RU2071624C1 - Gear for centralized directional protection against fault to ground - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: gear for centralized directional protection against fault to ground in network with neutral grounded through high-resistance resistor is designed for protection of aerial power lines in corresponding systems. Known gear for centralized directional protection against fault to ground incorporating first instrument voltage transformer of zero sequence which input is connected to first section of collecting buses of feeding substation and which output is connected to input of first filter 1 of commercial frequency to which output first input of first logic AND gate 4, actuators 30 in number equal to number n of protected lines are connected through phase shift unit 2 and first comparator 3 is additionally inserted with second instrument voltage transformer of zero sequence, three current transformers into each circuit of protected line two current transformers in circuits of high- resistance grounding resistors, n pickups of current of zero sequence, n+1 filters 9, 19 of commercial frequency, 3n+3 comparators 20, 23, 29, 8, 11, 13, 2n+1 logic AND gates 12, 21, 25, 2n converters 22, 28 of rectangular pulses to sawtooth voltage, n pulse stretchers 24, n+2 operational plates 31, 43, 46, four threshold elements 5, 14, 41, 44, two matching elements 6, 15 second phase shift unit 10, adder 7, 2n+2 signalling elements 16, 17, 32, 33, two time delay elements 42, 45, tester 40 of serviceability of gear and n diodes with corresponding couplings. Proposed gear uses information both from group of lines connected to one section of collecting buses of substation and of second section of collecting buses. EFFECT: higher selectivity and sensitivity of proposed gear as compared with prototype. 10 dwg

Description

 The invention relates to electrical engineering and is intended to protect overhead power lines from earth faults in networks with a neutral grounded through a high-resistance resistor.

 Recently (for example, in the electric networks of the Tyumen North), a tendency has appeared to ground the neutrals of transformers in 35 kV networks through a high-resistance resistor, the resistance of which is selected, in particular, based on the conditions for preventing the occurrence of an alternating arc.

 The installation of such a resistor, as the analysis shows, prevents the occurrence of significant overvoltages in the network associated with a moving arc, failure in this mode of high-voltage isolation, voltage transformers and measuring equipment connected to their secondary circuits, etc.

 Electric networks with a voltage of 35 kV are made in the Tyumen region, as a rule, by overhead power lines (110 kV in order to increase reliability), and responsible consumers are usually powered by double-circuit lines located on the same supports. Each of the chains is attached to its section of busbars of the supply substation. Due to the large interchain capacitance, a ground fault on one of the power lines leads to the appearance of zero sequence currents not only along the lines supplied from the “own” section of the busbars, but also along the lines powered from the “neighboring” section. The tests revealed one more peculiarity: when a 35 kV power line wire fell to the ground, a transition resistance of about 7-10 kOhm was often recorded at the point of earth fault.

 Another feature of these electrical networks is that for structural reasons it is not possible to install cable transformers of zero current sequence. It is necessary to use the neutral wire of conventional measuring current transformers included in the phases of the power line as a zero-sequence current source, which can significantly increase the unbalance current.

 In addition, the installation of a resistor in the neutral of the power transformer requires the action of protecting the lines from earth faults to disconnect the damaged line when a current flows through this resistor, which is dangerous from the point of view of its thermal stability for a corresponding time. At low fault currents that are not hazardous to the resistor, protection can act on the signal.

 Consider the extent to which known protections satisfy the above features of 35 kV networks.

A device is known for protection against a single-phase earth fault in an alternating current electric network, comprising a phase-shifting unit connected to a zero-sequence voltage transformer and a first rectangular pulse shaper, a main frequency filter and a second rectangular shaper connected to a zero-sequence current transformer of the protected connection pulses in series connected to the output filter the main frequency amplifier, a comparator, a pulse-to-DC voltage converter and a first logic element AND, a setpoint unit, the output of which is connected to the second input of the comparator, an ac-to-dc voltage converter with a voltage setpoint connected in series to a voltage transformer of a zero sequence and the first time block, the output of which is connected to the second input of the first logical element AND the executive body, six time blocks and, the second and third logical elements AND, the integrator and the key, and the output of the first rectangular pulse shaper is connected to two inputs of the second logical element And, respectively, through the second and third time blocks, the output of the second rectangular pulse shaper is connected to two inputs of the third logical element And, respectively, through the fourth and fifth time blocks, the outputs of the second and third logical elements AND are connected respectively to the third and fourth inputs of the first logical element And, the output of which through the integrator is connected to the executive body, the integrator's output through the key is connected to the second input, and the first integrator's input through the sixth time block with the key control input, the output of the first time block through the seventh time block is connected to the second input of the AC to DC voltage voltage setting [1]
The disadvantage of the described device is that it uses information only from "its own" line and therefore has a low selectivity and sensitivity in the 35 kV networks described above, since it will either falsely operate on lines connected to the undamaged section of the busbars when an earth fault occurs in the network due to the large current through the interchain capacitance, or if the current and voltage of its operation are increased to such an extent that it does not operate in this mode, it will not feel earth faults on the damaged line if These faults occur through large transient resistances.

A centralized device for directional earth fault protection in a network with isolated or compensated neutral is known, which contains a zero-sequence voltage filter common to all n connections, connected by its output to the input of the starting element, which includes a threshold element and a delay element for operation, and the input of the voltage signal driver, the automatic data erasing unit, the output of which is connected to the erasing inputs of the RAM elements, and to each of n a zero-sequence current filter connected through a current driver to current sensors of the instantaneous zero-value current sign, the outputs of which are connected to the first inputs of AND elements, the second inputs of which are connected to the outputs of the corresponding instantaneous voltage sign sensors, and the outputs of the mentioned AND elements are connected through series-connected element OR, elements of operational and long-term memory to the executive body, high-speed current start a new organ with 2n inputs, an automatic threshold change unit, a synchronization unit for recording information in the RAM elements, a signal differentiation unit and an OR element for 2 inputs, while 2n inputs of a high-speed current starting element are connected to the outputs of all the mentioned sensors of the sign of instantaneous current values, the output to the input of the automatic threshold change unit and through the OR element, the second input of which is connected to the output of the threshold element of the voltage trigger element, to the inputs of the auto block erasing the RAM information and the inserted synchronization unit for recording information in the RAM elements, the output of which is connected to the synchronizing inputs of the RAM elements, and the signal differentiation unit is connected by its input to the output of the signal voltage driver, and by the output to the sensor inputs of the sign of the instantaneous values of the reference voltage moreover, the output of the unit for automatically changing the threshold of operation is connected to the control inputs of the mentioned sensors of the sign of instantaneous current Achen [2]
The disadvantage of the described device is that it uses information only from a group of lines connected to one section of the substation's busbars, and therefore in the above 35 kV networks it has low selectivity and sensitivity, because it will either falsely operate on lines connected to the undamaged section of the busbar bus when shorted to ground in the network due to the high current through the interconnect capacitance, or if the current and voltage of its operation is increased to such an extent that it does not work in this mode, there will be no feeling earth faults on a damaged line if these faults occur through large transient resistances.

