SU1001289A2 - Device for protecting transformer from single-phase short circuiting - Google Patents

Description

The invention relates to a relay protection technique and is intended to disconnect a transformer having a winding connected to a star with a grounded neutral during single-phase short circuits in outgoing power lines.

According to the main author. St. No. 720610, there is known a device for protecting a trans-jq formatter from a single-phase short circuit, containing two magnetic conductive brackets fastened with first ends on different sides of the core of the transformer to be protected, interconnected by second ends through a non-magnetic gasket, the second ends of the brackets and a non-magnetic gasket equipped with a hole in which the reed switch ^ 1J is installed. The disadvantage of this device is its low sensitivity to earth fault currents, when a phase wire breaking off is connected not to the neutral wire, the network, but to the ground.

The aim of the invention is to increase the sensitivity of the device to earth fault currents.

This goal is achieved by the fact that a winding is inserted into the device for protecting the transformer from a single-phase short circuit to earth, covering the magnetic conductors and the reed switch, connected between the zero point of the transformer winding and the transformer ground.

The drawing schematically shows but the proposed device with a partial cutout of brackets.

Magnetic conductive brackets 1 and 2 are fixed at the ends of the rod 3 of the transformer; The brackets 1 and 2 are connected by a non-magnetic gasket 4. Along the longitudinal axis of the ends of the brackets 1 and 2 and through the gasket 4, a hole 5 is made in which the reed switch 6 is installed. The contacts of the reed switch 6 are connected to the actuator 7. Between the zero point 8 of the transformer winding and the ground 9 of the transformer an additional winding 10 is included, and the neutral wire of the network has repeated grounding 11.

The device operates as follows.

With three-phase load currents, with transformer turn-on currents, with two-phase and three-phase short-circuits in the supply network, the magnetic system of the transformer is balanced and the magnetic flux does not pass through staples 1 and 2. Only currents of direct and reverse sequence pass through the windings of the transformer in these operating modes, therefore, no currents pass through the neutral wire and through the grounding of the transformer. I A single-phase short circuit between the phase and neutral wires in the outgoing network causes zero-sequence magnetic fluxes which, in a conventional transformer, are closed through the casing and through the air. A part of the zero sequence flow passes through the bracket 1, the contacts of the reed switch 6 and the bracket 2, the contacts of the reed switch b are closed each half-period of the current of industrial frequency and supply a signal to the actuator 7, which gives a signal about a single-phase short circuit in the network.

When the phase wire does not connect to the neutral wire and is connected to ground during an open circuit, an earth fault current flows through the circuit, which is much smaller than the single-phase short circuit current when the phase and neutral wires are connected. The first part of the earth fault current flows through re-grounding 11 to the zero point 8 of the transformer winding. From the passage of this part of the earth fault current, the main zero-sequence magnetic flux is created, which closes through the brackets 1 and 2 and through the contacts of the reed switch 6. But this magnetic flux is insufficient to close the contacts of the reed switch b. The second part of the earth fault current flows through the grounding 9 of the transformer and through an additional winding 10 to the zero point 8 of the transformer. From the current flowing through the winding 10, an additional magnetic flux is created, which is added to the main magnetic flux. In this case, the contacts of the reed switch b are closed and provide a signal to the actuator 7, which signals damage.

The presence of magnetic conductors with a reed switch having an additional winding allows you to signal all types of single-phase damage in the outgoing lines and inside the transformer tank. The device signals a short circuit to the transformer case at any point, a phase wire closes with zero in the outgoing power lines, and a phase wire shorts to ground.

The proposed device is easier to manufacture and has wider functionality.

Claims (1)

The invention relates to a relay protection technique and is intended to disconnect a transformer having a winding connected in a star to a grounded neutron with single-phase short-circuits in the outgoing power lines. According to the main author. St. No. 720610 discloses a device for protecting a transformer from a single-phase short cable containing two magnetically conducting brackets fixed by first ends on opposite sides of the core of the protected transformer, interconnected by second ends through a non-magnetic pad, and the second ends of the brace and non-magnetic pad equipped with a hole in which the reed switch is installed 1 The disadvantage of this device is its low sensitivity to ground currents when the phase conductor does not connect with a zero wire, a network, and with the ground. The purpose of the invention is to increase the sensitivity of the device to earth fault currents. This goal is achieved by introducing a winding into the device to protect the transformer from a single-phase short circuit, which covers the magnetic conductor brackets and the reed switch, connected between the zero point of the transformer winding and the transformer grounding. The drawing schematically depicts the proposed device with a partial cut brackets. The magnetically conducting brackets 1 and i are fixed at the ends of the transformer rod 3; Staples 1 and 2 are connected with a non-magnetically padded gasket 4. Along the longitudinal axis of the ends of brackets 1 and 2, and through pin 4, a hole 5 is made in which the reed switch 6 is installed. The contacts of hermetic 6 are connected to the actuator with a gannum 7. Between the zero point 8 of the transformer winding and grounding 9 transformer included an additional winding 10, and the neutral wire network has repeated ground 11. The device operates as follows. With three-phase load currents, with transformer switching-on currents, with two-phase and three-phase short interlocking in the power supply network, the magnetic system of the transformer is balanced and the magnetic flux does not pass through brackets 1 and 2. In these operating modes, only the direct and reverse sequence currents pass through the transformer windings; therefore, no currents pass through the neutral wire and through the transformer grounding. A single-phase short circuit between the phase and neutral wires in the outgoing network causes a magnetic flux of zero-sequence, which in a conventional transformer is closed through the casing and through the air. A part of the zero-sequence flow passes through the clamp 1, the gvrkona b contacts and the clamp 2, the herk contacts b close each half-period of the industrial frequency current and give a signal to the executive unit 7, which signals a single-phase short circuit in the network. When a phase wire is not connected to the neutral wire when it is broken, but is connected to ground, a ground fault current flows through the location of the circuit, which is significantly less than the current of a single-phase short circuit when the phase and neutral wires are connected. The first part of the ground fault current flows through re-grounding 11 to the zero point 8 of the transformer winding. The flow of this part of the earth fault current creates the main magnetic flux of the zero sequence, which is closed through the brackets 1 and 2 and through the contacts of the reed switch 6. But this magnetic flux is not sufficient to close the contacts of the reed switch b. The second part of the ground fault current flows through the ground 9 of the transformer and through the additional winding 10 to the zero point 8 of the transformer. From the current flowing through the cover 10, an additional magnetic flux is created, which is added to the main magnetic flux. In this case, the contacts of the reed switch b are closed and give a signal to the executive body 7, which signals damage. The presence of magnetic conductive clamps with reed switches, having an additional winding, allows to signal all types of single-phase faults in the outgoing lines and inside the transformer tank. The device signals the closure to the transformer housing at any point, the closure of the phase conductor with zero B outgoing power lines and the closure of the phase conductor to ground. The proposed device is easier to manufacture and has more functionality. The invention The device for protection of a transformer from a single-phase short circuit according to aut. St. 720610, characterized in that, in order to increase the sensitivity to earth fault currents, a winding encompassing the magnetically conducting brackets and a reed switch is included between the zero point of the transformer winding and the transformer grounding. Sources of information taken into account during the examination 1. USSR Author's Certificate No. 720610, cl. H 02 H 7/04, 1978.