What Is Step Up And Step Down Transformer & There Use


Transformer is a device used to step up or step down the electrical voltage. It uses the process of electromagnetic induction to transfer energy from one circuit to another.

The transformer consists of three parts. The primary winding, Secondary windings, and magnetic core. We discussed different types of transformers. In this article, we will discuss Step Up and Step Down Transformer.

Step Up Transformer

Step Up Transformer is the type of transformer that converts low voltage into high voltage i.e its main job is to transform electrical power with increasing the voltage from one side to another and decreasing the current.

The transferred power is the same on primary and secondary sides of the transformer.

Similarly, In the term of current its the opposite of the voltage, i.e the transformer converts high current at the primary side to low current on the secondary side.

Step Up Transformer Increase Voltage because, it works on the principle of magnetic induction, it converts the low voltage high current into high voltage and low current.

 In the primary section of the transformer, the alternating electric flux produces the changing magnetic flux in the core.

This as a result, causes an alternating current in the secondary section of the transformer. If number of turns in the secondary winding is more than the number of turns in the primary winding, then the output voltage will be more than the input voltage and this is the case in the step up transformer.

In some appliances like inverter and microwave ovens, we need higher voltage at the input, so we use Step up transformers.

For longer distances, losses are low because of the high voltage and low current, that’s is why step up transformers are used.

Step up transformers are also used because it reduces the wire’s cost and the cost of transmission line. Because more voltage means lesser current and lesser current means the thinner wire. The less amount of material will be required to fabricate it.

Obviously the lesser the material, the low will be the cost. Less material means it is lighter, so small towers are required.

How Does A Step Up Transformer Increase Voltage?

We discussed in our previous article that the transformer consists of three parts i.e. Primary winding, Secondary windings, and magnetic core. These parts are the main parts, and also know as transformer active parts.

In step Up Transformer the number of turns on the secondary windings is greater than primary winding. And as we discussed earlier the transformer works on the principle of electromagnetic induction.

When we apply voltage at the primary winding, it produces a magnetic field which activates AC current in the secondary winding with the same frequency.

The increase of the turns number of the secondary windings increases the voltage on the output side of the transformer.

The Step Up transformer increases the level voltage at the secondary side (output side). According to the turns ratio between the primary and secondary windings the step up transformer increases the voltage. 

Transformer Turns Ratio Formula

A step up transformer is basically an electrical device which converts the low voltage and high current of the primary side to high voltage and low current of the secondary side.

In Step up transformer, there are more turns in the primary side and less turns in the secondary side.

As we know that, Power (PP )= VP * IP    and PS = VS * IS

Where P is for the primary side and S is for the secondary side.

Combining these two equations,

VP * IP = VS * IS

As we mentioned above, each winding, i.e the primary and secondary has it turns number. According to this number the voltage of the transformer increases or decreases. The turns ratio formula is:

n = Np / Ns = Vp / Vs


n : transformer turns ratio

Np is the primary winding number of turns.

Ns is the secondary winding number of turns.

Vp is the primary winding voltage.

Vs is the secondary winding voltage.

We know that the voltage ratio is proportional to the terns ratios. Therefore, the voltage on the secondary side depends on the secondary winding number of turns.

Turns ratio example:

If we have a transformer of turns ratio n = 1:2, primary voltage of 110 v. Its secondary voltage should be 110*2 = 220 v

Step up Transformer Applications

In electronic circuits:

Step Up Transformer is used in some electronic and electrical devices where there is a need to boost voltage.

In power systems:

Power transmission lines are used to transmit the electricity from power generation to consumers. These lines are very long. So the power losses will be very high value.

Here comes the main rule of the step up transformer in power systems, and this answers the important question of, Why is a transmission line operated at high voltage? Increasing voltage decreases current which in turns decreases power losses during transmission.

This is not the only advantages of the step up transformer use. Here under its advantages:

  • The Step Up Transformer is used at the generation point. It helps in the efficient transmission of electricity through overhead power lines. It decreases current value, therefore the power losses are less.
  • The decrease of the current makes the installation of the OHTL more economical. Lower current means smaller conductor size, smaller accessories which are required to carry these conductors.

Step-up transformer is used for transforming electrical energy for long distances, because there are quite huge losses in the transmission lines. The higher the voltage the lower the current for the same power.

According to the equation:

Power Losses P = I2 * R

High voltage and low current reduces the I2 * R losses.

Transmitting power by using a high voltage system means low energy loss. The low current saves the conductor material as it needs smaller conductor size.

Step-Up transformers are used in the electronic equipment like inverters, and voltage stabilizers for the stability in terms of low to high voltage.

