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What is an Isolation Transformer?

Author: Apogeeweb
Date: 31 Dec 2020
isolation transformer schematic


Ⅰ Isolation Transformer Definition

Ⅱ Isolation Transformer Construction

Ⅲ How Isolation Transformers Work?

Ⅳ What's the Main Function of an Isolation Transformer?

Ⅴ Special Purpose Isolation Transformers

 5.1 Pulse Transformers

 5.2 Austin Transformers

 5.3 Instrument Transformers

Ⅵ What are the Benefits of Isolation Transformers?

Ⅶ Isolation Transformers VS Autotransformers


Ⅰ Isolation Transformer Definition

Two copper coils that are wrapped around each other and are each supplied by their own power source make up an isolation transformer. While the term "isolation transformer" applies technically to any transformer, it is specifically a transformer that isolates an alternating current from a circuit. By separating two circuits with an induction loop or lowering the voltage of the alternating current until it enters the circuit itself, an isolation transformer does this. Transformers isolated from each other with main (input) and secondary (output) windings are known as isolation transformers. Under this configuration, a dielectric insulation barrier electrically separates the input power and output power.

what is an isolation transformer

Ⅱ Isolation Transformer Construction

Transformers can be described as two coils surrounding a core of ferromagnetic material, as shown in Figure 4.

Isolation transformer construction

The main and secondary coils are shown in the schematic representation; the electric source is connected to the primary, and the isolated output is taken from the secondary. Physically, the coils are distinct from each other and the heart. An early transformer was first used by Michael Faraday during his studies studying electromagnetism. Faraday found that a current-carrying wire generates a magnetic field surrounding the wire and that a current in one generated a magnetic field when two different wires were coiled around a toroid of soft iron, and the changing flux, in turn, induced a voltage in the other. Now known as mutual induction, Faraday is credited with finding that a shifting magnetic flux is caused in a circuit by an electromotive force according to the formula:

Isolation transformer construction formula 1

Sometimes this is shown using the absolute value of E:  The negative indicating the electromotive force opposes the current.

Although isolation is provided by any transformer consisting of two separate coils and no grounding shields, the term isolation transformer applies to transformers specifically designed for electrical insulation, the primary purpose of which is to isolate the AC source from circuits, devices and primary and secondary windings.

They also have special insulation between the primary and secondary coils and are built between windings to withstand high voltages. Since the capacitance and resistive paths of the coils can be connected to power line/transient voltage noise, isolation transformers have additional features to minimize common-mode noise (which occurs on both hot and neutral ground-referenced wires), transverse mode noise (which occurs between hot and neutral wires) and electromagnetic noise. DC signals and interference caused by ground loops are blocked by the transformer. To reduce any capacitance between the windings, electrostatic shields are used for sensitive equipment (computers or measuring instruments).


The insulation transformers used for protection generally have a 1:1 turn ratio, with the number equal to the turns in the primary and secondary windings, but when the voltage still needs to be changed, step-up and step-down isolation transformers are used. Check the specifications for the included features, the scores, and how they are designed when selecting an isolation transformer.

Ⅲ How Isolation Transformers Work?

Isolation transformers act in the same manner as other transformer types. To allow the primary coil to induce a current in the secondary coil, the isolation transformer is made of two electromagnets that are wrapped around each other. If more than the secondary coil is wound in the primary coil, the voltage is diminished. If more than the primary coil is wound into the secondary coil, the voltage is increased. In order to maintain the same voltage but to distinguish two circuits, an isolation transformer could have primary and secondary coils that are wound the same by causing a current from one coil to the other rather than providing a direct link.

Isolation transformer 3

Ⅳ What's the Main Function of an Isolation Transformer?

Its main role is to include certain circuits that are not capable of directly handling an alternating current safely. Not only does this ensure the full protection of your system, but it also helps to prevent short-circuits or fire accidents. It is included in most of the equipment to reduce the voltage until it hits the application for safety purposes. Another essential feature of using this transformer is that it helps to manage any required amount of voltage.

Ⅴ Special Purpose Isolation Transformers

Isolation transformers have been developed for specialized applications. Some examples are:

5.1 Pulse Transformers:

Optimized for the propagation of rectangular electrical pulses and to provide digital signal electrical isolation. These are used in the networking of computers.

