RU2174276C1 - Protective gear for insulated-neutral line - Google Patents

Abstract

FIELD: selective disconnection of double ground faults, single-phase ground faults, and all kinds of interphase short circuits in radial systems. SUBSTANCE: protective gear designed to selectively respond to double ground faults and to other kinds of short circuits has interphase shorts protective unit; zero-sequence current and voltage sensors, zero-sequence power direction relay, time relay, OR gate, and output gate, all connected to line under protection. Introduced in addition are two pulse shapers, inverter, threshold element, AND gate, one-shot multivibrator, and INHIBIT gate. Input of first pulse shaper is connected to that of power direction relay and output, to input of inverter whose output is connected to first input of AND gate; input of threshold element is connected to output of zero-sequence voltage sensor and output, to input of second pulse shaper whose output is connected to second input of AND gate whose output is connected to input of one-shot multivibrator; direct input of INHIBIT gate is connected to output of OR gate, inverted input, to output of one-shot multivibrator, and output, to input of output gate. EFFECT: enlarged functional capabilities. 2 dwg

Description

 The proposed device relates to relay protection lines with an isolated neutral radial networks 6-35 kV, in particular for the selective disconnection of double earth faults, single-phase earth faults and all types of interphase short circuits.

 A device for directional protection against earth faults of lines with insulated neutral [1]. The device comprises a zero sequence current sensor, a zero sequence voltage sensor, a zero sequence power direction switch, and an output element. The outputs of the zero-sequence current and voltage sensors are connected to the corresponding inputs of the zero-sequence power direction switch, the output of which is connected to the input of the output element.

 The known device provides selective operation with single-phase earth faults in radial networks with isolated neutral without overcompensation. This is due to the fact that the directions of current and power on the damaged and undamaged lines are opposite, and the directional relay can determine the damaged line by the sign of power.

 A disadvantage of this type of device is non-selective operation during the development of a single-phase earth fault into a two-phase earth fault. In connection with an increase in phase voltages in undamaged phases after a single-phase earth fault at one of the phases, an insulation breakdown or a spark gap is likely, which leads to a transition of a single-phase earth fault to a two-phase earth fault, usually at different points in the network. Disconnecting any connection will eliminate the two-phase earth fault. But disconnecting that connection where a single-phase earth fault originally occurred will lead to the elimination of both earth fault points if the insulation has not been destroyed. A well-known device installed in a radial network during the development of a single-phase earth fault into a two-phase earth fault will disconnect all connections shorted to ground.

 In addition, the known device does not provide shutdown of metal phase-to-phase faults, since it only controls the current and voltage of the zero sequence.

 Closest to the proposed invention is an insulated neutral line protection device that contains an interphase short circuit protection unit, a zero sequence current sensor, a zero sequence voltage sensor, a zero sequence power direction switch, a time relay, an OR gate, and an output element [2] . The outputs of the zero-sequence current and voltage sensors are connected to the corresponding inputs of the zero-sequence power direction switch. A time relay input is connected to the output of the zero direction power direction relay. The outputs of the block of protection against phase-to-phase faults and the time relay are connected to the corresponding inputs of the OR logic element. The output of the OR gate is connected to the input of the output element.

 Unlike an analog, the device allows you to control the magnitude of the phase currents by installing current sensors on the phases of the line. Monitoring the values of phase currents and the direction of the zero sequence power (due to the sensors of the current and voltage of the zero sequence, the relay of the direction of power of the zero sequence) provides selective disconnection of two- and three-phase metal short circuits, single-phase earth faults, two-and three-phase earth faults.

 The disadvantage of this device is non-selective operation during the development of a single-phase earth fault into a two-phase earth fault. Since after a single-phase earth fault the voltages of the undamaged phases increase to linear, a breakdown of the insulation or a spark gap is likely in the network, which leads to the appearance of a second earth fault point at another connection. The device carries out non-selective disconnection of one or both connections. This is due to the fact that according to the current and voltage of the zero sequence, the direction switches for the zero sequence power of the protection kits for damaged connections register only the presence of an earth fault, ignoring the order of occurrence of earth faults.

