What is galvanic isolation?
Galvanic Isolation is a method to isolate electrical functional sections and circuits from each other. There is no conduction between isolated functional sections of the electrical systems.
Yet the energy/signal can be transferred through the isolated region. The flow of the current through this region is not permitted. When there is a need for communication (sending a signal) from one functional block to the other functional block while keeping the grounds at different energy levels (potentials).
Galvanic isolation is an effective method to avoid interference, noise, and hum. Also, to avoid ground loops, galvanic Isolation is used. So, galvanic isolation prevents the current that is not needed/wanted. That is why it is a good principle to be used in the manufacturing of the safety purposes. The reason for using the galvanic isolation is to avoid the error or the faults that could occur in systems with different grounds.
Let me explain this to you using a very common example. Do you know the wired internet connection? It is called the Ethernet. So, basically, it has a sender and a receiver. During the communication, when the sender initiates the communication, the sender has a device that is getting its power from a power source on the sender’s end. While the same happens on the other side i.e., the receiver side.
On the receiver side, the receiver’s device receives the information but the ground between receiver and sender is not being shared. So, if the concept of galvanic isolation didn’t exist, it would be impossible to use Ethernet.
A very common example that uses galvanic isolation is transformers. In transformers the sending end is called the primary side and receiving end is the secondary side. Primary and secondary ends are not connected electrically (by wire).
There is isolation (galvanic isolation) between these ends. The connection is pure magnetic and energy is transferred by magnetic flux.
Another example is a capacitor. We have seen the general diagram of parallel plate capacitors. If we observe, just like the windings of transformers, the plates of capacitors are also galvanically isolated.
So, conclusively, we can say that galvanic isolation is needed for safety, preventing ground potential differences (ground loops), and improving noise immunity. It prevents current to flow through an operator to the ground while working on a high voltage system. It allows the communication of energy/ signal on equipment on different ground levels.
The noise immunity is one of the best features of galvanic isolation.As each LTI system has a transient state of operation, this state adds noise to the system that may change the levels of voltage. Galvanic isolation provides immunity from this noise.
For more information about capacitors read my detailed article here.
How does Transformer provide galvanic isolation?
The transformer (not auto-transformer) provides galvanic isolation by isolating the power source from the load using the isolation between its primary and secondary sides.
A galvanic transformer is used as a safety device. It should have a 1:1 primary and secondary turns ratio. The purpose of galvanic isolation in the transformer is to provide safety so the 1:1 will work.
A Galvanic transformer transfers electric AC power from the source to a device. This device is isolated from the AC power source and has a lesser effect of transient oscillations (harmonics) on itself.
There is no path for the current to flow from the AC power source to the device. The signal (voltage) has a DC component and an AC component. DC component is not very good for the health of the circuit as it plays a major role in heating up the circuit. Galvanic isolation suppresses the DC component of the voltage. The AC component, however, passes through the isolation.
The operation of galvanic isolation in a transformer is performed by capacitive coupling. Capacitive coupling is achieved between the energized (primary) winding and de-energized (secondary) winding. This coupling of the capacitance couples the primary and secondary windings’ too.
Due to the difference in the ground (different grounds) the problem of CMV (Common-Mode Voltage) occurs. CMV can not be eliminated but reduced by a properly designed derivative filter. In the transformer with galvanic isolation, CMV is reduced by a grounded Faraday shield.
So, the load device that is connected to a galvanic isolated transformer is saved from electric shocks, and undesired noise from the circuit is also removed due to the galvanic isolation in the transformer.
Where and why galvanic transformers are used?
Galvanic transformers are used for:
- Safety purposes
- Removal of noise
While testing the electrical devices, the conductors in that devices attain a very high level of voltage. This high voltage can cause a problem if the conductors come in contact with the ground.
So, a 1:1 galvanic isolated transformer is used for safety purposes. A galvanic transformer does not provide any conduction passage between the primary and secondary sides of the transformer.
As, the danger of a conductor finding a ground near itself eliminates, so does the danger of a short circuit. Let’s say that an electrical engineer has to check a device using a test device and he doesn’t know that the test device is short(ed) inside.
But, the power supply is connected through a galvanically isolated transformer. By chance, he touched the extreme terminals of the transformer at the secondary end. He wasn’t electrocuted in this scene. The reason is that there wasn’t any earth wire on the end of the engineer. So, the circuit was never completed and the current did not flow through the body of the engineer.
For the communication, devices at the sender and receivers’ ends are not always at the same ground level. To avoid ground loops and improve the accuracy of communication between the send and the receivers’ end, a galvanic transformer is used.
The special type of galvanic we use in the communication system is called the Pulse transformer. Instead of transferring the energy from one end to the other end, the pulse transformer sends the pulses from one end to the other. Pulse transformer sends the pulses that can be considered a bit.
So, pulse transformers not only avoid the problem of the common ground using the pulses but also come in handy for analog (and sometimes digital) communications. Normally pulse transformers are applicable in:
- LAN and Ethernet Networks
- Power distribution
- And audio signals transmission
From the input section to the output section, transformers that magnetically couple analog AC signals are used by special instrument amplifiers while effectively sustaining high CMV.
