RU2734107C1 - Method of protecting from receiving side two parallel lines with one-sided supply - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: use in power engineering for protection of parallel lines against short circuits. Method for protection from receiving side of two parallel lines with one-sided supply, in which instantaneous values of currents i₁ at first and i₂ on second line are measured in positive or negative half-wave of current at current rise, i₁ is compared to positive or negative half-wave with preset value of current i_ec, and when current i₁ reaches current value i_ec, while measuring instantaneous value of current i₁, beginning to count time t₁ to the moment, when to next positive or negative half-wave at current increase, value of current i₁ reaches specified value of current i_ec, measured time t₁ is compared to first and second preset time values t_ec1 and t_ec2, and if value t₁ is greater than a given time t_ec1, but less than a given time t_ec2, then the time count is repeated until the time value t₁ is greater than or equal to the preset time t_ec1 or the time value t₁ becomes less than or equal to the preset time t_ec2, then if one of these inequalities is satisfied, then disconnecting the first line, removing it for repair and after repair is included in operation, in the same way, with time reference t_1, time t₂ is counted when current i₂ reaches the second line with a given current value i_ec until the moment, when in next positive or negative half-wave at current rise value of current i₂ reaches i_ec, measured time t₂ is compared with first and second preset time values t_ec1 and t_ec2, and if value t₂ is more than preset time t_ec1, but less than a given time t_ec2, the time count is repeated until the time value t₂ is greater than or equal to a given time t_ec1 or the time value t₂ becomes less than or equal to a given time t_ec2, then if one of these inequalities is satisfied, then switching off second line, brought out for repair and, after repair, is put into operation, simultaneously with switching on deactivated second or first line in operation, when first or second line is in on position, starting to count time t₃ from moment, when current i₁ or i₂ reaches preset value of current i_ec in positive or negative half-wave of current till moment, when current i₂ or i₁ becomes equal to value of preset current i_ec, comparing t₃ with third preset time t_ec3, and if time t₃ is greater than or equal to value of preset time t_ec3, both lines are switched off, then through time t₄ includes first or second line, then after preset time t₅ after switching on its position is fixed, and if it is in on position, then second or first line is brought out for repair, if it is in disconnected position, then the second or the first line is switched on, and the first or the second line is brought out for repair.

EFFECT: detecting and reducing the time of disconnection of the damaged line when one of the lines is switched on for short-circuit during operation of the other line.

1 cl, 1 dwg

Description

The invention relates to the electric power industry, namely to relay protection technology, and can be used to protect two parallel lines from short circuits.

A known method of protection from the receiving side of two parallel lines with one-way power supply [Chernobrovov NV, Semenov V.A. Relay protection of power systems. - M .: Energoatomizdat, 1998. - P. 346-359], in which the difference in currents of the same phases of the lines is measured and compared with a given value, the voltage on the buses from which the lines are powered, then the angle between the resulting current and the voltage on tires and compare it with a predetermined value, and if it exceeds a predetermined value and the current difference is greater than a predetermined value, then the first line is disconnected, if the angle between the resulting current and the voltage on the buses is less than a predetermined value and the current difference is greater than a predetermined value, the second line is disconnected.

The disadvantage of this method is the low reliability of devices for its implementation, since it includes voltage measurement, which entails a significant error.

Closest to the proposed is the method of protection from the receiving side of two parallel lines with one-way power supply [RU 2640353, IPC H2H 7/22, publ. 12/28/2017], in which the instantaneous values of the currents i ₁ on the first and i ₂ on the second line are measured in the positive and negative half-waves of the current when the current rises, compare i ₁ in the positive or negative half-wave with a given value of the current i _et , and when the current reaches i _{1 of a} given value of current i _et , while continuing to measure the instantaneous value of current i ₁ , they begin to count the time t ₁ until the moment when in the next positive or negative half-wave of the current with an increase in current i ₁ reaches the specified value i _et , compare the measured time t ₁ s the first and second preset values of time t _et1 and t _et2 , and if the value t _{1 is} greater than the preset value of time ti _et1 but less than the specified value of time t _et2 , then the time is repeated until the value of time t _{1 is} greater than or equal to the specified value of time t _et1 or the value of time t ₁ will become less than or equal to the specified value of time t _et2 , then, if one of these inequalities is satisfied, then The first line is taken out, taken out for repair and after the repair is turned on, in the same way, simultaneously with the time t _{1, the} time t _{2 is} counted when the current i ₂ reaches the second line with a given value of the current i _et until the moment when the next positive or negative half-wave with increasing current, the value of the current i ₂ reaches i _et , compare the measured time t ₂ with the first and second preset values of time t _et1 and t _et2 , and if and if the value of t _{2 is} greater than the specified time value t _et1 but less than the specified time value t _et2 , then the time count is repeated until the value of time t _{2 is} greater than or equal to the specified value of time t _et1 or the value of time t ₂ becomes less than or equal to the specified value of time t _et2, then, if one of these inequalities is satisfied, then turn off the second line, take it out for repair and, after repair, turn it on.

