DEH Governing OG 660MW Turbine

Google yields this abstract from

http://www.freepatentsonline.com/4471446.html

Each time you come to a phrase or term that you don't understand Google on it and you will know more about this topic than most engineers.

"...A DEH (digital electrohydraulic) control system for a steam turbine generator having a steam bypass system. The turbine system includes a high pressure turbine having throttle and governor steam admission valves as well as an intermediate pressure turbine having stop and interceptor steam admission valves. The turbine is brought on line by initially controlling steam admission into the intermediate pressure turbine by modulating the interceptor valve in response to a speed error signal generated as a result of the difference between actual and a predetermined reference speed. During this initial control the throttle valve remains in a closed position. When the turbine speed has attained a preset value such as half of synchronous speed, the interceptor valve is held at the same position it was in when the preset speed was attained and the throttle valve is controllably open in response to the same speed error signal. After a preset transfer speed has been attained, control of steam admission to the high pressure turbine is transferred to the governor valve and after synchronous speed has been reached the DEH system switches to a load control mode wherein the signal which controls the positioning of the governor valve is also utilized to control the interceptor valve position. The interceptor valve thereafter will reach a wide open position at a predetermined load.

During the speed control mode of operation the control signal which controls the positioning of the interceptor valve is modified by certain pressure conditions at the input of the interceptor valve after the preset speed is attained..."

Normally DEH system supplier gives very good documents to make operation team understand the system. In fact these systems are standard with some tailor made add ons for specific turbines depending on the distance of the control room from the turbine and the requiremnet of controls at the local station.

You can get presentation from the supplier or manufacturer of the system.