Introduction of gas turbine control system

Structure of a gas turbine

A gas turbine is an internal combustion engine of the type of rotating machine that works by using the energy of gases resulting from combustion

Each gas turbine has a compressor to compress the air, a combustion chamber to mix the air with the fuel and ignite it, and a turbine to convert the combustion energy of the gases into mechanical energy. Part of the mechanical energy produced in the turbine is used to rotate the compressor of the turbine itself and the rest of the energy, depending on the application of the gas turbine, may rotate the electric generator (turbogenerator), accelerate the air (turbojet and turbofan) or directly (or after changing the rotation speed by the gearbox) should be used in the same way (turboshaft, turboprop, and turbofan)

 

Control algorithm

For correct and normal operation, various control and protection systems are used in gas turbines
Without the presence of a suitable control system in gas turbines, there are many risks that threaten the reliable and safe operation of the system, and it is possible that in a short time, the compressor will stall or the temperature of some parts of the turbine will exceed the permissible limit, or The speed of the turbine shaft exceeds the allowed speed, which means that a dangerous accident will occur
Therefore, a control system must have a reliable design and have high accessibility and reliability. Gas turbines may be used in various applications such as turbogenerators, turbopumps, turbocompressors, etc. Therefore, depending on the type of gas turbine application, the control systems must check various parameters and issue their control commands. The control system controls the power of the turbine by changing parameters such as the amount of fuel, the rotating speed of the shaft, the temperature of the inlet or outlet air of the turbine and the temperature of the inlet air of the compressor, and tries to keep the turbine in a safe and efficient range
In addition to the control sections, the protection sections also perform their operations in parallel and supervise the control sections
Usually, the control algorithm has three main tasks

Start and stop control
Common controls during work
Protection of critical parameters

Controller system

Gas turbines often have the following 4 controllers

Startup controller
Speed controller
Load controller
Turbine load controller

Control systems control the flow of fuel entering the combustion chamber to achieve the following
Maintaining constant shaft speed at all times
Shaft acceleration control within the permissible limits (during startup)
Temperature control of turbine blades and inner shell
Controlling the amount of loading to the required level of the production units

To control the above parameters, gas turbines often have the following 5 controllers
Starting controller, speed controller, acceleration controller, load controller, turbine temperature controller
These 5 controllers always perform the calculations related to their section in parallel, but the output of the controller suggests the safest amount of fuel is always used as the fuel control reference. For this reason, in a way, turbine protection discussions are included in the control system, so that in case of incorrect operation of one controller, the other controllers will back up the amount of fuel to the permissible limit

Protection system

Next to the controller and overseeing them, there are protection units that usually include
Temperature protection, vibration protection, over-speed protection, fire alarm system
As said before, the protection parts are always monitoring the protected parameter completely independently from the control part, and if the limit is exceeded, they first issue an alarm and inform the operator of the incorrect operation of the system. slow and if the defect is not resolved or there is a possibility of damage to the turbine and its accessories, there is a possibility of an emergency stop of the turbine by the relevant protection