Isolation Transformer | Purpose Of Isolation Transformer

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Isolation Transformer working Principle
Isolation Transformer working Principle

Isolation Transformer:

Isolation transformers are used to transfer electrical power from a source of alternating current power to a device, where the powered device is isolated from the power source for safety measures. They do not have direct ground path of the current flow. They provide galvanic isolation; Galvanic isolation is a principle of isolating functional sections of electrical systems to prevent current flow; no direct conduction path is permitted. Energy or information can still be exchanged between the sections by other means, such as capacitance, induction or electromagnetic waves, or by optical, acoustic or mechanical. However, these transformers block the transmission of the DC component in signals from one circuit to another, while letting the AC components to pass.




Isolation transformers are nothing but a 1:1 ratio transformer. Power source is connected between the primary, and the secondary windings are used to protect against electric shock between the ground and energized conductors. They are also used to suppress electrical noise and are used for supplying power in sensitive devices like computers, medical devices and laboratory instruments. There is special insulation between the primary and secondary in such transformers, and high voltage ranging from 1000 to 4000 volts can be borne between the windings.

isolation Transformer working Principle
Isolation Transformer working Principle Ref: fair use http://www.soundonsound.com/sos/nov06/articles/crosstalk_1106.htm

Now you see the picture. When the man touches the live terminal of the source, then the leakage current will flow through the human body to ground and the man get shock because of one terminal is already is connected to ground.

Also see:

Now you see the second picture the power source is connected through an isolation transformer. Now the same man touches the secondary terminal of the isolation transformer means, he do not get shock. Because there is no path for leakage current flow typically, the ground reference has removed completely.

Note:In the picture none of the secondary terminals are connected to the earth point.

Now You see the third picture: In the diagram the return path is shown as either capacitive or direct. If the coupling is capacitive then you may feel a “tickle” or somewhat mild “bite” from the live conductor. If the other conductor is grounded, then you are back to the original transformer less situation. (Capacitive coupling may occur when an appliance body is connected to a conductor but there is no direct connection from body to ground. The body to ground proximity forms a capacitor.

See: CVT in Electrical Capacitive Voltage Transformer CVT



This is why, an isolating transformer should be used to protect only one item of equipment at a time. With one item a fault in the equipment will probably not produce a dangerous situation. The transformer has done its job. But with the N number of equipment – if one has a fault from neutral to case or is wired wrongly (neutral touches the ground), this may transfer to just like a first condition and it is hazard to the user even if you use isolation transformer (isolation transformer become useless).

If you are working with the electrical or electronic repair equipment, You should use isolation transformer.

Key points of Isolation transformer:

  • Isolation transformers are used in electronics testing and servicing to provide safety, without which touching a live part of the circuit with hazardous voltage can cause severe damage.
  • Isolation transformers are used for power supply of devices that are not at ground potential.
  • Isolation transformers facilitate direct current power isolation. In case of telephone lines, where amplifiers are required at various intervals, it is isolation transformers that carry out the separation of direct current components from the signal to control every amplifier on the line.
  • Isolation transformers prevent the risk of electric shock by uniting a vessel to the electric power source. They facilitate separation of the person from the resource in a manner that the electric wirings do not touch the power line directly.




Video Explanation of isolation Transformer (English):

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