 The challenge facing the inventors was to create a device for protecting lines with an isolated neutral, which allows in radial networks to provide selectivity for disconnecting double earth faults while maintaining the ability to selectively disconnect other types of faults by controlling the sequence of occurrence of earth fault points according to the coincidence of voltage the zero sequence and the direction of the flow of power of the zero sequence in the line, as well as by introducing the appropriate interphase protection interlocks for connecting where a secondary earth fault has occurred.

 To solve this problem, in a well-known line protection device with isolated neutral circuit, containing an interphase circuit protection unit, connected to the protected line sensors of zero-sequence current and zero-sequence voltage, zero-sequence power direction relay, time relay, OR logic element, output element, moreover the outputs of the current and voltage sensors of the zero sequence are connected to the corresponding inputs of the power direction switch, the output of which is connected to the input For time, the inputs of the OR logic element are connected to the outputs of the phase-fault protection block and the time relay, two pulse shapers, an inverter, a threshold element, an AND logic element, a single-shot and a logic inhibit element are INHIBITED, while the input of the first pulse shaper is connected to the relay output power direction of the zero sequence, and the output with the input of the inverter, the output of which is connected to the first input of the logic element AND, the input of the threshold element is connected to the output of the voltage sensor I have a zero sequence, and the output is with the input of the second pulse shaper, the output of which is connected to the second input of the AND logic element, the output of which is connected to the input of the single-vibrator, the direct input of the logic element is PROHIBITED is connected to the output of the logical element OR, the inverse input is connected to the output of the one-vibrator, and output - to the input of the output element.

 The introduction into the device for the protection of two additional pulse shapers, an inverter, a threshold element, an AND logic element, a single-vibrator, a FORBID logic element provides selective disconnection of the connection on which a single-phase earth fault occurs when it develops into a two-phase earth fault. This is because the protection captures the initial single-phase earth fault by the coincidence of the moments of occurrence of the voltage of the zero sequence and the direction of the flow of power of the zero sequence in the line. The second circuit is detected by the appearance of a signal from the zero sequence power direction switch with an existing signal from the zero sequence voltage sensor.

 Thus, due to the combination of distinctive features and their interconnection, the device for protecting lines with isolated neutral provides selectivity for disconnecting all types of short circuits, including the case of the development of a single-phase earth fault into a two-phase earth fault. In the latter case, only the primary damaged connection is disconnected, which eliminates the two-phase fault, and also, if the insulation has not been destroyed, then the single-phase earth fault. This ensures uninterrupted power supply to consumers of other connections.

 In FIG. 1 is a diagram of an insulated neutral line protection device. In FIG. 2 shows a diagram of an isolated neutral radial network with installed protection devices.

 The device for protecting lines with isolated neutral contains an interphase short circuit protection unit 1, a zero-sequence current sensor 2 and a zero-sequence voltage sensor 3, a zero-sequence power direction switch 4, a time relay 5, an OR gate 6, an output element 7, a first shaper pulses 8, inverter 9, threshold element 10, second pulse shaper 11, logic element I 12, single vibrator 13 and logic element FORBID 14. Interphase fault protection block 1, current sensors zero 2 howling sequence and zero sequence voltage 3 is connected to the protected line. The output of the interphase fault protection unit 1 is connected to the first input of the OR logic 6. The outputs of the zero sequence current sensors 2 and the zero sequence voltage 3 are respectively connected to the inputs of the zero sequence power direction switch 4. Its output is connected to the inputs of the time relay 5 and the first pulse shaper 8. The output of the time relay 6 is connected to the second input of the OR gate 6. The output of the first pulse shaper 8 is connected to the input of the inverter 9. Its output is connected to the first the logical element And 12. The input of the threshold element 10 is connected to the output of the zero-sequence voltage sensor 3, and the output is connected to the input of the second pulse shaper 11. Its output is connected to the second input of the logical element And 12. Its output is connected to the input of the one-shot 13. Direct input the logic element is prohibited 14 is connected to the output of the logic element OR 6, and the inverse is connected to the output of the one-shot 13. The output of the logic element is prohibited 14 is connected to the input of the output element 7. The output element 7 is connected to the Executive circuits .

