3a appendix- ifp-flow discharge equipment reliability

7/29/2019 3A Appendix- IfP-Flow Discharge Equipment Reliability

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Summary Report of

Workshop on Reliability of Discharge EquipmentCEA Dam Safety Interest Group

Montreal, April 30 & May 1, 2001.

1.0 Introduction and Overview

This 2-day workshop was organized by CEA Technologies' Dam Safety Interest Group (DSIG) in response

to an OPG proposal made at the 2000 Fall DSIG meeting. Mona Bechai and Klaus Faisst of Ontario Power

Generation and Tai Mai Phat of Hydro Quebec were the workshop organizers. The objectives of the

workshop were to:

• Document current Dam Safety Design Review Standards and Criteria for discharge equipment.

• Document current methodologies and procedures for testing of discharge equipment and remote

control systems in actual or simulated adverse conditions.

• Identify reliability requirements for remotely operated equipment.• Identify problem areas in operation and reliability of discharge facilities.

The workshop was attended by 42 delegates from 14 companies/organizations, including two other CEA

Technology Interest Groups, the Hydraulic Integrated Resource Management Interest Group (HIRMIG)

and the Hydraulic Plant Life Interest Group (HPLIG).

The workshop featured 19 presentations on reliability issues with flow control equipment, including the

present state of practice, lessons learned and experience by the member countries. The last half-day was

structured as a panel discussion with the focus on common needs for future research and developmentopportunities. The panelists were:

Gary Salmon, Technical Coordinator DSIG (Chair)Don Coulson, Vice President, RSW

Bill McStraw, Senior Mechanical Engineer, USBR

The entire content of the workshop has been recorded on Compact Disk (CD-ROM in pdf Format) and

copies of the CD have been distributed to all participants. The content has been set up in the following

sequence:

• Summary Report

• Agenda

• 19 Presentations (in sequential order)

• List of Participants• Presentation Outlines and Biographies

• Invitation to Workshop



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2.0 Highlights

The highlights recorded in this summary report have been sorted into five topics:

- Risk Analysis as a Tool for Reliability Evaluation

- Inspections, Tests, Condition Assessments and Maintenance

-

Design Reviews- Human Factors and Operator Training

- Lessons Learned

2.1 Risk Analysis as a Tool for Reliability Evaluation

The spectrum of opinion expressed by workshop participants on this topic varied widely.

Marty McCann from the U.S. National Performance of Dams Program (NPDP) explained that risk analysis

is successfully practiced in other industries (e.g. Aircraft, Nuclear, Chemical). Although a component

reliability estimate is unlikely at this time, risk analysis can still be a useful tool for reliability evaluation,

because it can show which items are more critical than others , some times by an order of magnitude.

The U.S National Performance of Dams Program has a wealth of information on dam incidents, even

though, only a fraction of all incidents is being reported (perhaps 20%). The available information can be

used to support engineering assessments; e.g. failure events of gates and valves (number of events vs. type

of reason).

In Sweden, risk analysis is not yet considered a well-established tool for dam safety, mainly because of the

complex behaviour of the civil parts of the dam. Electrical and mechanical components are easier to deal

with.

Scottish & Southern Energy (S & SE) have introduced risk analysis in 1996, using a simplified FMECA

approach. Equipment components are numbered for systematic analysis and numerically evaluated for

their probability of failure. This value is then multiplied by an estimated "severity of consequence factor"

"and an assumed "likelihood of detection" factor, to arrive at a numerical criticality value for that particular

element or component. A composite criticality score for the entire discharge system is then computed from

the criticality values of the individual components. As a result of the assessment process S & SE have been

able to produce a planned form of action to rectify highlighted problems and investigate areas where

knowledge is lacking as part of their asset management program.

The USBR includes loss of human life in their risk analyses. They have some 3,500 gates and valves on a

database and use the database for prioritization of refurbishment work. However, meaningful numbers and

a methodology has yet to be developed in order to apply risk analysis as a tool for reliability evaluation.

FERC doesn't have much comfort in numerical analysis of risk and wants to "divorce" risk analysis from

reliability evaluation.

In Australia, recent studies of spillway gate failures show that reliability assessment should consider not

only equipment condition and performance but also human factors, poor design and policies. One of thehindrances in quantifying gate reliability is the lack of information on equipment performance and failures.