5.2 Austin Transformers:

These power the air-traffic obstacle lamps you see on antenna structures, invented by Arthur O. Austin. The lighting circuitry on the antenna mast would conduct radio-frequency energy to the earth, if not isolated. The AC building mains are also completely separated from the tower by these transformers.

5.3 Instrument Transformers:

They are used to provide reliable voltage for meters and to securely isolate control circuits from high voltages/current. The transformer's primary winding is linked to the high voltage/current circuit and the meter, much like the connections shown in Figure 3, is linked to the secondary circuit.

Note: Some transformers are manufactured with only one winding that is tapped on the winding at various locations to split it into main and secondary portions. Known as auto-transformers, as the single winding is shared, these devices do not provide isolation. Separate coils have isolation transformers, with no physical connection between the coils, no ground on earth.

Ⅵ What are the Benefits of Isolation Transformers?

Because of their diverse uses and advantages, different industries and companies use isolation transformers. Some of its most significant advantages are listed here.

• Isolation can be replaced by isolation transformers in various circuits. With a 1:1 ratio, the main and secondary windings can be separated by insulation transformers.

• Transformers of isolation allow direct current power isolation simpler. In the case of telephone lines, where amplifiers are needed at different intervals, the separation of direct current components from the signal is performed by isolation transformers to control every amplifier on the line.

• By uniting a vessel with the electric power source, isolation transformers eliminate the possibility of electric shock. They allow the isolation of the person from the resource in such a way that the electrical wires do not directly contact the power line.

• Without isolation in electronics testing and servicing, it can prove dangerous to contact a live portion of the circuit. For isolation, 1:1 ratio transformers are therefore used to provide protection. For gadgets that use electricity, isolation transformers have therefore proven to be an excellent choice.

• With the aid of isolation transformers, all kinds of noise and sound produced by connecting the signal from the audio amplifier to the speaker output circuit are minimized.

• The amount created by a radio frequency on wide circuit devices is separated from the transmitter line by isolation transformers. They facilitate the relation to the transmitted signals of the amount generated by the radio frequency amplifier and direct it toward the antenna.

Ⅶ Isolation Transformer VS Autotransformer

Autotransformer VS Isolation Transformer

An isolation transformer is a main and secondary coil winding electrical transformer. By insulation, these windings are isolated. This insulation reduces the possibility of electrocution by simultaneously contacting the active components and the ground.

An autotransformer is a single-winding electrical transformer. The term "auto" applies not to any kind of automatic system but single-coil working alone. Portions of the same winding serve as both the main and secondary sides of the transformer in an autotransformer.

• Operation of an Isolation Transformer

An isolation transformer's primary function is to separate circuits. These transformers are designed and produced between the two windings with attention to capacitive coupling. Alternating current (AC) current from the primary to the secondary will also be coupled by the capacitance between primary and secondary windings.

• Operation of an Autotransformer

An autotransformer's primary function is to control the transmission line voltage and can be used to convert voltages. An autotransformer automatically changes the voltage according to the load, with only one winding. Such transformers require the correct operation of AC currents and will not operate on direct current.

• Common Applications for an Autotransformer

Boost at end of the long transmission line to compensate for line losses

Reduced starter voltage for an induction motor

To enable rectifier output control, multi-tap feeding the primary

Fluorescent light fixture start-up

• Common Applications for an Isolation Transformer

Computers and peripherals

Medical Equipment

Remote control equipment

Telecommunication equipment



1. What is an isolation transformer?

Isolation transformer is basically a transformer with winding ratio of 1:1, i.e., it has same number of primary as well as secondary windings.

Isolation transformer provides electrical isolation between two circuits by transfering energy in magnetic form from one circuit to another.

First circuit is connected in primary of transformer. Electric supply on this circuit is converted to magnetic field on primary winding and magnetic field magnetises secondary winding which is converted into electrical energy again in secondary circuit. Since it has 1:1 winding ratio voltage and current level of secondary circuit are same as that of primary circuit. So both circuits are electrically isolated yet energy is being transferred between them.


2. Where and why are isolation transformers used?

As the name suggests, they are used to isolate the two circuits electrically by providing a galvanic isolation between them. There are many reasons to use an isolation transformer.