As a disadvantage of this method, narrow functionality can be noted, since during its implementation a short circuit is not detected if it occurs when the line is turned on after repair while another line is working; as a result, this short-circuit is tripped by the long-time back-up protection.

The technical problem, the solution of which is provided in the implementation of the invention, is to create a method of protection from the receiving side of two parallel lines with one-way power supply with extended functionality by identifying and reducing the time of disconnection of the damaged line when turning on after repair of one of the lines for a short circuit, when the other line working.

The solution to this technical problem is achieved by the fact that in the method of protection from the receiving side of two parallel lines with one-way power supply, as well as in the prototype, the instantaneous values of the currents i ₁ on the first and i ₂ on the second line are measured into positive and negative half-waves of the current when the current rises , compare i ₁ in a positive or negative half-wave with a given value of current i _et , and when current i ₁ reaches a given value of current i _et , while continuing to measure the instantaneous value of current i ₁ , they begin to count the time t ₁ until the moment when the next positive or negative half-wave of the current with increasing current i ₁ reaches the set value i _et , compare the measured time t ₁ with the first and second predetermined values of time t _et1 and t _et2 , and if the value of t _{1 is} greater than the specified value of time t _et1 , but less than the specified value of time t _et2 , then repeat the countdown until the value of time t _{1 is} greater than or equal to the specified value of time t _et1 or the value of time t ₁ will become less than or equal to the given value of time t _et2 , then, if one of these inequalities is fulfilled, then the first line is _turned off, taken out for repair and, after repair, turned on in operation, in the same way simultaneously with the time t ₁ time t _{2 is} counted when the current i ₂ in the second line with a given value of current i _{fl is} counted until the moment when, in the next positive or negative half-wave with increasing current, the value of current i ₂ reaches i _fl , the measured time t _{2 is} compared with the first and second given values of time t _et1 and t _et2 , and if and if the value of t _{2 is} greater than a given value of time t _et1 but less than a given value of time t _et2 , then the time is repeated until the value of time t _{2 is} greater than or equal to a given value time t _et1 or the value of time t ₂ will become less than or equal to the given value of time t _et2 , then, if one of these inequalities is fulfilled, then the second line is turned off, it is put into repair nt and after repair are included in the work.

According to the invention, simultaneously with the inclusion of the switched off second or first line into operation, when the first or second line is in the on position, the time t3 begins to count from the moment when the current i ₁ or i ₂ reaches the set value of the current i _et in a positive or negative half-wave of the current to the moment when the current i2 or i ₁ becomes equal to the value of the given current i _et , t _{3 is} compared with the third predetermined value of time t _et3 , and if the time t _{3 is} greater than or equal to the value of the specified time t _et3 , then both lines are _turned off, then after time t ₄ turn on the first or second line, then after a predetermined time t ₅ after turning on, fix its position, and if it is in the on position, then bring the second or first line for repair, if it is in the off position, then turn on the second or first line , and the first or second line is taken out for repair.

In the inventive method, in contrast to the prototype, the operation of measuring the time t ₃ is performed when the line disconnected during a short circuit is turned on from the moment when the current i ₁ or i ₂ is equal to i _et in the positive or negative half-wave of the current until the moment when i ₂ or i ₁ is i _et , which allows you to identify the presence of a short circuit when the lines are turned on. Operations are performed to turn on and off the lines after specified time values, which makes it possible to identify the damaged line. The combination of these operations makes it possible to expand the functionality of the method by identifying and reducing the disconnection time of the damaged line when one of the lines is switched on after repair for a short circuit, when the other is working, and the identification and disconnection is carried out faster than the backup protection of the lines.

The given drawing shows a device that implements a method for protecting two parallel lines with one-way power supply from the receiving side.