A device is known for centralized protection against earth faults in a network with isolated or compensated neutral, containing on each of n connections a zero-sequence current filter, to the output of which are connected sensors of positive and negative signs of the initial half-wave of the transitional current of zero sequence, as well as on each of n of interconnections is a prohibition element, memory and actuating elements, common to n connections is a zero-sequence voltage filter, to the output of which is connected a trigger element whose output is connected to the control inputs of the aforementioned inhibit elements, a mating unit common to n connections for comparing the number of initial positive and negative polarities, two AND elements to two inputs and an OR element to two inputs and a logical determination block common to all n connections faults on buses with (2n + 1) inputs, (n + 1) -th inhibit element, (n + 1) -th memory and (n + 1) -th actuator elements, common OR-NOT for two inputs, OR element on the (n + 2) input and the time delay element, and the fln with 2n inputs and two outputs, while the first n inputs of the majeurization unit are connected to the outputs of the aforementioned sensors of the positive sign, the second n inputs are outputs of the mentioned sensors of the negative sign, the first output of the majeure unit is connected to the first input of the OR-NOT element and to the first inputs of the elements And, the second inputs of which are connected to the outputs of the sensors of the negative sign, the second output of the majeur block is connected to the second input of the said element OR NOT and to the first inputs of the elements AND, the second inputs of which are connected to the outputs of the sensors of a positive sign, the output of the elements is NOT connected to one of the (2n + 1) inputs of the logic block for determining a short circuit on the buses, the remaining 2n inputs of which are connected to the outputs of all the AND elements, and the output to the recordable input (n + 1) a memory element, and the outputs of the AND elements of each of the n connections are also connected through the corresponding elements OR to the recording inputs of the corresponding memory elements, the outputs of all (n + 1) memory elements are connected to the inputs of the corresponding prohibition elements and to (n + 1) input odes of the OR element to the (n + 2) input, the output of which is connected to the blocking inputs of the storage elements and through the time delay element to the erasing inputs of all (n + 1) storage elements, and the output of the trigger is connected to the (n + 2) -th input of the said OR element at the (n + 2) input and to the control input of all (n + 1) prohibition elements, each of which is connected by its output to the input of the corresponding actuating element [3]
The disadvantage of the described device, as well as the previous one, is that it uses information only from a group of lines connected to one section of the substation busbars and therefore has a low selectivity and sensitivity in the 35 kV networks described above, since it will either falsely operate on lines connected with an intact section of busbars during an earth fault in the network due to the high current through the interconnect capacities, if the current and voltage of its operation are increased to such an extent that it does not work in this mode, udet feel earth fault on the faulted line, if the fault occurs through the large transient resistance.

It is also known a device for centralized directional protection against earth faults in a network with isolated or compensated neutral, containing a zero sequence voltage measuring transformer connected to the inputs to the busbar section, and the output to the input of the starting element, a short pulse shaper, as well as on each of n protected lines measuring zero-sequence current transformer and series-connected elements of comparison, prohibition, memory, discrepancy, executive body, the output of the memory reset unit is connected to the auxiliary inputs of all memory elements, the outputs of which are also connected to the corresponding inputs of the majeure block, the output of which is connected to the second inputs of the mismatch elements, common for all n protected lines is an industrial frequency filter, phase shifter, comparator and AND , the output of the zero-sequence voltage measuring transformer is connected to the input of the industrial frequency filter, the output of which is connected to a phase-shifted series-connected block, comparator, element And and shaper of a short pulse, the second input of the comparator is connected to a common wire, and the second input of element And with the output of the trigger, the output of each measuring transformer of the zero sequence current is directly connected to the input of the corresponding comparison element, and the control input of each element Prohibition of short-pulse former output [4]
The prototype of the proposed device for centralized directional protection against earth faults in a network with a neutral grounded through a high-resistance resistor is the last of the described devices.

 The disadvantage of the prototype, as well as previous devices, is that it uses information only from a group of lines connected to one section of the substation's busbars, and therefore in the 35 kV networks described above it has low selectivity and sensitivity, since it will either falsely operate on lines connected to an undamaged section of busbars, when shorted to ground in the network due to the high current through the interconnect capacities, or if the current and voltage of its operation increase to such an extent that it does not work in this mode If it does, it will not feel an earth fault on the damaged line if these faults occur through large transient resistances.

 The invention is aimed at increasing the selectivity and sensitivity of protection by using additional information from a zero-sequence voltage transformer connected to the second section of the busbars of the power substation, as well as from current transformers included in the circuit of high-resistance grounding resistors.

 This is achieved by the fact that in the known device for centralized directional protection against earth faults, containing the first measuring voltage transformer of zero sequence, the input of which is connected to the first section of the busbars of the power substation, and the output is connected to the input of the first filter of industrial frequency, to the output of which the first phase-shifting unit and the first comparator connected in series the first input of the first logical element And, the executive bodies in an amount equal to the number protected lines n, a second zero-sequence voltage measuring transformer was additionally introduced, three current transformers in the circuit of each protected line, two current transformers in high-resistance grounding resistor circuits, n zero-sequence current sensors, n + 1 industrial frequency filter, 3n + 3 comparators, 2n + 1 logic element AND, 2n converter of rectangular pulses into sawtooth voltage, n pulse expanders, n + 2 covers operational, four threshold organs, two matching elements, the second phase rotary unit, adder, 2n + 2 alarm elements, two time delay elements, a device health check unit, n resistors and n diodes, the current transformers in the circuits of the protected lines are connected according to the zero-sequence current filter circuit, the input of the second zero-voltage voltage transformer is connected to the second section of the busbars of the power substation, and the output is connected to the input of the second filter of industrial frequency, to the output of which is connected through the second phase shifter in series the first block of the second threshold element is connected to the output of the first zero-voltage voltage transformer, and its output serves as the output of the first signal about ground fault, the input of the second threshold organ is connected to the output of the second voltage transformer zero sequence, and its output serves as the output of the second signal on earth fault, the outputs of the first and second filters of industrial frequency through the first and W The second matching elements are connected to the first and second inputs of the adder, respectively, the output of the adder through the third and fourth comparators is connected to the second inputs of the first and second logic elements And, respectively, the outputs of which are connected to the inputs of the first and second signaling elements, respectively, the inputs of the third and fourth threshold organs are connected to current transformers included in the circuit of high-resistance grounding resistors, and their first outputs are connected respectively to the first terminals of the first and second Adok operative, the second outputs of the third and fourth threshold organs are connected to the inputs of the first and second time delay elements, the outputs of which serve as the outputs of the signals to turn off the corresponding switches, the inputs of the n zero sequence current sensors are included respectively in the zero wire of the current transformers of the protected lines, and their outputs through connected in series third industrial frequency filters, fifth comparators, third logical elements AND, first converters of rectangular pulses to pi Shaped voltage, sixth comparators, pulse expanders, fourth logic gates And, second converters of rectangular pulses to sawtooth voltage, seventh comparators and actuators are connected to the first conclusions of the third operational plates, the second conclusions of which serve as outputs of signals to turn off the corresponding protected lines, inputs of the third and the fourth signaling elements are connected respectively to the outputs of the fourth logical elements AND and the executive bodies, the first conclusions n res Stores are connected to the positive bus of the power supply, and their second terminals are combined with the anode terminals of the corresponding diodes and connected to the second inputs of the fourth logic elements. And, the cathode terminals of the diodes belonging to the line protections connected to the first section of the busbars are connected to the second terminal of the first lining of the operational and the cathodic terminals of the diodes belonging to the line protections connected to the second section of the busbars are connected to the second terminal of the second operational lining, the second inputs of the fourth elements And, belong the protection lines connected to the first section of the busbars are connected to the output of the first logical element And, and the second inputs of the fourth elements And belonging to the protection of the lines connected to the second section of the busbars are connected to the output of the second logical element And, the main outputs of the check unit the health of the device is connected to the inputs of the first, second and third comparators and the first input of the adder, the additional output of the health check unit of the device is connected to the second input of the adder.