Step-Up transformers are used to distribute the electrical energy. It is used for making Microwave Ovens, X-Ray machines, and the electric motors. It is used for the voltage boosting purpose in the small appliances. It is used inside of the rectifiers.

Because step-up transformers increases the voltage and decreases the current and ultimately decreases the resistance of the transmission, so they are the economical choice for any electrical system. Low maintenance cost is also the feature of step-up transformers.

Step-up transformers’ efficiency is nearly over 95% with the recent advancements in the technology.

I have written a detailed article about Overhead Transmission Lines, You can find it here  for more information.

Does Step Up Transformer Increases The Power?

No, Step up transformer does not increase the power. Step up transformer increases the voltage and decreases the current and ultimately power remains constant.

As, Power = Voltage * Current

For three phase transformer, the current equation is I = S / (3 V)

For example, if we have a 3 phase step up transformer of 160 KVA Power, the primary voltage is400V, The secondary voltage is 11KV.

This step up transformer primary current will be Iprimary = S / (3 Vprimary ) = 160*1000 / (√3 *400) = 230A

Secondary current will be Isecondary = S / (3 Vsecondary ) = 160*1000 / (√3 *11000) = 8.39A

As you can see, we use the same power for both primary and secondary current calculations. This is because Transformers Cannot Increase the Power, they can only convert the power. Transformers cannot produce the power, they can convert the power. The power remains the same on the primary and secondary sides.

In fact any device cannot give more power at the output than it took actually, because it is the Law of energy conservation too. This law states that energy cannot be produced or destroyed but only it can be converted.

Basic rule for the transformer is that power on the primary side is equal to the power on the secondary side.

Power and frequency remains constant in the transformer. Transformer maintains the constant power as it is a constant power device.

The basic principle in transformer is:

Input Power = Output Power

VP * IP   =   VS * IS

In this equation, it is assumed that no losses occur ideally.

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Is It Safe To Use A Step Up Transformer At Home?

Yes, it is safe to use a step up transformer at home, as microwave oven is a perfect example. Devices like microwave oven requires a high voltage to start.

A step up transformer is usually used for the conversion of existing power supply to the desired value of the voltage.

Usually, this transformer is present in the appliance most of the times. But devices like X-Ray machine sometimes requires a step up transformer externally.

Yep, it is safe to keep the transformers energized but make sure transformer is properly protected by the suitably rated fuse of the circuit breaker. Transformer consumes energy even without the load.

The reason for this consumption is that transformer’s primary winding or the coil circulates the current which as a result causes the core to raise the temperature.

Step Down Transformers

Step Down transformer is the opposite of the step up one. Its the transformers which primary side voltage is higher than secondary side or the output of the transformer. It is used to transform high-level voltage to a low-level voltage.

In this type, the number of turns on the primary side (Np) is greater than the secondary winding turns (Ns). The value of the secondary voltage depends on the number of turns on each side i.e turns ratio. If the number of turns in the secondary winding is half of the primary winding, The output voltage will be half of the value on the primary voltage. And so on.

We can make a simple Step Down transformer by using two coils with the ratio mentioned above. After that, we can wound it on an iron core. The formula for the secondary voltage calculation is simply the same turns ratio formula.

n = Np / Ns = Vp / Vs

If we have the same transformer mentioned in the example above, turns ration of = 2:1, primary voltage of 110 v. Its secondary voltage should be 110/2 = 220 v

Applications Of Step Down Transformers

Power transmission is done by the stepping up the voltage to high values, at the end user side a step down transformer is used to lower the high voltage to the consumption level, usually 110 or 220v.

Smaller step down transformers are used in the home appliances because in many appliances we need a low voltage level to convert it to DC voltage to run the appliances.

Step down transformer takes high voltage and reduces it to the safer level, so that it can be used at the household appliances, different electronic equipment, industrial and other applications.

There are a lot of applications of step down transformers including but not limited to:

  • Used in the adapters
  • Used in the cell phone chargers
  • Used in the stereos and the CD players
  • Step down transformers reduces the voltage and increases the current in welding machines.
  • Used in the television
  • Used in the inverters
  • Used in the Voltage stabilizers
  • Used at the substations
  • Used in the medical equipment
  • Used in the door bells
  • Used in the PCB Circuit modules
  • Used in the Rectifier Circuits
  • Used in the Refrigerators
  • One of the most common applications is to step down the voltage from medium to low voltage to be used in domestic applications. As you know electrical power is transmitted in high voltages. The end user voltages are low voltages, so we use step down transformers to decrease voltages before cities and end users.

