ABSTRACT

The desire for power to be controlled by means of phase angle variation of the conduction period brought about a digital ac power controller. Controlling the phase angle can be made simple and easy if we set different firing times corresponding to different firing angles. The circuit can be used as power controller in lighting equipment, hot air equipment, universal single phase ac motor, heater, etc. This project is aimed at constructing the circuit with necessary modification to serve this purpose.

CHAPTER ONE

1.0         Introduction

SCR power controllers were first developed in the late 1950’s. Originally available with ratings of only a few hundred amps and low voltage, the SCR power controller has steadily increased, the number of potential applications has increased as well. In fact, nearly every industrial process that uses process heating equipment can employ SCR power controllers.

SCR power controllers provide a relatively economical means of power control. SCR power controllers cost less and more efficient than saturated core reactors and variable transformers, compared to contractors, SCR power controllers offer a much finer degree of control and do not suffer from the maintenance problems of mechanical devices.

1.1.        FEATURES AND BENEFITS OF SCR’S

1. High Reliability: because the SCR power controller is a solid state device, it provides virtually limitless, trouble free operation with a minimum of maintenance
2. Infinite Resolution: power or voltage can be controlled from zero to 100% with infinite resolution.
3. Extremely Fast Response: the SCR controller can toggle load power on and off rapidly, providing the means to respond quickly to command, load, and power supply changes.

1.2         ADVANTAGES

The advantages of SCR power controls outweigh the disadvantages. The biggest advantages are high reliability and low maintence requirement. Because the SCR is a solid state device, there are no moving parts to wear. Simply keeping it clean and cool, provides users with many years of reliable service. Another advantage is control options with on/off electromechanical contactor, an SCR provides fast response and high resolution as well as the ability to limit current and regulate load voltage, current or power.

1.3  DISADVANTAGES

1. Low power factor
2. High harmonic current
3. Radio-frequency interference when using phase fired power controllers.

1.4  SCOPE OF THE STUDY

The scope of the study of this project work is describes as listed below.

1. It is an example of a controlled device used in electrical electronics engineering approach
2. This is a circuit for a digital ac power controller that can set different firing times.

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