 Figure 1 shows the structural diagram of the proposed device for centralized directional protection against earth faults; figure 2 diagram of the power substation, the second is proposed to use the proposed device; figure 3 diagram of the phase-shifting unit; figure 4 diagram of the matching element; figure 5 diagram of the Converter rectangular pulses in a sawtooth voltage; 6 is a diagram of a pulse expander; 7 is a network equivalent circuit for a single-phase earth fault mode; on Fig phase characteristic of the protection of the power line from earth faults; Fig.9 diagrams of the signals at the outputs of the circuit elements; figure 10 is an example of a circuit block verification of the proposed device.

 The proposed device for centralized directional protection against earth faults in networks with a neutral grounded through a high-resistance resistor (Fig. 1) contains a first industrial frequency filter 1, the input of which is connected to the output of the first voltage measuring transformer connected to the first section of the substation busbars. The first filter of industrial frequency 1 is designed to isolate a component with a frequency of 50 Hz from the input signal. It is made according to any of the standard schemes described, for example, in [5-8] and is taken without modification from the prototype.

 The output of the first filter of industrial frequency 1 is connected to the input of the first phase-shifting unit 2, designed to shift the signal supplied to it in phase. Its implementation will be explained below (figure 3).

The output of the first phase-shifting unit 2 is connected to the input of the first comparator 3, which is designed to form a single output signal, provided that the input signal exceeds the threshold value. It is made according to any of the standard schemes described, for example, in [5-8]
The output of the first comparator 3 is connected to the first input of the first logical element And 4, designed to perform logical operation I. The element And is made according to the standard scheme.

The input of the first threshold organ 5 is connected to the output of the first measuring voltage transformer. The threshold organ 5 is designed to form an input signal provided that the input signal exceeds a predetermined value. The output of the threshold organ 5 serves as the output of the first signal on the ground fault. As a threshold organ 5 can be used a voltage relay from among, for example, described in [9]
The input of the first matching element 6, designed to form a rectified and smoothed output signal proportional to the input, is connected to the output of the first filter of industrial frequency 1. The matching element 6 can be implemented, for example, according to the circuit shown in figure 4, and described below.

The first input of the adder 7 is connected to the output of the matching element 6. The adder 7 is designed to generate an output signal proportional to the sum of the input signals taken with opposite signs. It can be performed according to any of the schemes described in [5-8]
The output of the adder 7 is connected to the input of the third comparator 8, designed to generate a single output signal, provided that the value of the input signal exceeds a predetermined value. This comparator, like 3, can be performed according to the circuits described in [5-8]
The output of the comparator 8 is connected to the second input of the first logical element And 4.

 The input of the second filter of industrial frequency 9, similar to 1, is connected to the output of the second measuring transformer of zero sequence, and its output is connected to the input of the second phase-shifting unit 10, similar to 2.

 The input of the second comparator 11, similar to 3, is connected to the output of the second phase-shifting unit 10, and its output is connected to the first input of the second logical element And 12, similar to 4.

 The input of the fourth comparator 13, similar to 3, is connected to the output of the adder 7, and its output is connected to the second input of the second logical element And 12.

 The input of the second threshold organ 14, similar to 5, is connected to the output of the second measuring transformer of the zero sequence voltage, and its output serves as the output of the second signal about the earth fault.

 The input of the second matching element 15, similar to 6, is connected to the output of the second filter of industrial frequency 9, and its output is connected to the second input of the adder 7.

The input of the first signaling element 16, designed to signal the presence of a signal at its input, is connected to the output of element 4. The signaling element 16 can, for example, be made in the form of a chain of series-connected LEDs and a current-limiting resistor [5-8]
The input of the second signaling element 17, similar to 16, is connected to the output of the element 12.

The input of the current sensor 18, designed to convert the input current of the zero sequence into a signal convenient for processing in subsequent elements, is connected to the terminals of the current transformers of the protected line, assembled according to the zero-current filter circuit [9] The current sensor 18 can, for example, be made in as a transreactor as described in [9]
The input of the third filter of industrial frequency 19, similar to 1 and 9, is connected to the output of the current sensor 18, and its output is connected to the input of the fifth comparator 20, similar to 3, 11.

 The first input of the third logical element And 21, designed to implement the corresponding logical function, is connected to the output of the comparator 20, and its second input to the output of the first logical element And 4.

 The input of the first converter of rectangular pulses into a sawtooth voltage 22 is connected to the output of the logic element And 21. The Converter 22 is designed to convert rectangular pulses to a sawtooth voltage and can be performed, for example, in accordance with Fig.5.

 The input of the sixth comparator 23, similar to 3, 11, is connected to the output of the converter 22, and its output is connected to the input of the pulse expander 24, designed to generate a pulse with a width of at least one and a half periods of industrial frequency when a short pulse arrives at its input. The pulse expander 24 may be performed, for example, according to the scheme of Fig.6.

 The first input of the fourth logical element And 25 is connected to the output of the pulse expander 24, and its second input is connected to the combined terminals of the resistor 26 and diode 27. The second output of the resistor 26 is connected to the positive bus of the power source.

 The input of the second converter of rectangular pulses into a sawtooth voltage 28, similar to 22, is connected to the output of the fourth logic element 25, and its output is connected to the input of the seventh comparator 29, similar to 3, 11.

The input of the actuator 30, designed to generate the output signal for disconnecting the line, is connected to the output of the comparator 29. The actuator 30 is connected, as in the prototype, in series with the power amplifier described, for example, in [10] and the output intermediate relay from the number described , for example, in [9, 11]
The first output of the third operative cover plate 31, designed to close and open the output protection circuit during operation, is connected to the output of the actuator 30. The operational cover plate 31 is the simplest electrical switch widely used in relay protection circuits, and is shown, for example, in [9 ] The second output of the third operative lining serves as an output signal to disable the protected line.

