirl is completely removed from the water

column in the discharge; the water flowing out of the turbine has no spin left.

Test Report

The first validation of the ITB uses data from USACE acceptance test of the 33

MW Kaplan turbine at Clarence Cannon Dam in Missouri. Analysis was

performed by DOE’s Lee Sheldon:

1986-04-01 Analysis of Clarence Cannon Data (Sheldon)

This report compares real-world data from two index tests run one week apart on a

Kaplan turbine at test used traditional index testing methods, and the other used the

new Constant Power index testing method. Results of these two tests were virtually

identical; both showing an approximate ¾% efficiency increase at 33MW output

would result from optimizing this turbine.

The design head of this unit is 75 feet “net-head.” Because the conventional test by

USACE was an official acceptance test, the operating head for the traditional

fixed-blades test was held at 75 feet net head utilizing the re-regulation dam 10

miles downriver. For the ITB Constant Power index test, head was at the seasonal

norm of 82 feet. (The downstream neighbors didn’t like the higher water level that

resulted from raising the tailwater to maintain the turbine design head of 75 feet so

we took what we could get and normalized the data using the affinity relationships.

Normalization range should be kept below 2%, but this analysis needed 9.3% so a

second index test by DOE was performed at PGE’s Bull Run Dam 30 miles east of

Portland, Oregon. Ultimately the 33 MW Unit was de-rated to 28 MW due to

cavitation limits identified during these index tests.) During the USACE index test

that used the fixed-blades, swept-gates method the test point timing needed long

settling times due to the sloshing water levels resulting from large flow swings

typical with this traditional test method. Because power and flow remain relatively

constant the Constant Power method does not suffer this problem.

As different head levels become available as the seasons change, the index test

should be repeated to define a new optimum cam line at the new head – but this is

rarely, if ever done; index test results from a single head are typically extrapolated

across the entire family of heads as shown in figure 3 and that’s the end of it. The

ITB is an automatic instrument that is comprised of a low-cost COTS Personal

Computer with a few software programs. Cost of an ITB installation is low, so it

can be installed and left on the unit as a continuous performance monitor of turbine

performance, collecting data year-round. Using the new Hybrid Index Testing

method, costs are reduced even more.

Figure 3 Standard Display of 28MW Kaplan 3-D Cam Surface Data

The American Society of Mechanical Engineers (ASME) Power Test Code #18

(PTC-18) defines index testing procedures to determine efficiency at a single

operating point. Test definitions range from absolute-flow “code acceptable” tests

to verify contract guarantees to the relative-flow “index test” that simply

determines the optimum blade to gate relationship without measuring flow in

absolute terms. PTC-18 defines the method to collect and reduce a single data

point. This procedure is repeated at several different gate strokes at a single blade

angle to define a single point on the “best cam” line. This process is then repeated

at a number of fixed blade angles across the full power spectrum of the turbine at a

single head. The 3-D cam surface is then fully defined by repeating this process at

a number of heads. This Cartesian coordinate relationship of blade angle to head

and gate stroke for this turbine are shown as the standard display of a Kaplan 3-D

cam data surface in Cartesian coordinates in figure 3. This graph consists of a

family of curves for seven different operating head levels with gate stroke as the

X-axis, and blade angle as the Y-axis.

Wicket gate opening is the X-axis across the bottom, which may be expressed in

several ways.

Gate Stroke is the linear extension of the servo piston that moves the bullring,

which is the easiest to measure and control.

Wicket Gate Angle is the rotary angle of the gate shaft(s).

Gate Opening is the area of the opening between the wicket gates through which

the water flows.

Wicket gates are designed so that the area of the gate opening increases linearly

with piston stroke and gate rotation as closely as possible. In addition to flow

increasing, the vector-angle of the water flowing into the runner section becomes

more vertical as the gates are opened. To accommodate this steepening vector

angle of the water flow, the blades are rotated to more steep angles as power level

increases.

The purpose of index testing is to perfect and “fine tune” this angular relationship

of blade angle to the flow vector angle.

Why Index Test

Errors in the initial 3-D cam data surface for a Kaplan turbine arise from many

sources. For model tests, data is taken from measurements on a scale model of the

prototype (or full-sized turbine) and scaled-up to predict the initial best-cam

surface for the prototype. For model tests “net head” is generally used to determine

the 3D-cam data map; prototype units generally use “gross head” as the input to

the 3D Cam function. Model test rigs lack a trashrack and have smooth surfaces in

the water passageways; the prototype does have a trashrack, and usually has a

rougher surface finish, which increases losses due to the orifice drop of the

trashrack and friction & drag from the passageways. The optimum cam profile for

Kaplan turbines can also be altered by errors in scaling-up the model to the

prototype in fabrication, manufacturing tolerance stack-ups and variations in the

turbine setting at the dam.