 The device is implemented by minimal changes in existing circuit protection lines with isolated neutral. Moreover, the logical part of the device can be implemented on the basis of the logical and functional elements of any typical systems. So, for example, the AND, OR, and NOT functions can be implemented on K155LA3, K155LE3 microcircuits of the K155 series, made using the TTL technology [3].

 A radial network with isolated neutral consists of a power source 15, power buses 16, connections 17 and 18, protection devices 19 and 20. Power buses 16 are connected to power source 15. Connections 17 and 18 are connected to power buses. In these connections, protective devices 19 and 20 are installed.

 Possible points of damage: 21, 22, 23 and 24 - points of earth faults; 25 and 26 - points of two-phase short circuits to the earth; 27 and 28-point metal phase to phase short circuits.

 At each connection, departing from the supply bus, one set of the proposed protection is installed. Moreover, the number of connections is unlimited.

 The operation of the claimed device with various types of damage to the protected line is as follows. In each example, we will consider all processes for protection 19. In this case, the initial state of circuit elements of the line protection device with isolated neutral is as follows: at the outputs of the phase-to-phase short circuit protection block 1, zero-sequence power direction relay 4, time relay 5, OR OR 6 , pulse shapers 8 and 11, a threshold element 10, a logical element And 12, a single vibrator 13, a logical element FORBID 13 installed potentials of the logic zero level; the output of the inverter 9 is set to the potential level of the logical unit; at the outputs of the sensors of the current zero sequence 2, voltage zero sequence 3 signals are absent.

 Example 1. A single-phase earth fault at the protected connection.

 With a single-phase earth fault at point 21, currents in the intact connection phases are determined by the capacitances of these phases to earth. Therefore, the phase-to-phase protection unit 1 does not work. At the first input of the OR gate 6, the potential of the logic zero level is saved. The directions of the zero sequence current flowing to the ground and the zero sequence voltage are such that they trigger the zero sequence power direction switch 4. After the time relay 5 is activated, the logic level signal goes to the second input of the OR 6 logic element and is installed at its output.

 A change in potential at the output of the zero direction power direction switch 4 leads to the operation of the first pulse shaper 8, the output of which receives a single pulse of the logical unit level. The output of the inverter 9 and, therefore, the first input of the logical element And 12 receives a pulse level of logical zero. The triggering of the second threshold element 10 and the change in potential at its output leads to the triggering of the second pulse shaper 11. The pulse of the level of the logic unit from the output of the pulse shaper 11 goes to the second input of the logical element And 12. In this case, the logical element And 12 remains in its original state. Therefore, the one-shot 13 is in its original state. In this case, a logic zero is stored at the inverse input of the logic element FORBID 14, which allows the signal to pass from the direct input of the element FORBID 14. From the output of the logical element OR 6, the signal of the level of the logical unit goes to the direct input of the logical element BAN 14, passes it and goes to the input of the output element 7. Thus, a time delay signal is applied to disconnect the connection in case of a single-phase earth fault at the protected connection.

 Example 2. A single-phase earth fault "behind" the protection.

 With a single-phase earth fault at point 22, the currents in the intact connection phases are determined by the capacitances of these phases to earth. Therefore, the blocking protection against interphase faults 1 does not work, and at the first input of the logic element OR 6 the signal of the level of logic zero is stored. The directions of the zero sequence current and the zero sequence voltage are such that the zero sequence power direction relay 4 does not operate. A logic zero level signal is stored at its output. Therefore, the logic element OR 6 remains in its original state. Then the signal of the logic zero level is stored at the direct input of the logic element PROHIBITED 14. Since the potential at the output of the zero direction power direction switch 4 does not change, the pulse shaper 8 does not work. The inverter 9 remains in its original state, respectively, at the first input of the logical element AND 12, the logical unit is stored. The threshold element 10 is triggered by the appearance of a zero-sequence voltage, and at its output, the potential level of the logical unit is established. A change in the potential at the input leads to the operation of the second pulse shaper 11. The pulse of the level of the logical unit goes to the second input of the logical element And 12. Since all the inputs of the element And 12 receive pulses of the level of the logical unit, then the output comes from the pulse of the level of the logical unit, which triggers single vibrator 13. At the output of the single vibrator 13, a signal of the logic unit level is stored for some time. This signal is fed to the inverse input of the logic element BAN 14 and prohibits the passage of the signal from the direct input of this element to its output. At the input of the output element 7, a signal of the logic zero level is stored.