 The input of the third signaling element 32, similar to 16, is connected to the output of the I-25 logic element, and the input of the fourth signaling element 33, similar to 16, is connected to the output of the executive body 30.

 Elements from 18 to 33 are part of the first line protection block 34. The composition of the proposed device includes n such blocks (34, 35, 36, 37, 38, 39.) according to the number of protected lines.

 The main outputs of the health check unit 40 of the device designed to test the health of the proposed device are connected to the inputs of the first and second comparators 3 and 11, as well as to the inputs of the fifth comparators 20, which are part of the protection blocks of each line and the first input of the adder 7. An additional output of the block 40 is connected to the second input of the adder 7.

 The second inputs of the third logical elements And 21, which are part of the blocks 34, 35, 36 of the protection lines connected to the first section of the busbars are connected to the output of the first logical element And 4.

 The second inputs of the third logical elements And 21 included in the blocks 37, 38, 39 of the protection lines connected to the second section of the busbars are connected to the output of the second logical element And 12.

The input of the third threshold organ 41, designed to generate the output signal provided that the input signal exceeds a threshold value, is connected to a current transformer connected to the high-resistance grounding resistor of the first busbar section. The third threshold organ 41 is a standard current relay described, for example, in [9-11]
The input of the first time delay element 42, designed to delay the output signals for predetermined times relative to the input signal, is connected to the second output of the threshold organ 41. The outputs of the time delay element 42 serve as the signal outputs for switching off the corresponding switches. The time delay element 42 is made on the basis of standard time relays described, for example, in [9, 11]
The first output of the threshold organ 41 is connected to the first output of the first operational patch 43, similar to 31. The second output of the patch 43 is connected to the cathodes of the diodes 27 belonging to the line protection units 34, 35, 36 connected to the first section of the busbars of the power substation.

 The input of the second threshold organ 44, similar to 41, is connected to a current transformer included in the circuit of the high-resistance resistor of the second section of the busbars.

 The input of the second time delay element 45, similar to 42, is connected to the second output of the threshold organ 44, and its outputs serve as signal outputs for switching off the corresponding switches.

 The first output of the threshold organ 44 is connected to the first output of the second operational lining 46 similar to 31. The second output of the lining 46 is connected to the cathodes of the diodes 27 belonging to the line protection units 37, 38, 39 connected to the second section of the busbars of the power substation.

 In FIG. 2 shows an example of a circuit of a power substation, on which it is proposed to apply the proposed protection device. Here: 47 and 48 are power transformers, which are connected through switches 49 and 50, for example, to 110 kV power lines, and through switches 51 and 52, they feed 35 kV the first section 53 and the second section 54 of the substation busbars, respectively. The neutrals of the 35 kV windings of the supply power transformers 47 and 48 are grounded correspondingly through high-resistance resistors 55 and 56, in the circuits of which current measuring transformers 57 and 58 are installed. Measuring voltage transformers 59 and 60 are connected to the busbars of the substation, the conclusions of the windings connected in an open triangle of which are intended for use in the proposed protection device. Three outgoing lines are connected to each busbar section: to the first section 53 of the line 61, 62, 63, to the second section 54 of the line 64, 65, 66, and the lines 61 and 64, 62 and 65, 63 and 66 are placed in pairs on the same and the same supports, designed to power the same consumers and have significant interchain capacities between them. The circuits of the respective lines are equipped with switches 67, 68, 69, 70, 71, 72, as well as three-transformer zero-sequence current filters 73, 74, 75, 76, 77, 78, intended for use in the proposed protection device. To connect the busbar sections to each other, a sectional switch 79 is designed, which is normally disconnected.

 In FIG. 3 shows an example of a phase-shifting block circuit. Here is 80 block input, 81 its output. A resistor 82, one output of which is connected to the input of the unit, and a capacitor 83, through which the resistor 82 is connected to a common wire, are designed to shift the input signal of the industrial frequency by the required angle. An adjustable resistor 84, connected in parallel with the capacitor 83, is designed to control the output signal of the phase-shifting unit in magnitude.

 In FIG. 4 shows an example circuit matching device. Here 85 is the input of the device, 86 is its output. The divider of the series-connected resistors 87, 88 is designed to reduce the incoming signal (triple voltage zero sequence) to the required value, and the diode 89 with a capacitor 90 for rectification and smoothing of the signal.

 Figure 5 shows an example of a circuit converter 22, 28 of rectangular pulses in a sawtooth voltage. For example, the input of the converter 22 is connected to the output of the logic element And 21, which is shown in Figs. 1, 5. The left terminal of the resistor 91 serves as the input of the converter 22, the right terminal of the diode 92 is connected to the output of the converter 22. A resistor 93 is connected between the positive voltage bus of the power source and the output of the converter 22, a capacitor 94 is connected between the output of the converter 22 and the neutral wire.

In FIG. 6 shows an example of a pulse expander 24 circuit. The input of the pulse expander 24 is the top terminal of the resistor 95, the second terminal of which is connected to the neutral wire. The base of the transistor 96, designed to operate in the mode of the emitter follower, is connected to the input of the pulse expander, and the collector through the resistor 97, designed to limit the current, is connected to the positive voltage bus of the power source. The emitter of the transistor 96 through a diode 98 is connected to the output of the pulse expander 24. Between the output of the pulse expander 24 and the neutral wire, a resistor 99 is included to ensure the normal operation of the AND gate
25 (in FIG. 1), and a capacitor 100, designed to "memorize" the pulse received on it.

7 shows a circuit equivalent circuit for single-phase earth fault mode. Here, the electromotive force E is applied at the point of earth fault, the transition resistance r _p includes the resistance of the arc, ground loop and other factors at the point of fault. R ₅₅ and R ₅₆ are the resistances of the corresponding grounding resistors, C ₁ and C ₂ are the capacitances of the power lines to the ground connected to the corresponding sections of the substation busbars, C _{3 is the} interchain capacity of the lines.

 In FIG. Figure 8 shows the phase response of line protection against earth faults.

 Figure 9 shows the plot of the signals at the outputs of some elements of the proposed device.

 Figure 10 shows an example circuit block check 40 of the proposed device. Here, the bus of the positive potential of the power source through the electric button 101, diodes 102 and resistors 103 is connected to the main outputs 104 of the block 38. In addition, the bus of the positive potential of the power source through the electric button 105 and the resistor 106 is connected to the additional output 107 of the block 38.

 Buttons 101, 105 are intended for switching test signals in the test mode of the proposed device, diodes 102 for "decoupling" the corresponding circuits, and resistors 103, 106 for limiting the currents in the corresponding circuits.

 The proposed device for centralized directional protection against earth faults in networks with a neutral, grounded through a high-resistance resistor, operates as follows.

 The inputs of the proposed device (figure 1) from the measuring current and voltage transformers receive signals about currents and voltages of zero sequence, as well as currents in grounding resistors. Depending on the magnitude of these signals and the phase shift between currents and voltages of the zero sequence, the proposed device generates its output signals.

 Let us first consider the processes in a 35 kV network.