Kaplan turbines should be immediately index tested when commissioned in order

to correct for scaling errors and variations in the turbine setting. The model test

surface that is initially installed in the turbine’s 3-D cam is only an approximation

of the optimum cam surface for the full-sized prototype turbine. Only index testing

can delineate the actual optimum surface and yield maximum turbine efficiency. It

also behooves the powerplant to periodically retest their Kaplan turbines every 5

years or so because years of wear and tear on the machine will alter the actual

optimum cam profile due to strain relief on the metal and cavitation & erosion on

the gates & runner blade surfaces.

Index testing produces three main benefits:

1. The optimal 3-D cam surface profile is defined for the turbine blade control

system to maximize operating efficiency from the unit; and

2. Benchmarks are created for subsequent index tests to be compared against,

providing ‘trending’ information to help determine proper inspection and

maintenance intervals - but only for an individual turbine; index test data from one

turbine is not applicable to another.

3. Operating limits to define cavitation regions of operation are identified; staying

out of these areas prolongs the interval between time consuming and expensive

cavitation repairs.

When exact differences between the model test and prototype are defined and the

prototype is optimized; the resulting performance increases can be significant.

Index test results for one turbine are meaningless for another turbine, except only

to note similarities.

For budgetary considerations, planning numbers for index testing a turbine that has

never been previously index tested are for a 2%-3% increase in turbine efficiency.

Actual results often achieve more than this range, and some less - but without

actually testing every turbine it’s impossible to know for sure. Typical costs of

index testing run in the $30k to $50k ballpark, depending on the degree of

difficulty and extensiveness of the testing procedures. This is minimal considering

the payback possible from optimization of hydroelectric turbines.

For example, here are planning numbers worked out to budgetary figures for index

testing a Kaplan turbine. Assume a turbine is operated at 12MW output, 24

hours/day and 365 days/year. And then assume a 10-cents/kWh retail price for the

added power output; know that all overhead expenses are already paid - so the

increase from index testing will be pure profit.

Starting with the most conservative estimate – a 1% efficiency increase will bring

in an additional $105,120/year.

• A more ambitious estimate of a 5% efficiency increase would

return $525,600/year.

• Not too shabby for a $50,000 tune-up.

• Using the new Hybrid Index Testing method this can be reduce to

$5,000 per index test because the bulk of the labor is done by site

personnel and the test engineers do not go to the dam.

Comparison of two tests

The six following graphs present the data and results from a traditional “fixed-

blades, moving-gates” index test first, and then for comparison the data and results

from a “Constant Power swept-gates and blades” index test on the same 28MW

Kaplan turbine run a week later.

(Notes: To allow a direct comparison of the results from these two test procedures,

the X-axis scale of all three of these graphs are the same and to allow a more direct

comparison, the X-axis for all plots is gate stroke, instead of power, which is

typically used in the traditional method.)

Traditional fixed blades, moving gates test

Figure 4 Traditional Index Test points sweep across the On-Cam line

The traditional index testing method blocks the turbine runner blades at a constant

angle while the gates are stepped or “indexed” to several positions across the On-

Cam line with efficiency measurements at each step as shown in figure 4.

Efficiency data is collected at each step to locate the optimum gate to blade

relationship for optimum efficiency. This method is time consuming and required

coordination of wide power output swings with the dispatcher and delays in order

to wait for forebay and tailwater levels to settle out. Power and flow swings with

gate stroke are shown in figure 5.

Figure 5 Traditional Index Test relative flow and generator output power

Using the PTC-18 data reduction techniques for each test point, a relative

efficiency plot for a number of fixed-blade to gate pairs is created to determine the

fixed-angle turbine propeller efficiency curve. The procedure is repeated for

different blade settings to obtain sufficient efficiency data to define the optimum

cam curve for a family of fixed-angle turbine propellers.

Field test data are dependant on existing head and tailwater availability. To fully

map the 3-D cam surface, this procedure should be repeated at three or more

different heads across the turbine design head range. But this is rarely possible

because the range of heads doesn't normally occur within a relatively short time

period.

Figure 6 Traditional Index Test relative efficiency profile

The classical method of index testing turbines is made more difficult, tedious,

time-consuming and expensive due to repeated manual positioning of gates &

blades, coordinating the resulting power level changes with the dispatcher or

control room, and then waiting for the sloshing that results from varying the flow

rates on forebay and tailwater levels.

Constant Power Method

The Constant Power Method of index testing is easier, less tedious and time-

consuming and saves money because the Index Test Box from Actuation Test

Equipment Company can perform a “transparent” index test in an unattended

manner, while the unit is operating normally.

