A transformer is an essential electrical device that plays a critical role in power transmission and distribution. It is a device that is used to transfer electrical energy from one circuit to another by electromagnetic induction. Transformers are widely used in power stations, substations, and other electrical applications.

The primary function of a transformer is to step up or step down the voltage of an alternating current (AC) power supply. This is achieved by changing the number of turns of the primary and secondary windings of the transformer. The transformer works on the principle of mutual induction, where a change in the magnetic field caused by the movement of electrons in the primary coil induces a voltage and a current in the secondary coil.

The three-phase transformer is the most commonly used type of transformer in electrical power transmission and distribution systems. It is a device that has three separate windings, each of which is connected to a different phase of a three-phase AC power supply. The primary windings of the transformer are connected in a delta configuration, and the secondary windings are connected in a star configuration.

To calculate the full load primary current of a three-phase transformer, you need to know the full load current of each of the available phases. This can be calculated by dividing the total load by the three-phase voltage.

For example, if the transformer has a capacity of 500 MVA and a voltage of 33 kV, the full load current in each phase would be approximately 15,151 amps (500 MVA/33 kV/3). The full load primary current can then be calculated by multiplying the full load current in each phase by the square root of 3 (1.732).

Assuming that the transformers secondary will be connected to a load that requires a full load current of 150 amps, the transformer's primary current would be approximately 260 amps (150 amps/0.577). This calculation takes into account the transformer's efficiency, which can vary depending on its design and operating conditions.

In conclusion, electrical transformers are essential components of the power transmission and distribution system. They play a critical role in changing the voltage and current levels of electrical power to match the specific requirements of different applications. Understanding the basic principles of transformers and how to calculate their full load primary current is essential for anyone working in the electrical engineering field.