Electrical Engineering - Transformer, Study notes of Electrical and Electronics Engineering

Download Electrical Engineering - Transformer and more Study notes Electrical and Electronics Engineering in PDF only on Docsity!

TRANSFORMER

Outline of the lecture

• (^) Ideal Transformer
• (^) Practical Transformer
• (^) No load condition of an Ideal Transformer
• (^) No load Phasor Diagram of an Ideal Transformer
• (^) No load Equivalent Circuit of a Ideal Transformer
• (^) On load condition of an Ideal Transformer
• (^) On load Phasor Diagram of an Ideal Transformer
• (^) On load Equivalent Circuit of a Ideal Transformer

Practical Transformer

Winding Resistances

• (^) Since the windings consist of copper conductors, it immediately follows that both primary and secondary will have winding resistance.
• (^) The primary resistance R 1 and secondary resistance R 2 act in series with the respective windings as shown in Fig.

Practical Transformer

Winding Resistances

• (^) When current flows through the windings,

there will be power loss as well as a loss in

voltage due to IR drop.

• (^) This will affect the power factor and E

1 will be

less than V 1 while V 2 will be less than E 2.

Practical Transformer

Leakage reactance

• (^) Similarly, secondary current would produce

some flux  that would not link the primary

winding.

• (^) The flux such as 

1 or^  2 which links only one

winding is called leakage flux.

• (^) The leakage flux paths are mainly through

the air.

Practical Transformer

Leakage reactance

Practical Transformer

Leakage reactance

• (^) Similarly, the secondary leakage flux  2

introduces an inductive reactance X 2 in series

with the secondary winding.

Practical Transformer

Leakage reactance

• (^) However, due to the presence of

leakage reactance in the windings

• there is voltage loss due to IX drop.
• Change in power factor.

Transformer

no-load phasor diagram for

Ideal Transformer

• (^) The core flux is common to both primary and secondary windings in a transformer and is thus taken as the reference phasor in a phasor diagram. In the phasor diagram assuming no losses, shown in Figure, current I 0 produces the flux and is drawn in phase with the flux.  i 0

Transformer

no-load phasor diagram for Ideal

Transformer

• (^) On no-load the primary winding takes a small no- load current I 0 and since, with losses neglected, the primary winding is a pure inductor, this current lags the applied voltage V 1 by 90°  i 0 V 1

Transformer

no-load phasor

diagram for

Ideal Transformer

No-load condition for Practical

Transformer

• (^) For no load condition the secondary of a transformer is left open- circuited.
• (^) At this condition primary current is very low and is called the no-load current.
• (^) In case of practical transformer losses are there and important to consider.
• (^) No-load current produces the magnetic flux and supplies the hysteresis and eddy current losses in the core.
• (^) The no-load current (Io) consists of two components: the magnetizing current (Im) and the core loss (IH).

A no-load phasor

diagram for a

practical

transformer is

shown in

Figure

Transformer

no-load

phasor

diagram

for

Practical

Transformer

Transformer

no-load phasor diagram

for Practical Transformer

If current flows then losses will occur. When

losses are considered then the no-load

current I 0 is the phasor sum of two

components—

• (^) (i) I

M , the magnetizing component, in phase

with the flux, and

• (ii) IC , the core loss component (supplying

the hysteresis and eddy current losses).