WHAT IS A POWER TRANSFORMER?

WHAT IS A POWER TRANSFORMER?

A power transformer is considered to be a major electrical equipment found in every substation because of its function and since it is the largest, heaviest, and the most expensive device. That is why proper care and protection are done to insure that this device would not be easily damage if faults and overloading will occur. Protective devices like circuit breakers, surge arresters and fuses are usually used to do so.

A Power Transformer is the same as a distribution transformer with respect to its functions, although a power transformer has higher capacity compared to a distribution transformer. A transformer is considered to be a power transformer if it has a KVA rating of about 500KVA or more. The most obvious parts of a power transformer that an individual can see in a substation are the following; transformer tank, radiators, cooling fans, bushings, conservator tank and gages that shows different readings found in the transformer. An oil-conservator tank is necessary since transformer oil has to be kept free from contact with outside contaminants like moisture that is always present in the atmosphere. By means of this tank, the oil is allowed to expand and contract without having a contact with the atmosphere. Cooling fans and radiators are needed since during peak load or when the sun is scorching hot the temperature of the transformer tends to increase beyond its ideal level. The temperature condition of a transformer greatly affects the efficiency of the operation of the power transformer. In every increase in temperature, the capacity of the transformer also diminishes. Because of this problem, methods of cooling were established to meet and solve this kind of loss. These methods of cooling are, self-cooled, self-cooled & assisted by forced-air, and self-cooled assisted by forced-air and forced-oil which is very effective in raising the KVA capacity of a power transformer. Every stage of cooling raises the KVA rating of a transformer by a fixed percentage depending to the method of cooling used. Cooling fans used on the transformer are actuated by the help of a relaying device which when senses a relatively high temperature enables the fan to automatically run.

Power transformer used in a substation may either be a conventional multi-winding transformer or an auto-transformer. A multi-winding transformer has a primary and secondary winding that is insulated from each other and has a common core while an autotransformer has a winding common to both the primary and secondary circuit. In general, autotransformer is considered primarily of its cost advantage where the voltage transformation ratio is favourable. Also, since the connection of this autotransformer is in wye to wye connection, thus provide an angular in-phase relationship between the primary and the secondary voltages. Other advantage of this kind of transformer is it has a smaller physical size, lighter weight and lower voltage regulation. However, the main disadvantages of an autotransformer is its lower reactance, because of its lower reactance thus results to a lower impedance that should be sufficient enough to make the transformer self-protecting under secondary faults.. Furthermore, an autotransformer has a more complex design, and adverse affect on ground relaying.

Basically, a power transformer in a utility industry plays a very important role in the system. It is considered to be the heart of a substation and through the use of power transformers; effective distribution of energy until to the least customer is achieved. Proper use and proper care to the transformer could mean that unwanted outages can be prevented and service would not be hampered.