  • Isolation transformers block transmission of the DC component in signals from one circuit to the other, but allow AC components in signals to pass.
  • Isolation transformers are used for impedance matching to get the most efficient power transfer between stages and to keep different stages electrically isolated to prevent ground loops.
  • Isolation transformers prevents harmonics from transferring from one side to other side.


3. How does an isolation transformer protect against an electric shock?

It doesn’t always protect against an electric shock but it will protect against an electric shock to earth for a single fault in a Multiply Earthed Neutral (MEN) system. Current needs a return path to the source and if teh secondary windings of the isolating transformer are not earthed then there is no return path for current flowing through the person back to the other terminal of the secondary winding. All that happens is that the contacted winding assumes the earth potential.

You will still get shocked if you contact both terminals or if you have multiple devices with earth faults that provide a return path for the current.

The benefit is that the isolating transformer continues to supply current even in the event of a short to earth on one of its secondary windings.


4. What are the disadvantages of isolation transformer?

The Isolation Transformer is a specially designed transformer which is used to isolate two different electrical circuits. The Isolation Transformer is mainly used to isolate the load or powered device from the power supply.

Some Disadvantages of Isolation Transformer are given below.

• When the Isolation Transformer operating as Pulse Transformer and it operate at low frequency there is distortion produces in secondary or output waveform.

• When isolation transformer operating at DC pulse signal, the saturation property of the core reduces.

• Isolation Transformer specially designed, that is why it is costlier than a normal transformer.


5. What's the difference between an isolation transformer and a regular transformer?

• The transformers having primary and secondary winding which are separated from each other known as Isolation transformer where as Regular Transformer are used for sending and receiving electricity .

• Isolation transformers are not used to increase or decrease voltage and Regular Transformer is used to increase or decrease the voltage and current in an electrical circuit.

• There are used to breaking the circuit into primary and secondary, so direct current noise can’t get through. Regular Transformers are designed to modify an alternating current voltage that runs from one electric circuit to another through electromagnetic induction.


6. What is the difference between isolation transformer and step up transformer?

Main purpose of isolation transformer is to electrically isolate two sides or circuits. This is done mostly for safety reasons. You may make the second side shock proof, or it may have its own DC supply.Usually the turns ratio of isolation transformer is one, meaning input and output will be same in magnitude, though occasionally it could be different.

While primary of transformer may be connected to live wire, secondary becomes safe from electric shock. Two different circuits can be connected this way.

Step up transformer is used for increasing the voltage from one level to a higher one. Main purpose is to have higher voltage level for the circuit on secondary side. The two sides may or may not be isolated, and turns ratio is greater than one.


7. What is the working principle of an isolating transformer?

Isolation transformer is just similar to our normal transformer but the difference is in the transformation ratio. It is 1:1 in isolation transformer. So it also works on the Faraday's law of mutual induction. It says that the emf induced in the secondary coil due to te production of magnetic flux by the voltages and currents of the primary coil.


8. What are the applications of isolating transformers?

• The main application of Isolation Transformer is, to make the isolation between a power supply and a powered circuit or powered device for the safety purpose.

• Isolation Transformer is used to transform electrical power between two circuits which are not connected electrically to each other. Those two circuits are may have the same voltage level or different voltage level.

• Isolation transformers are can be used as Pulse Transformer.

• Isolation transformers are used for computer network design. Here isolation transformer act as Pulse Transformer.

• Sometimes the Isolation Transformer used in electrical circuits as well as an electronic circuit to provide protection against Electrical shock.


9. Why do we need an isolation transformer to connect an oscilloscope?

The scope input shield is connected to the power outlet ground via the scope chassis for safety. It should never be connected to any point not at the same potential as that ground.Either the device under test should also be grounded, or completely isolated from ground. The isolation transformer is the preferred method in most cases.

When testing circuits solely using DC power, a lab type DC supply may have outputs isolated from ground. This is also acceptable.

It is important to think of all possible paths that arise through connections to other equipment, or parts of a system. The isolation transformer is safe in the most situations. 


10. What is the working process of an isolation transformer?

Isolation transformers are very important for providing isolation in medical instruments powered by the mains grid (220 V or 110 V AC), which is connected to the primary of an isolation transformer, but where the electronic network connected to the patient is connected to the secondary of the transformer. Since the secondary network is isolated from the primary, there is no path for an AC current from the mains to go to the ground through the patient. 

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