SURGE TANKS FOR HYDEL POWER STATIONS

Abstract

The Surge Tank is provided in most hydroelectric schemes with long conduit system. Power systems are always liable to sudden load changes giving rise to water hammer pressures in the conduits, Surge tank will limit the influence of increased pre-ssure to the section of the conduit between the power house and the surge tank, It also serves the auxiliary and complementary purpose of storing the water diverted or needed by those load changes, The various types of surge tanks most commonly used are dealt herein. The magnitude, period and duration of surging which are the primary hydraulic design requirements, determine whether the design is acceptable for the turbine and conduit system. Normal design methods are based on approximations from a basic diffe-rential equation, which is itself not soluble directly. By making various simplifying assumptions it is possible, however, to develop equations or charts that can be used for preliminary design purposes. Thoma produced a solution of the basic equations in si npli - fied form. This equation gives the minimum area of tank nece-ssary for the surges to be dapped out. In practice, at least 25 percent should be added to the Thoma Area for safety, Further work on these equations has been done by Frank and Schuller, Paynter, Evangelisti, Jaeger, Zienkiewicz, Marris, Sideriades, Ruus &c. Various methods of solutionof the basic equations have been attempted. A direct solution by ignoring the friction effects in the conduit is mainly of academic interest but has been des-cribed by Jaeger and Stucky. Calame and Gaden, and Warren re-placed the square law friction equation by a linear function, which gave approximate solutions or charts suitable for prelimi-nary design or comparison purposes. Pressel made the same substi- tution but used a graphical method. Jurney made a 'least square fit' and Johnson a 'modified linear substitution', again leading to approximate solutions. In order to obtain an accurate solution some form of step- by-step integration is necessary. The basic arithmetical method was used by ,Johnson and improved upon by Escande; this _ method is especially suitable for use with digital computers. Calame and Gaden devised a graphical integration technique using relative value,, whilst Schoklitsch,.. Church and Leiner, all developed their own graphical methods. Gibson has developed the technique for scale-model experiments on surge chambers in which the vertical scale is .exaggerated. Various methods of Surge Analyses and their applicability to different types of surge tanks togetherwith stability criteria have been compiled and discussed in detail..