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NEK IEC TS 63111:2025

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Abstract

This Technical Specification (1) describes hydraulic transient phenomena of hydro turbines, storage pumps and pump-turbines and the factors that affect them, (2) provides modelling and measurement best practice guidelines and resulting limitations (3) defines relevant equipment design criteria, and (4) identifies potential mitigation solutions. Definitions of the relevant terms and quantities are provided along with descriptions of the system components that are considered.Various types of hydraulic transient phenomena are covered in the current specification, including waterhammer, surge tank mass oscillation, and speed variation of the hydraulic machine for operational modes such as start-up, normal shutdown, emergency shutdown, and load rejection and acceptance. Combinations of the individual transient modes are also considered. The links between these transient characteristics and operation across the relevant quadrants for each machine type are illustrated. Methods for mitigating extreme transient values of pressure, surge tank water levels, and unit rotational speed are suggested.In this Technical Specification, abnormal transient phenomena are also defined and described, including component malfunction and catastrophic events like component rupture. The probability of the occurrence of these extreme events and how this can influence the relevant safety margin is described.Different stages of hydroelectric development correspond to unique sets of available data with differing levels of detail and uncertainty. The various stages of project development are described in relation to transient analysis. The corresponding uncertainty margins associated with each stage and analysis technique are discussed.This Technical Specification provides guidelines and commonly accepted practices to model and compute transient conditions. It provides a summary of the basic hypotheses and equations, together with relevant characteristic quantities and system time constants. Accepted methods of modelling hydraulic components, and related numerical simulation methods are identified. This specification details the input data, including best practices for model testing of hydraulic machines, valves, gates, etc. to acquire reliable transient modelling.Different calculation methods with different levels of uncertainty are described so that the most suitable approach for the available data or project stage can be selected. Limitations of one-dimensional modelling methods are described. Additional means of investigation, such as physical model tests or CFD computation, can be used to improve the simulation results.For various configurations of equipment and operating regimes, typical scenarios for consideration are defined.Procedures to determine uncertainty margin, with respect to the modelling and computation methods and available input data are described.Finally, this Technical Specification describes methodologies for on-site measurements with respect to transient such as load rejection tests, runaway tests, etc. Recommendations are provided for quantities to be monitored during these tests, with related instrumentation, calibration and data acquisition systems. Procedures for comparing on-site measurements with numerical simulation results are proposed.Note that the following aspects influence hydraulic transients and are therefore introduced; however, the associated modelling and related design guidelines will not be addressed in the Technical Specification:waterway design and optimization;upstream and downstream free surface flows;fluid structure interactions;cavitation and water column separation;unsteady friction and viscoelasticity;two phase flows;turbine governor design;flow induced pressure fluctuations.

Document information

  • Standard from NEK
  • Published:
  • Edition: 1.0
  • Version: 1
  • Document type: TS
  • ICS 27.140
  • National Committee NEK/NK4

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  • Adopted from: IEC TS 63111:2025