The method of protection from the receiving side of two parallel lines with one-way power supply can be implemented using a device that contains current sensors 1 (DT1), 2 (DT2), installed near the conductors of the same phases of the first and second lines. To the current sensor 1 (DT1) are connected in series block 3 (PP1) for extracting a positive half-wave of current, block 4 (ST1) for comparing instantaneous current values, block 5 (IV1) for measuring time, block 6 (CB1) for comparing measured time, OR element 7 ( OR1) and an actuator 8 (IO1), the output of which is connected to the opening coil of the first line circuit breaker. To the output of block 5 (IV1) time measurement is connected block 9 (CB2) time comparison, the output of which is connected to the element OR 7 (OR1). To the current sensor 1 (DT1) are connected in series a unit 10 (OT1) for extracting a negative half-wave of current, unit 11 (CT2) for comparing instantaneous current values, unit 12 (IV2) for measuring time, unit 13 (CB3) for comparing time. To the output of block 12 (IV2) time measurement is connected block 14 (CB4) time comparison. The outputs of blocks 13 (CB3) and 14 (CB4) time comparison are connected to the OR element 7 (OR1). To the current sensor 2 (DT2) are connected in series a block 15 (PP2) for the selection of a positive half-wave of the current, a block 16 (ST3) for comparing instantaneous current values, a block 17 (IV3) for measuring time, a block 18 (CB5) for comparing time, an OR element 19 (OR2 ) and an actuator 20 (IO2), the output of which is connected to the trip coil of the second line switch. The output of the time measurement unit 17 (IV3) is connected to the time comparison unit 21 (CB6), the output of which is connected to the OR element 19 (OR2). To the current sensor 2 (DT2) are connected in series a block 22 (OT2) for extracting a negative half-wave of current, a block 23 (ST4) for comparing instantaneous current values, a block 24 (IV4) for measuring time, and a block 25 (CB7) for comparing time. To the output of the block 24 (IV4) for measuring time is connected to the block 26 (CB8) for comparing the time. The outputs of blocks 25 (CB7) and 26 (CB8) time comparison are connected to the OR element 19 (OR2). Units 27 (IV5) and 28 (IV6) time measurement are connected to units 4 (CT1), 16 (CT3) and 11 (CT2), 23 (CT4) comparing instantaneous current values, respectively. Blocks 29 (CB9) and 30 (CB10) time comparison are connected to blocks 27 (IV5) and 28 (IV6) time measurement. Block 31 (BL) logic inputs are connected to blocks 29 (CB9) and 30 (CB10) time comparison, and one of the outputs to executive bodies 8 (IO1) and 20 (IO2). Blocks 32 (BVL1) and 33 (BVL2) fixing the on state of the lines are connected to the auxiliary contacts of the switches of the first and second lines. Blocks 34 (BOL1) and 35 (BOL2) fixing the disconnected state of the lines are connected to the auxiliary contacts of the switches of the first and second lines. Logic block 31 (BL) is connected by inputs to blocks for fixing 32 (BVL1), 33 (BVL2) and off 34 (BOL1), 35 (BOL2) line states and executive bodies 8 (IO1) and 20 (IO2), and outputs to time relay 36 (РВ1), 37 (РВ2), 38 (РВ3), 39 (РВ4). Time relay outputs 36 (PB1), 37 (PB2) are connected in the signaling circuit and to the logic block 31 (BL). The outputs of the time relay 38 (PB3), 39 (PB4) are connected in the switching circuit of the switches of the first and second lines, respectively. Setter 40 (ЗВ) of the set time values with one output is connected to the inputs of blocks 6 (CB1), 13 (CB3), 18 (CB5), 25 (CB7) time comparison, the next output to the inputs of blocks 9 (CB2), 14 (CB4) , 21 (CB6), 26 (CB8) time comparison, another output to the inputs of blocks 29 (CB9), 30 (CB10) time comparison.

Reed switches of the KEM-2 type can be used as current sensors 1 (DT1) and 2 (DT2). Blocks 3 (ПП1), 15 (ПП2) allocation of the positive half-wave of current, blocks 4 (ST1), 11 (ST2), 16 (ST3), 23 (ST4) comparison of instantaneous current values, blocks 5 (IV1), 12 (IV2) , 17 (IV3), 24 (IV4), 27 (IV5) and 28 (IV6) time measurements, blocks 6 (SV1), 9 (SV2), 13 (SV3), 14 (SV4), 18 (SV5), 21 (SV6), 25 (SV7), 26 (SV8), 29 (SV9), 30 (SV10) time comparisons, block 31 (BL) logic, blocks 10 (OT1), 22 (OT2) for selecting a negative half-wave of current, and elements OR7 (OR1), 19 (OR2), latching blocks 32 (BVL1), 33 (BVL2) and off 34 (BOL1), 35 (BOL2) line states, time relay 36 (RV1), 37 (RV2), 38 ( РВ3), 39 (РВ4), setpoint adjuster 40 (ЗВ) can be implemented on the microcontroller series 51 from atmel AT89S53. Relays of RP 16-1 type can be used as executive bodies 8 (IO1), 20 (IO2).