Why isolation transformers are used in UPS?
Isolation transformers are used in UPS to isolate the power supply from the load end. We know that UPS is a widely used device in IT data centers and telecommunication networks.
Isolation transformers supply a safe and uninterrupted DC supply with negligible noise to the devices that work non-stop. Isolation transformers remove the noise that causes the oscillation in the system.
UPS provides the power to its load that should not have any noise in it. So, an isolation transformer should be used in the UPS for the uninterrupted and lesser noise power supply by conversion of high-frequency DC into steady DC voltage.
Another reason for using the isolation transformer in UPS is to provide safety to the load equipment. Also, the voltage conversion can be done using the isolation transformer in a UPS. Sometimes the required output at the load end is not as same as the input voltage level.
So, we need to either step down or step up the voltage. This can be done using the turn ratio concept for providing the required output at the load end of the UPS. So, an isolation transformer in UPS comes in handy in such a situation where we know the load voltage at the time of construction of UPS. Otherwise, an external isolation transformer can be attached to a UPS where no transformer is already placed inside while building it.
So, the isolation transformer is really necessary for UPS, where DC supply is to be provided 24/7 and safety, is needed while noise should not affect the system.
Are all transformers the isolation transformers?
No. Not all the transformers are isolation transformers. Auto-transformers are not isolation transformers. In isolation transformers the primary and secondary sides are electrically isolated, all the transformers are isolation transformers except Auto ones.
Due to the very limited use of the Auto-transformers, isolation transformers are the ones that can be used for general purposes to step up or step down the voltage. If you see the simple transformers placed on the poles, they are the isolation transformers.
The transformers used in the power supply of the computer systems are also isolation transformers. The transformers in communication network devices are also isolation transformers.
So, we can say that not all transformers are isolation transformers but most of them are.
For more details about Auto transformer read my article.
If you need more details about step up and step down transformers read my article.
Why are Isolation transformers safer?
Isolation transformers are safer because they isolate the neutral wires from the live wires. If somebody now touches the live/phase wire while not in contact with the earth or with the neutral connection, he/she will not get electrocuted.
So, why does this happen? How is this safety achieved? Let me explain it by the bird and the transmission line example.
We know that transmission lines can transmit power by a voltage of magnitude up to a thousand volts. This voltage is AC. But the birds standing on the wire do not feel anything! The reason is that the potential level of the bird becomes equal to the transmission line, the moment it touch the line.
And there is no ground or neutral in contact with the bird. If the same bird touchs the edge of the pole and touches his beak on the transmission line, he’ll be shocked. This is because the bird’s feet were at potential zero i.e., the potential of the pole. When the beak was put on the wire, the potential of the beak became equal to the potential of the transmission.
This arises the potential difference that flows the current from the higher potential side to the lower and the body of the bird cannot bear it (obviously).
So, now let’s get back to the track. The person who touches the phase line of the isolation transformer at the secondary side while in contact with no ground potential/ neutral is the analogy of the bird sitting on the transmission line.
There is no potential difference between any point of the body. so, there will be no current flow through the body. while if the person touches the ground potential (like not wearing rubber shoes) he or she will be electrocuted.
The isolation transformer is the best because you can not get electrocuted due to the isolation of the phase from the neutral. And neutral is inaccessible at the secondary end.
Can we make galvanic isolation for a power supply without a transformer?
Yes. Power supplies can achieve galvanic isolation without transformers. The best device after transformers in power supplies is the relay.
Relay also provides galvanic isolation. Just like transformers relays are also electrically operated. Outputs are isolated from the input side.
Whatever happens at any end does not directly affect the other side. The device on which the solid-state relay works is the optoisolator. Optoisolator is an IR (infrared) sensor that transfers energy between 2 isolated blocks of the system.
There is a phototransistor in front of this optoisolator. There are two states of LED of the optoisolator, ON and OFF. When the LED is on the photo-transistor becomes forward biased and lets current flow through itself.
So, to turn on the system the phototransistor must get energized. A high level of isolation is achieved as the input side of the circuit is totally isolated and the only connection is now established using the LED of the optoisolator on the input side and phototransistor on the output side.
In a transformer, we may have some impedance on the input side. This impedance is reflected on the output side. In the DC input circuits of the solid-state relay are the limiting resistor and an LED of optoisolator.
In the solid-state relay input circuit, that is connected before the DC input containing LED and resistor, there is Bridge rectifier and a capacitor to smooth out the pulses. These pulses will add oscillations in the system if not removed.
We have to equate the value of the resistor and capacitor of the input side to the power supply (like 220V) to get their values. Based on the requirements of the user or the load, the output side can be either DC or AC. Relays are normally used in the power supplies of the motor control systems, light intensity control, and switching on/off an AC load.
