1. Assessment of hydropower system safety using a systems approach and dynamic resilience
June 27, 2017
Civil and Environmental Engineering

2. Introduction

3. Dam Systems

4. Dam Systems Operator Operating decisions Reservoir level sensors
Turbines
Inflows
Spillway Gates
Outflows

5. Dam Systems Operator Operating decisions Reservoir level sensors
Turbines
Inflows
Spillway Gates
Outflows

6. Dam Systems

7. Traditional Risk Assessment
Shortcomings:
Linear event progression (eg. event tree) that ignores interactions and system feedbacks
Subjective judgement for selection of events and their likelihoods
Events assumed to be independent
Emphasis placed on failures when control flaws or design errors can be just as dangerous
Systems decomposed to make them more manageable
Human failures and software flaws difficult to deal with
Focus on edge of design envelope events (low probability)

8. A New Approach Viewing system safety as a control problem
Using simulation to assess outcomes of the full range of operating conditions, putting possibilities ahead of probabilities
Using dynamic resilience to assess safety outcomes of simulation

9. Methodology Overview

10. Project Methodology
Generic control system base structure (adapted from Leveson, 2011)

11. Project Methodology
Generic control system base structure (adapted from Leveson, 2011 for a hydropower system)
Input scenarios of starting reservoir elevations and system states
Base structure converted into simulation model that includes the detailed system structure, feedbacks and interactions
Simulation outputs used to assess resilience and develop improved mitigation and response strategies

12. Project Methodology

13. Project Methodology
Use of Systems Theoretic Process Analysis and component functions Database to come up with scenarios

14. Project Methodology
Deterministic system dynamics simulation engine to derive scenario outcomes

15. Simulation Model Sectors
Generic control system base structure (adapted from Leveson, 2011)

16. Simulation Model Sectors
Example: Hydraulic system state

17. Project Methodology
Processing of simulation model outputs to extract useful information about safety, which can be used to refine and improve response and mitigation strategies

18. Resilience Replacement of static risk estimates
Focus on system performance before, during and after disturbance event
Explicit consideration of system’s adaptive capacity
Development of preventative strategies and emergency response plans

19. Resilience
System performance used to calculate resilience with respect to safety (need to define safety performance measures)
Transformation
4Rs – Redundancy, Robustness, Resourcefulness and Rapidity
Damage and propagation / Evolution and Recovery
With and without restoration