 Thus, with a single-phase earth fault behind the back, the device prohibits the protected connection from being protected by any other types of faults while the single-vibrator is operating.

 Example 3. A single-phase earth fault at the protected connection caused a breakdown of the arrester or damage to the insulation. The point of the second earth fault is at the protected connection.

 With a single-phase earth fault at point 21, currents in the intact connection phases are determined by the capacitances of these phases to earth. Therefore, the blocking protection against interphase faults 1 does not work, and at the first input of the logic element OR 6 the signal of the level of logic zero is stored. The directions of the zero sequence current and the zero sequence voltage are such that they trigger the zero sequence power direction switch 4. Through the time relay 5, the logic level signal goes to the second input of the OR gate 6 and is installed at its output.

 A change in potential at the output of the zero direction power direction switch 4 leads to the operation of the first pulse shaper 8, the output of which receives a logic level level pulse. The output of the inverter 9 and, accordingly, the first input of the logical element And 12 receives a signal level of logical zero. The triggering of the second threshold element 10 and the potential change at its output leads to the triggering of the second pulse shaper 11. The pulse of the level of the logic unit from the output of the pulse shaper 11 comes to the second input of the logical element And 12. At the output of the logical element And 12, the potential of the logic zero level is stored. Therefore, the one-shot is in its original state. At the inverse input of the logic element BAN 14, a signal of the logic zero level is stored, allowing the signal to pass from the direct input of this element.

 Due to the increase in voltage at one of the intact phases of connection 17, a breakdown of insulation or a spark gap occurs. There is a second point of earth fault 23. This causes a sharp increase in phase currents and the operation of the block of protection against interphase faults 1. At the first input of the logic element OR 6 receives the signal level of the logical unit. Since the zero sequence voltage was previously detected by the zero sequence voltage sensor 3, the potential at the output of the previously triggered threshold element 10 does not change. Therefore, the second pulse shaper 11 does not work. At the second input of the logical element And 12 the potential of the level of logical zero, which is established after the passage of a single pulse, is stored. Accordingly, at the output of the logical element And 12 is stored logical zero. The one-shot 13 remains in its original state. At the inverse input of the logic element PROHIBIT 14, a logic zero is stored, allowing the passage of the signal from the direct input. The logical unit from the output of the logical element OR 6 is fed to the direct input of the logical element FORBID 14. The potential of the level of the logical unit comes to the input of the output element 7. The device responds by disconnecting connection 17, where a single-phase earth fault initially occurred.

 Thus, with the development of a single-phase earth fault at the protected connection into a double earth fault with a second fault point at the protected connection, the device trips. This leads to the localization of earth faults and maintains a normal mode of power supply to consumers of other connections.

 Example 4. A single-phase earth fault at the protected connection caused a breakdown of the arrester or damage to the insulation. The point of the second earth fault is at another connection.

 With a single-phase earth fault at point 21, currents in the intact connection phases are determined by the capacitances of these phases to earth. Therefore, the blocking protection against interphase faults 1 does not work, and at the first input of the logic element OR 6 the signal of the level of logic zero is stored. The directions of the zero sequence current and the zero sequence voltage are such that they trigger the zero direction power direction switch 4. Through the time relay 5, the logic level signal goes to the second input of the OR gate 6 and is installed at its output.