 The substation on which it is planned to install the proposed protection device (Fig. 2) contains two sections of busbars 53 and 54, powered by transformers 47, 48 with voltages 110, 35 and 10 kV. The neutrals of the 35 kilovolt windings of both transformers are supposed to be grounded through high-resistance resistors 55, 56, in the circuits of which disconnectors and current transformers 57, 58 are installed. Through the switches 51, 52, these power transformers 47, 48 are connected to the corresponding busbar sections 53, 54. On each sections installed measuring voltage transformer 59, 60, connected in an open triangle, the winding of which is intended for use in the proposed protection device. Section switch 79 is normally open.

 Several sections of 35 kV lines are fed from each section of busbars (in this example, three lines from each section), and the lines are double-circuit. For example, lines 63 and 66 are structurally located on the same supports and are designed to power the same consumer of electricity. The same applies to pairs of lines 62 and 65, as well as 61 and 64. At the opposite end, these lines are open to each other, but due to the significant interchain capacitance, an electrical connection arises between them. Disconnectors and switches 67, 68, 69, 70, 71, 72, as well as three-phase groups of measuring current transformers 73, 74, 75, 76, 77, 78 are installed in the line circuits. These current transformers are used for conventional line protection, and their zero the wire is designed to connect to the proposed protection device.

 The parameters of the high-resistance resistors 55 and 56 are selected in such a way that the current flowing through them during a metal earth fault is approximately equal to the capacitive current. Moreover, as the corresponding calculations and experiments show, the level of overvoltages in the system during ground fault is significantly reduced, and an intermittent arc at the site of damage is practically eliminated.

 In the absence of an earth fault in the system on the neutrals of the transformers there are only insignificant voltages due to the asymmetry of the load and lines. The currents in the resistors and the zero sequence currents along the lines are almost zero. In the neutral wire of current transformers 67, 68, 69, 70, 71, 72, unbalance currents flow due to the non-identical characteristics of the measuring current transformers. From these unbalance currents, the protection should be detuned, that is, the response currents of the blocks 34, 35, 36, 37, 38, 39. (Fig. 1) the protection of the corresponding lines should be greater than the corresponding unbalance currents, for example, 1.5-1, 7 times.

When an earth fault occurs, for example, in line 61 (Fig. 2), a zero-sequence electromotive force E is formed at the fault location (Fig. 7), which is switched on in series with the transition resistance r _p arising at the fault location. The magnitude of this transition resistance in different cases is different. In the event of a metal short circuit to a grounded lightning protection cable or support armature, it may be close to zero. When the phase wire fell to the ground in a failed experiment, a transition resistance of the order of 7-10 kOhm was recorded, and when the wire fell, for example, on a snowdrift in winter, this value can be even higher.

In the equivalent circuit of FIG. 7, R ₅₅ , R _{56 are the} resistances of the corresponding grounding resistors, C ₁ and C ₂ capacitance to the ground of the power lines connected to the corresponding sections of the substation busbars, C ₃ interchain capacitance of the lines. It can be seen from the circuit of Fig. 7 that when a ground fault occurs on line 61, not only voltage U _{n1 arises} on the neutral 35 kV of transformer 47, but also voltage U _n2 on the neutral 35 kilovolts of transformer 48. At the substation under consideration in the experiment, the voltage U _n2 was approximately 0.25 U _n1 . In the General case, the ratio between U _n1 and U _n2 is determined by the parameters of the elements of the _equivalent circuit shown in Fig.7.

For convenience, the protection in the experiment conducted at one of the substations in the Tyumen region, the polarity of the current circuits 3 I _o was adopted inverse relative to the polarity of the voltage 3 And _o . Then, when an earth fault current 3 I _{o of the} damaged line leads ahead of the voltage 3 U _from its section by an angle close to 45 ^o electric (when changing the operating mode of the network, this angle may vary somewhat, for example, within 30-60 ^o ). If, according to the operating conditions, only one line remained in operation on the busbar sections, then the current 3 I _o will be close to the active when shorted to ground, that is, the electric angle is close to 0 ^o . Phasing of current and voltage protection circuits is conveniently carried out at a working substation, but with resistors turned off (otherwise they will quickly overheat when shorted to ground and may fail). With the resistors disconnected and an earth fault in the damaged line under the conditions described above, the current 3 I _{0 is} ahead of the voltage of 3 AND _o by an angle close to 90 ^o . Thus, the zone of operation of the protection must reliably cover the range from 0 to 90 ^o electrical and have the form depicted in FIG. 8. At the same time, the current 3 I _o in the intact line connected to the same section of busbars as the damaged bus lags 90 ^o from 3 U _o , as a result of which this angle must be reliably in the zone of protection failure (Fig. 8 )

While on the "damaged" section of busbars, the currents in the damaged and undamaged lines differ by an angle of about 135 ^o , on the "undamaged" section the situation is different. All lines here are in the same conditions, and the zero-sequence currents flowing through them can be conditionally divided into two components.

The first component of the current 3 I _o closes through the interchain capacitance C ₃ (Fig.7) and the capacitance of the lines to the ground C ₂ . This current component does not flow through current transformers 76, 77, 78, but closes directly through the capacitance of C ₂ lines.

The second component of the current 3 I _o closes through the interconnect capacitance C ₃ and the grounding resistor 56. It is this component that flows through the current transformers 76, 77, 78 and enters the protection device. The magnitude of these line currents is proportional to their length (or, if the double-circuit line "diverges" in some section of the route, then it is proportional to the length of their "joint" section). Since all these currents are closed through the grounding resistor and are of the same nature, the angle of shift of these currents relative to the zero sequence voltage (voltage at the grounding resistor) is approximately 0 ^o electric, that is, it falls into the protection operation region. Therefore, there are two options for detuning protection against these currents:
detuning in size, which can significantly ruin the protection;
hardware detuning.

The proposed protection device adopted the second option. Here, permission to operate is issued (in the form of a reference voltage U _op ) only to those line protection units that belong to the "damaged" section of the substation busbars. A “damaged” section is one that corresponds to a larger current in the grounding resistor, that is, a greater voltage across the neutral 35 kV transformer.

For a similar reason, the proposed protection device is directional, otherwise the line protection units would have to be detached from the capacitive current of their lines [9, 10]
In a 35 kV network with overhead lines, there is no need for a quick shutdown of the lines when an earth fault occurs. Limitations are imposed only by the grounding resistor, which can overheat and fail if the current is dangerous to it for a long time. In this regard, based on the thermal characteristics of the developed resistors, line protection can be performed with a time delay, for example, of the order of 2.5-5 s, and protection of resistors with a time delay, for example, 7-8 s. with the action to turn off the switches 51, 52 (from the 35 kV side of the supply transformers 47, 48) and with a time delay of the backup stage of about 8-9 s. with the effect of turning off the switches 49, 50 (from the side of 110 kV).

 In this regard, there is no need to consider the effect of the proposed device in transient conditions, since during 2.5-5 s. transients fade.

