This work is aimed at the design and construction of an AVR for a 500KVA generator, with particular reference to Flicker/Stability control. The versatile, Regulating properties of the Thyristor (SCR) is utilized here as the principal controller. The Transistor–Transistor circuitry is configured here as the logic differential comparator amplifier. It forms the basis for the main comparator amplifier, Pedestal and ramp, level detector circuit and synchronising circuit respectively. A viable stability and SCR gate conditioning circuits are also developed in the design. The sensing resistors take some amount of generator output voltage and attenuate it. The comparator compares the Sensing voltage to the Reference voltage and amplifies the difference (Error) to provide a controlling logic signal for the power output device via the pulse transformer. Based on the dynamic mode of the circuitry, a determined logic output level triggers the SCR. It synchronises the Pedestal and Ramp circuit to the generator waveform and infinitely control the conduction period of the output device over each half cycle (phase control), and hence supply the exciter with adequate power to maintain the generator voltage within specified limits. The systems control and transfer functions are develop here for system utmost control in the closed loop domain. A more sensitive AVR is thus achieved which takes care of Flicker/stability phenomena with a +/- 1% Regulation of the Generator rated output terminal voltage with respect to load and generator inherent properties. The device was constructed at a cost of N31,500


Ever since the existence of man on earth; from early times, the medieval, renaissance and the ever innovative world of science and technology today, man has always yearned for better and innovative ways of aiding and reinforcing his existence on earth. Consequent upon man’s yearnings, electricity was discovered by Michael Faraday in his early experimental works that span through 1800-1860 Hall (1988), Sigvard (1979). In the wake of the discovery of electricity, the challenges faced by engineers have been that of generating, transmitting and distributing regulated electric power for the dare need of electrical equipment and appliances.

The Automatic Voltage Regulator (AVR) is a close-loop electronic Regulator circuitry that interfaces the stator and exciter windings of especially brushless generators. It regulates the terminal output voltage of the Generator to a specified rated output level, inspite of varying load conditions and varying inherent conditions and losses of the alternator Say (1976), Lawrence (1921), .

This unit automatically constrains the output voltage to about 100% regulation of the rated terminal voltage of the Generator Franklin et al (2005).

The need for a viable and affordable close-loop electronic control interface to control and stabilize the terminal voltage , devoid of Transient and Flicker phenomenon eminent in varying load conditions and alternator constituents varying condition is the thrust of this Research.

The Research in a more succinct and pragmatic approach considers the inherent challenges faced by power systems engineers in the design and construction of AVR in the magnitude of 500KVA as evident in the nature of some brand of AVR’s in the power market. All these challenges are studied and evaluated in this Research to make amend and innovation in designing and constructing a viable 500KVA AVR with special reference to Transient/Flicker stability control.

The motivating drive in steering the course of this research is consequent upon the statement of the problem evident in foreign AVR’S in especially the third world power systems market. Epileptic and lack of appropriate power infrastructures in the third world as growing nations have made the use of power generators a geometric progression phenomenon.

Some of the AVR’S are sold at exorbitant costs and lack the design properties that would fulfill a close- loop control criteria in constraining transient/flicker conditions in the generator exciter. When these generators have faults in their AVR’S, some of these AVR’S are not easily adoptable to these generators. The disparity in adaptation is due to unstable magnetic flux and current demands in the exciter armature windings of some generators John (1989).


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Theraja B.L., A.K. Theraja A.K, Ibid pp. 200 – 210.

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