CHAPTER ONE
1.0 INTRODUCTION
Electrical energy has been considered as one of the numerous form of energy and it distinguished itself vividly by the widest application in the recent years.
Electrical energy is particularly useful by reasons of the case with which it can be distributed and converted to other desired forms lighting effects, heating effect magnetic effect of electrical energy can be used to ran our inclustrus, boil our water, provide light for our homes as well as servicing and easing other human endeavours.
The wide use of electricity has necessitated the development of systems of transmission and distribution. Transmission systems are required (a) to enable sources of natural energy (eg water fails – dams, or storage loaves, reservoirs for hydropower station, fuel fields, coal gas, diesel – for thermal generating station), for distant from the centre of energy demand (e.g large works, industrial areas of cities), to be economically utilized, (b) to enable generating plant to be concentrated in a few large. Favourably situated stations; and (c) to per met of the in for connection of network or distributing areas to ensure reliability economy and stability or continuity of supply.
There are three main facts in the production and utilization of electricity namely: generations transmission, and distribution generation of electrical energy employs electrical power stations. These power stations generate electrical energy making use of fuel (e.g coal, gas, diesel) as mom raw material; hence thus type is called steam or thermal power station. Other power stations make use of water falls or storage haves – hence called hydro electric power station: etc.
No mater the type of the power station employed, the voltage generated is usually in a low level e.g 11KV or 25KV. Owing to the distance between the centre of energy dim and (consumption areas) to the power stations, transmission system of energy times into play. A high voltage is desirable for transmitting large power in order to decrease the 12R losses and reduce the amount of conductor material. Therefore, a transformer is employed to step up the generated voltage to 3300KV/ the highest National Grid voltage although effort are being made to increase it to 765KV for transmission. This 330KV is transmuted to the distribution ends. A very much however voltage, on the other hand, is required for distribution, for various reasons connected with safely and convenience. The transformer also mavies this easily and economically possible as the 330KV is stepped down to 132KV, 66KV, 33KV, 11KV, 415KV and to a minimum level of 240V for distribution to various load centre (consumption area).
1.1 BACKGROUND
The device to increase (step up) or decrease (step down) the generated voltage is called the transformer. It is a static (stationary) alternating consent machine.
Basically, transformers are classified according to purpose namely:- power transformer, distribution transformer, Auto-transformer and instrument transformer, power transformer are large transformers generally used at generating stations to step up the voltage, and at the substations to step d0wn the voltage for supplying distribution systems. They may also be used for tionving together two power stations. The power transformer has a high utilization factor, e.g it is arranged that they run with an almost constant load which is equal to their rating. The maximum efficiency is designed to be at fall load. This means that the fall-load winding losses must be equal to the here losses.
According to common usage, a transformer rated over 500KVA is termed a power transformer.
The distribution transformer has a intermittent and variable head which is usually considerable less than fall-head rating. They are therefore, designed to have their maximum efficiency at between half and three – quarter of fall head.
The instrument transformers are of two types depending on the mode of operation voltage or current transformers. The current (series) and voltage (shunt) transformers are used for extending the range of a.c. instruments in preference to shunts and series resistors.