Turbine Governing System

From www.itfrindia.org/ICCIC/Vol2/528ICIPCI.pdf

It is necessary for the Power load operators and regulators to manage distribution services efficiently to maintain reliability of the power system.
Frequency regulation is one of the distribution services to be supplied by the electricity market participants. The only way to regulate frequency is to maintain the balance between demand and supply in real time.


In India, it is achieved through a regulatory approach. In this Paper, an investigation is made on Free Governor Mode of Operation to demonstrate Frequency Regulation by adopting Free Governor Mode of Operation.




Simulation is a powerful technique used to predict the performance or analyze the
behavior of any closed loop control system. It is also used to tune the controller gains or to design a control system. Development of mathematical model is the first step in the simulation study. Matlab and Simulink of Mathworks Inc. are widely used in the academic and industrial world. A simple model of a speed governing system of the steam turbine is taken for illustrating the dynamic simulation.


INTRODUCTION
The developing countries have sustained power shortage problems compared to developed countries for many reasons, mostly financial in nature. The developed
countries have to address the power deficient areas occasionally. The research literature on operation of generation deficient power system is scanty.

The problems faced by developing countries are fundamentally of different nature. The developing countries have to search for alternatives to suit their requirement. The deficient systems have typical features like frequency deviations, abrupt arising of deficiencies of power, low voltages and lack of coordination among the
constituents under a region due to indiscipline.

In India speed governors have been prevented from responding by the utilities, with dead band configuring from 47.5 Hz to 51.5 Hz. Emergency unloading of a unit is available only when frequency reaches 51.5 Hz. As a consequence excursions in frequency are common up to 1 Hz in a time block of 15 minutes. For the sake of better control efforts are being made to enable the frequency governors to respond to entire range of frequency. This is called free governor mode of operation (FGMO)


FREE GOVERNOR MODE OF OPERATION
The Governor is an important controller in the power plant as it regulates the turbine speed, power and participates in the grid frequency regulation. It is the main operator interface
a) To start the turbine from still condition,
b) To vary the load on the turbo-generator when it is on bars (Synchronized) and
c) To protect the turbine from damages in the cases of any unsafe operating conditions.

The steady state and dynamic response behavior of the turbine is influenced mainly by the characteristics of the Governing system.


Need for the Governing System
The load on the turbo-generator does not remain constant but vary as per the consumer (Grid) demand requirements. The presence of a perpetual mismatch between the
generation and the demand in a larger network results into variations in frequency and necessitates a continuous adjustment of generation at the turbo-generators.

If not, the speed / frequency will be oscillating which is an indication of poor power quality. A state of unchanging system frequency and zero acceleration indicates that the generation meets the system demand. The governing system provides for this regulation /adjustment, when the turbo-generator is on bars, by controlling the steam inflow to the turbine.

The regulation is envisaged by various control logics and by operating the control valves in the turbine. Stop valves provided in the governing system protect the turbine in case of unsafe conditions by blocking the steam flow into the turbine.














How Governing System Works
The Speed / Power of the steam turbine are controlled by varying the steam flow to the turbine, which in turn is valve is operated by a servomotor driven by a hydraulic
signal. The governing system is a closed loop control system which processes speed error, power error and pressure error to operate the steam control valves.

In a Mechanical Hydraulic governing system,mechanical speed sensors viz., fly balls and hydraulic speed transmitters to sense the speed and hydraulic servomotors and hydraulic amplifiers to drive the final control elements (i.e.) control valves are employed.

In an Electro Hydraulic governing system, Halls probe or pulse generators to sense the speed, various logics and control circuits to process the error and electro
hydraulic converters / amplifiers and a hydraulic actuator to drive the control valves are used.



























To be continue to http://idpowerstation.blogspot.com/2011/09/frequency-regulation-by-free-governor.html