In our age of high technology, people from all sides are surrounded by a huge number of instruments and devices operating with the help of electricity. And the greater their number, the higher the likelihood of a person being struck by electric shock. To avoid this, an RCD was invented. What is it and what is it for, we will describe in detail in this article.
Appointment
The residual current device (RCD) is intended for differential protection of a person from electric shock when touching the body of electrical equipment (household appliances), which, when insulation is broken, is energized.
When the RCD trips
We continue the story of the RCD. What is it and how does it work? An electric current starts to flow through a person touching the energized case of the appliance. When it reaches a value of 30 mA, the RCD is turned off. As a result of this, the voltage is automatically disconnected from the damaged equipment. At the same time, a person does not feel anything, since painful sensations arise at much higher currents (from 50 mA). Fatal for humans is a current of 100 mA.
What is an RCD?
The protective shutdown device includes a current transformer, an actuator (relay and a system of breaking levers), a self-test circuit. More advanced devices contain in their design a system of electromagnetic and inversely dependent on the value of the cutoff current (protection against short circuit currents and overload).
The principle of operation of the RCD
What it is? How is this device powered? Now we will tell about all this in the most detail. The basis of the RCD is the principle of operation of a current transformer (CT). Phase and working neutral conductors pass through a current transformer. With normally operating equipment (with intact insulation), the magnitudes of the currents flowing through them are equal in magnitude, but inverse in direction. As a result of this, they induce magnetic fluxes in the CT winding, identical in magnitude but reverse in direction, which completely compensate each other (there is no voltage at the ends of the secondary CT winding). If the insulation of the equipment is violated, part of the current of the phase conductor leaks to the ground through the grounding conductor (if the device is grounded) or through a person who has touched this appliance. As a result of this, the magnitude of the current flowing through the zero working conductor becomes less than the current along the phase conductor. This leads to the fact that the magnetic flux in the transformer winding becomes different in magnitude. As a result, voltage appears at the ends of the CT winding. Through the relay connected to them, current flows. When a difference of 30 mA is reached, a relay is activated, which activates a system of breaking arms. The equipment is shutting down.
Turn on the RCD
It is made only after the identification and elimination of a malfunction of electrical equipment that led to the operation of the device by pressing the cocking levers.
Conclusion
In this article, we introduced you to RCD in sufficient detail: what it is, how it works, and what it is used for. We hope you find this information useful.