Difference between a transformer and an isolation transformer
An isolation transformer and an ordinary transformer share the same working principle but have different goals to achieve. The main purpose of an ordinary transformer is to step-up or step down the input voltage. No matter the isolation is achieved or not.
For example, in the auto-transformers,the secondary and the primary turns are not isolated from each other. They share a common ground. Due to his, the safety at the load end is compromised.
The transformer with the galvanic isolation in between its primary and secondary turns. The issue of getting electrocuted is resolved.
Also, if there is a problem at the load end circuit, the supply windings aren’t much affected. The isolation transformer provides safety not only to the devices at the load end but also to the workers. The properties such as high resistance and great stability also make isolation a better solution.
Isolation transformers have lower noise, more environmental protection, lower energy consumption, and improved efficiency.
On the other hand, the ordinary transformer does not clean out or even lower the noise. The efficiency of an ordinary transformer is also not as good as that of the isolation transformer. Along with the safety and other features of the isolation transformer, they can be used for stepping up or down the voltages very efficiently.
Is a VARIAC an isolation transformer?
The answer to this question is “mostly not”. Most of the VARIACS are not isolation transformers. But some of them are. The general concept of VARIACs is that they are only auto-transformers. While that is not always true.
For example, VARIAC SC-10t is an isolation transformer. The data sheet provided online tells that the input lines and output lines are isolated from each other. The neutral line at the output end is also isolated from the input line from the input end. But the ground, however, is connected. That is not a problem.
We can manually isolate the grounds of both ends manually. There is a three-pin plug hub for the output. If we use a three-pin plug then the grounds at the input and the output ends will be connected. If we observe old devices, they have only two prongs/legs.
So, if we plug in two prongs plug in the VARIAC, the grounds will be simply isolated. Or if our deice is having 3 legs then we can use a three-to-two pin plug and then insert it in the VARIAC. Some other examples of VARIACs with isolation are J201B, 3PNJ201BV(A), and 3PNJ201B.
So, conclusively, not all VARIACs are auto-transformers and isolated transformers. It just depends upon the company and how they design it.
What isolation systems are used for prevention?
Isolation of a power system is totally optional but if a system is isolated it will have enhanced life, reliability, and lesser faults occurring. But if you choose not to, there can be dangerous consequences to this decision.
Let’s take an example, say there is an operation going on in an operating room. Now there is equipment that uses fluids and it is touching the live wires. This can be dangerous for the operator and the one being operated.
So, if there is no isolating then people will be electrocuted. While if the system is isolated the current will simply not find any ground and will not flow through the bodies of the channel. So, let’s see why we use isolation in the systems.
- Isolation provides safety. (To the load/equipment we use and to the operators).
- Isolation makes communication without sharing ground possible.
- Isolated systems do not share grounds and thus the voltage spikes, and not needed currents at either side of the system will not affect each other.
- We can avoid the phenomenon of ground loops by isolating the power systems.
- We can efficiently shift the power level from one side to the other side of the system using isolation.
How electrical isolation is achieved in wet locations?
The isolation is achieved in wet conditions by the GFCI outlets. GFCI outlets are isolation devices that turn off the power if power is found somewhere it should not be. Like in a short circuit if power keeps regulating, the damage keeps increasing.
So, in case of a short in wet conditions, GFCI outlets simply cut off the power. GFCI are isolation circuit breakers. A GFCI (Ground Fault Circuit Interrupter) monitors the electric current moving through the circuit very accurately. It prevents fatal electric shocks. Water is a major cause of ground loops.
GCFI comes in handy in dealing with ground loops. With time GFCI outlets wear out. So, it is necessary to check if they are still working just alright or not. A small test to check the outlet is to press the button on which “Rest” is written. Now plug a device in the GFCI outlet.
The devices should work okay. Now press the “Test” button. Power will be immediately cut if the GFCI is working fine. Otherwise, you need to replace the GFCI. Some GFCIs are GFCI receptacles, GFCI Circuit breakers, and portable GFCI. Each of them has different locations to be at but the same principle to work on.
I have written a detailed article about GFCI circuit breakers you can find it here.
What is an isolated and non-isolated power supply?
In the isolated power supply, the input power supply is not directly connected to the loads. There is no direct flow of current. The energy still transfers. The non-isolated circuits do not have this facility. Rather there is a passage for current flow.
Current flows from the input end to the output end. Now if there is a problem in the circuit like a short circuit. It will affect the whole system and the other devices connected to the main supply.
But in the case of the isolated power supply, if such a fault occurs in the device at the load end the main supply will not be affected. Because of the ground,both sides are isolated from each other.
How do you select an intrinsically safe barrier?
The selection of intrinsic safe barrier approvals from different agencies and analysis of some conditions. These conditions are the measure of
- Maximum number of Input/Output channels of the system
- Maximum open circuit voltage
- Maximum circuit current
- Short circuit current
- Operating temperature
A simple device is connected through the intrinsic safe barrier. Such devices do not generate energy. They do not store the energy and even if they do, they do not store energy of more than 25mW (1.2V or 0.1A). Otherwise, IS barrier is not connected to the circuit.
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