SU152015A1 - Device for the protection of electrical installations - Google Patents

Description

The proposed device for the protection of electrical installations on an alternating operational current relates to a known type of devices having two current relays connected to current transformers, as well as a time relay and a cut-off roller made of two identical counter-connected sections and powered from a common intermediate transformer.

A feature of the device that constitutes the subject matter of the invention and makes it possible to increase its sensitivity is the presence of two capacitors introduced into the circuit, pushing current relays and a time relay through normally open contacts of one time relay and disconnecting coils, which form a resonant circuit with the corresponding section .

The drawing shows a circuit diagram of the proposed device.

The device includes: two maximum current relays ET-A and ET-C, connected via current transformers GTL and TTC for phase currents, time relay RV, intermediate saturating PNT transformer and disconnecting coil OK. For protection operation with a current cutoff, the resistance R "is connected to the circuit of the disconnecting roller OK" by pushing by the time relay contact RV. Capacitors serve to reduce the power consumed by the cut-off roller OK and the winding of the time relay PB. and, accordingly, Wed. .

The disconnecting coil is made of two connected opposing identical sections, the magnetic fluxes of which are normally subtracted, as a result of which the coil almost does not generate tractive effort, and its resistance is equal to the ohmic resistance of the winding and the inductance of the dissipation flows, i.e. relatively: little.

No. 152015-2 -

When a capacitor C d connected by a normally open contact of the time relay RV is connected, parallel to one section of the tripping coil, resonance of the voltage in the branch capacitor + inductance of the mutual induction of the tripping coil resonates and, since the capacitive resistance is somewhat greater than the inductance of the mutual induction, the resonance is also achieved currents between the branch capacitor + inductance of mutual induction and branch of active resistance + inductance of dispersion of the half section. Therefore, the current through the inductance of the mutual induction increases to the magnitude that causes the tripping coil to be triggered, but its total resistance increases slightly and remains lower than when both sections are turned on. It is advisable to connect the capacitor Cd „in parallel with the section with lower ohmic resistance, i.e. parallel to the internal section. The resistance is chosen so that before the time relay RV closes, the shut-off coil OK has a starting current equal to the cut-off setting.

The coil time relay PB is connected in series with the tripping coil in the secondary circuit of the intermediate transformer :; PNT and also consists of two identical sections connected oppositely. The normally open contacts of current relays EH-A and ET-C of maximum protection are connected in parallel to one section of the relay RV capacitor Cp ,.

The PNT intermediate transformer is saturating. to limit the current through the relay contacts. Since at all positions of the tripping coil and time relay a relatively small active-inductive resistance is connected to the secondary winding of this transformer, however, the voltage peaks on its windings are limited.

Subject invention

A device for protection of electrical installations with alternating operational current, containing two current relays connected to current transformers, a time relay and a disconnecting coil, made of two identical counter-switched sections, as well as one. An intermediate transformer supplying a time relay and a disconnecting coil, characterized in that, in order to increase the sensitivity of the device, there is one of the time relays and the breaking coil. sections are shunted respectively through normally open contacts of current relays and time relays with a capacitor forming a resonant circuit with this section.

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