Implementation of the Automatics for Switching the Combined-Cycle Plant of Power-Generating Unit No. 5 at Hrazdan Thermal Power Plant to the Steam Power Plant and Gas Turbine Modes

The article describes an automated technology put into practice for switching power-generating unit no. 5 at Hrazdan Thermal Power Plant from the combined-cycle plant (CCP) mode to the steam power plant or gas-turbine unit (SPP and GTU, respectively) modes upon an emergency shutdown of the gas or steam turbine. The layout of the power unit based on the waste-gas heat utilization scheme enables the thermal power plant to operate with a partial mix of the equipment, viz., without the gas turbine or steam turbine. However, the initial project did not provide for changing the operational mode without the total shutdown of the power unit. During a sudden shutdown, the considerable unit output of the power unit results in considerable disturbances in the entire electric power system of the Republic of Armenia. The maintenance of a partial capacity of the power unit under emergency shutdown of the equipment reduces unwanted consequences for both the power plant and the electric power system as a whole. A great scope of urgent switching operations and changes in the automatic regulator settings upon sudden shutdown of the gas or steam turbine makes successful actions of the operator under the manual changeover from the CPP mode to the SPP or GTU modes unlikely. Such a changeover can be performed only by the automatics with the operator performing fine correction of the mode upon completion of first-priority switching operations if necessary. The appropriate algorithms for automatic change of the mode when shutting down the gas or steam turbine were implemented in the Automated Process Control System (APCS) of the power unit. In the article, the basic scope and the sequence of actions performed by the automatic devices upon shutting down the gas or steam turbine, as well as the principles of automatic adjustment of the circuits for automated control of the fuel-to-water and fuel-to-air ratios and the temperature conditions of the boiler, are set forth. The article also provides the results of full-scale tests and an example of the behavior of the basic parameters upon shutting down the gas turbine and switching the power unit over to the SPP mode.