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Step Up vs Step Down Transformer

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The difference between step-up and step-down transformers is that step-up transformers increase the voltage level while step-down transformers are used to decrease the voltage level. There are also key differences in voltage, current, winding, coil spins, and conductor thickness.

Step-up and step-down transformers are designed to change the voltage level of AC (or Alternating Current) for many different applications and devices. Basic electrical power control of transformers comes down to our necessity and it’s done by either increasing the voltage (step-up) or decreasing it (step-down). 

Transformers work on the principle of Faraday’s Law of “mutual – inductance” in which changing flux in primary winding induces a voltage in the secondary winding.

The following video gives a more detailed explanation of step-up and step-down transformers:

Step up/Step down Transformers explained in under 10 minutes

Transformers consist of an iron core around which two copper windings are wrapped in such a way that they are electrically insulated from each other and are magnetically connected.

These windings are known as primary windings and secondary windings. One of the winding is connected to the AC power and acts as an input (primary winding) while the other is connected to the load that supplies output (stepped-up or stepped-down) voltage to the load (secondary winding).

Here is more information on that:

GCSE Physics - How Transformers Work #82

How can we find whether a transformer is step-up or step-down? The voltage ratio is determined by looking at the rating plate. Then, the connections can be examined.

  • It’s a step-up transformer if the infeed is on the lower-voltage winding.
  • It’s a step-down transformer if the infeed is on the higher voltage winding.

Finding out which side is connected to the source and which side is connected to the load is another way of telling. If the source side bushings are taller, the transformer is a step-down transformer.

There are many uses of these devices and the most well-known one is the National Grid:

GCSE Physics - National Grid #19

Electricity is transferred over long distances at very high voltages and this is why generating stations use a huge number of step-up transformers. If the generated voltage is 11kV and 132kV is needed to transmit electrical power, this type of transformer will accommodate this conversion.

At the distribution sites, you may find step-down transformers. If the input voltage is 132kV and 11kV is needed, this is where step-down transformers are needed.

At the substations, you may find a majority of transformers being step-down transformers. Both step-up and step-down transformers change the voltage level and the basic difference between them is:

  1. Step-up transformer – increases the voltage.
  2. Step down transformer – decreases voltage.

Different countries have different voltage standards. Depending on where you live, your power circuit carries anywhere between 110-120v (USA) or 220-240v to use for your energy needs.

Small devices like doorbells, may only require 16v or you may have a 24v thermostat. A step-down transformer will be able to reduce the voltage from 110v or 220v to 16v or 24v.

For safety reasons the voltage must be “stepped down” before it enters our homes or businesses. This is achieved by using a step-down transformer. In our daily lives, we see the use of these transformers everywhere!

A step-up transformer may be used as a step-down transformer and vice versa. It all comes down to its connection to the circuit.

We can use a step-up transformer as a step-down transformer by connecting the input/output wires to either side of the transformer in the circuit. As the formula of power is:

or:

The transformers themselves do NOT transfer voltage or current. It is the power that is transferred by the transformer from its primary to the secondary side. The voltage and current are opposite to each other, so, if voltage increases then current decreases or vice versa.

When we supply the input power to the low voltage winding, the transformer behaves as a step-up transformer. The transformer will become a step-down transformer if the input power is given on the high voltage winding.

Besides the difference in the function of these two transformers, there are also some other distinctions:

  1. Voltage
  2. Current
  3. Winding (number of coils)
  4. Number of coil spins (turns)
  5. Conductor thickness

Now, let’s look at the differences between step-up and step-down transformers in greater detail:

1. Voltage

Of course, the voltage level is the basic difference between step-up and step-down transformers:

  • In a step-up transformer, the secondary side voltage is more than the input voltage.
  • In the step-down transformer, the secondary side voltage is less than the input voltage.

2. Current

Since the current and voltage are inversely proportional to each other, this is what we get:

  • In a step-up transformer, the secondary coil has a lower current than the primary coil (which has a higher current).
  • In a step-down transformer – vice versa (secondary coil has higher current, and primary has lower current).