EDF (France) has lots of data for risk analysis in the nuclear field, but no comparable database in

hydroelectric. The principal in making risk analysis a useful tool for reliability evaluation is good but more

work at the foundation and training is required.



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Ontario Power Generation observations are that failure rates exist for all kind of components; e.g. motors,

breakers, relays. However, there is no specific data bank on discharge equipment failures because

components and discharge systems are very site-specific with respect to their evaluation parameters; e.g.

type, size, age, manufacturer, environment, life cycle use, maintenance history. A standard procedure is

needed by dam owners to enter component failures into a shared data bank. This will require a free

exchange of experience and information by a pool of contributors.

Other Comments and Observations by Workshop participants:

- Not all gate failures lead to catastrophic consequences.

- Large, high profile gate failures such as Folsom reduce public confidence in the industry.- Risk factors should determine inspection rigor.

- Many mechanical systems fail without prior warning.

- Gates can fail in both open and closed position. Hence, the upstream and downstream consequences of

each failure scenario must be considered.

- Most electrical component failures are random failures (not predictable). Therefore, all critical

components should be backed-up by redundancy.

- Companies are down-sizing, hence corporate knowledge is getting lost which impacts on reliability.

- Contracting out of equipment maintenance is on the increase, hence there is potential for conflict

between plant staff and outsourcing, with potential for more human errors.- De-regulation will bring a reduction of people and more telemetry.

- As we add more and more programmable logic controls (PLC's) we are loosing the "feel" for the

equipment.- Evaluation of the reliability of discharge facilities is a very important part of an overall risk assessment

for a dam.

2.2 Inspections, Tests, Condition Assessments and Maintenance

The workshop presentations and discussions confirmed that periodic inspections, tests, condition

assessments and proper maintenance are the most conventional methods to demonstrate system and

equipment reliability.

Scottish & Southern Energy is using the results from inspections, tests and condition assessments on two

fronts: (a) risk assessments for dam safety and (b) prioritization of refurbishment work. Inspection results

for key components are recorded on standardized data collection sheets, specifically developed for gates.

This asset management approach has identified the need for regular inspections of gates and valves both

for safe operation and to determine long term maintenance and refurbishment plans. A program of

inspections has been established based on the following format: weekly visit and visual check by operative;

3 monthly test operation by operative; yearly test operation by engineer; and 5 yearly engineering

inspection.

Hydro Quebec has three inspection levels:

- Routine inspections: 1 per year, mostly for electrical and mechanical components of heated gates.

- Regular or limited inspections: 1 per year to 1 per 5 years, to check gates, stop logs, gantry cranes,

cable hoists and other components. This includes a full or partial (at least 10%) opening testing.- Full Inspection: 1 per 10 years, synchronized with a facility reviews.

The USBR is using qualified engineers for inspections, condition assessments and ranking of priorities.

Test results for 3,500 gates and valves are stored on a database. The USBR's state of practice is:

- Test all system initiation modes for gate operation (local, remote, back-up power).- Test headgates under full unit flow.

- Measure and record motor currents on gate hoists as an indicator of lifting forces.

- Verify all calibrations.



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Hydro Quebec, the USACE and the USBR are collaborating in the development of a condition indexing

technique to gauge the condition of discharge equipment and to prioritize maintenance requirements. In

condition indexing, the weak elements (links) are identified. The failure potential of each element is

evaluated. The concept is based on a standard framework of tests and measurements, systematic

inspections and available site information from operating and maintenance personnel, and is then tailored

as required to fit a specific site.

The Australian Practice is to open gates fully where practical once a year, partly open some gates every

month. Unfortunately, test results are not yet consistently recorded.

FERC's Practice:- Visually inspect each gate (Tainter Gate Initiative).

- Test often enough, analyze equipment for design deficiencies.

- Measure electric current drawn by motors during gate lifts.

- Five year safety inspections by independent consultants.

- Yearly site inspections by FERC staff (operations inspections).

- Five year full-height gate tests.

- Yearly certification of gate operation.

- Inspection efforts are based on consequences of failures.

- Yearly participation in conferences/workshops on discharge equipment.

FERC has asked the Licensee's to document their lubrication procedures, in particular for trunnions of

radial gates (Tainter Gate Initiative).

