Here's how electricity is transmitted to your home:
Step 1. Electricity is made in power plants by generators
Step 2. The electric current is sent through transformers to increase the voltage for long distance transmission.
Step 3. High-voltage transmission lines carry electricity throughout the country.
Step 4. When electricity reaches a substation, it is sent through transformers to decrease the voltage for distribution lines.
Step 5. Electricity is then transmitted through distribution lines closer to your home.
Step 6. Right before entering the house, electricity voltage is once more lowered by smaller transformers mounted on poles.
Why do we keep on increasing and decreasing the voltage? Can't we just transmit electricity at a constant voltage?
Remember that power = voltage X current.This means for the same power output, the higher the voltage, the lower the current. Since power loss = current2 X resistance, the lower the current, the lower the power loss.
!!!We can minimize the power loss when electricity is transmitted at a high voltage!!!
The voltage is reduced first for local distribution when it reaches the neighborhood and reduced the second time before entering the house to everyday use voltage.
How do transformers work?
Transformers are basically devices that increase or decrease the voltage of electricity. Transformers work on the principles of electromagnetic induction.
The transformer consists of an iron core, and two coils wrapped around the core (they are not electrically connected!).
- Iron core: Iron cores are easily magnetized and can carry magnetic field from the primary coil to the secondary coil.
- Alternating current is provided to the primary coil by a primary potential difference.
- The current in the primary coil produces a magnetic field.
- As the current alternates in the primary coil, the magnetic field also changes.
- The change in the magnetic field is carried on through the iron core to the secondary.
- The change in the magnetic field through the secondary coil induces alternating potential difference in the secondary coil.
Relationship between primary and secondary voltages and the turns ratio:
primary voltage / secondary voltage = primary # of coil turns / secondary # of coil turns
If you want to increase the voltage output compared to the voltage input, you should have more secondary coil winding around the core. This is a step-up transformer and is used to increase the voltage for electricity transmission.
If you want to decrease the voltage output compared to the voltage input, you should have less secondary coil winding around the core. This is a step-down transformer and is used to decrease the voltage near your home.
