SU570948A1 - Device for selective current protection from ground favlt in radial lines possessing heavy capacitance current - Google Patents

Description

The selective current protection device consists of a zero-sequence current transformer 1, a rectifying bridge 2, a starting element in the form of two series-connected polarized matching relay 3 and prohibition 4, a capacitor 5 connected in parallel to the output of the rectifying bridge, a capacitor 6 connected in parallel with the relay winding 3. The closing contact 7 of relay 3 and the opening contact 8 of relay 4 are connected in series to the power supply circuit of the intermediate relay 9. The closing contact 10 of the intermediate relay 9 is connected to the power supply circuit cut-off coils 11 oil switch 12 protected line. Potentiometer 13 serves to regulate the operation current of the relays 3 and 4 by supplying the additional direct current to the additional windings from a stabilized source 14. The operation current of the relay 3 is selected according to the formula:

/ c.3.3,

Ah

and the current relay 4: (/ o- / s). z.4 -

Ah

where / c.3.3 and / c.3.4 are the tripping currents of relays 3 and 4, reduced to the primary currents of the zero-sequence current transformer;

/ o - full capacitive current of ground fault of the given network;

/ с - own capacitive current of the protected line;

/ MF - sensitivity coefficient of 1.1;

/ СН - reliability coefficient

1.1.

The device works as follows.

When a single-phase ground fault occurs in the protected line, a zero-sequence current transformer passes a current equal in magnitude to the total capacitive current of the other network lines.

i.e. / o- / s, therefore, the relay 3 is activated and with its closing contact 7 closes the power supply circuit of the intermediate relay 9, which through its closing contact 10 supplies power to the shut-off device 11 of the oil switch 12 of the protected line, i.e. it turns off. If a single-phase ground fault occurs on any other line of the network, a zero-sequence current transformer will pass a current equal to the value of the own capacitive current of the protected line / s, which is greater than the total capacitive current of the other lines of the network. In this case, work

both relays 3 and 4, contact 8 of relay 4 opens, and contact 7 of relay 3 closes, as a result, the power circuit of intermediate relay 9 remains de-energized, therefore, the protected line does not turn off, i.e. non-selective

no protection action.

Thus, the reliability of the protection of the radial lines is increased.

Claims (1)

Invention Formula Device for selective current protection against single-phase earth faults of radial lines with a large inherent capacitive current exceeding the total capacitive current of the remaining lines network, containing a zero-sequence current transformer with a rectifying place at its output, supplying a matching polarized relay with a closing contact in the power supply circuit of the intermediate relay, the closing contact of which is included in the power supply circuit of the shut-off coil of the oil switch of the protected line, characterized in that in order to increase the reliability, a banned relay is additionally introduced into it, the winding of which is connected in series with the winding of the matching polarized relay, and the opening contact ban polarized relay is connected in series with NO contact matching polarized relay. Li WOB