18-08-2012, 11:50 AM
Governing of Pelton Turbine
governing of pelton turbine(1).ppt (Size: 203.5 KB / Downloads: 98)
Oil pump and oil sump :
System uses oil in servomotor or relay cylinder since the force required to actuate the spear valve would be enormous. For this reason, the system requires an oil sump to store the oil and an oil pump to regulate the oil supply in the mechanism.
Oil pump is a positive displacement type of pump like gear pump or axial piston pump. lt's function is to pressurize the oil.
Relay or control valve :
Relay valve is a spool valve having 5 ports. It is also called as control valve or distributor valve. It receives the pressurised oil from the oil pump which is diverted towards the ports to pipe A or pipe B. Through these pipes the oil is transferred to corresponding sides of double` acting servomotor cylinder. Simultaneously, the oil will be returned from the servomotor from the opposite pipe to the sump.
Servomotor or relay cylinder :
It is a double acting cylinder which acts as hydraulic actuator. It receives oil from relay valve say through pipe A. The piston of the cylinder will be displaced towards left, thus forcing the oil through the pipe B into the relay valve and finally to oil sump. It will simultaneously more the spear valve to the left and increase the area of flow through the nozzle.
Governor and linkages :
A centrifugal governor is used as the measuring element of the closed loop control system. It is driven by the turbine shaft through bevel gears. The sleeve of the governor is connected through linkages to relay valve. The movement of is transferred through the lever to move the piston rod of relay valve.
Working
Consider the case when the load on the generator increases, the speed of the generator and turbine will decreases. Since the governor is driven by the turbine shaft, its speed will also As a consequence, the flyballs of the governor will move inwards due to reduced centrifugal force on the balls. As a result the sleeve of the governor will move downwards.