Transformer Positioning Case Study

TRANSFORMER SIZING

6.1. Introduction:

Transformers are widely used in power systems and it is considered as the most essential component of every power system. A transformer is a static device that works on Faraday’s law of electromagnetic induction and it is used to transfer electrical energy from one circuit to another or in other words it is a device which is used for decreasing or increasing the voltage of an alternating current. Basically there are two types of transformer i.e. step up and step down transformer but in general transformers are classified in different ways, depending upon their use, purpose, construction etc. Therefore transformer sizing helps us to select an appropriate type of transformer based on the purpose and use of

Why we need transformer in power system?

We need transformers in power system because of several reasons one most important reason is that electricity is generated at low voltages and in receiving end we also need low voltages but due to the high cost of transmitting low voltages and high currents we use step up transformers to step up the low voltage into high voltages and low currents which will also reduced the I2R losses during transmission of electricity and at receiving side this high voltage is step down to low voltage by using step down transformer.

6.1.2. Why calculation of transformer sizing is necessary in power system?

Transformer sizing is necessary so that the selected transformer is capable of supplying the power needed by the load, able to bear the short circuit current and the inrush current without being damaged.

6.2. General Method Of Transformer Sizing:

The general method of transformer sizing follows five basic steps that are: Collection of data about the source and the

The VA is short for Volt-Ampere a designation of power. A transformer rated at 2 KVA is another way of saying 2000 VA or 200 volts at 10 amps of current.

Select the transformer size from the table given below from the KVA of the transformer calculated from the above mention formulae

6.2.3. Behavior Of Transformer During Large Motor Start-Up Or Impact Of Inrush Current:

Motors have a very high initial inrush current (i.e. the maximum instantaneous input current drawn by a motor when it is turned on) when they are energized and draw a heavy load at low power factor (about 0.16 lagging for 1000 hp motor) for a short duration of time, this is partly similar to the short circuit condition. This increase in current due to the inrush current is flowing to the load which will cause momentary increase in voltage drop at the supply transformer terminal, voltage drop along the distribution system and voltage drop at the utilization