Large transient resistances at the site of damage facilitate the work of grounding resistors, as they reduce the fault current, virtually eliminate the possibility of using higher harmonics of 3 I _o currents as a working signal and increase the requirements for protection sensitivity. In this regard, it seems advisable to divide the protection response zone into two parts, depending on the current flowing along the lines:
at low currents that are not dangerous from the point of view of thermal resistance of the resistor, ensure the action of the line protection blocks on the signal in order to selectively signal the damaged line;
at significant currents that are dangerous from the point of view of thermal resistance of the resistor, ensure that the line protection blocks act on shutdown.

 In the initial state, in the absence of earth faults in the network, the voltage 3 Uo at the terminals of the measuring transformers, the voltage 59, 60 (figure 2) are close to zero, therefore, the signals at the inputs of the threshold organs 5 and 14 are close to zero (figure 1) as well as filters 1 and 9 of industrial frequency. There are no signals at the outputs of the threshold organs 5, 14.

 Since in this mode the voltages at the neutrals of 35 kV of the transformers 47, 48 are close to zero (Fig. 2), the currents through the grounding resistors 55, 56 are close to zero, and, therefore, the currents in the measuring current transformers 57, 58. Thus, they are close to zero signals at the inputs of threshold organs 41 and 44 (Fig. 1), there are no signals at the outputs of these threshold organs and at the outputs of time delay elements 42, 45.

 The unbalance currents in the neutral wires of the measuring current transformers 73, 74, 75, 76, 77, 78 (Fig. 2) are small and the protection units of the lines 34, 35, 36, 37, 38, 39 (Fig. 1), to which the signals are received with appropriate current transformers do not work.

With a metal earth fault, for example, on line 61 (Fig. 2), a significant (close to the morning phase voltage) voltage 3 U occurs at section 53 of the substation busbars $\genfrac{}{}{0ex}{}{\text{I}}{\text{o}}$ , and on section 54 the lower voltage is 3 U $\genfrac{}{}{0ex}{}{\text{II}}{\text{o}}$ , the value of which is determined by the parameters of the network equivalent circuit (Fig.7). Typically, 3 U $\genfrac{}{}{0ex}{}{\text{II}}{\text{o}}$ several times less than 3 3U $\genfrac{}{}{0ex}{}{\text{I}}{\text{o}}$ . At the same time, at the terminals of the winding of the measuring voltage transformer 59 connected in an open triangle (Fig. 2), a voltage close to 100 V occurs, and at the terminals of the voltage transformer 60, the voltage is several times lower than 100 V.

Simultaneously, in the circuits of grounding resistors 55 and 56, currents occur proportional in magnitude to the voltages 3 U _{o of the} respective sections. The corresponding currents flow through the secondary windings of the current transformers 57 and 58, and the current in the secondary winding of the current transformer 57 is several times higher than the current of the current transformer 58.

In the same mode, significant currents appear in the neutral wires of current transformers 73, 74, 75, 76, 77, 78. In accordance with the previously described current 3 I _o current transformer 73 lies in the protection zone (Fig. 8) (ahead voltage 3 U _o at an angle of 0-60 ^o ) <currents 3 I _o of current transformers 74 and 75 are outside the protection zone (they are 3 _{o o} behind about 90 ^o . Currents 3 I _o of current transformers 76, 77, 78 have approximately the same phase and match the phase angle with a voltage of 3 U _o its section 54 (figure 2).

The voltage 3 U _o from the voltage transformer 59 is supplied to the input of the industrial frequency filter 1 (Fig. 1), which extracts a component with a frequency of 50 Hz from the incoming signal, from it to the phase-shifting unit 2 (Figs. 1, 3). Depending on the ratio of the parameters of the resistors 82, 84 (usually the resistance of the resistor 84 is taken several times greater than the resistance of the resistor 82) and the capacitor 83, the voltage at the output of the phase-shifting unit is behind the voltage supplied to the input of this block by an angle lying in the range from 0 up to 90 ^o . An appropriate selection of the parameters of the phase-shifting unit ensures the location of the middle of the zone of operation of the phase characteristic of the protection (Fig. 8) at about -45 ^o electrical.

Signal 3 3U $\genfrac{}{}{0ex}{}{\text{I}}{\text{o}}$ from the output of the phase-shifting unit 2 (Fig. 1), it is input to the comparator 3, which generates single logical signals in the case when the signal arriving at it is greater than the threshold value (Fig. 9). Threshold U $\genfrac{}{}{0ex}{}{\text{I}}{\text{since}}$ the operation of the comparator 3 is selected greater than the voltage of the unbalance of the zero sequence in the absence of an earth fault in the network. Thus, the signal at the output of the comparator 3 (Fig. 1) (reference voltage U _op in Fig. 9) is a rectangular voltage pulse with a repetition rate of 50 Hz. These pulses carry information about the phase of the voltage 3 U _o , as well as information that the voltage 3 U _op exceeded the sensitivity threshold of the proposed device.

The reference voltage U _{op is} supplied to the first input of the logic element And -4 (figure 1).

The signal from the output of the industrial frequency filter 1 also goes to the input of the matching element 6 (Figs. 1, 4), decreases in value on the divider from resistors 88, 87, is rectified and smoothed by means of the diode 89 and capacitor 90. As a result, the signal at the output of the matching element 6 by a DC voltage proportional in magnitude to the voltage 3 U _{o of} section 53 (FIG. 2).

Similarly, the voltage 3 U _o section 54, coming from a voltage transformer 60 (figure 2) to the filter of industrial frequency 9 (figure 1), and from it to the matching element 15, is also converted to a DC voltage proportional to the voltage 3 U _o section 54 (figure 2) (at the output of element 15 of figure 1).

These two voltages are summed on the adder 7 (figure 1), and the summation is carried out with opposite signs. The voltage coming from element 6 is assigned a plus sign, and the voltage coming from element 15 is assigned a minus sign. Since in this mode the voltage 3 U _{o of} section 53 (Fig. 2) is greater than the similar voltage of section 54, the sign of the voltage at the output of adder 7 (Fig. 1) is positive. When a short to ground on one of the power lines from the number of substations fed from section 54 (FIG. 2), the sign of the voltage at the output of the adder 7 (FIG. 1) will change to the opposite.

The sign of the voltage at the output of the adder 7 is decisive for selecting the "damaged" section of the switchgear at the substation. Since in the case under consideration (with an earth fault on the line 61 of Fig. 2), the signal sign at the output of the adder 7 is positive, permission should be given to operate the line protection blocks powered by section 53, and the protection of the lines powered by section 54 (Fig. 2 ) are blocked. This is achieved as follows. The comparator 8 (figure 1) is triggered by signals of positive polarity and gives a single logic signal to the second input of the logic element And -4, after its reference voltage U _op from the output of element 4 is supplied to the corresponding inputs of the blocks 34, 35, 36 (figure 1 ) protection lines 61, 62, 63 (figure 2), powered by section 53 of the busbar.

