What is Isolation Transformer and how it works?

[Ch. Zeshan YousafParticipant]

Isolation transformer:

An isolation transformer is a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source, usually for safety reasons. Isolation transformers provide galvanic isolation and are used to protect against electric shock, to suppress electrical noise in sensitive devices, or to transfer power between two circuits which must not be connected. A transformer sold for isolation is often built with special insulation between primary and secondary, and is specified to withstand a high voltage between windings.

Isolation transformers block transmission of the DC component in signals from one circuit to the other, but allow AC components in signals to pass. Transformers that have a ratio of 1 to 1 between the primary and secondary windings are often used to protect secondary circuits and individuals from electrical shocks. Suitably designed isolation transformers block interference caused by ground loops. Isolation transformers with electrostatic shields are used for power supplies for sensitive equipment such as computers, medical devices, or laboratory instruments.

Terminology:

Sometimes the term is used to emphasize that a device is not an autotransformer whose primary and secondary circuits are connected. Power transformers with specified insulation between primary and secondary are not usually described only as “isolation transformers” unless this is their primary function. Only transformers whose primary purpose is to isolate circuits are routinely described as isolation transformers.

Operation:
Isolation transformers are designed with attention to capacitive coupling between the two windings. The capacitance between primary and secondary windings would also couple AC current from the primary to the secondary. A grounded Faraday shield between the primary and the secondary greatly reduces the coupling of common-mode noise. This may be another winding or a metal strip surrounding a winding. Differential noise can magnetically couple from the primary to the secondary of an isolation transformer, and must be filtered out if a problem.

The Advantages of an Isolation Transformer:

Engineers often use an isolation transformer to maintain equipment separation from a power source. As a result, users are able to keep sensitive items like healthcare and laboratory equipment powered and protected. Due to the effective design, there are four main advantages that come with using an isolation transformer.

Safety:

Perhaps the biggest advantage that isolation transformers offer is improved safety. This is particularly important in a setting such as a hospital or nursing home where expensive, life-supporting equipment has the potential for getting damaged. Using an isolation transformer also reduces the potential for doctors and patients to experience electrical shock as the result of defective equipment.

Reduces Surges:

Another advantage of isolation transformers is that they reduce power surges.
Electrical equipment can run smoothly without the risk of power surges because the DC signals from a power source are isolated. This means that equipment can function at a high level even if there is a power malfunction.

Noise Reduction:

Another reason why isolation transformers are efficient is because of their noise reducing capabilities. The design of these devices naturally filters noise from power lines by using what are called separate Faraday shields. These shields help to block electric fields from interrupting the power flow. In turn, there is less electromagnetic noise involved with running electrical equipment.

Better Power Quality:

There is usually better overall power quality when users employ an isolation transformer. The Faraday shields also help with efficiency because they reduce the potential for current leakage. As a result, important electrical devices can function at an optimized level.

Advantages of Standard Isolation Transformer:

An isolation transformer is a type of transformer which has symmetrical windings. This is used to decouple two circuits. The two windings are called primary winding and secondary winding. Both of them are not connected in isolation transformers. Thus they are said to ‘insulate’ as they are insulated from one another. Isolation transformers are transformers in which the mains transformers give isolation rather than voltage transformation. They are 1:1 laminated core transformers. As a safety precaution it is used in electronics servicing and testing as a 1:1 power transformer. The neutral wire of an outlet is connected to the ground. The objects, such as the lamp or the floor that are grounded near the device that is being tested, might be at a hazardous potential difference in comparison with the device that is tested. The use of the isolation transformer eliminates bonding and it contains the shock hazard within the device.

In isolation transformers, unless it is bonded when being installed, the output winding will be floating or isolated from the earth ground. As there is no secondary neutral to ground bonding, common mode noise is done away with. This is especially apt for circuits of sensitive equipments and for site electrical upgrades.

The advantage of an isolation transformer is that it is able to take AC power or signal from one device to another without the two being electrically connected. The isolation transformers block DC signals from one circuit to another from being transmitted, but allow AC signals. The ground loops that cause interference are also blocked. Computers and sensitive equipments in laboratories use isolation transformers with electrostatic shields for power supply.

There are many advantages in using standard isolation transformers.

1. The primary and secondary windings may be used to step up or step down the voltage output. So, it can be made in such a way that a 120 V load can match a 208V load.

2. Isolation transformers which have the Faraday shield will have improved power quality because of attenuated higher frequency noise currents. They Faraday shield also decreases the leakage current of the equipment and the isolator below 300 microamphs.

3. They help in giving a better impedance matching of a critical load to an electrical circuit.

4. In hospitals the hospital grade isolation transformers protect the sensitive equipments.

5. When surge suppression parts are used at the input and the output, with the whole line isolation, it helps in the continuous filtering of power line noises in all modes.
Microprocessors face the problem of reliability. Neutral-to-ground voltage and noise can be eliminated by the isolation transformer. This gives a ‘code-legal’ way to re-bond the electrical system safety ground to the neutral conductor on the transformer secondary.

In our day to day life we all depend on electrical and electronic equipments which are very sensitive. Reliable current at the necessary voltage becomes an absolute necessity. The use of isolation transformers controls power surges. Noise is also reduced. It is of great use in electronic testing and servicing. It is also useful to step up and step down the voltage. This is useful in preventing electrocution. We need to know all about isolation transformers since their advantages are many. We need to get the best isolation transformers so that we can handle the power supply to our electrical and electronic equipments effectively.

How does an isolating transformer work?

Isolating transformers work by having a regular step-up or step-down transformer in which two coils of insulating wire are wound around an iron containing core, but it includes a Faraday shield which isolates the coils from each other and grounds the transformer case. This effectively isolates the transformer’s coil, protecting the device from grounded objects and protecting people from the dangerous, deadly high voltages.

Transformers themselves work based on magnetic currents. One coil, called the primary coil, is connected to a source of alternating current which produces a varying magnetic field in the iron containing core. This varying magnetic field then produces an alternating current in the second coil, which is connected to a separate circuit. The ratio of the number of turns in the first coil to the number of turns in the second coil, also called the turns ratio, determines the ratio of the voltage change that the transformer provides. Step-up transformers increase the voltage output by having more turns in the secondary coil than in the primary coil. Step-down transformers work in the reverse. Power remains the same through a transformer, and since the electrical power is equal to the voltage times the amperage, the ratio of the change of the voltage through a transformer is inversely proportional to the ratio of the change in the current.

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