Can We Use a Step Down Transformer as a Step up Transformers?

You can use a step down transformer as a step up transformer only theoretically, and not practically.

If we have a 300KVA transformer, its low voltage side is 400V, while the high voltage side is 11000V. Let’s do some math.

The current of the transformer in both sides formula is I (low voltage side) = S (power in VA) /(1.73 * Voltage)

I (low voltage side) = 300*1000 / (1.73*400) = 433 A

I (high voltage side) = 300*1000 / (1.73*11000) = 15A

Then, we have the low voltage side designed for voltage of 400 V and a current of 433 A, While the high voltage side is designed for voltage of 11000 V and current of 15 A.

In case of connecting the transformer sides in a reverse position, i.e connecting the high voltage on the low voltage side, then the winding insulation will breakdown due to the high voltage. This can cause it to burn.

On the other side, the high voltage side current will increase from 15 A to 433 A this mean the winding will break down.

As a conclusion, you cannot use a transformer as step up or step down if it is not designed to work in both directions. You can ask the manufacturer about that. I’m not sure there is a dual use transformer or not.

How Do You Identify If A Transformer Is A Step Up Or A Step Down?

The first thing you should check to identify a step up and step down transformer is to check the transformer nameplate. The primary and secondary side voltages are the data to seek for.

Of course the data will tell you the primary voltage values, and the secondary voltage values. As you know, the step up transformer primary voltage is lower than the secondary voltage and vice versa.

In other words if the transformer increases the voltage from the primary to the secondary, it is a step up transformer. If the transformer reduces the voltage, its a step down transformer.

step down transformer 11KV to 400V
step down transformer 11KV to 400V in my workplace

Another thing to consider to identify if a transformer is a step up or a step down, is the bushing of the primary and the secondary.

If the transformer is in service and is connected to the power source and a load, if the transformer is a step up its incoming bushing should be smaller in size than the outgoing bushing size, i.e the bushing of the primary is smaller in size than the secondary bushings, because it handles lower voltage than the secondary side.

In my work, distribution step down transformers are connected to the 11KV OHTL , while the loads are low voltage 400V.

Its easy to identify that these are step down transformers when looking at the primary bushing which are connected to OHTL, they are larger than the secondary bushings which are connected to 400V loads.

On the other hand, a power transformer is connected to the power generation station, 3.3KV, while the secondary is connected to 11KV OHTL.

It requires no experience to tell which bushing is larger in size, i.e the primary is lower in voltage, 3.3KV, while the secondary is higher in voltage, 11KV, this is a step up transformer.

Which Transformer Is Used In Substation (Step Up Or Step Down)?

Step down transformers are used at the distribution substations. They are used to reduce the voltage level comes from the transmission lines to levels that are safe for transmission in cities and residential areas.

In these substations, voltage value has to be stepped down for the additional distribution. This is one of the major applications of the step down transformer. As we know, electrical energy transmission is done at high voltage levels for economical purposes.

Before the high voltage overhead power lines enter a city, the voltage levels should be reduced. This voltages reduction is done through substations which have step down transformers to do this job.

Voltages at our homes are low voltages, usually 110V, this voltage reaches our homes after many stepping down stages using step down transformers in substations.

The transformers which we see near our residential places are step down transformers that further reduces the voltage level and then this voltage can be used by the end users like residential or the commercial customers.

In my workplace, The generation of electrical energy is 3.3KV, Then we step up the voltage to 11KV and transfer it through overhead power lines.

Before loads we step down the voltage again to 220V to be used in residential and work place, we don’t use substations because the distance between the generation and end user is not long.

Is Distribution Transformer A Step Up Or A Step Down Transformer?

Distribution transformer is a step down transformer. In the system of electric power distribution, a distribution transformer is that transformer that gives the final voltage transformation. It steps down the voltage for the distribution purposes for the commercial and the residential customers.

Step down transformers are used to step down the voltage which is used in the distribution lines to that level bearable by the end user.

Distribution transformer has the perfect voltage regulation. It operates 24 hours in a day with the maximum efficiency at almost 50% of the full load.

Usually the distribution transformers’ rating value is up to the 200 kVA.

Is Power Transformer A Step Up Or Step Down Transformer?

In general, power transformers are used in the transmission network for stepping up and stepping down the voltage level.

Power transformer can either be a step up or a step down transformer depending upon the need. Usually it mainly operates during the peak or the high loads.

It has maximum efficiency at the full load or near to the full load. A power transformer is a type of static machine which is used for the transforming power form one circuit to another circuit without altering the frequency.

Because there is no moving or the rotating part, that is why it is called the static device. A transformer operates on the principle

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