 A change in the potential at the output of the zero direction power direction switch 4 leads to the operation of the first pulse shaper 8, at the output of which a logic level level pulse appears. At the output of the inverter 9 and, accordingly, at the first input of the AND gate 12, a pulse of the logic zero level appears. The triggering of the second threshold element 10 and the change in potential at its output leads to the triggering of the second pulse shaper 11. The pulse of the level of the logic unit from the output of the pulse shaper 11 comes to the second input of the logical element And 12. At the output of the logical element And 12, the potential of the logic zero level is stored. Therefore, the one-shot 13 remains in its original state. The potential level of the logic zero from the output of the one-shot 13 is stored on the inverse input of the logic element BAN 14, allowing the passage of the signal from the direct input of this element.

 Due to the increase in voltage at one of the intact phases of connection 17, a breakdown of insulation or a spark gap occurs. There is a second point of earth fault 24. This causes a sharp increase in phase currents and the operation of the block of protection against interphase faults 1. At the first input of the logic element OR 6 receives the signal level of the logical unit. Since the zero sequence voltage was previously detected by the zero sequence voltage sensor 3, the potential at the output of the previously triggered threshold element 10 does not change. The second pulse shaper 11 does not work. At the second input of the logical element And 12 the potential of the level of logical zero, which is established after the passage of a single pulse, is stored. The single vibrator remains in its original position. At the inverse input of the logic element PROHIBIT 14, a logic zero is stored, allowing the passage of the signal from the direct input. The logical unit from the output of the logical element OR 6 passes to the direct input of the logical element FORBID 14. At the input of the output element 7 receives the level potential of the logical unit, the device operates to disconnect the connection 17, where initially a single-phase earth fault occurred.

 Thus, when a single-phase earth fault develops on a protected connection into a double earth fault with a second earth fault point “behind”, the device trips. If the insulation has not been destroyed, the point of the secondary earth fault self-destructs after the first point is disconnected due to a decrease in phase voltage. The normal mode of power supply to consumers of other connections is maintained.

 Example 5. A single-phase earth fault “behind” the protection caused a breakdown of the arrester or damage to the insulation. The point of the second earth fault is at the protected connection.

 With a single-phase earth fault at point 22, currents in intact phases are determined by the capacitances of these phases to earth. Therefore, the blocking protection against interphase faults 1 does not work, and at the first input of the logic element OR 6 the signal of the level of logic zero is stored. The directions of the zero sequence current and the zero sequence voltage are such that the zero sequence power direction switch 4 does not operate. A logic zero level signal is stored at its output. At the second input of the logical element OR 6 and, accordingly, a logical zero is stored at its output. The potential of the logic zero level is stored at the direct input of the logic element PROHIBIT 14. Since the potential at the output of the zero direction 4 power direction relay does not change, the pulse shaper 8 remains in its original state. Therefore, at the first input of the logical element And 12, the potential level of the logical unit is preserved. The threshold element 10 is triggered, and at its output, the potential level of the logical unit is set. A change in the potential at the input leads to the operation of the second pulse shaper 11. The pulse of the level of the logical unit goes to the second input of the logical element And 12. Since at this moment all the inputs of the logical element And 12 are logical units, then the pulse of the level of the logical unit comes to the output, which starts one-shot 13. At the output of one-shot 13 for some time the signal level of the logical unit. The logical unit is supplied to the inverse input of the logical element BAN 14 and prohibits the passage of the signal from the direct input of this element to its output.

 Due to the increase in voltage at one of the intact phases of connection 17, a breakdown of insulation or a spark gap occurs. There is a second point of earth fault 23. This causes a sharp increase in phase currents and the operation of the block of protection against interphase faults 1. At the first input of the logic element OR 6 receives the signal level of the logical unit. Since the zero sequence voltage was previously detected by the zero sequence voltage sensor 3, the potential at the output of the previously triggered threshold element 10 does not change. The second pulse shaper 11 does not work. At its output, a logical zero is stored, which is fed to the second input of the logical element And 12. Accordingly, at the output of this element, the potential of the level of logical zero, which is established after passing a single pulse, is stored. At the output of a previously launched single-shot 13, a signal of the logic unit level is stored. Then the output element 7 remains in its original state. While at the output of the single-shot 13, the logic level signal is stored, the protection will not work.