Woodward Governor Company acquired a patent in 1987 (U.S. Patent 4,794,544)

for the Automatic Index Test Box for Kaplan turbines with George H. Mittendorf

Jr. and this author named as co-inventors, but was never utilized effectively – until

now -the patent expired and the invention has come into the public domain.

The patent text describes a “Method and apparatus for automatically determining

the set of optimal operating angles for the variable pitch blades of a Kaplan-type

turbine which has moveable gates that are controlled by a governor, and an

electronic 3-D cam” that works like this:

1. The unit is loaded up to the desired power level for testing.

(Note: All unit safety features and interlocks remain in force during this entire

procedure.)

2. The blades are decoupled from the setpoint output from the head & gate to

blade 3-D cam, allowing the ITB to provide the blade angle setpoint while

the governor controls the gates to maintain the turbine at the power setpoint.

(Decoupling the blades provides the benefit of more stable unit operation for

the Constant Power test; the cascaded control algorithm typical in Kaplan

governor system has a tendency to make the units “wobblier” & unstable -

and more difficult to get good steady state data.)

3. An initial “on cam” data set is captured; all data values are normalized to a

common head using the ASME PTC-18 technique (ref: ASME PTC 18-

2002, Hydraulic Turbines and Pump turbines, Performance Test Codes,

paragraph 5,2,1, page 70). Both raw and normalized values are stored.

4. 2 The ITB moves the blades slightly off-cam, and then the governor resets

power back to the load-setpoint by moving the gates. The ITB software

SteadyState routine waits for the unit to settle out at each new operating

point before capturing another data point.

5. Using these two degrees of freedom (shown in fig 7) the unit’s gates and

blades transcribes a curve along the Constant Power axis of the turbine when

the blades are swept across the “best cam” line and a load-feedback

governor moves the gates to hold the power constant.

6. The power (red lines) and flow (blue lines) in figure 8 are relatively flat

across the test range of gates (and blades) when compared to the traditional

test methods plot shown in figure 5. Flow dips noticeably at peak turbine

operating efficiency while power remains constant. Efficiency values of the

collected data points are evaluated for a peak and two decreasing efficiency

values on both sides of the on-cam line as shown in figure 9. When enough

data is collected, the ITB releases the blades to normal operation.

Figure 7 Best-Cam lines for 80 and 85 feet and Constant Power Curve for

28MW Kaplan

Figure 7 shows the parabolic Constant Power (brown) curve for 55% power and

the "80 & 85 ft Best Cam" lines (violet & orange) from the 3-D cam. These are all

mechanical control parameters (blade vs. gate) of the turbine. The test is initiated

with the unit operated at a point where the blades are open enough to provide room

under the blade angle starting point for the below-cam test points.

The operating head at the start of this test was 82 feet, so the on-cam point would

be approximately ½ way between the two best-cam lines shown on Fig 7. This

example test started at 45% gate and 8% blade. After measuring efficiency data at

the "on-cam" test point, the blades are stepped (or indexed) off cam in 3%

increments on both sides while the load-feedback governor holds power and flow

constant, or nearly so.

Figure 8 Relative Flow and Power Output as percentage

Figure 8 shows how closely the unit was held at a constant 55% power output, and

maintained a constant relative flow of about 35% as the blades were swept from

2% to 20% and the gates were swept from 42% to 58% as the unit was swept along

the Constant Power Line. The output power and flow of the unit remains quite

constant all along this curve, allowing index testing to locate the optimum blade to

gate point without disrupting power output or changing flow level. The constant

power level allows testing without the necessity of changing power generation

level every 5 minutes or so, alleviating the need for constant coordination of

changing power levels with the dispatcher to conduct an index test. The constant

flow level expedites the testing; during traditional index tests, delays result from

waiting for the water levels to settle out after a flow change.

Figure 9 Relative Efficiency during Constant Power sweep

The optimum efficiency point from the Constant Power test is easily seen in Figure

9 as the point of highest relative efficiency. Relative efficiency is again computed

using the conventional efficiency calculation methods documented in PTC-18.

Kaplan turbine variable gate and blade geometry provides an infinite combination

of gate and blade positions that will yield the desired power level, which makes the

Constant Power method of testing possible.

Unit Requirements and ITB features

In early Kaplan control system designs the governor and blade control system

could only track one of the cam profiles (shown in Fig 2) at a time. For the index

test, blades had to be manually disconnected and blocked in the desired positions

and then the gates were positioned using the governor “Gate Limit” function. New

computer based electronic 3-D cams allow Constant Power index testing for

Kaplan unit because the blades can be decoupled from the gates & 3-D cam profile

and positioned independently. The load-feedback governor holds the unit at a

constant power while the blades are swept across the range of interest for the index

testing.

