Arab J Sci Eng DOI 10.1007/s13369-016-2142-2 RESEARCH ARTICLE - CIVIL ENGINEERING Investigation of Waterhammer Problems in Wind-Hydro Hybrid Power Plants Ali Ersin Dinçer 1 · Zafer Bozku¸ s 1 Received: 17 March 2015 / Accepted: 14 April 2016 © King Fahd University of Petroleum & Minerals 2016 Abstract Sudden flow changes in confined pipe systems generate transient flow (waterhammer) conditions accompa- nied with very high or sometimes very low pressures traveling back and forth in the system. Depending on the magnitude of those pressures, pipe collapse or pipe bursting may take place at the weakest points of the system, resulting in costly damages as well as loss of human lives in some cases. In gen- eral, it may be encountered in the penstocks of hydropower plants, water transmission lines and water networks, etc. It is essential that the safe operation guidelines of the hydropower plants be defined accurately, in advance. To achieve that, de- tailed numerical simulations should be done with reliable software. In some cases, even physical modeling may also be necessary. In the present study, waterhammer problems in the penstocks of Yahyali Wind-Hydro Hybrid Plant are in- vestigated (the construction of the plant has not started yet). Time-dependent flow conditions in the penstocks are simu- lated by the help of computer software. It solves nonlinear differential equations by using the method of characteristics that uses the principles of finite difference method. Firstly, hydraulic transients for various operational cases are inves- tigated using some scenarios. Then, a surge tank, protective device, for waterhammer, is added to the system, and for the same operational cases, hydraulic transients are studied again. Keywords Waterhammer · Hydraulic transients · Pumped- storage hydropower plants · Wind-hydro hybrid systems · MOC B Ali Ersin Dinçer aliersin@metu.edu.tr 1 Department of Civil Engineering, METU, Ankara, Turkey 1 Introduction Energy is the key for social and economic development of any country. The major part of the energy is obtained by fossil fuels. However, renewable energy has gained a great importance, since it is abundant in the nature [1]. The ten- dency of the renewable energy will surely increase, because the cost of electricity from renewable energy has decreased and in the future it will certainly decrease more [2]. The most important part of the renewable energy is generated by hy- dropower plants (HPPs). The increase in the number of HPPs is remarkable, but not enough. This is because the demand has been more than the supply. Especially for the peak times, which are the hours when the electricity demand is the high- est, the energy generation may not be enough. Therefore, the energy generation should be increased during the peak hours. This can be achieved by operating HPPs during these times. However, this may still be not enough. The other solution is to operate pumped-storage hydropower plants (PSHPs). The main purpose of the pumped-storage systems is to store elec- tricity in terms of pumped water in a reservoir when the price of electricity is low and generate it when the price is high. De- veloped countries, like Japan and USA, have increased their pumped-storage capacity. According to 2009 data, Japan has the largest pumped-storage capacity around 25.5 GW and USA has 21.5 GW generating capacity [3]. Wind energy is also used as a renewable energy. Europe, having nearly 29,000 MW wind energy production, was pre- viously the leader in the energy market of the world, but in 2009, Asia took the lead with the great contribution of China [4]. The wind energy capacity of Turkey is one of the high- est in Europe. Despite the potential, the use of wind power was 20 MW in 2005. With the Law of Renewable Energy Resources in 2005, the installed capacity was increased to almost 150 MW just in 2 years. As of January 31, 2014, the 123