Transformers & Electricity Distribution

Question 1

What is a transformer?

Answer 1

A device that increases or decreases the voltage in an electrical circuit.

Question 2

What is the features of a transformer?

Answer 2

Consist of two coils of insulated wire - primary coil and secondary coil, which are linked by a soft iron core.

Question 3

Why do transformers use “soft” cores?

Answer 3

Because they are “magnetically changeable” - its magnetization is pliable

Question 4

What occurs in the primary coil in a transformer?

Answer 4

The current is inputted through the primary coil, which creates a changing flux, and induces the current in the secondary coil.

Question 5

Can transformers operate on DC or AC? What relationship does it have?

Answer 5

Transformers only operate on AC, in order to create a constantly changing flux. The secondary coil will have the same freq. as the AC supply.
(sinusoidal relationship)

Question 6

What does the soft iron core do?

Answer 6

It conducts the magnetic flux, in order to maximize the flux created by the primary coil that threads the secondary coil (flux linkage).

Question 7

What would occur if DC was flowed into the transformer?

Answer 7

There would be no change in the current, hence no change in mag. field, and mag. flux. In acc. to Fara. Law, an EMF will not be produced, hence no energy or power transfer.

Question 8

What is an ideal transformer?

Answer 8

100% efficient transformer, meaning the flux passes through the secondary coil and no energy is lost anywhere

Question 9

What is Faraday’s formula?

Answer 9

V = - N delta flux//delta time

Question 10

What is a step down transformer?

Answer 10

More voltage to less voltage,
more turns to less turns

Question 11

What is a step up transformer?

Answer 11

Less Voltage to More Voltage

Question 12

State some of the limitations of transformers.

Answer 12

• Energy lost through heat
• Power output is lower than the power input
• flux linkage
• magnetic permeability

Question 13

What is magnetic permeability?

Answer 13

Refers to the degree of ease a material can be magnetised. Using cores with high MP allows it to carry and direct magnetic flux, hence increasing flux linkage

Question 14

What is the resistive heat production?

Answer 14

It occurs in the wires that make up the coils. The resistance of wires causes a current to pass through and lose energy to heat.

Question 15

What is the formula for power loss?

Answer 15

P = I^2R or P = V^2//R

Question 16

What do we want to do when we transfer electricity?

Answer 16

We want to minimise the current, to minimise the power loss

Question 17

What are eddy currents and where are they induced?

Answer 17

Eddy currents are induced inside the soft iron core of the transformer, where there is a constantly changing magnetic flux.

Question 18

What is 2 ways to minimise the heat loss from eddy currents?

Answer 18

The core can be constructed using layers of iron coated with an insulator - laminated core.
Secondly, we can replace the core with a ferrite - good transmitter of flux, but poor conductors of electricity

Question 19

What is the most efficient lamination of a transformer?

Answer 19

1. Cut vertically sideways
2. Cut horizontally forwards
3. Cut vertically fronton

Question 20

Is step up/down transformers used in power plants?

Answer 20

Step-up transformers are used to increase the voltage which will decrease the current and minimise the power loss

Question 21

When are step down transformers used in electricity?

Answer 21

Step down transformers are used at substations to lower the voltage for commercial consumers and safe transmission in residential areas.

Question 22

What is always true for a step up transformer?

Answer 22

The power output is lower than the power input.

Question 23

What is flux linkage?

Answer 23

Flux linkage is the flux which goes from the primary to the secondary that is to say it links both coils and thus is not lost to the environment

Question 24

What happens to the flux that doesn’t make it?

Answer 24

The magnetic field might escape the core and just alternate in the air around the transformer and thus does not link the primary and secondary. Thus it has leaked out and is flux leakage