5KVA Transformer With A Variable Output Voltage

ABSTRACT

Since the invention of the first constant potential transformer in 1885, transformers have become essential for the transmission, distribution, and utilization of alternating current electrical energy. A wide range of transformer designs are encountered in electronic and electric power applications which also include variable transformer.

Variable transformer is transformer that can put out differing amounts of voltage from the same input voltage. Variable Transformers provide excellent power regulation with negligible variation in output voltage from no-load to full-load current. They provide a simple, rugged method of controlling electrical voltage, current and power. They take in utility line voltage and provide continuously adjustable output voltage.

One main reason for changing the secondary voltage is for compensation when the incoming line voltage changes. By using automatic equipment, the secondary voltage that serves the load will remain basically constant, or regulated, should the line voltage fluctuate.

CHAPTER ONE

INTRODUCTION

A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. Electromagnetic induction produces an electromotive force across a conductor which is exposed to time varying magnetic fields. Commonly, transformers are used to increase or decrease the voltages of alternating current in electric power applications.

A varying current in the transformer’s primary winding creates a varying magnetic flux in the transformer core and a varying magnetic field impinging on the transformer’s secondary winding. This varying magnetic field at the secondary winding induces a varying electromotive force (EMF) or voltage in the secondary winding due to electromagnetic induction. Making use of Faraday’s Law (discovered in 1831) in conjunction with high magnetic permeability core properties, transformers can thus be designed to efficiently change AC voltages from one voltage level to another within power networks.

 Variable-voltage transformers are efficient means of changing voltage, especially if you want a greater degree of flexibility in changing the ratio between the primary and secondary coils. They are simple to operate, and controls are available for automatic adjustment to maintain “constant” (regulated) voltage output. The amount of voltage change obtained depends upon the type of variable transformer used.

One main reason for changing the secondary voltage is for compensation when the incoming line voltage changes. By using automatic equipment, the secondary voltage that serves the load will remain basically constant, or regulated, should the line voltage fluctuate. To avoid a continual voltage hunting condition, a voltage tolerance limit is maintained, usually from about a half volt to a few volts.

Variable transformer can put out differing amounts of voltage from the same input voltage. There are trademarked versions of these transformers and there are versions that are simply sold as variable transformers, some of which are built to custom specifications. These are used in a wide variety of different applications and are among the most common electrical components found in the home and in industrial settings.

Variable transformers are a type of autotransformer, which is a transformer that does not have the dual-coil core design. Variable transformers are oftentimes controlled with a dial, which allows them to be utilized as lighting dimmers and in other applications where precise control over the amount of voltage that a load receives is desired.

Variable transformers, even though they operate on similar principles, do vary substantially from standard transformers. The autotransformer design means that they only have a single coil. Because they only do have a single coil, there is actually no physical separation between the source voltage and the load. This means that they are not as suitable for certain applications, particularly when keeping a device or an operator safe by isolating them from a high-voltage is a consideration.

Variable transformers in particular, are used in low-voltage applications and the design itself is typically not suitable for use in high-voltage applications. They do, however, make it possible to conduct sophisticated tests and to exert a great deal of control over the amount of voltage put out by a power source to a given load.

1.2                                             OBJECTIVE  OF THE PROJECT

The main objective of this work is to design and construct a transformer whose function is to provide a variable output to a load when the need arises. Accordingly, one of the objective of this invention is to provide a novel variable output transformer device which can be made to null when the movable member is in a position different from the position in which the null is normally produced.

Another objective is to provide means for eliminating the necessity for mechanical adjustments in order to produce coincidence between the null positions of a mechanical coupling attached thereto.

One of the features of the invention is the rapid, convenient and easy manner with which any necessary alignment, adjustments, etc., between a pick off and a mechanical member attached thereto can be affected by reason of the novel electrical null shifting arrangement herein described.

1.3                                              PURPOSE OF THE PROJECT

One main reason for a variable output transformer is for changing the secondary voltage is for compensation when the incoming line voltage changes.

1.4                                         SIGNIFICANCE OF THE PROJECT

The significance of a variable output voltage transformer will be one or two things. The output voltage transformer can increase or decrease the voltage a bit. The variable output voltage transformer can also increase or decrease the voltage by a bit if that is what is needed. But in this work, a variable output voltage transformer was designed to reduce 240VAC to any value below 240vac primary supply.

1.5                                           LIMITATION OF THE PROJECT

The only limitation of this work is that variable autotransformers do not provide the electrical insulation between their windings like regular transformers do. This presents a safety hazard as it possibly allows a high primary’s full input voltage to pass directly to a low secondary’s output.

1.6                                          APPLICATION OF THE PROJECT

Variable transformers have an immense number of different applications. Essentially, in any application where the amount of voltage that a load is receiving needs to be varied on the fly, a variable transformer is likely employed.

These types of transformers can be used to speed up and slow down electric motors, make lights brighter or dimmer or to simulate specific conditions so that various testing procedures can be carried out.

Variable transformers, due to their control knobs, have the quality of allowing for a very smooth and continuous variation on voltage. This makes them markedly different from digitally controlled devices, which go up or down in terms of output based on a specific interval.

In testing, the fact that variable transformers can be utilized to change the voltage on a circuit to such fine degrees is particularly useful. This allows people conducting tests to lower voltages to extremely low levels or to easily increase that voltage to above the levels at which a component being tested was designed to operate.

Variable transformers are not used as isolating devices. They are, however, found in numerous different devices where separation from a source voltage is not as much a concern as providing control over the amount of voltage that is provided to a load. These devices, under the trademarked name Variac, have been common sense the early 20th century and remain among the most common electrical components today.

Variable Transformer is used to increase voltage before transmitting electrical energy over long distances through wires. Wires have resistance which loses energy through joule heating at a rate corresponding to square of the current. By transforming power to a higher voltage transformers enable economical transmission of power and distribution. Consequently, transformers have shaped the electricity supply industry, permitting generation to be located remotely from points of demand. All but a tiny fraction of the world’s electrical power has passed through a series of transformers by the time it reaches the consumer.

Variable Transformer also used extensively in electronic products to step-down the supply voltage to a level suitable for the low voltage circuits they contain. The transformer also electrically isolates the end user from contact with the supply voltage.