Technology

Isolation Transformer: All You Need to Know

Isolation transformer refers to the transformer with electrical isolation between the input winding and the output winding. The isolation transformer is used to avoid accidental contact with the live body at the same time. The isolation of the transformer is to isolate the respective currents of the primary and secondary windings. In the early days, it was used in the power industry in European countries and was widely used in the control power supply of general circuits, security lighting, and indicator lights in the electronics industry or industrial and mining enterprises, machine tools, and mechanical equipment.

There is a special transformer with high insulation strength between the primary side and secondary side windings to isolate different potentials and suppress common-mode interference. The transformation ratio of the isolation transformer is usually 1:1.

Isolation Functions

isolation transformer’s function will be to fully block the electric current between the primary as well as the second side in order to create a circuit that is completely isolated. Additionally the loss of high-frequency energy in the iron core of the transformer is used to limit the entry of high-frequency noise within the loop of control. Utilizing the isolation transformer in order to connect the secondary in the ground is only utilized in circumstances when the power supply range is limited while the power line itself is not long. The capacitance current that the system is sending to the ground is small to result in personal injury. Another important aspect is to safeguard your safety! Isolate hazardous voltages.

With the constant development of technology for power, transformers is playing an increasing role as a vital component of the power system. its operation safety is directly linked to the security of the whole power system. The distortion of the transformer’s coil is a result of dimensions that change amplitude and axial in body displacement, coil twist and twist, etc. when the coil is exposed to force.

There are two major reasons for the deformation the transformer coil. One could be that it is invariably subject to short-circuit faults from outside during its operation. The second is an accidental collision of the transformer in transportation and lifting.

Isolation Transformer Work Principle

Isolation transformers create the electrical separation in between AC electricity cables (mains) and equipment powered by them. This means that there’s no DC route through the 2 windings. They are mostly utilized for three reasons:

  1. The secondary winding should be isolated from the the ground
  2. Allow the operation of rise and fall in the main line (mains) voltage
  3. Limit the propagation of lines noises from primary to the secondary and reverse

Isolation transformers have the same characteristics in transformers (Figure 1). Secondary and primary windings are connected to an identical ferromagnetic base.

Figure 1: Schematic of a simple power transformer consisting of an NP-turn primary winding and an NS-turn secondary winding on a common ferromagnetic core.

In the figure, the primary winding has NP turns around the ferromagnetic core and the secondary winding has NS turns. The relationship between the primary voltage (VP) and the secondary voltage (VS) is shown in Equation 1:

If the primary winding has more turns than the secondary winding, the voltage on the secondary winding will be lower than the voltage on the primary winding. This is a buck configuration. If the primary winding has fewer turns than the secondary winding, the voltage on the secondary winding will be higher than the voltage on the primary winding, resulting in a boost configuration. Most isolation transformers have the same number of turns in the primary and secondary windings, therefore primary and secondary voltages are the same.

Energy in a transformer is conserved, so if we ignore losses, the product of VP and the primary current (IP) will be equal to the product of VS and the secondary current (IS). The power rating of a transformer is determined by multiplying the RMS voltage of the primary winding by the RMS primary current. This is “apparent power,” measured in volt-amperes or VA.

The points on the schematic are phasing points that indicate the primary and secondary current directions. As shown, the current flowing into the primary side of the winding causes a secondary current to flow out of the secondary side of the winding. This is important if the windings are to be placed in series or parallel. Failure to follow the phasing of the windings can lead to errors.

Figure 2: Cross-sectional view of an isolation transformer in shell construction, where the primary and secondary windings are concentrically wrapped around insulating layers with a Faraday shield inserted between the two layers.

A Faraday shield is an electrostatic shield that reduces the capacitance between the primary and secondary windings and is usually grounded. This shielding reduces the magnitude of common-mode noise and transients passing through the transformer.

The primary and secondary windings in an isolation transformer are highly insulated to minimize direct conductance between them. The measure of insulation effectiveness is leakage current. Most isolation transformers are also tested using a high potential or withstand voltage tester. When checking for leakage current, these instruments apply a high voltage across the insulation.

