Message from Chairman PEC Engr. Dr. Muhammad Akram Sheikh

ENGINEER PEC September 2007channel. The only difference is an additional lake at thelower end in which tail water is stored up for pumping in theexisting powerhouse, additional machinery has to beprovided for pumping. Reversible units would be used fornew powerhouse. The conduit system in some cases hasto be designed for the two-way movement of water. Thetransmission lines connecting the powerhouse to the gridcan also be used to draw power from the grid duringpumping operations. Figure-8, typically represents thepumped storage scheme configuration.Why pumped storage/generation?Electricity itself cannot be stored, but the potential togenerate electricity can ---- for example, in a battery.Pumped storage plants provide a way to store the potentialenergy of water. This enables meetings peak powerdemands by pumping tail basin water to upstreamreservoir during low demand period and utilizing thisadditional water to generate electricity during peakdemand period of the day.a. Economic Justificationi. Many countries have a special tariff for peak-loadpower which is about 2 to 3 times more than thenormal tariff. In future, a similar situation maydevelop in Pakistan. Therefore, the plant can bemade to earn additional revenues because of theconversion of cheap off-peak power to costlierpeak power. These revenues can pay back theinvestments made in the plant.ii. The alternative of generating peak power by usingfossil fuels is prohibitively costlier.In the year 2000 the United States had 19500 MW capacityof pumped storage. They consume more power filling theirreservoirs than they generate by emptying them. Still thetechnique is considered a worthwhile addition to theelectrical grid as the most cost effective means forregulation of electrical power.Load Factors (LF) of Tarbela, Mangla and GBHP at 4Representative Days and the Average Daily LoadFactor (LF) Table - 2DateTARBELA% LFMANGLAGHAZIBAROTHAJan 10, 04 16.3 41.1 33.1Apr 20, 04 31.3 78.0 57.4Aug 20, 04 94.7 46.0 87.2Dec 20,0444.1 53.6 29.3Averagedaily LF46.6 54.675 51.75b. Need of Reserve PlantThe base units are deficit in providing the peak demand.The deficiencies of a base unit can be over come byproviding pumped storage as an auxiliary plant whichshould be able to perform following functions:-i. To generate peak power quickly and efficientlyduring the peak demand periodii. To create an artificial load during low demandperiod and to improve the load factor of the baseplantiii. To adjust the power generation to match the loadfluctuations of the networkiv. To be able to take the full load quickly from thestand-still or from shut down position.ConstitutionThe plant has most of the components of a normalhydroelectric plant namely the high level lake, the powertunnel or penstocks, the powerhouse and the tail race26