Ontario Power Generation has two levels of tests and inspections:

- Functional Tests, carried out once per year, consisting of limited inspections and partial opening of all

flow control devices.

- Design Tests, carried out during periodic reviews (every 5 to 7 years, depending on the structure's

Incremental Consequence Category), consisting of a thorough inspection and full opening of the flow

control device under design conditions. In the future, the embedded steel components and the

normally inaccessible parts of the gates will also be included in these inspections. In addition, design

checks will be carried out on system components affected by wear and deterioration.

Ontario Power Generation has initiated a maintenance program known as Streamlined Reliability CenteredMaintenance (SRCM), which is really a qualitative reliability-centered approach. It's main objective is to

reduce the incapability factor of all production and discharge facilities. Maintenance is done according to

assumed criticality measures. System components (e.g. gates, hoist motors, power supplies) are assigned

criticality ratings based on regulatory requirements and experience (subjective judgement by joined staff).

Component failures, as well as corrective and preventive maintenance for all hydroelectric plants will be

entered into a data bank. Once completed, the data bank should provide valuable information on type and

frequency of failures.

Operation and Maintenance Manuals should be updated every year.

Maintenance (and testing) of discharge equipment at N.B. Power is done prior to spring run-off.

Proper maintenance/inspections inside of some of their larger spillway gates is not possible because of confined space access restrictions.

To enhance overall reliability of retrofitted control systems, BC Hydro is subjecting new system

components (new on the market) to extensively bench tests prior to their installation in the field. Some are

subjected to seven different tests to verify their reliability prior to site installation.



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2.3 Design Reviews

In FERC's definition a design review should identify the consequences of failure, the failure mechanisms

and the required analyses for a given failure scenario.

The USBR is performing selective stress analysis with earthquake loads, mainly on older gate designs.

Their experience and recommendations are:- Tainter gates are most at risk.

- More stress analysis with realistic seismic load assumptions needs to be done, particularly on high

dams.

- Vertical lift gates are not nearly as much effected by seismic loads.

- Re-evaluate margin of reserve on factors of safety.

- Re-evaluate welded joints from inspection results.

- Prof. Wilson (California) is doing finite element stress analysis for the USBR.

- More research is needed in this field.

- Design reviews on headgates and intake gates should also include an air vent analysis, particularly on

older designs, to re-evaluate negative pressure in tunnels and penstocks on emergency gate closure.

Hydro Quebec's Recommendation:

A design review should identify the "weak links" in the system, which in their experience has been:

#1: Loss of power supply - must have redundancy

#2: Problems with gate lifting mechanisms

#3: Gate jamming (poor tracking)

In Sweden, where discharge facilities are generally remotely controlled, the weak links were reported to be

in the control system.

As part of a design review, Ontario Power Generation is studying potential benefits and consequences of

reduced gate heating in winter. If a plant has, say, 10 sluice gates but requires only a fraction of that

number to handle load rejects plus winter flow conditions, the remaining gates could be allowed to ice up if the gates can withstand the ice loading.

Comment by Don Coulson on "Old Gates - New Standards":

Older structures are usually not designed to meet to-days standards (e.g. ice loads, seismic). However, their fitness for service can still be evaluated against the background of past performance, operation &

maintenance history and their present state of repair based on tests and inspections.

BC Hydro's reliability improvement projects at Seven Mile Dam and John Hart Dam were identified as

good example available for a reliability case studies. They include a review of the design criteria and

reliability improvements at existing dam sites to "best industrial practice". The improvements included

multiple sensors with a "majority vote" to trigger an action; e.g. to open sluice gates before the reservoir

reaches the critical maximum operating level.

2.4 Human Factors

BC Hydro and NSW (Australia) have highlighted the importance of the "Human Factor" in risk assessments. NSW have consulted a human psychology expert on the subject who concluded that the probability for human error is 3 times higher than for others failures. The USBR and FERC are taking

steps toward formal certification of discharge equipment operators as a measure to enhance overall system

reliability.

