Current relay - a variety and device

A current relay is a device that is often used to signal an excess of current in a particular monitored circuit. It is also used to disconnect an electrical circuit in the event of short circuits or overloads. The current relay of the minimum is used much less often. Such devices are designed to break the electrical circuit when a certain minimum current value is reached.

There are many different kinds of electrical devices such as current relays. They differ in their design and principles of operation. If we talk about the so-called classical device, it is a mobile anchor on the springs that controls contacts, and a coil with a core (usually iron). When the current passes through the coil, a certain magnetic field is created. The core of the coil is magnetized by the action of this magnetic field and begins to attract the anchor. Thus, contacts will work.

The coil of such a device contains few turns, but the wire has a large diameter (in contrast to, for example, the same voltage relay). The diameter of the wire depends directly on the current, more precisely, on the value of the design current value. Due to this, a certain voltage drop is achieved. This is very important, because the coil is connected in series to the controlled circuit.

Some DC relays have an adjustable tripping current. Most often this is achieved by changing the tension of the armature spring. The AC current relay , which is used to monitor large currents, can be turned on via transformers.

The most important characteristic of such a protective device is the response time. Devices of this type that can be used to protect against short circuits have a response time of no more than a few tens of milliseconds.

The DC solid state relay delays when the circuit is disconnected. This excludes the possibility of false triggering in the case of a short-time increase in current. Such a device usually has a response time control.

One of the most common types of protective devices is a thermal current relay . It is a bimetallic plate provided with a heating element made of a material with a high resistivity value (for example, from nichrome). The plate consists of materials with a different coefficient of thermal expansion, which is bent when heated and acts on the mechanism of the relay. The response time of such a device depends on the current - the larger it is, the faster the plate warms up, and the shorter the response time.

The electronic current relay is used for virtually instantaneous tripping during overload. The circuit of the electronic relay can process signals in accordance with predetermined parameters and characteristics. It is possible to set the permissible maximum current and the delay time when switching off. Such current relays can be both variables and constants. These devices often come in an integrated form in many devices.