The physical construction of an isolation transformer can take many forms, including shell construction (Figure 2). Among them, the primary and secondary windings wrap the insulating layers in a concentric manner, and the Faraday shield is inserted between the two layers.

Faraday shields can be foil layers or close-wound windings as shown. The ground is usually on the primary side and is connected to the ground. Since the primary and secondary windings already use enameled wire, this construction is called “double insulation”.

Alternatively, the windings can be placed side-by-side on the core, which is called a “multi-slot bobbin” configuration, or wound on a toroidal core.

Commercial isolation transformers

Isolation transformers are available in open construction or enclosed in shielded construction (Figure 3). Hammond Manufacturing’s 171E isolation transformer uses a shielded case construction. The end cap shield contains the transformer’s magnetic field and is also used to minimize interference from magnetic fields outside the transformer. This 500 VA 1:1 transformer also includes lead, NEMA, three-wire ground input and output connectors, and an integrated overload circuit breaker.

Although the ground wire is connected to the secondary output connector, it is not used in most isolation transformer applications. The leakage current between the primary and secondary of this transformer is less than 60µA at the rated input voltage.

Figure 3: Example of an isolation transformer with a shield on the end cap

The DU1/4 from Bel/Signal Transformer is a 250 VA isolation transformer with open construction with two sets of multi-tap windings. There are two primary and two secondary windings each (Figure 4).

Figure 4: Bel/Signal Transformer’s DU1/4 is an open isolation transformer with two sets of primary and secondary tapped windings.

The primary and secondary windings have the same voltage ratings, 0, 104, 110, and 120 volts, respectively. This allows series or parallel connections on the primary or secondary windings. Therefore, for a 110 or 220-volt input, the nominal 1:1 ratio can be maintained. Also, it is possible to configure a step-up transformer from 110 volts to 220 volts, or a step-down transformer from 220 volts to 110 volts. Additionally, multi-tap windings allow intermediate voltage ratings such as 208 volts, 214 volts, or 230 volts (Figure 5).

The power connection of the transformer is screw terminals.

Figure 5: The dual winding of the DU1/4 allows for many possible wiring configurations, including 1:1, 2:1, 1:2 voltage ratios.

If both primary and secondary windings are in series, the transformer is a 220-volt input with a 1:1 voltage ratio. If both the primary and secondary windings are in parallel, it is a 110-volt input, a 1:1 voltage ratio, and the available current is twice that of a single winding. If the primary windings are placed in series and the secondary windings are in parallel, the primary voltage will drop by a factor of two. A 2:1 boost can be achieved if the secondary windings are in series and the primary windings are in parallel.

Medical isolation transformers

Isolation transformers used in medical applications must meet stricter leakage current requirements. There are maximum leakage current specifications for ground leakage, enclosure leakage, and patient leakage. Ground leakage refers to the leakage current in the ground wire of the equipment. Enclosure current describes the current flowing from exposed conductive surfaces to the ground through conductors other than the ground wire. Patient leakage is the current flowing through the patient to the ground when normally connected to the device. Most devices in this category are certified to UL/IEC 60601-1.

Triad Magnetics’ Model MD-500-U is a 500 VA isolation transformer for medical applications (Figure 6). The transformer is certified to the UL 60601-2 specification by Underwriters Laboratories (UL) with a typical leakage current of 10 µA and a maximum leakage current of less than 50 µA.

Figure 6: The Model MD-500-U is a 500 VA isolation transformer for medical applications with a leakage current of 10 µA (typ) and uses a toroidal transformer to keep it compact and minimize stray magnetic fields.

The MD-500-U utilizes a toroidal transformer to minimize stray magnetic fields and maximize efficiency while minimizing size. Like most stand-alone medical transformers, it is securely enclosed in a steel case with built-in fuses and thermal cutoff switches.