In the load mode, from the current sensor 1 (DT1), a signal proportional to the current in the phases of the first line is sent to the inputs of blocks 3 (PP1) and 10 (OT1) for separating the positive and negative half-waves of the current. A signal proportional to the current in the phases of the second line is sent from the current sensor 2 (DT2) to the inputs of blocks 15 (PP2) and 22 (OT2) for separating the positive and negative half-waves of the current. Blocks 3 (PP1) and 10 (OT1) allocate positive and negative half-waves of the current select the positive and negative half-waves of current i ₁ and supply them to the inputs, respectively, of blocks 4 (CT1) and 11 (CT2) comparing instantaneous current values, where instantaneous values current ii with increasing, respectively, in the positive and negative half-waves of the current is compared with a given value of the current i _et . Blocks 15 (PP2) and 22 (OT2) allocate positive and negative half-waves of current select positive and negative half-waves of current 12 and supply them to the inputs, respectively, of units 16 (ST3) and 23 (ST4) comparing instantaneous current values, where instantaneous current values i ₂ with an increase, respectively, in the positive and negative half-waves of the current are compared with a given value of the current i _et . When currents i ₁ , i ₂ first reach the set value of current i _et in a positive half-wave, units 4 (CT1) and 16 (CT3) for comparison of instantaneous current values give signals to the inputs of units 5 (IV1) and 17 (IV3) for measuring time, starting counting the time t ₁ and t ₂ in the positive half-wave of the alternating current. When the currents i ₁ , i ₂ reach the positive half-wave of the set value of the current i _{et, the} first counting of the time t ₁ and t _{2 is} stopped, and the blocks 5 (IV1) and 17 (IV3) of the time measurement give signals, respectively, to the inputs of blocks 6 (CB1), 9 (CB2) and 18 (CB5), 21 (CB6) time comparisons, and start the next timing. The first achievement of the currents i _1, i ₂ in the negative half-wave of a predetermined amount of current values i _fl blocks 11 (CT2) and 23 (FT4) comparing the instantaneous values of the current output the signals at the inputs, respectively, blocks 12 (IV2) and 24 (IV4) Measurement time, starting the timing t ₁ and t ₂ in the negative half-wave of the alternating current. When the currents i ₁ , i ₂ reach the negative half-wave of the set value of the current i _{et, the} first time counting t ₁ and t _{2 is} stopped, and the time measurement units 12 (IV2) and 24 (IV4) output signals, respectively, to the inputs of the units 13 (CB3), 14 (CB4) and 25 (CB7), 26 (CB8) compare the time, and start the next timing. Blocks 6 (CB1) and 9 (CB2) compare the time measured in block 5 (IV1) time measurement in the positive half-wave of the alternating current time t ₁ with the first t _et1 (for example, 0.015 s) and the second t _et2 (for example, 0.025 s) given time values, which are supplied to blocks 6 (CB1) and 9 (CB2) for comparing time from the master 40 (ЗВ) of predetermined time values. Blocks 13 (CB3) and 14 (CB4) compare the time measured in the second block 12 (IV2) for measuring time in the negative half-wave of the alternating current time t ₁ with the first t _et1 and the second