Design Of 3 Phase 50 Kva, 11/0.415V Completely Self- Protected, Oil Filled, Amorphous Transformer

CHAPTER ONE

1.0                                                        INTRODUCTION

The role of a transformer is to convert high-voltage electricity supplied from a power station into lower-voltage electricity for safe use. Transformers operate 24 hours a day, seven days a week during which time they undergo constant losses of 2 to 4% of the electricity that passes through them. This loss is divided into two different categories: load losses caused by the load on the transformer during the use of electricity and no-load losses (standby electricity) caused regardless of whether a load is present. Amorphous core transformers significantly reduce no-load losses by using an amorphous alloy *3 for the iron core, which the transformer windings that carry the electricity are coiled.

Amorphous transformer is a distribution transformers, and distribution transformers are made using a core made from laminations of sheet steel stacked and either glued together with resin or banded together with steel straps. Where large numbers of transformers are made to standard designs, a wound C-shaped core is economic to manufacture. A steel strip is wrapped around a former, pressed into shape and then cut into two C-shaped halves, which are re-assembled on to the copper windings.

An amorphous transformer is a type of energy efficient transformer found on electric grids. The magnetic core of this transformer is made with a ferromagnetic amorphous metal. The typical material (Metglas) is an alloy of iron with boron, silicon, and phosphorus in the form of thin (e.g. 25 µm) foils. These materials have high magnetic susceptibility, very low coercivity and high electrical resistance. The high resistance and thin foils lead to low losses by eddy currents when subjected to alternating magnetic fields. On the downside amorphous alloys have a lower saturation induction and often a higher magnetostriction compared to conventional crystalline iron-silicon electrical steel.

^1.1                                                         BACKGROUND OF THE PROJECT

The core of first practical transformer was developed in 1885; it was made of carbon steel. Later, carbon steel was substituted by silicon steel and today most of the power and distribution transformer cores in service are of cold rolled grain oriented silicon steel laminations. Due to global movement of environmental protection, energy saving and noise reduction have been required for transformers, leading to a demand for low core loss and low magnetostriction material. Amorphous alloy exhibit properties of low core loss and low magnetostriction, compared to conventional grain oriented silicon steel.

Amorphous alloy exhibits a structure in which the metallic molecules exists in a random pattern. As opposed to the rigid grain oriented structure of silicon steel, this unique structure enables easy magnetization and demagnetization. When energized, the core material switches its magnetization 100 times per second. The extent of energy losses that occur in the core is determined by how easily the core switch magnetization; the easier the switching capability, the lower the losses. The key feature of the amorphous core transformers is the sharp reduction in the no-load losses that occur in the core of transformer. There are several amorphous alloys in market, among them iron-boron-silicon alloy (Fe₇₈B₁₃Si₉) has presented the best performance; the core loss in this alloy is about 1/10 of core loss in amorphous transformer steel.

1.2                                          APPLICATION OF THE PROJECT

The main application of AMTs are the grid distribution transformers rated at about 50–1000 kVA. These transformers typically run 24 hours a day and at a low load factor (average load divided by nominal load). The no load loss of these transformers makes up a significant part of the loss of the whole distribution net. Amorphous iron is also used in specialized electric motors that operate at high frequencies of perhaps 350 Hz.

1.3                                         SIGNIFICANCE OF THE PROJECT

More efficient transformers lead to a reduction of generation requirement and, when using electric power generated from fossil fuels, less CO₂ emissions. This technology has been widely adopted by large developing countries such as China and India where labour cost is low

1.4                                              PROBLEM OF THE PROJECT

Amorphous transformers are in fact more labor-intensive than conventional distribution transformer, a reason that explains a very low adoption in the comparable (by size).