The same voltage U _op generated at the output of the comparator 11 (Fig. 1) does not pass to the output of the And-12 element, since the comparator 13 is triggered only by signals of negative polarity, and in the considered mode, a positive signal is output from the adder 7 polarity. As a result, at the second input of the And-12 element, a single logical signal is absent and the signal at the output of the element 12 is zero. The reference voltage U _op to the inputs of the protection blocks 37, 38, 39 of the lines 64, 65, 66 (Fig. 2) is not issued, as a result, these blocks cannot work and the lines 64, 65, 66 in the considered mode are not disabled.

 If an earth fault occurred on one of the lines 64, 65, 66, then similarly as described above, the reference voltage would be issued to the protection blocks 37, 38, 39 (Fig. 1) and would not be issued to the blocks 34, 35, 36.

 The alarm elements 16, 17 show which protection blocks are given the reference voltage.

 Simultaneously with the processes described above, currents from measuring current transformers 57 and 58 (FIG. 2) are supplied to the inputs of threshold organs 41 and 44, respectively. Both of these threshold organs have a trip current of about 1.2-1.4 times higher than the current in the grounding resistor of the “intact” section. Therefore, the threshold organ 44 (Fig. 1) does not work, and the threshold organ 41 is triggered. The threshold organs 41 and 44 are ordinary current relays described, for example, in [9-11]. As the first output of these threshold organs, one output of the relay opening contact is used, the second output of which is connected to a common wire. As the second output of these threshold organs, one terminal of the relay closing contact is used, the second terminal of which is connected to the positive bus of the operating current source.

 Thus, the threshold organ 41 (FIG. 1), when activated, reduces the blocking signal from its first output. Previously, this signal through the patch operative 43 was supplied to the cathodes of the diodes 27, which are part of the protection units 34, 35, 36, preventing the protection from working. The signal from the second output of the threshold organ 41 starts the time delay element 42. The time delay of the element 42 is higher than the time delay of the line protection (blocks 34, 35, 36, 37, 38, 39), therefore, when the lines are properly protected, the damaged line will be disconnected with a margin earlier than act on the shutdown element 42.

At the same time as described above in the considered mode (when an earth fault occurs on line 61 of figure 2), currents 3 I _o from current measuring transformers 73, 74, 75, 76, 77, 78 are fed to the inputs of blocks 34, 35, 36, 37, 38, 39 (FIG. 1) of line protection.

Current sensors 18 convert the current arriving at them into values convenient for use in semiconductor elements of blocks 34, 35, 36, 37, 38, 39. Current sensors 18 can be made, for example, in the form of transformers in accordance with [9]
The industrial frequency filter 19 extracts a component of 50 Hz from the signal arriving at it. screening out various interferences.

The comparator 20 generates rectangular unit signals in the case when the signal arriving at it (3 I $\genfrac{}{}{0ex}{}{\text{I}}{\text{o}}$ Fig.9) is greater than the threshold value of I _then . The response threshold of the comparator 20 (Fig. 1) is selected greater than the unbalance entering this comparator in the absence of an earth fault in the network. Thus, the detuning of protection against unbalance currents in the standby mode of protection is performed. Thus, in the considered mode, the signal at the output of the comparator 20 (U ₂₀ in Fig. 9) is a rectangular voltage pulse with a repetition rate of 50 Hz. These pulses carry information about the phase of the current 3 I _o , as well as information that the current 3 I _o exceeded the sensitivity threshold of the proposed device.

The angle of rotation of the signal in the phase-shifting unit 2 (Fig. 1) is chosen so that the pulses at the output of the comparator 20 coincide in phase with the reference voltage U _op coming from the I-4 logic element when the current 3 I _{o is} ahead of the voltage 3 U _o approximately 45 ^o electrical. The signals from the output of the I-4 element and the comparator 20 (Fig. 1) are fed to the inputs of the I-21 logic element and, in the described case, cause the output of the I-21 element with the maximum duration of rectangular pulses, the duration of each of which does not exceed half the industrial period frequency.

If the angle between 3 I _o and 3 U _o deviates from -45 ^o , then the duration of the rectangular pulses generated at the output of the I-21 logic element decreases (U ₂₁ in Fig. 9).

In the converter of rectangular pulses into a sawtooth voltage 22, the rectangular pulses U ₂₁ coming from the output of the And-21 element (FIG. 1) are converted into a sawtooth voltage (U ₂₂ in FIG. 9).

Figure 5 shows an example of a converter 22 circuit. The input signal here is the output signal of the And-21 element. When this signal is zero, the diode 92 (Fig. 5) is open and the resistor 91 shunts the capacitor 94. Since the resistance of the resistor 91 is many times less than the resistance of the resistor 93, the voltage across the capacitor 94 is close to zero. When the voltage at the output of the And-21 element becomes unity, the diode 92 closes and the capacitor 94 starts charging through the resistor 93. After the rectangular pulse U ₂₁ ends, the capacitor 94 again quickly discharges through the resistor 91 to the output of the And-21 element. As a result, the voltage across the capacitor 94 (and, therefore, at the output of the converter 22) has the form U ₂₂ shown in FIG. 9.

In the comparator 23 (figure 1), the voltage U _{22 is} compared with a threshold value U $\genfrac{}{}{0ex}{}{\text{II}}{\text{since}}$ defining the width of the response zone. On the phase characteristic of the device depicted in Fig. 8. Rectangular pulses And ₂₃ (Fig.9) are formed at the output of the comparator 23 (Fig.1) at those moments when U ₂₂ ≥ U $\genfrac{}{}{0ex}{}{\text{II}}{\text{since}}$ ..

 The pulse expander 24 (Fig. 1) increases the width of the signal pulses taken from the comparator 23. An example of a pulse expander 24 is shown in Fig.6.

The input pulse U ₂₃ is allocated on the resistor 95 (Fig.6) and opens the transistor 96. Through the resistor 97, limiting the maximum current value, and through the diode 98, the capacitor 100 is charged. Since the permissible transistor current is much higher, for example, the output current of the microcircuit, the charge of the capacitor 100 occurs quickly enough, since the value of resistance 97 can be taken low. The resistor 99 is necessary based on ensuring the zero value of the input signal of the I-25 element in the normal mode, but the resistance value of the resistor 99 can be taken about one to two orders of magnitude higher than the resistance of the resistor 97. Therefore, the discharge of the capacitor 100 occurs an order of magnitude or two slower, than his charge. As a result, the waveform of the signal on the capacitor 100 U ₂₄ has the form shown in Fig.9.

The signal U _{24 is} fed to the lower input of the I-25 element (Figs. 1, 6). Since the zero potential from the cathode of the diode 27 in the considered mode is removed (that is, the blocking signal is removed from the line protection block 61), a single logic signal also arrives at the output of the element to the second input of the I-25 logic element through the resistor 26 (Fig. 1) I-25 will also appear a single signal. The signal element 32 signals that the operating conditions of the block protection unit 34 of the line 61 are provided.

