Galvanic isolation
Encyclopedia
Galvanic isolation is a principle of isolating functional sections of electrical systems
, thus preventing the movement of charge
-carrying particles from one section to another, i.e. no direct current
flows between the sections. Energy or information can still be exchanged between the sections by other means, e.g. capacitance
, induction
or electromagnetic waves, or by optical, acoustic or mechanical means.
Galvanic isolation is used in situations where two or more electric circuits must communicate, but their grounds
may be at different potentials
. It is an effective method of breaking ground loops
by preventing unwanted current from flowing between two units sharing a ground conductor
.
Galvanic isolation is also used for safety, preventing accidental current from reaching ground through a person's body
.
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
, thus preventing the movement of charge
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
-carrying particles from one section to another, i.e. no direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
flows between the sections. Energy or information can still be exchanged between the sections by other means, e.g. capacitance
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
, induction
Electromagnetic induction
Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, induction motors, electric motors, synchronous motors, and solenoids....
or electromagnetic waves, or by optical, acoustic or mechanical means.
Galvanic isolation is used in situations where two or more electric circuits must communicate, but their grounds
Ground (electricity)
In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....
may be at different potentials
Electric potential
In classical electromagnetism, the electric potential at a point within a defined space is equal to the electric potential energy at that location divided by the charge there...
. It is an effective method of breaking ground loops
Ground loop (electricity)
In an electrical system, a ground loop usually refers to a current, almost always unwanted, in a conductor connecting two points that are supposed to be at the same potential, often ground, but are actually at different potentials. Ground loops created by improperly designed or improperly installed...
by preventing unwanted current from flowing between two units sharing a ground conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
.
Galvanic isolation is also used for safety, preventing accidental current from reaching ground through a person's body
Electric shock
Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....
.
Overview
- TransformerTransformerA transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
s couple by magnetic fluxMagnetic fluxMagnetic flux , is a measure of the amount of magnetic B field passing through a given surface . The SI unit of magnetic flux is the weber...
. The primary and secondary windings of true transformers are not connected to each other (but autotransformerAutotransformerAn autotransformer is an electrical transformer with only one winding. The auto prefix refers to the single coil acting on itself rather than any automatic mechanism. In an autotransformer portions of the same winding act as both the primary and secondary. The winding has at least three taps where...
s do not provide galvanic isolation). The voltage difference that may safely be applied between windings without risk of breakdown (the isolation voltage) is specified in kilovolts by an industry standard. The same applies to transductorsMagnetic amplifierThe magnetic amplifier is an electromagnetic device for amplifying electrical signals. The magnetic amplifier was invented early in the 20th century, and was used as an alternative to vacuum tube amplifiers where robustness and high current capacity were required...
. While transformers are usually used to change voltages, isolation transformerIsolation transformerAn isolation transformer is a transformer used to transfer electrical power from a source of alternating current power to some equipment or device while isolating the powered device from the power source, usually for safety...
s with a 1:1 ratio are used in safety applications.
If two electronic systemElectronic SystemElectronic System is a Belgian synthesizer group .Disco Machine is an album of seven original compositions from Dan Lacksman, who’s better known as being part of the group, TELEX. This material was first recorded in 1977.- External links :*...
s have a common ground, they are obviously not galvanically isolated. The common ground might not normally and intentionally have connection to functional poles, but might become connected. For this reason isolation transformers do not supply a GND/earth pole. - Optocouplers transmit information by light waves. The sender (light source) and receiver (photosensitive devicePhotosensitivityPhotosensitivity is the amount to which an object reacts upon receiving photons, especially visible light.- Human medicine :Sensitivity of the skin to a light source can take various forms. People with particular skin types are more sensitive to sunburn...
) are not electrically connected; typically they are held in place within a matrix of opaque, insulating plastic. - CapacitorCapacitorA capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
s allow alternating currentAlternating currentIn alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
(ac) to flow, but block direct currentDirect currentDirect current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
; they couple ac signals between circuits at different direct voltages. As capacitors can and do fail by going short circuit, connecting together circuits that should be isolated, there are special ratings for capacitors used for safety isolation, such as "Class Y" . - Magnetocouplers uses giant magnetoresistance (GMR) to couple from AC down to DC.
Applications
- Optocouplers to decouple a function block from another connected to the power grid or other high voltage, for safety and equipment protection.
- Optocouplers to transmit a signal between circuit blocks at different potentials.
- Transformers to allow the output of a device to "float" relative to ground to avoid potential ground loops.
- Isolation transformers to increase the safety of a device, so that a person touching a live portion of the circuit will not have current flow through them to earth.
- Power sockets intended for electric razor supply must employ a residual-current deviceResidual-current deviceA Residual Current Device is a generic term covering both RCCBs and RCBOs.A Residual-Current Circuit Breaker is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor...
or an isolation transformerIsolation transformerAn isolation transformer is a transformer used to transfer electrical power from a source of alternating current power to some equipment or device while isolating the powered device from the power source, usually for safety...
(to prevent an electric shock if the razor should be dropped into water). - Boats connected to improperly grounded shore supply systems should employ a galvanic isolator to isolate from any stray currents in the marina (either from the shore mains or neighbouring boats). Without the isolator, a galvanic corrosion path may be created damaging metal equipment below the waterline. Zinc anodes may help to prevent this, but often prove insufficient when the boat stays in the marina for extended periods.