16-07-2014, 01:03 PM
The function of a governor is to maintain the speed of an engine within specified limits whenever there is variation of speed. Here it control the speed of turbine.
Governing system.pptx (Size: 532.96 KB / Downloads: 9)
Introduction
The function of a governor is to maintain the speed of an engine within specified limits whenever there is variation of speed. Here it control the speed of turbine.
Governor has a role of detecting speed of revolution of generator, amplifying that signal and operating the guide vane.
Power system performance is affected by dynamic characteristics of hydraulic governor turbine .
From the view point of supplying power of good quality, a high performance governor widely required.
Types of Governor
Conventional Mechanical Governor
Electro hydraulic Governor (PMG type)
Electro hydraulic Governor (PID type)
Microprocessor base Electro hydraulic Governor
Conventional mechanical governor
Here the fly ball rotate when the speed decrease the fly ball pulled inward due to centrifugal force causing the down ward movement of the sleeve. As the sleeve moves down the lever turns down subsequently the V1 open and V2 closes .
The oil pumped from the oil sump to the control valve under pressure will flow through V1 and will exert force on the face m of the piston of the relay cylinder. The piston along with piston rod and spear move towards left.
The conventional Governor has certain limits in its stability and response and therefore now-a-day these are not used.
Electro hydraulic governor
Electro hydraulic Governor is more stable and response quicker than that of conventional governor
It consist of two part
Electric controller
Hydraulic controller
In Burla power house PMG type governor used in unit 3,4,5 and 6 .PID controlled Governor used in unit 7. Microprocessor based governor used in unit 1 and 2.
Gate limit control device
This can be controlled either manually at the actuator or electrically from the control switch board by a D.C. reversing motor.
In increasing the gate limit from the control switchboard, the control motor is operated and its revolution is transmitted to the cam which raises the roller permitting the upward movement of the pilot sleeve.
Thus the governor becomes feasible of taking on greater load.
Speed drop adjusting device
The amount of speed drop between full gate opening and zero gate can be adjusted between 0 to 5 percent.
Auxiliary servomotor
It is used in combination with the pilot valve to amplify a slight displacement and operating force of the actuator solenoid and thereby control the secondary distributing valve.
When an open signal is applied to the actuator solenoid and the pilot spool of the pilot valve rises the pressure passes through the load limit valve and actuator lock valve and reaches the bottom of the auxiliary servomotor piston and then lifts the piston getting over the top pressure, this causes the auxiliary servomotor to perform close operation
Distributing valve
It supplies the pressure oil to the closing or opening side of the doubling acting gate servomotor .The pilot valve of the servomotor moves up or down according to the movement of the auxiliary servomotor.
Gate limit device
The gate limit device is to limit the servomotor within a certain opening
In case of gate limiter has been released ,when the system frequency changes, the governor system controls the gate .
The opening limit is adjustable by the gate limit motor.
Continue
Under steady state condition the electronics cabinet provides balance current of o milliamp to the EHT.
In the event of frequency raising or lower command it provides proportional negative current for closing of the gate and in the event of frequency falling or raise command it provides proportional positive current for opening of the gates.
Once the gates acquire new steady position the output current resets to 0 milliamp under action of the permanent drop signal. During dynamic condition o/p current vary from -100 milliamp to +100 milliamp.
Conclusion
The governor design to control the Unit speed and also to provide the Unit start and stop when the Unit is operating.
Sensitivity of the governor is defined as the ratio of the difference between maximum and the minimum speed to the mean equilibrium speed.
Sensitiveness of a governor is a desirable quantity however if a governor is too sensitive ,it may fluctuate continuously results in hunting.
A governor is said to be stable if it brings the speed of the engine to the required value and there is not much hunting.
The stability and sensitivity are two opposite charactertics.