 Thus, with the development of a single-phase earth fault "behind" the protection action into a double earth fault with a second fault point on the protected connection, the device does not disconnect the second fault point.

 Example 6. A single-phase earth fault “behind” the protection caused a breakdown of the arrester or damage to the insulation. The point of the second earth fault is located “behind” the protection kit.

 With a single-phase earth fault at point 22, the currents in the connection phases 17 remain unchanged. Therefore, the blocking protection against interphase faults 1 does not work, and the potential of the logic zero level is stored at the first input of the OR 6 logic element. The directions of the zero sequence current and the zero sequence voltage are such that the zero sequence power direction relay 4 does not operate. A logic zero level signal is stored at its output. The OR 6 logic element remains in its original state. The signal of the logic zero level is stored at the direct input of the logic element PROHIBIT 14. Since the potential at the output of the zero direction power relay 4 does not change, the pulse shaper 8 does not work. The inverter 9 remains in its original state. At the first input of the logical element And 12 is stored logical unit. The threshold element 10 is triggered, and at its output, the potential level of the logical unit is set. A change in the potential at the input leads to the operation of the second pulse shaper 11. The pulse of the level of the logical unit goes to the second input of the logical element And 12. Since there are logic units at all inputs of this element, the pulse of the level of the logical unit comes to the output, which starts one-shot 13. At the output of one-shot 13 for some time the signal level of the logical unit. The logical unit is fed to the inverse input of the logical element BAN 14 and prohibits the passage of the signal from the direct input of this element to its output.

 Due to the increase in voltage at one of the intact phases of the connection 18, a breakdown of insulation or a spark gap occurs. A second earth fault point 24 occurs. Since connection 17 is not included in the circuit, the phase currents of this connection remain unchanged. The phase-fault protection block remains in its original state. At the first input of the OR gate 6, the potential of the logic zero level is saved. Since the zero sequence voltage was previously detected by the zero sequence voltage sensor 3, the potential at the output of the previously activated threshold element 10 does not change. Then the second pulse shaper 11 does not work. At its output, a logical zero is maintained, which is established after the passage of a single pulse. Accordingly, at the output of the logical element And 12 is stored logical zero. At the output of a previously launched single-shot 13, a signal of the logic unit level is stored. This signal is supplied to the inverse input of the logic element FORBID 14. At the input of the output element 7, the potential of the logic zero level is stored. Protection will not work.

 Thus, with the development of a single-phase earth fault “behind the back” of the protection into a two-phase earth fault “behind the back”, the device does not disconnect the protected connection.

 Example 7. Two-phase earth fault on the protected connection.

 When a two-phase earth fault occurs at point 25, the currents of the damaged connection phases 17 increase sharply. The protection module against phase-to-phase faults 1 is triggered. A signal of the logic unit level appears at its output. The current directions and the zero sequence voltage appearing in the line are such that the zero sequence power direction switch 4 and the threshold element 10 are triggered. At the inputs of the pulse shapers 8 and 11, pulses of the logical unit level appear. The output of the inverter 9 receives a pulse level of logical zero. At the output of the logical element And 12 the potential of the level of logical zero is preserved. The one-shot 13 remains in its original state, and a logic zero is stored at the inverse input of the logic element FORBID 14. With a time delay at the output of the time relay 5 and, accordingly, at the output of the logic element OR 6, a signal of the level of the logical unit appears. At the direct input of the element BAN 14 from the output of the logical element OR 6 comes a logical unit, which is installed at the input of the output element 7. The device disconnects the damaged connection 17.

 If a two-phase earth fault occurs on the protected connection, the device disconnects this connection.

 Example 8. Two-phase earth fault "behind" the protection.

