1. Lecture 3: Transformer

4. 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.

5. 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.

6. • 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=V1I0cos0
• where, cos0 is primary power factor under
no-load conditions.
Transformer on No-Load

7. W0=V1I0cos0

8. 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)

9. I0 is the vector sum of Iw and Im
22
0 wIII  m

10. • 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.

11. 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.

12. Next Class
Transformer on Load