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ISOLATION TRANSFORMER

What is 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; no conductive path is present between source and load. 


This isolation is 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 between energized conductors and earth ground. 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. 

Advantage of Isolation Transformer

Isolation transformers are generally used in critical equipment that must work properly such as equipment in the operating room, data center, machinery, etc. By using an isolation transformer, it is hoped that there will not be a mall function from the resulting equipment

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.

Medical Isolation Transformer

Medical grade isolation transformers are designed to isolate the patient and the operator from an electric shock and to protect the equipment from power surges or faulty components.For the safety of the patient in hospitals, all diagnostic or therapeutic medical equipment (medical electrical devices and non-medical electrical devices in the patient’s environment and areas for medical use) should be completely isolated from the supply line using strengthened isolation. Complete patient/operator safety is assured by medical-grade isolation transformers with very low leakage current (IEC 60601-1 medical electrical equipment).

Medical grade transformers are designed to isolate the patient and the operator from an electric shock and to protect the equipment from power surges or faulty components.Medical grade transformers also maintain strict adherence to the following:

  • Maximums on earth, patient or enclosure leakage current
  • Compliance to the harmonized IEC 60601 standard
  • Minimums on creepage distance and air clearance
  • Maximum temperature rise

Benefit of Medical Isolation Transformer

  • Maximums on earth, patient or enclosure leakage current
  • Compliance to the harmonized IEC 60601 standard
  • Minimums on creepage distance and air clearance
  • Maximum temperature rise

A secure galvanic separation is provided from the public power supply, within the leakage current limits of connected devices. The low stray magnetic fields and fault-tolerant design makes these transformers suitable for use near monitors. They are not only an ideal solution for medical diagnosis or medical electronic devices, but they can also be used in IT equipment and video systems in the patient environment.

Isolation Transformer Design Methods

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Medical grade isolation transformers use two design options to achieve isolation: safety ground, and reinforced insulation.

Safety Ground — Safety ground transformers utilize standard transformer isolation. A safety shield between the primary and secondary coils, with insulation between the shield and each coil, maintains leakage current maximums. The safety shield has to be thick to be able to meet required tests in the safety standard. If the isolation breaks, the electrical path goes directly to ground, providing safety.

Double/Reinforced Insulation — For a transformer that relies on double or reinforced insulation there is no “safety” shield, but the insulation, as indicated by the name, is much thicker. It is designed so that all layers of the insulation can pass the thickness and high potential voltage tests required by the standard. If one insulation layer breaks, the next layer will be able to provide the required safety.

In both design options, the construction design must still meet the required creepage and clearance requirements. If the transformer includes a static shield for noise reduction, it is important to note that this shield does not provide the transformer with safety ground but rather works as a functional earth. When the shield is grounded, it attenuates the common mode noise and can reduce the leakage current from the primary to the secondary winding (please note that this leakage reduction is not the same as when measured primary to ground).

Normally, without extra mechanical barriers between the primary and shield and secondary, a transformer with double/reinforced insulation has lower leakage current than the one with a safety shield.

A safety shield wire should be connected to the protective earth terminal in the equipment while the static shield, if included, should be connected to the functional earth terminal.

Medical Grade Isolation transformers are mostly used in a 1:1 ratio (the primary voltage rating equals the rated secondary voltage value). The two windings will have the same number of turns. There might be a slight difference in the number of turns to compensate for voltage drops; otherwise, the secondary voltage would be slightly less than the primary voltage.

By using isolation tape and a screen winding between the primary and secondary windings the required dielectric strength of ≥ 4 kV for reinforced and double insulation is achieved, plus the required “general earth leakage current” of < 100 µA is also achieved.
   

Isolation Transformer for Data Centre or Critical IT Device !

DC power supply systems such as the UPS are widely used as the source of power for modern-day IT and telecom applications. Public digital infrastructure such as IT Data Centers, mobile towers, or digital home applications such as laptops and modems rely on UPS devices for safe, uninterrupted, 24X7 DC power supply. Sometimes we may wonder why are isolation transformers used in ups systems or what is the role of an isolation transformer in UPS? Isolation transformers play a critical role in these DC power systems as they safeguard the expensive and sensitive equipment from the irregularities of the AC mains power supply.

The critical functions that an isolation transformer performs in safeguarding a UPS include:

  • Isolation of the output from the source and its associated noise
  • Step down of voltage from the supply line to suit the equipment under the protection
  • Reduction of harmonic currents within the UPS (blocks 3rd, 9th, 15th, other multiples-of-three harmonic currents)
  • Providing impedance to limit fault current
  • UPS supply may be on a high resistance grounding system and the loads require a solid grounding
  • Creating a local ground-bonded neutral
  • Safeguarding against extremely high or low mains voltage
  • Conformance to international standards and specifications for equipment safety