Scada Based Automated Control System for Turbo Gas Units

Abstract

Turbo gas units are combined gas and steam turbine. In the turbo gas unit, turbine gets the momentum to run by the appropriate injection of the gas and air in correct proportion. In order to obtain the turbo speed another superheated steam sources are used. Hence in the turbo gas unit turbine control can be controlled precisely by two variables namely gas injected in the fuel stock and the inlet speed of the superheated steam. Since turbo gas units operate at high speeds and often speed varies with respect to changing loads,the acceleration and deceleration rates have to be controlled precisely in order to prevent the turbine vibrations which causes the increased torsional and   shear stresses in the shaft of the turbine. Hence the problem objective is to control the acceleration and deceleration rate by controlling the pressure and temperature for gas inlet and steam inlet by a valve. Earlier methods used make use of the PIDcontrol which controls the fuel gas injection control and steam inlet control. This results in increased vibration during the changing loads. Also when there is sudden change between the reference speed and error the higher control action causes bumps in the controlled outputs. In order to achieve the bumpless control DL450 PLC is used. DL450 PLC has the option of ramp control which can be used with a PID control in cascaded form to prevent the vibration of the turbine. The work proposes to implement the Turbogas unit turbine speed control to minimize the turbine vibration using PLC DL450.The ladder logic is implemented for the speed control and results are compared with other control techniques with only PID as a control unit without cascading it with ramp control.