t _{et2 with} predetermined time values, which are supplied to blocks 13 (CB3 ) and 14 (CB4) comparing the time from the master 40 (ZV) set time values. Blocks 18 (CB5) and 21 (CB6) compare the time measured in block 17 (IV3) time measurement in the positive half-wave of the alternating current time t ₂ with the first t _et1 and second t _{et2 with} predetermined time values, which are supplied to blocks 18 (CB5) and 21 (CB6) comparing time from the set time unit 40 (CB). The time comparison units 25 (CB7) and 26 (CB8) compare the time t ₂ measured in the time measurement unit 24 (IV4) in the negative half-wave of the alternating current with the first t _et1 and the second t _{et2 with} predetermined time values, which are supplied to the units 25 (CB7) and 26 (CB8) comparing the time from the setpoint generator 40 (SB). In this case, the blocks 6 (CB1), 13 (CB3), 18 (CB5) and 25 (CB7) do not issue time comparisons of signals, since t ₁ and t _{2 are} greater than t _et1 . Blocks 9 (CB2), 14 (CB4), 21 (CB6) and 26 (CB8) time comparisons do not work, since t ₁ and t _{2 are} less than t _et2 . Therefore, there are no signals at the outputs of the OR elements 7 (OR1) and 19 (OR2). Simultaneously with the issuance of signals to the inputs of blocks 5 (IV1), 17 (IV3) and 12 (IV2), 24 (IV4) time measurement blocks 4 (ST1), 16 (ST3), 11 (ST2), 23 (ST4) compare instantaneous current values give signals to the inputs of blocks 27 (IV5) and 28 (IV6) time measurement, and blocks 4 (ST1) and 16 (ST3) comparing instantaneous current values - to the inputs of block 27 (IV5) time measurement, blocks 11 (ST2) and 23 (ST4) comparing instantaneous current values - to the inputs of block 28 (IV6) for measuring time. Block 27 (IV5) measuring time measures the time t ₃ from the moment when i ₁ or i ₂ is equal to i _fl , to the moment when i ₂ or i ₁ is equal to i _fl in the positive half-wave of the current. Block 28 (IV6) measuring time measures the time t ₃ from the moment when i ₁ or i ₂ is equal to i _fl , to the moment when i ₂ or i ₁ is equal to i _fl , in the negative half-wave of the current. Suppose that in the positive and negative half-wave current value i has reached the first _floor in the first line current phase, while blocks 27 (IV5) and 28 (IV6) measure the time measurement start time t _3. When the current i ₂ reaches the value i, _these blocks 27 (IV5) and 28 (IV6) stop timing measurement of time t ₃ and send a signal to the inputs of blocks 29 (CB9) and 30 (CB10) for time comparison. Since in the load mode the currents in the phases of the lines coincide in phase and are equal in magnitude, t ₃ does not exceed a predetermined value of time t _et3 , which is fed to blocks 29 (CB9) and 30 (CB10) for comparing the time from the master 40 (ЗВ). Therefore, blocks 29 (CB9) and 30 (CB10) time comparison of signals to the inputs of block 31 (BL) logic do not issue. At the same time, signals from blocks 32 (BVL1) and 33 (BVL2) of fixing the switched-on state of the lines are sent to the other inputs of the block 31 (BL) of logic and are not received from blocks 34 (BOL1) and 35 (BOL2) fixing the switched-off state of the lines. Therefore, the block 31 (BL) logic does not issue a signal. The executive bodies 8 (IO1) and 20 (IO2) do not issue signals, the protection does not work.