The differences in Isolation Transformers and Normal Transformers Isolation Transformer and the Normal Transformer

The main goals of both work are distinct. Modifying the voltage on demand and then transferring it to the output is the primary objective of the normal transformer. Normal transformers can be divided into step-down and step-up ones based on their intended purpose. The isolation of voltage isn’t the primary function of normal transformers. Certain transformers do not have any separation between the voltages of the primary side and that of the secondary side. Normal transformers are focused on changing the voltage , and are unable to be able to isolate the voltage.

An isolation transformer one that is designed for use with special purpose. The main difference between these transformers is not just that the secondary wire is not grounded, but also that there exists an isolated layer in between the secondary wires and the cutting point. It is linked to the grounded terminals that is the main. This means that the secondary will not be isolated from the electric grid , but as well be isolated the electrostatic field.

Isolation transformers have also something that is similar to ordinary transformers. They’re operating principles are built on the concept of inductive electromagnetic energy.

The differences in Control Transformers in addition to Isolation Transformers

1. Different uses

A control transformer serves as the power source for the circuit for electrical power control in order to satisfy the voltage requirements of various electrical components.

Isolation transformer

  1. Different voltages on both sides of the transformer, or the necessary voltage signals to be transmitted via the isolation transformer, to ensure that the various voltages at each end of the transformer won’t cause interference or harm to each other for instance, like certain Thyristorsas well as IGBT circuits.

2. It is utilized for applications which require different impedance matching like Audio power amps.

It is utilized for personal security in certain applications like lighting transformers.

2. Different effects

The control transformer is the source of the power needed to run the control system in the operation of electrical equipment.

The purpose of the isolation transformer is to stop electronic equipment to avoid being impacted by the harmonics from the supply of power. It is actually an unreliable filter. The typical input voltage for the control transformer will be 6.3V 12V 24V, 36V, 50V 110V, 127V etc. To reduce expenses, certain control transformers can only produce just one low voltage which is three or more voltages. The isolation transformer usually is equipped with a transform ratio of 1:1. The two types of transformers perform distinct functions, which means they can’t be used together.

3. Connection

For instance when you are using an imported electrical circuit for driving all electrical relays contactors and contactors. are at 220 volts and that power source is a 3-phase 4-wire. The control circuit could be constructed directly making use of Zero Line. However, this car’s steering wheel includes a control handle and the electrical engineer used an isolation transformer. the secondary transformer is the power source of an electrical circuit controlling. Because this circuit’s secondary is not grounded so even if a person gets in contact with any two volts control voltage, no danger of electric shock as this transformer functions as simultaneously a control transformer and an isolation transformer.

Differentialities Between Single Phase Isolation Transformer and Three Phase Isolation Transformer

An isolation transformer is usually referred to an 1:1 transformer. The secondary coil of the transformer isn’t connected to ground, and there is no differences between any line between its secondary coil or ground, making it secure to utilize it.

Isolation transformers can also be classified into isolation transformers with a single phase as well as 3-phase isolation transformers. While they share similar functions but they are different kinds of transformers. What are the main differences between them?

1. Different types of I/O switching power sources

Single-phase isolation transformers differ in comparison to three-phase isolation transformers in the sense of their output and input switching types of power supply. The output and input of the single-phase isolation transformer is 100% signal-phase AC power that produces single-phase power sources. The output and input of the isolation transformer all have three-phase identical AC currents that are able to produce two kinds of switching power sources that are three-phase power supply as well as the single-phase switch power source.

2. Principal uses

Single-phase isolation transformer has a simple in its structure and weightless, which makes it more suitable to be used in distribution room network that has the smallest load density. The construction of the three-phase isolation transformer is extremely complex and is therefore used in many industrial production automation machines like printing and packaging equipment, petrochemical, post and telecommunications and many other areas where a normal operating voltage is required.

The main difference between isolation transformers that are single-phase or three-phase isolation converters is apparent in the different types and principal applications of I/O switching power sources. As you can see in the introduction to this article that follows, both single-phase isolation transformers and three-phase isolation transformers possess distinct advantages and characteristics.

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