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SAFETY SYSTEMS FOR WATER PUMPING WINDMILLS A. KRAGTEN Apsil 1989 ROD ‘Winn ENERGY GROUP ‘Tecate! Univetty Eindhoven Aaborlary of Fis Byun tn Heat Troster al bd Dyannicy a Heat Tras P.O. bar sis 600 MB Bindhoven, the Nethdands Consutancy Services po. ox 05 oe Wind Energy —s800ab amersiocrt Developing Counvies holon CONTENTS List of symbols 1, GENERAL 2, THE PURPOSE OF A SAFUTY SYSTEM 3. OVERVIEW OF SAFETY SYSTEMS 3.1 Systems acting on the rotor blades 3.2 Systoms acting on the whole ator 4. SAFETY SYSTEMS WHICT TURN THE ROTOR SIDEWAYS 4.1 General 42 Non-automatic systorn 4.3 System activated by sideforce only. 44 Reliptic with eoventelcally placed cotor 4.5 Keliptic with auxiliary vane 46 Inetined hinge wnain vane with eccenitically placed rotor 4.7 Inclined hinge main vane with aualiary vane 4.8 Hinged side vane with eccent 4.9 Hinged sida vane with auxil §, THE IDEAL SAFETY SYSTEM 6, DEVIATION FROM THE IDEAL SAFETY SYSTEM 6.1 Rotor ie placed before the towar axis 6.2 Rotor is provided with awaliary vane in stead of eccentricity 5.2 Bain vane has no comstaal moment 64 Other disvurbing effects 6.5 Combination of deviations F 7. DETAILED DESGRIPION OF THRER SYSTEMS TA General 1.2 Moment of eccentrically placed rotor around the tower axis 7.8 Moment of ventricaly placed rotor plas auxiliary vane around the tower axis TA The eolipsic eyster 741 General 742 Ealiptc system with eccentrically placed rotor f08 V < Vaasa 74.3 Ealiptic syste with auailiary vane fot V $ Vesead 7d Beliptie systein with eccentrially planed rotor V > Vy, 7.4. Teliptic system with auxiliary vane for V > V, 740 Example 1.5 ‘The inclined hinge main vane sysiom 751 General 78.2. Example 1.6 The hinged side vane system 16.1 General 1.8.2 ‘The binged side vane system far low wind speeds 7.6.8 ‘The hinged side vane eystem for high wind ypeeds 1.6.4 ‘The hinged side vane system for moderate wind speeds 165 Example ted rated 8, FIBLD MPASUREMENTS 9. SCALE LAWS 10, CONCLUSIONS HITBRATURB ANNEX 1 (TUE internal note 03.88) 101 108 107 LIST OF SYMBOLS (-a) Aur A ay reduction factor of wind speed behind the rotor auxiliary vane area main vane area umber of blades blade chord drag coefficient vane arm drag coefficient WA coeliciens pitch moment ovetficient rotor moment coefficient (around tower axis) auxiliary vane moment cocficient coeificient of rotor moment + auxiliary vane moment normal force coefficient ‘auriliary vane normal force coetficient main vane normal forve eveffiient rotor torque coefficient rotor side force caefficient rotor self orientating moment cocficient rotor thrast coetiicient pipe diameter vane arm pipe diameter rotar diameter drag eccentricity (distance hetwean rotor avis and tower axis) distance between rotor plane and tower a specific values foe f rotor side force rotor thrust at yaw angle 5 bat ated wind speed vane arm deag force “wz a2Z23 RR 4E EE ronan Mex Movs Mr Mray Mapcing ‘aceeleration of gravity (8.81) Aistance between vane asis and tower aris ‘vane weight vane chord perpendicular to vane axis scale fastor aspect ratio Aistance between aerodynamic center and leading edges ofa vane ‘value fori at low wind speeds value for iat high wind spoode srtin size (of pipe zoughnoss) ‘blade length tin pileh moment (of binged side vane) ausiliary vane moment (around tower txis) raoment of vane weight (around vane axis) ‘maximum moment of rane weight (al y= 90°} ‘ain vane momeat (around vane axis) rain vane moment around tower axis main vane moment around vane axis rotor moment (around tower axis) moment of rotor + amliary vane (around tower anit) spring moment ‘maximum spring momeul ‘winimem spring moment spring moment at cettain angle 7 rotor self orientating moment ‘vane moment (around towet axis) vane ara: oment rotor speed normal foree ausilary vane normal force smain vane notmal force Aistance betwcon pring axis and vane axie olor powat zolot torque totor radius (half rotar diameter} suailiary vane radius Reynolds number radius of vane weight in center of gravity nai vane radius vane radius vane Licences ind speed rated wind speed (wind epcod at maximum power) ‘vane chord parallel {o vane axis: Angle of attack, angle between vane chord w and wind direction (at low wind speeds) angle between vane chord h and wind direction (at high wind speeds) — angle of actack auxiliary