Critical parameters of hydraulic transient regimes in hydropower plants with complex water conveyance systems Jernej Mazij, Anton Bergant, Uroš Karadžić Litostroj Power d.o.o. Mašinski Fakultet Univerzitet Crne Gore CIGRE , Herceg Novi, Montenegro

Contents: 1. Introduction 2.Transient control 3.Modern analysis approach 4.Case study 5.Conclusions and discussion

1. Introduction Transients….. change from one steady-state to another with change of hydrodynamical and mechanical quantaties Transients can cause damage and jeopardize the economic viability Causes can be forseen or unforseen Interdisplinary knowledge is needed Transient modelling using commercial software Case study of Doblar I HPP  Moste HPP

2. Transient control - I Transients in hydropower plants in the view of impact and probability:  normal,  emergency,  catastrophic (exceptional) The goal of transient load control:  safety of the plant and personnel,  identification of the most severe conditions with adequate measures,  design limits.

2. Transient control - II When to Use Protection Reliability Special Demands Problems in Restarting Frequency of ApplicationCost High pressure Low pressure Surge tank High head, long tunnel/penstockYes Very goodNone Very oftenVery high Air Vessel High head, long tunnel/penstockYes GoodAir compressorRoutine controlRarelyModerate InertiaAll typesYes ExcellentNone OftenModerate RegulationAll typesYes Good High-pressure oil installationRoutine controlVery oftenLow Air Valves Protection of penstocksNoYesGood Frequent maintenance and controlRoutine controlVery oftenLow Aeration Pipes Protection tunnel/penstockNoYesGoodNone OftenLow Rupture Membrane As a last measureYesNoGood Outlet for water discharge Replace membraneRarelyVery low PRVAll typesYesNoVery goodNone OftenLow

2. Transient control - III

3. Modern analysis approach Hydraulic transients are inevitable! Identify → Solve → Treat SCOPE OF ANALYSIS CUSTOMERSTAGE OF DEVELOPMENT TYPE OF MACHINE

4. Case study – Doblar I HPP - I Storage/run-of-river development on the Soča river, Slovenia. Continuous operation since 1939, equipment by Riva Milano for 42 Hz electrical grid. Rehabilitation in period 2011 – Three vertical shaft 13.6 MW Francis units at H n = 42 m. Limit of supply: turbine, spherical valves, spherical valve, generator and auxiliary equipment. Case study of sudden load-rejection.

5. Case study – Doblar I HPP - II Overflow weir Connection tunnel Ellipsed surge tank Cylindrical surge tank Downstream surge tank – NOT ON THE DRAWING! Overflow weir Two side chambers Machine hall

5. Case study – Doblar I HPP - III PROBLEMS!! Lack of as-built documentation Change of ownership (Italy →Yugoslavia) On-site geodetic surveying Refurbishment →Responsibilty of the owner to provide all the relevant documentation.

5. Case study – Doblar I HPP - IV Simultaneous sudden load- rejection of three units. Simplified modelling of a complex surge tank system! Pulse burste radar level transmitter was used for surge tank water level measurements

6. Case study – Moste HPP - I First HPP to begin operation on the Sava River. Continuous operation since 1952, 60 m arch gravity dam is the highest in Slovenia. Combined energy system with the potential of the Završnica Creek. Two vertical shaft 7.5 MW Francis units at H n = 58 m. Limit of supply: turbine, spherical valves, butterfly valve, generator and auxiliary equipment. Case study of sudden load-rejection and closure of the butterfly valves.

6. Case study – Moste HPP - II

6. Case study – Moste HPP - III Simultaneous sudden load - rejection of two units. Beneficial effects of the surge tank Simultaneous closure of the inlet butterfly valves.

7. Conclusions Overwiev regarding hydraulic transients in schemes with complex water conveyance systems. Broad interdisciplinary range of konwledge is required. Two case studies of refurbishment presented, analysis performed using commercial software. Complete documentation is important in cases of refurbishment. Results of the computation agree well with the measured results.

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