In order to ascertain maximum turbine efficiency, the accuracy and robustness of

the cam surface profile and hydraulic amplifiers must be verified. Testing in

accordance with industry standards will assure the turbine gates and blades can be

positioned accurately enough to realize the economic benefits of index testing.

Nominal positioning accuracies of 0.1 percent gate stroke span and 1.0 percent of

blade motion span are recommended by the IEEE Standards, Std-125& Std-1207.

Basic requirement for an ITB test is an electronic computer-based 3-D cam and

load-feedback governor controlling the gates of a Kaplan turbine. Many vendors

provide suitable equipment for this; an upgrade to a state-of-the-art computer-

based control system is a prerequisite for an ITB Constant Power test; this does not

rule-out index testing units with older mechanical systems with the Index Test

Box.

If at all possible - it is recommended to start with a dewatered inspection to verify

full stroke and linearity of gates and blades with protractors on wicket gate shafts

and at the oil head for blade angle. The ITB has built-in utilities to make a few

checks of steady state accuracy and dynamic robustness before proceeding with the

index test. The ITB instrumentation inputs are calibrated with a simple “zero &

span” procedure, with a few data points across the measured parameter’s span to

verify the calibrations.

To check the design and condition of turbine gate and blade actuators the servo

pressures are both recorded while the unit is in operation. This is to look for

hysteresis and friction, and as a safety check to make certain the unit will return to

a safe operating condition in the event of a catastrophic failure such as a linkage

pin breaking off or loss of oil pressure.

Strip chart recording is provided to facilitate ASME PTC-29 deadband and

deadtime performance testing; this recorder function can be started and stopped by

internal triggering on collected data stream levels to make these tests easier to

perform.

The ITB has its own 3-D cam routine. By entering the 3-D cam profile that is

supposed to be in the unit under test into the ITB computer, the ITB will provide a

reference blade value to verify the 3-D cam’s ideal blade setpoint values. The

ITB’s StripChart and XY displays will verify the accuracy and robustness of the

blade control and actuator, thus both steady state accuracy and dynamic robustness

can be compared with industry standards quickly and easily with the ITB turbine

control system checkout routines.

A full efficiency profile using the Constant Power method would look like this:

To run the constant power test the procedure is as follows:

1. An operator adjustable bias is added to the control algorithm to allow the

blades to be offset from the on-cam position up to 25%.

2. Governor droop is set to zero so the governor will always hold power, or

flow constant.

3. Blade to gate offset is stepped away from the on-cam position in 1 or 2%

increments with a dwell at each position of 10 minutes.

4. Sometime in that 10 minutes the unit will be steady-state, and the ITB will

glean every steady-state point in the data set.

5. Sorting the head-normalized data points to a common head and then sorting

by power level and plotting the data as shown above creates the overall

efficiency 3-dimensional efficiency profile for the machine.

Doug Albright

Actuation Test Equipment Company

Bibliography:

Reference Materials:

1. Winter, I. A., "Improved Type of Flow Meter for Hydraulic turbines" ASCE

Proceedings, Vol 59, April 1933.

2. Voaden, G. H., "Index Testing of Hydraulic turbines," Transactions of the

ASME, July 1951.

3. Sheldon, L. H., "Field Testing and Optimizing the Efficiency of Hydraulic

Turbines," International Waterpower and Dam Construction, January, 1982

4. Kirkland, J. E. & Brice, T.A.," Checking Turbine Performance By Index

Testing," Hydro Review, Winter 1986, page 49.

5. Hydraulic Turbines and Pump-Turbines, Performance Test Code PTC-18,

American Society of Mechanical Engineers, 2002.

6. Speed Governing Systems for Hydraulic Turbine-Generator Units,

Performance Test Code PTC-29, American Society of Mechanical Engineers,

2005.

7. IEEE Std-125, IEEE Recommended Practice for Preparation of Equipment

Specifications for Speed-Governing of Hydraulic Turbines Intended to Drive

Electric Generators, IEEE Power Engineering Society, 2007.

8. IEEE Std-1207, IEEE Guide for the Application of Turbine Governing Systems

for Hydroelectric Generating Units, IEEE Power Engineering Society, 2004.

9. Sheldon, L. H., "Reviewing the Approaches to Hydro Optimization" Hydro

Review, June 1998, page 60.

10. Albright, D. J., "A little Black Box for Index Testing" Hydro Review,

June 1987, page 36.

11. Albright, D. J. & Mittendorf, G. H. Jr., "Method and Apparatus for

Automatically Index Testing A Kaplan Turbine, U.S. Patent #4,794,544, December

27, 1988.

12. Albright, D. J., "Testing Time for Kaplans" International Water Power and

Dam Construction, June 2008, page 42.

13. 2019-04-

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