A Research on Generators with Constant of Active Power and Variation of Excitation Current in Thermal Power Plant

International Journal of Research and Scientific Innovation (IJRSI) | Volume VIII, Issue IX, September 2021 | ISSN 2321–2705

A Research on Generators with Constant of Active Power and Variation of Excitation Current in Thermal Power Plant

Nguyen Thi Thu Huong
Electrical Faculty, Thai Nguyen University of Technology, Thai Nguyen, Viet Nam

Abstract: This paper presents a method to determine critical points to adjust operating parameters for a thermal generator in case of constant of active power and variation of excitation current. Operating thresholds corresponding to above points are defined by maximum reactive power generating to the power system (positive), zero reactive power and maximum reactive power absorbing from the power system (negative). Curves representing the relation between power factors, angle of electromotive cross force and reactive power are also created in this paper corresponding to above operating points. Due to exactly determining critical points in this case, an algorithm is also proposed to help the controller have correct thresholds to adjust the excitation current for parallel couple of a thermal generator and the power system. This paper also presents a detailed calculation for a thermal generator having 57.5 MW rated active power to illustrate the proposed method. Calculation results showed the meaning of the proposed method to create a full and clear profile for any thermal generator that helps to control and dispatch power systems.

Index Terms— Active power, angle of electromotive force, excitation current, reactive power, thermal generator.

I. INTRODUCTION

Generators are very important units in thermal power plants and used to work in parallel with power systems. Active power is always generated to the power system while reactive power can be generated to the power system or absorbed from the power system. Corresponding to the demand of electric loads, output power of generators must be adjusted continuously to balance power and hold voltage/frequency stability for power system. By adjusting excitation current, values of active/reactive power can be changed but they are only in allowable ranges [1], [2].
In almost operating modes, value of active power from the generator to the power system is often from minimum value (Pmin) to maximum value (Prated) while value of reactive power is often from -Qmin (the generator absorbs reactive power) to +Qmax (the generator generates reactive power) [1], [2]. In the process of adjusting active/reactive power, its power factor is also changed. Value of power thresholds depends on allowable thermal operating condition and the characteristic of each generator. Moreover, electromotive cross force (Eq) is also adjusted in module and angle to ensure instantaneous operating requirements [1].

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