Power Transformer Characteristics

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figure 1 power transformers

Here are some of the Power Transformer Characteristics.

figure 1 power transformers
The components of a typical power transformer

Power Transformer Characteristics

1. Because of the iron in their core, transformers can be quite large and cumbersome, like the ones found on telephone poles. Power transformers in electronic gadgets, on the other hand, are typically much smaller and more variable in size.

2. With a laminated iron core, eddy-current losses are minimized.

3. To lessen the amount of magnetizing energy required and to limit leakage flux, the flux path has been kept as short as possible.

4. Core types use two distinct legs of the core for the primary and secondary windings, as shown in Figure 1, while shell types use a single leg for both sets of windings. All of them have primary and secondary windings.

5. The autotransformer in Figure 2 is an example of a device that could have a single tapped winding.

6. The autotransformer is an uncommon type of transformer with just one winding.

With the input source connected to the tap and the output connected across the entire coil, the voltage is increased.

The input voltage is “stepped down” when applied across the full coil and the output is “tapped off” at one end. Autotransformers with a slidable wiper-arm tap, commonly known as Variacs or Powerstats, allow the input voltage to be adjusted from zero volts to the maximum setting. They are commonly incorporated into experimental setups as a variable ac power supply.

7. These devices prevent the secondary of an AC transformer from being affected by the voltage from the mains (e.g., the ac power line). Isolation uses typically call for a transformer with a turns ratio of 1:1, as shown in Figure 3. (Note that autotransformers are the only transformers that don’t rely on turns ratios to isolate the secondary from the primary source.)

figure 2 autotransformer
figure 2 autotransformer
figure 3 using an isolation transformer for safety when using a powerstat or variac type variable voltage autotransformer
figure 3 using an isolation transformer for safety when using a powerstat or variac type variable voltage autotransformer

There is no physical connection between the secondary load and the primary power supply when using this unique isolation transformer with a turns ratio of 1:1. As a result, those tinkering with the wiring that is connected to the secondary of the isolation transformer are protected.

8. They can’t run at high frequencies because that would cause too many losses.

9. Figures 4a and b depict only two of the many color codes in use today.

figure 4 typical power and audio transformer color coding systems
figure 4 typical power and audio transformer color coding systems

Safety Hints Caution

There is no protection against electrical shock from the raw line voltage and ground connections in the autotransformer circuit if an isolation transformer is not used on the input side.

Because of this, autotransformers with a movable wiper-arm tap shouldn’t be used unless they’re plugged into an isolation transformer output, which protects them from the mains voltage.

Practical Notes

Some power transformers have a switchable primary voltage input of either 120 or 240 volts, making them useful in situations where either voltage is required. That’s why there are transformers with dual primary windings.

When using a 240 V supply, these primary windings can be connected in series (i.e., the end of one winding is connected to the beginning of the other winding, being careful to pay attention to phasing of the two windings).

The transformer primary can also be fed from a 120-V source by connecting the two primaries in parallel (again, with care for the phasing). Using these methods, whether the input voltage is 120 or 240 volts, the resulting secondary voltage will be consistent.

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