Current transformer: principle of operation and scope

When working in high-current alternating voltage circuits, it becomes necessary to use compact devices that can be used to control the necessary parameters in a non-contact way. For these purposes, a current transformer is widely used, which, in addition to measuring, also performs a number of useful functions. Such devices are produced on an industrial scale and have very different designs. The distinctive properties of these devices is the measuring range, the degree of protection of the device itself and its design features.

The modern current transformer uses in its work a simple principle, known since the invention of electricity. When working under load in the conductor generates an electromagnetic field, which is captured by a sensitive device. The greater the intensity of the field, the greater the current flowing in the conductor, respectively. It remains only to recalculate the gain of the device and give the selected signal in the control, monitoring or protection circuit.

Thus, the current transformer plays the role of a frame on the power cable and reacts to changes in the supply network. Modern devices consist of a large number of turns and have a good transmission factor. When setting such a device, the current-voltage characteristic is taken to determine the inflection point of the curve. This is necessary to find the section of the graph, which determines the range of stable operation of the device. The current transformer also has its gain factor, which is specified during commissioning.

In addition to measuring functions, the device allows galvanic separation of power and control circuits. This is important for security reasons. It is difficult to imagine a contact device that works in electrical networks with a voltage, say, 10,000 volts. Using modern measuring current transformers , it is possible to obtain a low power signal, galvanically separated from the power circuit, with which it is convenient and safe to operate.

The load of such devices can be any measuring device capable of working with a measuring transformer. If the distance between them is large enough that the internal resistance of the line begins to affect, then the instrument is calibrated. In addition, the measured signal can be fed into a protection or control circuit based on modern electronic devices. With their help, it's easy To make emergency switching-off of power lines and to look through pre-accident history. Such devices monitor the network status and calculate all the necessary parameters: active / reactive power, current, power consumption, etc.

In the design process, the problem arises: to select devices for monitoring and measurement. The choice of current transformers is carried out, based on the average design parameters of the operated network and the design features of the measuring device itself. Typically, powerful power units are supplied with measuring devices, meaning: powerful power transformers, high voltage panels, etc.

Without measuring devices it is difficult to imagine modern production and our daily life. Sensitive devices protect expensive equipment and are responsible for human safety. They work perfectly in electrical circuits, providing control over the measured parameters.