# Transformers - PowerPoint PPT Presentation

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Transformers. Transformers. The "simple transformer law" relates output voltage to input voltage and turns ratio. Investigate the importance of frequency and other parameters in determining the non-ideal behaviour of transformers. The "simple transformer law".

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Transformers

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## Transformers

### Transformers

• The "simple transformer law" relates output voltage to input voltage and turns ratio. Investigate the importance of frequency and other parameters in determining the non-ideal behaviour of transformers.

### Neglects

No magnetic hysteresis

We also need to separate running with load and free running, as it’s particular case.

Dependence of coefficient against frequency (with load)

### Part 1

• Measuring parameters of our transformer

### 1st experiment: VAC

A

Ohm’s law:

V

We used small DC voltages to measure the resistance of the winding

### Theory

We will seek the solution of this equations in form:

~

V

theory

experiment

### Dependence M against frequency

M(mutual inductance factor) depends on frequency because of depending µ on it

Diffusion flux

Inside flux

### Rotation

Dependence of coefficient against angle

### Part 2

• Describing all looses in the transformer

### Losses

We measured steel losses using the chain (right).

A

V

V

~

r

h

### Dependence ofsteel losses against voltage

Dependence ofdiffusionfluxagainst voltage

### Rebuilding a chain

We can rebuild our chain using diffusion inductance

### Part 3

• Measuring and modeling hysteresis

### Modeling hysteresis loop

If we know all the coefficients, we can have as a result of our model real hysteresis loop

### Changing n

• We are changing numbers of coil turns

A

V

V

~

### Resonance mode

We can imagine a real winding as system of coils, resistances and capacitors.

### Conclusions

• Transformer coefficient depends on

• frequency because of the resistances of windings and the dependence of induction on frequency

• the load because of the resistance of the 2nd winding

• input voltage because of hysteresis mode

• turns number of the windings because of dependence M on it

### Доп слайды

Dependence ofsteel losses in the 2nd winding of voltage

Dependence of coefficient against frequency (with load)

### Changing amplitude of U0

Unideal transformer

Resistance of the winding

Losses of the flux

Losses in the core