Электр энергиясын өндіру, тасымалдау және пайдалану. Трансформатор. Физика, 11 сынып, дидактикалық материал.

What are Transformers?

 Transformers use electromagnetic induction to change the voltage of alternating currents. The voltage and current changes can be calculated, as the power transfer is constant. A transformer is a device that can change the potential difference or voltage of an alternating current:

• a step-up transformer increases the voltage (and decrease the current)
• a step-down transformer reduces the voltage (and increase the current)

Design and use of transformers

 A basic transformer is made from two coils of wire, a primary coil from the alternating current (ac) input and a secondary coil leading to the ac output. The coils are not electrically connected. Instead, they are wound around an iron core. This is easily magnetised and can carry magnetic fields from the primary coil to the secondary coil.

When a transformer is working:

• a primary voltage drives an alternating current through the primary coil
• the primary coil current produces a magnetic field, which changes as the current changes
• the iron core increases the strength of the magnetic field
• the changing magnetic field induces a changing potential difference in the secondary coil
• the induced potential difference produces an alternating current in the external circuit

From Faraday’s Law, it can be shown that:

 This is when:

• V_p is the potential difference in the primary (input) coil in volts (V)
• V_s is the potential difference in the secondary (output) coil in volts (V)
• n_p is the number of turns on the primary coil
• n_s is the number of turn on the secondary coil

In a step-up transformer, Vs > Vp. In a step-down transformer, Vs < Vp.

If the transformer is 100 % efficient (no energy losses) the power out must equal power in:

=

 For an ideal transformer: =

Using transformers

Transformers are essential part of an electricity supply system, enabling electrical energy to be transferred efficiently from power stations to consumers. Once electrical energy is generated at a power station, the potential difference of the electricity generated is then increased in step-up transformer. This decreases the current in the distribution cables, making the energy lost in the cables much smaller. Near the consumer, the potential difference of the electrical supply is decreased (using a series of step-down transformers) to provide suitable voltages for consumers to use with electrical appliances.

 SOURCES:

 https://www.bbc.co.uk/bitesize/guides/z2wh3k7/revision/1

 Exam Success in Physics by John Quill pp.183-184