Assessing the Operation of the Cooling Water System of a Hydro-Power Plant Using EPANET

Abstract

This paper focuses on the Cooling Water System (CWS) of Vidraru Hydro-Power Plant (HPP) − a 220 MW underground HPP, on the Arges River in Romania. It is equipped with 4 high head vertical Francis turbines of 55 MW each, 4 hydropower generators of 61 MVA each, and 7 step-up transformers of 40 MVA each. The goal is to model the above CWS and to analyse the system response under normal and critical operating scenarios. The numerical model built in EPANET is complex: the cooling water network is normally fed by pumping from the underground tailrace (using up to 3 pumps of 110kW each), but there is a backup supplying circuit fed directly from the penstock bifurcation pipe (using pressure reducing valves). Within the power plant, the following equipments need cooling water: air-water heat exchangers (related to generators and HVAC system); oil-water heat exchangers (related to bearings, speed governors and transformers); coolers of the turbines seals. Since EPANET lacks such physical components, they are artificially replaced by throttle control valves set with equivalent loss coefficients, established upon pressure drop values available for each equipment. The computed flow rate and pressure values match the existing recordings for normal operation. The numerical model also provides data on the system behaviour under critical operation conditions, e.g. when the HPP is operating at full capacity with CWS fed only by 2 pumps, out of 3 available pumps.