Lecture 3: Transformer

Transformer with Losses but no Magnetic Leakage

We will consider two cases:

(i) when such a transformer is on no-load, and

(ii) When it is loaded.

Transformer on No-Load

In practical conditions, when an actual transformer is put on load, there is iron loss in the core and copper loss in the windings (both primary and secondary) and these losses are not entirely negligible.

• The primary input under no-load (secondary side open) condition has to supply (i) iron losses in the core (hysteresis loss and eddy current loss) (ii) a very small amount of copper loss in primary.

• No-load input power: W0=V1I0cos0

• where, cos0 is primary power factor under no-load conditions.

Transformer on No-Load

W0=V1I0cos0

primary current I0 has two components:

1. one in phase with V1.

- active or working or iron loss component Iw (mainly supplies the iron loss plus small quantity of primary Cu loss)

2. The other component is in quadrature with V1

- magnetizing component Im

(its function is to sustain the alternating flux in the core)

I0 is the vector sum of Iw and Im

220 wIII

• no-load primary current I0 is very small as compared to the full-load primary current.

• As I0 is very small, the no-load primary Cu loss is negligibly small which means: no-load primary input is practically equal to the iron loss in the transformer.

• Since the core-loss is responsible for shift in the current vector, angle 0 is known as hysteresis angle of advance.

The no-load current I0 is simulated by pure inductance X0 taking the magnetizing component Im and non-inductive resistance R0 taking the working component Iw connected in parallel across the primary circuit as shown in the following Fig.1.

The value of X0=E1/Im and of R0=E1/Iw.

Next Class

Transformer on Load