3. Winding (coils)

There is also a difference in winding:

  • There is a low voltage primary winding and high voltage secondary winding in the step-up transformer.
  • There is a high voltage primary winding and low voltage secondary winding in the step-down transformer.

4. Number of coil spins (turns)

The amount of turns in their primary and secondary coils is another important distinction between step up and step down transformers. It determines whether a transformer raises or reduces voltage.

  • If the number of turns of the secondary coil is more than the primary coil, then it’s a step-up transformer (the output voltage is higher than the input).
  • If the number of turns of the secondary coil is less than the primary coil, then it’s a step-down transformer (the output voltage is smaller than the input).

This means that a transformer will be called a “step-up” transformer if it increases the voltage level and it will be called a “step-down” transformer if it decreases the voltage level

5. Conductor thickness

How much current can flow through a wire is determined by its thickness.

  • The primary winding coils of a step-up transformer are made out of thicker wire while the secondary is made out of thinner wire.
  • The secondary winding coils of a step-down transformer are made of thicker wire because the output current is high while the primary is made of thinner copper wire.

Step-up transformer

If the voltage on the output side of the transformer is increased, then we call that transformer a step-up transformer. The decrease or increase in voltage is determined by the ratio of the number of turns on the primary winding to the number of turns on the secondary winding.

You can recognize a step-up transformer by lower turn count on the primary coil and higher – on the secondary:

You can also download a PDF version of this diagram.

Step-up transformers are generally used at generating stations. The reason for this is high voltage is accompanied by a low current and therefore more efficient energy transfer by the utility company.

Step-up transformers could be used to improve the performance of electrical and medical instruments (like x-ray machines, etc). At the household level, they can assist in starting an electrical motor or a microwave oven.

If you buy an electrical appliance from a country that has higher input voltage coming from its grid, you will need a step-up converter to use it.

Step-up transformers are efficient in operations but are quite expensive and require a lot of maintenance.

Step-down transformer

This transformer takes a high-voltage (low-current) and turns it into a low-voltage (high-current). Step-down transformers have a higher number of turns on the primary coil and a lower number of turns on the secondary coil.

The increased current requires the use of thicker wire in the secondary winding. The thinner wire is used for the primary coil, which does not have to carry as much current.

The output voltages of a step-down transformer are reduced. This means the high voltage and low current are converted to low voltage and high current.

Here is a diagram of a step-down transformer:

Feel free to download the PDF file to get a closer look.

High-voltage lines are wired to substations with step-down transformers that lower the voltage for nearly all residential, commercial, and industrial users. Step-down transformers are used significantly in daily life applications.

At the residential level, we find step-down transformers in doorbells, home appliances, and mobile chargers, you name it! Everything! It is also used in welding machines where a high output current is required.

Step down transformer is a key component in the power distribution system. At grid stations, these transformers are used to reduce the high transmitting voltages of 500KV, 770KV, 220KV to low distributing voltages of 110KV, 60KV, 33KV, and 11KV.

At street level, this transformer is used to step down the 11KV line voltage to just 220/110V.mThese transformers are very reliable, cost-effective, durable, and very efficient in performance.

Transformers key differences

Here is a table to summarize many differences between step-up and step-down transformers:

Step-up transformer

Step-down transformer

A step-up transformer is used to boost (increase) the output voltage. The output voltage is reduced (decreased) by a step-down transformer.
The voltage on the output side is high while on the input side the voltage is low. The voltage on the output side is low while on the input side the voltage is high.
On the secondary coil, the current is low, and on the primary – high. On the primary coil, the current is low, and on the secondary – high.
The amount of coil turns in the primary winding is less than the amount of coil turns in the secondary winding. The amount of coil turns in the primary winding is more than the number of coil turns in the secondary winding.
A thick copper wire with insulation is used for the primary winding of the step-up transformer, while in the secondary winding thin wire is used. A thin copper wire with insulation is used for the primary winding of the step-down transformer, while in the secondary winding thick wire is used.
Common applications include power plants, electrical motors, x-ray machines, microwaves, etc. Mostly used in residential areas, such as doorbells, thermostats, mobile chargers, and power distribution stations.

Feel free to leave a comment and download a PDF file of both transformers.


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