HYDRAULIC GOVERNOR

            Hydraulic governor in a thermal power plant is the system with the help of which the steam entering into the turbine is controlled thereby controlling the load of a thermal power plant. There are two types of governors

1) Mechanical Hydraulic governor

2) Electro hydraulic governor 

             The important functions of the hydraulic turbine governor are as follows:

• To start, maintain and adjust unit speed for synchronizing with the running units/grid. The speed should be maintained to attain the frequency of the grid
• The system frequency is maintained during the running i.e., after synchronization by adjusting turbine output to load changes, as the frequency on the grid changes this will be change the speed of the rotor as the frequency and speed are directly related.                                               Speed = 120 * Frequency/Poles

• To adjust output of the unit in response to operator or other supervisory commands this is done by providing the command through the interface which indeed will adjust the pressure of oil supplied to the control valves of HP control valve and IP control valve, as the valves are turbine valves are controlled by the oil the valves will be acted based on the oil pressure.
• To perform normal shut down or emergency over speed shut down for protection, as the speed of the turbine gets past the limit, the over speed device must act and cutoff the oil supply to the valves of the turbine which will be closed and results in unit shut down.

Governing system in a thermal plant includes the following 

1. Speed sensing elements 
2. Governor control
3. Hydraulic pressure supply system.

During the shut down of the system if any work is done on the hydraulic governor, then the governing system must be calibrated again as per the desired characteristics so that the valves i.e., HP and IP control valves does not arise problems. The characteristics will be taken at particular temperature of the oil in the control fluid tank, that is set or designed for, otherwise the characteristics will be differ during operation.

 Electro hydraulic governor is the one which uses digital controller. Apart from that both the Electro hydraulic governor and mechanical hydraulic governor will perform same operation. If Electro hydraulic governor fails then mechanical governor will take charge but vice versa is not possible and results in unit shutdown.