Transformers

Transformer Is an electric static machine used in power system to transfer the electrical power from voltage and current level to another level.

Transformer is the main unit in the transformer stations; as it step up or down the voltage.

The network have many transformers which have different powers depends on the demand load.

The values used for unified electrical net work for transformers are:
 220kv/66kv   125MVA -75MVA.

66KV/11KV     25MVA-20MVA-12.5MVA.

Principle Of Operation:

When the ac voltage is applied to the primary winding, a current will pass trough it producing AC magnetic flux in the iron core. This flux cuts the secondary winding which produce e.m.f across it. When the transformer is loaded , the current will pass trough the secondary winding.As shown in the following figure.

Input power= output power+ power losses.

Input power= (√3) * ip* vp * cosØ.

Output power=(√3) * is* vs * cosØ.

Modeling of Transformer:

Generally, the model of power transformer is as shown in the following figure:

Where:

    R_1, X ₁ : Resistance & reactance of primary side respectively.

    R₂ , X₂:  Resistance & reactance of secondary side respectively.

    R_o: Iron-loss resistance,     X_m: Magnetizing Reactance.

    E₁: Induced emf  in primary side.

    E₂: Induced emf  in secondary side.

Transformer is represented only by equivalent reactance = Z_eq.

Where:

    Noting that:

1 - The ratio  X/R is always >15 .

2-  r_trans. can be negleted

3 - In most time X_trans. is added to X_Line (Series reactances).

4 -  All represented impedance (or reactance or resistance) are in per unit.

 Where:

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Ahmad Mohammad

Hi. I’m Designer of Mawsoo3a Blog. I’m Electrical Engineer And Blogger Specializing In Electrical Engineering Topics. I’m Creative.I’m Working Now As Maintenance Head Section In An Industrial Company.

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