Content:
- Appointment
- Device and principle of operation
- Application area
Appointment
First, consider what the purpose of the residual current device is (in the photo below you can familiarize yourself with its appearance). Leakage current occurs in the event of a violation of the integrity of the cable insulation of one of the wiring lines or in the event of damage to structural elements in a household appliance. Leakage can lead to fire of electrical wiring or an operated household electrical appliance, as well as electric shock during the operation of a damaged electrical appliance or faulty electrical wiring.
RCD, in the event of an unwanted leak, in a split second, turns off the damaged area wiring or damaged electrical appliance, which protects people from electric shock and prevents the occurrence of a fire.
Very often the question is asked about what is the difference between a difavtomat and an RCD. The difference between the first is that this protective device, in addition to protection against electricity leakage (RCD function), additionally has protection against overload and short circuit, that is, it functions as a circuit breaker. The residual current device does not have overcurrent protection, therefore, in addition to it, automatic switches are installed to implement protection in electrical networks.
Device and principle of operation
Consider the design of the residual current device and how it works. The main structural elements of the RCD are a differential transformer that measures the leakage current, starting a body that acts on the shutdown mechanism and directly on the power contact decoupling mechanism itself.
The principle of operation of an RCD in a single-phase network is as follows. The differential transformer of a single-phase protection device has three windings, one of which is connected to the neutral conductor, the second to the phase conductor, and the third serves to fix the differential current. The first and second windings are connected in such a way that the currents in them are opposite in direction. They are equal in normal operation of the electrical network and induce magnetic fluxes in the magnetic circuit of the transformer, which are directed oppositely to each other. The total magnetic flux in this case is zero and, accordingly, there is no current in the third winding.
In the event of damage to the electrical appliance and the appearance of phase voltage on its case, when touching the metal case of the equipment, a person will fall under the influence of an electricity leak, which will flow through his body to the ground or to other conductive elements that have a different potential. In this case, the currents in the two windings of the RCD differential transformer will differ, and, accordingly, different magnetic fluxes will be induced in the magnetic circuit. In turn, the resulting magnetic flux will be different from zero and will induce in the third a certain value of the current - the so-called differential. If it reaches the triggering threshold, then the device is triggered. The main causes of RCD tripping we have described in a separate article.
More details about how the RCD works and what it consists of is described in the video lessons:
Would you like to know how a residual current device works in a three-phase network? The principle of operation is similar to a single-phase device. The same differential transformer, but it already compares not one, but three phases and a neutral wire. That is, in a three-phase protective device (3P + N) there are five windings - three windings of phase conductors, a neutral conductor winding and a secondary winding, through which the presence of a leak is recorded.
In addition to the above structural elements, a mandatory element of a residual current device is a test mechanism, which is a resistor connected via the "TEST" button to one of the differential windings transformer. When this button is pressed, the resistor is connected to the winding, which creates a differential current and accordingly, at the output of the secondary third winding, it appears and occurs, in fact, an imitation the presence of a leak. The operation of the residual current device indicates its good condition.
Below is the conventional designation of the RCD in the diagram:
Application area
The residual current device is used to protect against current leaks in single-phase and three-phase electrical wiring for various purposes. At home electrical wiring An RCD must be installed without fail to protect the most dangerous household electrical appliances from the point of view of electrical safety. Those electrical appliances, during the operation of which there is contact with the metal parts of the case directly or through water or other objects. First of all, this is an electric oven, washing machine, water heater, dishwasher, etc.
Like any electrical device, an RCD can fail at any time, therefore, in addition to protecting outgoing lines, it is necessary to install this device at the input of home wiring. In this case, the RCBO will not only reserve the protective devices of individual wiring lines, but also perform a fire-fighting function, protecting all household wiring from fires.
That's all that I wanted to tell you about the design, purpose and principle of operation of the RCD. We hope the information provided has helped you figure out how this modular device looks and works, as well as what it is used for.
You probably don't know:
- What is UZM-51M?
- How does a circuit breaker work
- How to choose an RCD for an apartment