Consider a short circuit (SC), for example, on the first line when currents i ₁ , i ₂ pass from positive to negative half-wave before current i ₁ is equal to i _floor . Until the occurrence of the short circuit, blocks 5 (IV1) and 12 (IV2), 17 (IV3) and 24 (IV4) began to count, respectively, the time t ₁ , t ₂ . When a short circuit occurs due to a 180 ° current phase change, signals to the inputs of blocks 5 (IV1) and 12 (IV2) arrive, respectively, earlier than 0.015 s and later than 0.025 s. Therefore, t ₁ in the positive half-wave becomes less than t _et1 , and in the negative half - more than 0.025 s. Blocks 6 (CB1) and 14 (CB4) give signals to the input of the OR element 7 (OR1), which is triggered and starts the executive body 8 (IO1). The last 8 (IO1) gives a signal to the disconnection circuit of the first line. Protection works. Therefore, the block 32 (BVL1) fixing the on state of the signal line to the input of the block 31 (BL) logic does not, and block 34 (BOL1) fixing the off state of the line outputs. Block 31 (BL) logic fixes that only the second line is in operation.

After turning off the switch of the first line, it is taken out for repair, and then turned on again. Consider a mode when the first line is short-circuited. Then the currents i ₁ , i _{2 are} shifted by 180 °. In this case, the time t ₃ between the moments when i ₁ is equal to i _fl and i ₂ is equal to i _fl becomes greater than t _et3 . Therefore, blocks 29 (CB9) and 30 (CB10) time comparison output signals to the inputs of the logic block 31 (BL). Since before the first line was turned on, the block 33 (BVL2) for fixing the switched on state of the line and block 34 (BOL1) for fixing the disconnected state of the line were sent to the input of the logic block 31 (BL), the block 31 (BL) of the logic starts the executive bodies 8 (IO1) and 20 (IO2). The executive bodies 8 (IO1) and 20 (IO2) issue signals in the circuit for tripping the switches of the first and second lines, as well as to the inputs of the logic block 31 (BL). Both lines are disconnected. Therefore, the blocks 32 (BVL1) and 33 (BVL2) for fixing the switched on state of the lines do not issue signals, and blocks 34 (BOL1) and 35 (BOL2) for fixing the switched off state of the lines do. Since the inputs of block 31 (BL) logic receive signals from both executive bodies 8 (IO1) and 20 (IO2), from blocks 34 (BOL1) and 35 (BOL2) fixing the disconnected state of the lines, and it was also previously recorded that in work only the second line, then the logic block 31 (BL) gives a signal to the inputs of the time relay 37 (PB2) and 39 (PB4). The time relay 39 (PB4), after a time delay t ₄ , for example, 0.04 s, supplies a signal to the second line switching circuit (the line that was in operation before both were turned off). As a result, the block 33 (BVL2) for fixing the switched on state of the lines gives a signal to the input of the logic block 31 (BL), and the block 35 (BOL2) for fixing the switched off state of the lines does not. If after a time t ₅ , for example, 1 s, the block 33 (BVL2) for fixing the on state of the lines continues to give a signal, then the time relay 37 (PB2) is triggered, signaling that there is no short circuit on the second line. Therefore, the first line is taken out for repairs again. If after time t ₅ block 33 (BVL2) for fixing the on state of the lines does not give a signal, then time relay 37 (PB2) returns to its original state, and logic unit 31 (BL) outputs a signal to the inputs of time relays 36 (PB1) and 38 ( PB3). Time relay 38 (PB3) after time t ₄ gives a signal to the first line switching circuit. If after time t _{5 the} block 32 (BVL1) for fixing the on state of the lines continues to issue a signal, then the time relay 36 (PB1) is triggered, signaling that there is no short circuit on the first line. Therefore, the second line is taken out for repair.

Claims (1)

A method of protection from the receiving side of two parallel lines with one-way power supply, in which the instantaneous values of the currents i ₁ on the first and i ₂ on the second line are measured into a positive or negative half-wave of the current when the current rises, i _{1 is} compared to a positive or negative half-wave with a given value of current i _et , and when the current i ₁ reaches the set value of the current i _et , continuing to measure the instantaneous value of the current i ₁ , they begin to count the time t ₁ until the moment when in the next positive or negative half-wave with increasing current the value of the current i ₁ reaches the set value of current i _et , compare the measured time t ₁ with the first and second predetermined values of time t _et1 and t _et2 , and if the value t _{1 is} greater than the predetermined value of time t _et1 , but less than the predetermined value of time t _et2 , then repeat the countdown until the value of time t ₁ will not become greater than or equal to the given value of time t _et1 or the value of time t ₁ will become less or equal to this value of time t _et2 , then, if one of these inequalities is fulfilled, then the first line is turned off, taken out for repair and after repair is turned on, in the same way, simultaneously with the time t _1, time t _{2 is} counted when the current reaches i ₂ in the second line with a given value of current i _et until the moment when, in the next positive or negative half-wave with increasing current, the value of current i ₂ reaches i _et , compare the measured time t ₂ with the first and second preset values of time t _et1 and t _et2 , and if the value of t _{2 is} greater than a predetermined value of time t _et1 , but less than a predetermined value of time t _et2 , then the time count is repeated until the value of time t _{2 is} greater than or equal to a predetermined value of time t _et1 or the value of time t ₂ becomes less or equal to a given value of time t _et2 , then if one of these inequalities is satisfied, then the second line is _turned off, taken out for repair and after repair included in work, characterized in that simultaneously with the inclusion of the disconnected second or first line into operation, when the first or second line is in the on position, they begin to count the time t ₃ from the moment when the current i ₁ or i ₂ reaches the set value of the current i _et in the positive or negative half-wave of the current until the moment , when the current i ₂ or i ₁ becomes equal to the value of the specified current i _et , compare t ₃ with the third predetermined value of time t _et3 , and if time t _{3 is} greater than or equal to the value of the specified time t _et3 , then both lines are _turned off, then after time t ₄ turn on the first or second line, then after a predetermined time t ₅ after turning on, fix its position, and if it is in the on position, then take the second or first line for repair, if it is in the off position, then turn on the second or first line, and the first or second line is taken out for repair.

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