TURBINE GOVERNING SYSTEM: WHAT IS IT AND HOW DOES IT WORK?
A governor in general refers to:A device that is used to sense the quantity (that is proportional to speed) and regulates the speed of a machine.
There are many types of governors used in many applications. One of which we will be focusing in this article is the Fly ball Governor.
Turbine Governing System:
|Turbing Governing System (Credit: Vaishnav Chathayil)|
Where, H.P. Oil refers to High Pressure Oil
NOTE: Point E is always fixed.
The turbine governing system consists of the following parts:
This part of the system is used to provide a constant power setting to the turbine in order to get a constant output under steady state condition.
It has a lever that can be lowered or raised. Changing the position of the lever changes the position of the Steam Inlet valve.
NOTE: Changing the position of the lever does not alter the position of the fly balls.
In this governing system a Fly ball Governor is used. It is also called a centrifugal Governor. This part of the system senses the change in frequency.
It has two main sub parts:
- Pilot Valve
- Piston Arrangement
The amplifier also has an inlet through which High Pressure Oil is let in.
This is the most important part of the system as, based its movement the piston changes and also it controls the position of the Steam Inlet Valve.
Working Of Turbine Governing System
The working of this system can be considered in two cases:
- CASE 1: When the point B is fixed
- CASE 2: When the point A is fixed
Let us see in detail what happens in each case.
CASE1:WHEN POINT B IS FIXED
Depending on the demand (load) the lever at the speed changer is varied. Let us see the case when the load high as a result more steam need to be let in to increase the mechanical input to the generator. The lever lowered and point A moves downward. Notice that B is fixed, the downward movement of A leads to an upward movement of C and D as well. Point D is in turn connected to the pilot valves. Now, when D moves upwards, the upper pilot valve opens and let the High pressure in to push piston in the Hydraulic Amplifier downward.
The piston is connected to the Steam Valve on the upper end, and it opens thus letting in the steam. Hence, the needed mechanical input is provided to meet the demand.
CASE 2: WHEN POINT A IS FIXED
Now the power system is under steady state condition. But, it is seen that the load decreases. This results in a change in frequency in the system. We know that when there is an increases in load the frequency increases and this change is sensed by the governor in the governing system.
The fly ball governor works in such a way that:
- If there is an increase in frequency (indicates increase in shaft speed) the fly balls move outward.
- A decrease in frequency (indicates decrease in shaft speed) the fly balls move inward.
Consider a case when the load is reduced then it results in increase in frequency which results in the outward movement of the fly balls. On moving outwards the point B is pushed downwards that further results in pulling the points C and D downward. Now, when D moves downwards, the lower pilot valve opens and lets the High pressure in to push piston in the Hydraulic Amplifier upward thus closing the Steam Valve and reducing steam input.
Hence, reducing the surplus mechanical input provided.
|Change in load||Speed||Fly ball||Point B||Point C & D||Inside Hydraulic Amplifier||Input Steam Valve|
|Increases||Decreases||Move outward||Downwards||Downwards||Upper valve moves upwards||Open|
|Decreases||Increases||Move inward||Upwards||Upwards||Lower valve moves upwards||Close|
Thus, this is how the steam input to the turbine is controlled during the variation of loads.
Author: Vaishnav Chathayil is pursuing his B.Tech. in Electrical and Electronics engineering at National Institute of Technology, Calicut.