CFBC BOILER KNOWLEDGE

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steam turbine speed control governor

In a Steam Turbine system we control it's speed that is Turbine needs to rotate at fixed speed. Now if we want to add some additional load say if we want to raise its Power output, speed will tend to reduce as equivalent amount of heat energy is not available at that moment . Now at that condition we have to introduce more steam that is heat energy to increase that load maintained at the same speed. Now how that steam will be introduced in the turbine either someone has to operate the control valve or through some mechanized arrangement. that mechanized arrangement is its governing system. Which is either hydraulic or electro hydraulic . 
Now take the case of load increase as the speed of the turbine tends to decrease, in case of a fully hydraulic governing system , a pump which is mounted in the governing system through some gear arrangement at turbine main shaft receives oil and produces a fixed discharge pressure(This is your primary oil pressure) corresponding to the preset rotation per minute,  will also reduce as when the speed of the turbine reduced , the pump speed also reduced as it is coupled with gear arrangement. This reduced oil pressure will facilitate to introduce more secondary oil pressure in to the pilot valve which is through its hydraulic piston system will open steam entry valve to turbine , as more stem will enter into the turbine its speed will increase, now two phenomenon will occur simultaneously, primary oil pressure will rise as turbine speed has increased and one feedback mechanism fitted in the pilot valve will restrict pilot valve movement and controlled secondary oil will try to maintain the rated speed. 
Now it is the function of secondary oil and primary oil. 
Now how to protect the turbine if we want stop or trip the turbine when it is dangerous for the machine. This is the function of the trip oil. Trip oil generates from control oil which is through some mechanical device and through some solenoid valves are routed throughout the governing system. It has the mechanism to be drained rapidly so trip oil drains and blocks the oil passage of control oil. Mostly by spring arrangement steam stop valve(ESV) and control valve(regulating valve) stem stops to turbine. 
ANY HOW THIS ARE VERY BRIEF DESCRIPTION .

Now more sophisticated mechanism has been introduced which is electro hydraulic control . This system maintains turbine speed almost steady at all load condition with minimum variation.

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