vane angle of attack main vane angle which determines position of auxiliary vane blade before tower axis - angle of rotation of the main vane around ite axis, ‘maximum angle of rotation of the main vane around itt axis yaw angle (ongle between rotor axis and wind direction) pre-angle between main vane and rotor axis angle between vane axis and vertical ‘angle between vane blade and vertical tip speed ratio (ratio between tip speed and wind speed) unloaded tip speed ratio kinematic viscosity pre-angle of amliary vane pl (8.1416) ait density vane density angle between vane arm axis and rotor axis, angle between vane arm axis and vane axis rotational spoed of the head rotational speed (angular velocity) of the rotor marimum rotational speed rotational epeed at yaw angle & GENERAL, Most Titerature available about safety eystems for water pumping windonlls haa been vesiten by CWD in pacticelar by the Wind Energy Group of the University of ‘Techaology Sindhoven. An overview of all literature about this subject available within CWD has beco prevented in TUE internal note 03-89 [1] (see annex). Th chapter 11 of the CWD publiation 2-1. Introduction ta wind energy [2] some information has been given about stfety systems especially about the inclinod hinge salut vane system based upon the knowledge available up to 1961. It is found 0 be necessary to write this separate publication about safety systems to cover the Jnowledge and experience gained by CWD in the period 1981-1680 However, even this publication ean not claim co be 2 complete collection of all {information availabe in all separate reports a6 mentioned in annex T. Chapter 2 till 6 and chapter § till 10 give more general information ahout salety systems and can be anderetoud by under graduates ‘Chapter Tin which three safety systems have been descsibed is more complicated and hus 4 more mathematical orientation. 2, TIE PURPOSE OF A SAFETY SYSTEM ‘Windmills without a safety system usually have a short Ife, An exeention can be made for very sualt windills with a diameter less then onc meter which cam be mate 40 strong or have a tower which is so low, that they can survive cay storms, Normally a well designed safety system is required which must perform three Iunetions 1, Limitation of the axial force or thrust on the rotor. ‘Too high a thrust can cause the following problems: 2. The bending momont and therefore the bending stress in the rotor syary becomes ‘oo high which results in blades snapping off b, ‘Ihe bonding moment in a tubular tower. or the buckling force in the guy wires of & guyed tower can become too high which con cause collapse af the tower ot pulling the foundation out of the ground. 2, Timitataon of the rotational speed of the rotor. ‘Too bigh a rotational speed can cause the following problemns: a. High centrifugal forces in the blades resulting in high tensile forces in the blade spars. ‘This cam result in layaching of one of the blades, leaving behind an ‘unbalanced machine which soon will logte other blados or even the tatal head. 1. A high rotational peed im combination with a emall nbglanee of the rotor causes strong vibrations which can resull in high fatigue loads in several windmill ‘components like blades, rotor shaft, head bearing, vane arms cte, . A combination of « high rotor specd and a bigh yawing spocd of the head gives rise to high gyroscopic moments in the blades and the rotar shad. 4. Tigh tip speeds can introduce 9 dangerous aero-clastic behaviour called "utter", ‘Thia is a combination of sovere torsional and bending vibrations in the blade. 1k specially cecurs in tall blades with a small tortion stifiness of fast running cotors. ©. Tn case of water pumping windmills the high pmp frequencies lead to a hight pump rod forve in the transmission from pump rod ta rotor shaft ‘The bigh pump rod force is caused by high acceleration foroes and shock forees due ‘to delayed closure of the valves. 4. Litulation of the yawing speed (rotation of the head around (he tower axin) A high yawing apced results in a high gyroscopic moment (see pt 2) Most safety systems have & direct inluence ow the axial force on the rotor and an the rotational speed, ‘The inluence on the yawing speed ia more indirect. 1 depends on the (V curve of the system (see chapter 7), the inertia of head and vane and the variation in wind speod aud wind dizetion