Some failure examples, when analyzed, sound like a conspiracy (accumulation of circumstances + random

bad luck + mistakes). For instance, at one dam site the power supply from a transformer to a gate hoist

motor had the phases wired up in reverse. Hence, pushing the raise button made the gate go down and vice



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versa. The reverse phase condition remained unnoticed for seven years. In another example relevant to

risk analysis, power to a gate hoist motor was unavailable when needed due to maintenance of a component

of the power supply system. This occurred in spite of the fact that the system had nine alternative power

sources for this motor.

2.5 Lessons Learned

Saguenay Flood (Quebec)

Following the Saguenay Flood in 1996, and conclusion by the Nicolet Commission, Hydro Quebec is

putting more emphasis on:

- Re-evaluation of hydrologic risks under different floods, up to PMF.

- Systematic inspection, testing, maintenance and rehabilitation of spillways and outlet works.

- Wider sluice flow passages (at least 4 m) to pass large floating debris and sunken tree stems (Sweden

considers 7 m a minimum width, based on physical model studies).

- Replacing wooden stop logs with metal gates (to permit gates to be opened under high reservoir

levels).

- Alternative power sources for gate hoists.

- Access to gate structures at all times.

- Strong cooperation and involvement by all disciplines (civil, mechanical, electrical).

Folsom Dam Spillway Gate #3 Failure (1995)

- This Tainter gate failed due to strut arm end moments, which were not considered in the original

design ( design deficiency).

- The end moments were produced by trunnion friction, however, lubrication was not clearly deficient.

- The design deficiency could not be detected by visual inspection.

- Strut arms were slender and not well braced.

Carlos Zumaran, (Hydro Quebec) reported on a drum gate refurbishment project. The gates were 8 m wideand featured a self-actuating operating mechanism with a counter-weighted wire rope & pulley

arrangement. This simple system has been working problem-free without operators and communication

links for 71 years, confirming the point that reliability can also be found in simplicity.



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3.0 Conclusions

Reliability Guidelines

There was modest support from workshop participants to the idea of developing reliability assessment tools

geared to discharge facilities with emphasis on condition assessment and indexing techniques, as opposedto an abstract numerical analysis.

• The HIRMIG and the HPLIG will investigate their member's support and report back on their Group's

interest in participating towards this development.

• Hydro Quebec, the USACE and the USBR have an ongoing project on condition indexing. Hydro

Quebec will contact S & SE to discuss potential co-operation. Hydro Quebec may be in a better

position to report on their efforts at the next DSIG meeting.

Inspection and Testing

• Pre-inspection work should include review of maintenance and repair history, operating and

maintenance manuals, flow charts, EPP manuals and information from field staff. It should alsoinclude interviews with operators to check their knowledge.

• Inspection and testing should be scheduled to obtain maximum information.

• Testing should be done of all systems (including redundant ones) and should include a calibration

exercise of remote as well as local/actual read-outs.

• Tests must be performed and documented by qualified engineers and technicians.

Design Reviews

• Inspections and testing alone will not reveal all deficiencies. The original designs must be reviewed

and compared to current standards (for seismic loading, ice loading, etc.)

• Feedback on shortcomings and design deficiencies must be given to designers of new gates to avoid

future problems.

Human Factors / Operator Training

Dam operator training should cover:

• Theoretical subject knowledge.

• Knowledge of the specific site and systems characteristics.

• Refresher training and simulation of emergencies.

• Personnel should be certified before they are permitted to operate emergency discharge equipment.

• Sweden is developing a simulation river model that could be very useful in operator training. There is

considerable interest from some workshop attendees in this model.



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Abbreviations:

ANCOLD Australian National Committee on Large Dams

ASDSO Association of State Dam Safety Officials

BC British Columbia (Canada)

CEA Canadian Electrical Association

DSIG Dam Safety Interest Group

EDF Electricite de France

EPP Emergency Preparedness Procedure

EPRI Electric Power Research Institute

FERC Federal Energy Regulatory CommissionFMECA Failure Mode Effects and Criticality Analysis

HIRMIG Hydraulic Integrated Resource Management Interest Group

HPLIG Hydraulic Plant Life Interest Group

NPDP National Performance of Dams Program (Stanford University, California)

NSW New South Wales (Australia)

OPG Ontario Power Generation

PMF Probable Maximum Flood

S & SE Scottish & Southern Energy

USACE U.S. Army Corps of EngineersUSBR U.S. Bureau of Reclamation

3a appendix- ifp-flow discharge equipment reliability

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