HYDRAULIC TRANSIENT IN PENSTOCK OF MILD STEEL AND GLASS FIBRE REINFORCED PLASTIC FOR HYDRO POWER PLANTS

Abstract

The power demand in an electric grid to which power generating plants including hydropower plant is connected, may change suddenly for a variety of reasons like grid failure, and disconnect of main load etc. The energy delivered at any moment by the hydro turbines depends on the quantity of water passing through and thus the flow in water conductor system including penstock is to be as per power demand. The velocity of water in the penstock before the change in power demand is related to corresponding discharge. If the discharge and thus the velocity increases or decreases to match the power demand, the mass of water moving in the penstock has to be accelerated or decelerated. The acceleration or deceleration of the water column moving in the penstock is produced and governed by elastic forces developing in the penstock itself. Sometime this phenomenon, popularly known as water hammer or hydraulic transient, caused due to these hydraulic transient may be destructive for both civil and mechanical components such as penstock, valves and turbines of the hydro power plants (HPPs). Penstocks are a major proportion of the capital investment of a HPP project. Therefore, the penstock material is selected not only from the point of view of durability, installation and maintenance cost but with a view to ensuring that the required function and safe performance of the penstock last throughout its life span. The study and analysis of hydraulic transient is necessary for the selection of penstock material, its pressure classes and the specifications of surge protection devices. Formation of hydraulic transient in penstock is greatly influenced by its material. More rigid the material, higher the transients formation and conversely, if the materials are elastic lower transients waves are generated in the penstock.