Very often in electrical devices there is a need to exclude the electrical connection between high power voltage and low voltage control circuits. In other words, it is necessary to protect low-voltage devices from voltage power circuits of hundreds or even thousands of volts. Technically, this means that in a given system or electrical device, it is necessary to exclude the flow of current through common circuits. The absence of current means the presence of a large ohmic resistance between the common wires of the two devices, which is equivalent to an open circuit. This problem is solved by galvanic isolation - a device that excludes galvanic coupling between electrical devices.
Imagine a conventional industrial electric motor. In production conditions, most engines have a working supply voltage above 200V, which is dangerous for personnel. Therefore, the supply voltage to the windings, i.e. the engine is turned on by using additional devices that switch power circuits. On the other hand, the switches must also be controlled, for example, by a button, and at the same time galvanic isolation protects the operator from being struck by dangerous voltage.
Switching devices themselves, for example, contactors and starters, are devices in which the design excludes electrical contact between the input (contacts of the electromagnet coil) and the output (power contact group of the starter). The connection between them is carried out only through the mechanical interaction of the magnetic field with the structural elements of the starter, so that the high voltage of the motor does not get to the control panel.
There are other options for the technical solution of galvanic isolation. First of all, these are transformers. With their help, galvanic isolation for nutrition is easily solved. This method has been especially widely used in household electrical radio engineering. The fact is that the supply voltage of household appliances is dangerous to humans. For example, in the absence of galvanic isolation between the household electrical network and the television signal processing board, the life-threatening potential will be found on all the metal elements of the TV structure, and access to the “television insides” is quite accessible to home-made “homemade” ones. The issue of protection against electrical voltage for such devices is solved simply: at the input of the household appliance a transformer is placed between it and the mains. Its primary winding is connected to the network, and the secondary one supplies the current induced in it to power the TV. Here, one of the useful features of the transformer is manifested - with its help, galvanic isolation of the analog signal is realized , which is widely used in various devices.
With the development of power semiconductor devices, switching devices — optothyristors — with an optocoupler (light) control channel have become widespread. The input (control) circuit of the optocoupler contains a light bulb or LED that turns on when a control signal is applied. The luminous flux hits the photosensitive control electrode of the thyristor, which includes the power circuit of the anode-cathode. This ensures a 100% absence of galvanic input-output communication. Another option for optocouplers is optotransistors, which easily solves the galvanic isolation of an analog signal, for example, in sensors of measuring instruments.
The use of galvanic isolation in technology has a much larger range of tasks than is covered in this article. Modern technology is constantly expanding the list of such devices for engineering applications.