 With a two-phase earth fault at point 26, the phase currents of the connection 17 do not change. At the output of the block of protection against interphase faults, a signal of the logic zero level is stored. The directions of the zero sequence current and voltage lines are such that the zero sequence power direction switch 4 does not work. The pulse former 8, the inverter 9 and the relay 5 remain in their original state. The triggering of the threshold element 10 to the appearance of a zero-sequence voltage leads to the operation of the second pulse shaper 11. A pulse of the logic unit level is output. At the output of the logical element And 12 there is a pulse level of the logical unit, which triggers the single-shot 13. The logical unit from the output of the single-vibrator, fed to the inverse input of the logical element BAN 14, prohibits the signal from passing from the direct input of this element. At the input of the output element 7, the potential of the logic zero level is maintained. Protection does not work.

 If a two-phase earth fault occurs “behind” the protection, the protection does not work.

 Example 9. Two-, three-phase metal circuit on the protected connection.

 With a two- or three-phase metal circuit at point 27, the phase currents in connection 17 increase sharply. This causes the protection unit to interphase faults 1. The corresponding potential of the logic unit level is set at the output of the OR logic 6 element. Since there is no earth in the metal circuit, there is no current or zero sequence voltage. The zero direction power direction switch 4, the threshold element 10, the pulse shapers 8 and 11, the logic element And 12 and the single-shot 13 remain in the initial state. Logic zero is stored at the inverse input of the FORBID 14 logic element. The logical unit from the output of the logical element OR 6 passes to the input of the output element 7. The device disconnects the damaged connection 17.

 The device disconnects the metal phase-to-phase short circuits on the protected connection.

 Example 10. Two-, three-phase metal circuit "behind" the protection.

 If a two- or three-phase metal circuit occurs at point 28, then the phase currents of the connection 17 do not change. Since there is no earth in the metal circuit, there is no current and zero sequence voltage. In this case, neither the phase-fault protection unit 1, nor the zero-sequence voltage sensor 3, nor the power direction relay 4 are triggered. All elements retain their original state. Protection does not work.

 With metallic phase-to-phase short circuits “behind”, protection does not work.

 From the foregoing it can be seen that for all types of short circuits, the proposed device operates selectively.

 The application of the proposed device provides the selectivity of disconnecting a two-phase earth fault, developed from a single-phase earth fault. Moreover, if the insulation was not destroyed, only that connection is disconnected, on which the initial single-phase earth fault occurred. This leads to self-destruction of the second earth fault point. At the same time, power supply to consumers of other connections is not interrupted.

Sources of information
1. Chernobrovov N.V., Semenov V.A. Relay protection of energy systems. M .: Energoatomizdat, 1998, p. 305-307.

 2. Gelfand Ya.S. Relay protection of distribution networks. M .: Energoatomizdat, 1987, p. 278-280, p. 300-301.

 3. Microprocessors and microprocessor sets of integrated circuits: Reference: 2 t. / Ed. Shakhanova V.A. M .: Radio and communication, 1998, v. 2, p. 362.

Claims (1)

 A device for protecting lines with an insulated neutral, comprising an interphase circuit protection unit, zero-sequence current and zero-sequence voltage sensors connected to the protected line, a power direction switch, a time relay, an OR logic element, an output element, and the outputs of the zero-sequence current and voltage sensors respectively connected to the inputs of the power direction switch, the output of which is connected to the input of the time relay, the inputs of the logic element OR are connected to the outputs of the block protection against phase-to-phase faults and a time relay, characterized in that it additionally includes two pulse shapers, an inverter, a threshold element, an AND logic element, a single-shot and a logic inhibit switch, while the input of the first pulse shaper is connected to the output of the power direction relay, and the output - with the input of the inverter, the output of which is connected to the first input of the logic element AND, the input of the threshold element is connected to the output of the zero-sequence voltage sensor, and the output is connected to the input of the second driver pulses, the output of which is connected to the second input of the AND gate, the output of which is connected to the input of the single-vibrator, the direct input of the logic element is FORBID connected to the output of the OR logic element, the inverse input to the output of the one-shot, and the output to the input of the output element.

Images