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Pylons are an integral part of everyday life, and whilst many people complain about their “ugliness”, they perform essential functions that enable the population to have electricity in their homes and workplace. Pylons transport electricity from the power grid to buildings, but the voltage of the electricity in pylons is too high for use in everyday electronics, so a transformer is required to bring the electrical current down to a useable level. In this article, we look at how these transformers work.
When electricity is produced in a power plant, or by renewable means, it needs to be distributed to various homes and businesses around the country. The electricity passes through a step-up transformer at a transmission substation to create high voltages that pass along the large metal pylons. The electricity in these pylons travel long distances before entering a power substation. At a power substation, the high voltage electricity is passed through a step-down transformer and the electricity is then passed through smaller, local power lines and into buildings.
Transformers are a critical part of the power grid and are the reason why electricity can be carried for long distances and be distributed among the population. The increase in voltage enables the electricity to travel at higher speeds, thus reaching a building quicker. By decreasing the voltage, transformers enable the electricity to be suitable for use in everyday life.
How Transformers Work
Transformers have two sides – a high voltage side and a low voltage side. The structure of a transformer is a square iron core (with a hollow centre) with coiled wires either side. This structure causes a transformer to act as a kind of electromagnet, where the magnetic flux density is dependent upon the electric current supplied to the transformer. Because transformers work using fluctuating currents, they are only compatible with alternating currents (AC) and not direct currents (DC).
When the magnetic field fluctuates around a coil, it sends a fluctuating electric current around the first coiled wire which sends an electrical current to the second coiled wire. In transformers, the coiled wire which creates the first current is called the primary current, and the second current generated is known as the secondary current.
What happens, is that the electrical current passes from the first coil and into the second coil through the empty space of the iron core. The process is known as electromagnetic induction because the secondary current is induced by the primary current.
Now, for a transformer to work, there needs to be a change in the size of the current when it passes from the primary current to the secondary current. If the number of coils around each side of the iron core are the same, the electrical current generated in the secondary current (or voltage) will be the same as the primary current (or voltage). For transformers to generate a secondary current that is different to the primary current, the number of coils on both sides of the transformer cannot be the same.
Step-Up Transformers
Step up transformers convert a smaller voltage into a larger voltage and are used to increase the voltage of the electricity for the long-range, high-speed metal pylons that you see towering over the countryside. To create a current with a higher voltage, the primary coiled wire needs to have fewer coils that the secondary coiled wire.
In step-up transformers, the greater the number of coils in the secondary coil, the higher the secondary voltage will be and the lower the secondary current will be. The general rule of thumb for the generation of the secondary voltage (or current) as a function of the number of coils, is as follows:
Secondary voltage ÷ Primary voltage = Number of coils in secondary ÷ Number of coils in primary
and
Secondary current ÷ Primary current = Number of coils in primary ÷ Number of coils in secondary
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Step-Down Transformers
Step-down transformers are used to convert the high voltage current from pylons into lower voltage electrical currents that can be used in electronics in the home (or any building). If these transformers did not exist, the voltage from the pylons would be too high and would fry any electronic devices.
In step-down transformers, the lower number of coils in the secondary coil leads to a smaller voltage than the primary voltage (although the current in the secondary coil becomes greater than the primary coil). There is a balancing act involved with step-down transformers because the secondary voltage can’t be left too high as it will cause electrical damage to appliances, nor can it be too low, otherwise many devices won’t work efficiently. On the flip side, the new generated current can’t be too high.
For step-down transformers, the coil-current and coil-voltage relationships can be found using the following:
Secondary voltage ÷ Primary voltage = Number of coils in secondary ÷ Number of coils in primary
and
Secondary current ÷ Primary current = Number of coils in primary ÷ Number of coils in secondary
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