Ideal Transformer & Actual Transformer: what is it? | electricalTpoint

Q:Explian the various features of an ideal transformer on no load ?


Q:Explain the various features of an ideal transformer .

Ideal Transformer

Ideal transformer on no load: An ideal transformer is one which has no losses i.e. its windings has no ohmic resistance, there is no magnetic leakage and hence it has no I2R and core losses. In other words an ideal transformer consists of two purely inductive coils wound on a loss – free core.

Consider an ideal transformer whose secondary is open and primary is connected to voltage V1. The transformer is at no load. This potential difference causes an alternating current in transformer to flow in the primary. Since the primary coil is purely inductive and there is no output. the primary draws the magnetising current Iu only. The function of this current in transformer is to magnetise the core, it is small in magnitude and lags V1 by 900. This current in transformer I produces an alternating flux ϕ , which is proportional to the current in transformer and hence in phase with it. This changing flux produces self induced emf E1 in primary which is equal to and in opposition to V1 and mutually induced emf E2 in secondary which is in antiphase with V1. In an ideal no-load V1= E1 and V2 = E2.

Actual Transformer

Q: What is significance of magnetizing current Of a Transformer ?

Actual Transformer on ‘NO LOAD’: When no is connected across secondary winding, secondary current in transformer I2 is zero . Theoretically I1 must be zero but in practice, in transformer a very small primary current I0 (known as NO-LOAD current) flows in primary circuit. current in transformer I0 has to supply .

  1. iron loss in the core and very very small amount of loss and
  2. produces flux in the core i.e. to magnetise the core. The phasor diagram of a transformer at no load is shown in figure.

Current I0 is divided into two components:

  1. I0sinϕ0 is in the direction of flux (ϕ) .This current maintains flux in the core. It is known as magnetising component ( Iusinϕ0A) .
  2. Other component I0cosϕ0 is in phase with V1 and supplies iron loss plus small amount of primary Cu loss. This is known as active or working or iron components (lw).

∴ Iw = I0cosϕ0 A

∴ I0 =( Iu2 + Iw2 )

The no load primary current of transformer has two components – active component and magnetising component.

The function of magnetising component is to sustain the alternating flux in the core of the transformer, which is mainly responsible for the emf in secondary winding of the magnetizing current in transformer is wattless component. As I0 is very small, the primary Cu loss can neglected and hence all the input power at NO LOAD is practically equal to the iron loss or core loss of transformer.

Iron loss = V1I0cosϕ0 watts. and p.f.= cosϕ0 (lag).

I0 always lags behind V1 by ϕ0 .

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