Protection components

    Protection components are designed for the protection of electric equipment against overcurrents. Overcurrents cause short-circuit or overload. The short circuit is a short-ti me but heavy increase of current. The overload is a long-time but smaller increase of current. Protection equipment is a general name for fuses, breakers, and voltage/current protection devices.

    Fuses are one-off protection components protecting electric circuits against overcurrents. A fuse contains a fusible wire forming part of electrical circuit. Its cross-section is dimensioned according to the trip current when the fuse should react. After the trip current is crossed, the wire is fused apart and the electric circuit is mechanically cut.
    Circuit-breakers are protection components protecting electric circuits against overcurrents. There is a short-circuit trip consisting of an electromagnetic coil. This coil, after short-circuit current flows through it, creates electromagnetic field which opens main contacts.
On overload there is a thermal trip with thermocouple reacting through mechanical bending thus opening contacts.
    Voltage and current protection devices – there 2 types: surge arrestors and residual current devices. Surge arrestors cut off all phase as well as neutral conductor in a time less than 0,2 s (i.e. the transfer of a failure to protected devices is excluded). The disconnection from the source is made by a voltage trip which gets the information on frame voltage presence from the PE conductor. A voltage is induced on the trip coil and the resulting magnetic force opens contacts of all four conductors.
    Current residual devices work in a similar way. There is a difference that the disconnection from the source is made by a summing transformer which forms the main part of residual current device. The primary side of the transformer consists of 4 conductors (3 phase and 1 neutral conductor). The transformer is summing the instant values of incoming phase currents and outcoming N current. In the failure-less state the sum is equal 0 (incoming is equal to outcoming), i.e. the secondary side of transformer is idle. Only if there is a change on the primary side, a voltage is induced on the secondary side and the resulting magnetic force opens the contacts of all 4 conductors. The differential current, the RCD is sensitive to, is up to 30 mA.

protection components