SU440737A1 - Device for blocking relay protection in case of breaks in the secondary circuit of a voltage transformer - Google Patents

Description

one

The invention relates to the field of relay protection and can be used in networks of 35-330 KB to prevent incorrect actions of protection of lines and other connections in case of malfunction of the secondary circuits of voltage transformers.

Devices are known that react to a zero-sequence voltage in a secondary circuit of a voltage transformer connected in a star. These devices become inoperative when all three phase voltages on the protection fail due to faulty voltage circuits.

In the proposed device, the zero-sequence voltage filter is a multi-winding transformer included for the sum of all three phase voltages.

To increase the reliability of the device, one primary winding of the transformer is connected to zero and all three phases of the main secondary circuit of a voltage transformer connected in a star through additional resistors identical in two phases and unequal in the third phase, and the second to additional winding voltage transformer of the same third phase in an open triangle circuit.

FIG. Figure 1 shows the circuit of the proposed device and its inclusion in the line voltage circuits that receive power from the voltage transformer via the contacts of the relay-repeaters of the position of the disconnectors and automatic machines protecting the voltage transformer; in fig. 2 is a circuit for connecting a voltage transformer; in fig. 3 - vector diagram of currents.

The four-winding transformer 1 has two primary windings and one compensation winding, connected to the voltage through additional resistors. To the secondary winding of transformer 1, through rectifier 2, a polarized relay 3 is connected with one switching contact.

Resistance r of resistor 4 should be less (or more), resistances of identical resistors 5, 6. Therefore, when the voltage symmetry Ua, L / b, the currents in these resistors are not the same, as shown in the vector diagram (see Fig. 3 ) corresponding to the condition. The current and current, equal to the geometric sum of the currents / a, 1i, 1s, has the opposite direction.

Under normal operating conditions, when the transformer secondary circuits are in good condition, the voltages coinciding in phase, but the opposite currents in the primary windings of the transformer 1 create currents / o and / hell in the core, mutually balancing forces. Therefore, there is no current in the core of the transformer I and the current in relay 3. The magnetizing forces created by the currents / o and / hell will also be balanced against any voltage symmetry violations from the primary windings of the voltage transformer that are not associated with the appearance of zero-sequence voltage.

When a zero-sequence voltage appears on the higher voltage side of a voltage transformer (for example, when it is closed to earth), the equilibrium n. with. in the core of the transformer 1 is broken. Its restoration is provided by the compensation winding of the transformer 1, which is connected to the circuit at a voltage of 3 Uo through the additional resistor 7.

When one or two phases are broken in the protection voltage circuit, the zero-sequence voltage appears and the magnitude and phase of the current in the winding of the transformer 1 connected to the neutral conductor change. As a result, the balance is broken. " c., and in the core of the transformer 1 magnetic flux appears. This leads to the activation of relay 3, which outputs protection from the action and gives a signal on the failure of the voltage circuits.

When disconnecting the machine due to damage in the secondary circuits fed from the windings

440737

a voltage transformer connected in a star, or in the event of a zero break, the power is removed from the winding of the transformer 1 connected to the neutral wire. At the same time, due to the presence of power on the primary winding of the transformer connected through a resistor 8 to the auxiliary winding of a phase A transformer, the equilibrium n is also disturbed. C. and the relay is triggered 3.

Subject invention

Device for blocking relay protection - in case of breaks in the secondary circuits of a voltage transformer, responsive to zero-sequence voltage, containing a multiwinding transformer with additional resistors in the primary and compensation windings, to which the secondary winding through a rectifier connects a polarized relay that is different in order to increase the reliability of the device, one primary winding of the transformer is connected to zero and all three phases of the main secondary windings ransformatora voltage connected in star, through additional resistors, which are identical in the two phases and unequal to them in the third phase, and the second - to the additional winding of the transformer voltages of the same phase in the third 1tsePI open triangle.

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