The signal from the output of the I-25 element also arrives at the converter of rectangular pulses in a sawtooth voltage 28, made similarly to 22. The signal U ₂₈ at the output of the converter 28 has the form shown in Fig.9. When its value reaches the threshold of the comparator 29, the comparator 29 is activated and a single signal appears on its output (signal U ₂₉ in Fig.9). The converter 28 and the comparator 29 realize the time delay of the line protection from earth faults. The adjustment of this time delay is provided by changing the threshold of the comparator 29 (Fig.1).

 The signal from the output of the comparator 29 is fed to the input of the executive body 30, which includes a power amplifier (for example, a transistor switch) and an output relay with sufficiently powerful contacts that can switch line disconnection circuits. Cover operative 31 in the considered mode is closed and the signal from the output of the executive body 30 acts to trip the switch 67 (figure 2) of the damaged line 61.

 Since the protection time delay of the lines is selected with a margin less than the time delay of the element 42 (Fig. 1), after the damaged line is turned off, the threshold organ 41 returns to its original state and with it the time delay element 42 returns to its original state, without having time to act to turn off.

In this mode, the reference voltage is issued not only to the block 34 (Fig. 1) of the protection line 61, but also to similar blocks 35, 36. However, as noted above, the currents 3 I _o in lines 62, 63, on which the blocks 35 are mounted , 36, lag behind the voltage of 3 U _o in the considered mode by approximately 90 ^o and go beyond the protection operation zone. As a result, the pulses at the outputs of the elements 21 (Fig. 1) in blocks 35, 36 are not long enough and these blocks do not work.

In the mode of earth fault on line 61 through a significant transition resistance, the currents through the resistors 55, 56 (Fig.2) are less than in the previous case. If their value is insufficient to trigger the threshold organs 41, 44 (Fig. 1), that is, these currents are not dangerous from the point of view of thermal resistance of the resistors 55, 56, then the threshold organs 41, 44 do not work and do not remove the blocking signal (signal of zero potential ) from the cathodes of diodes 27 (Fig. 1). In this case, the I-25 logic element belonging to block 34 does not pass the signal arriving at it from the pulse expander 24, and the protection unit 34 does not disconnect the damaged line. In this mode, the proposed device operates as a selective signaling organ. In this case, threshold organs 5 and 14 are triggered by a voltage of 3 U _o and give a signal to the operating personnel that a ground fault has occurred in the network. According to this signal, the team of service personnel is sent to the place of installation of the protection and according to the testimony of voltmeters available at the substation measuring 3 U _o , or according to the glow of the alarm elements 16, 17, it is determined which group of lines the damage occurred (voltage 3 U _o will appear on the corresponding section higher). After that, if it is decided to immediately disconnect the damaged line, you should open the pad 43 or 46 (figure 1), corresponding to the "damaged" section. In this case, the blocking signal will be removed from the line protection blocks and the block that corresponds to the damaged line will be triggered, after which the line will be disconnected in accordance with the description of the previous mode. After disconnecting, trim lines 43 and 46 should be closed again.

 If, before disconnecting the line, it is desirable to notify the consumer of the impending disconnection, then in the described mode, first open the output plates 31 (Fig. 1) in the line protection circuits, and then open the plates 43, 46. In this case, the protection block 34 ( or 35, 36, 37, 38, 39) will work, but will not work on disconnecting the line. On the triggered block, the signal LEDs in the alarm elements 32, 33 will light. By the glow of these LEDs, a damaged line is detected, which then, after notifying the consumer, can be turned off in the usual way. All covers after disconnecting should be returned to their original position.

 When a ground fault occurs on the substation's busbars or when the line protection fails during a ground fault on the line, the line protection units do not work and the power lines will not be disconnected. The triggered threshold body 41 (Fig. 1) or 44 will start the time delay element 42 (or 45), which first gives a signal to turn off the section switch 79 (if it was turned on), then to turn off the switch 51 (or 52) and, if currents in the chains of grounding resistors will not decrease (for example, when a ground fault occurs on a busbar between switch 51 and transformer 47 of FIG. 2), to turn off switch 49 (or 50) on the 110 kV side of the supply transformer.

 To verify the health of the proposed device, briefly press the button 101 (figure 10) in block 40 health. In this case, through the diodes 102 and resistors 103, the test signals are supplied to the inputs of the elements 3, 11, 7, 20 (Fig. 1), the corresponding elements will work and the LEDs in the alarm elements 32 of the line protection units 34, 35, 36 should light up. Protection at the same time will not affect the shutdown due to the available time delay for operation (implemented in blocks 28, 29).

 Then, briefly and simultaneously press buttons 101 and 105 in block 40 (Fig. 10, Fig. 1). Since the resistance of the resistor 106 is selected to be approximately two times lower than that of the resistor 103, this time the voltage at the output of the adder 7 (Fig. 1) will be negative and the LEDs in the signaling elements 32 of the line protection units 37, 38, 39 should be lit.

 If it is necessary to check the serviceability of the executive bodies 30, as well as the elements 28, 29, you should first open the pads 31, and then perform the check as described above, but with a long press of the corresponding buttons.

 From the described it can be seen that in the proposed device, unlike the prototype, information is used not only from a group of lines connected to one section of the substation's busbars, but also from the second busbar section. As a result, it does not work non-selectively from the currents of undamaged lines that arose due to the large interchain capacitance. Since the detuning from these currents is not required, the sensitivity of the proposed device may be higher than that of the prototype. As the experiment showed, in relation to the substation under consideration (figure 2), the sensitivity of the proposed device can be taken 2-2.5 times higher than that of the prototype. This allows the proposed device to feel earth faults through such transition resistance (10-15 kOhm), in which the prototype would not work.

 In addition, the proposed device is able to provide protection for grounding resistors, as well as selective signaling without disconnecting the damaged line at low earth fault currents (at significant transient resistances), and at high currents dangerous to resistors, act on the automatic disconnection of the damaged line, to which the prototype is not capable.

 All this increases the efficiency of relay protection and the power system as a whole.

Claims (1)

 A device for centralized directional earth fault protection in a network with a neutral grounded through a high-resistance resistor containing the first zero-sequence voltage transformer, the input of which is connected to the first section of the busbars of the power substation, and the output is connected to the input of the first industrial frequency filter, to the output which, through the first phase-shifting unit and the first comparator, connected in series, the first input of the first logical element And, the actuators are connected equal to the number of protected lines n, characterized in that a second zero-sequence voltage transformer is introduced into it, three current transformers in the circuit of each protected line, two current transformers in high-resistance grounding resistor chains, n zero-sequence current sensors, n + 1 industrial frequency filter, 3n + 3 comparators, 2n + 1 logic element AND, 2n converters of rectangular pulses to sawtooth voltage, n pulse expanders, n + 2 covers operational, four threshold org ana, two matching elements, a second phase-shifting unit, an adder, 2n + 2 signaling elements, two time delay elements, a device health check unit, n resistors and n diodes, and the current transformers in the circuits of the protected lines are connected according to the zero-sequence current filter circuit, input the second measuring voltage transformer of the zero sequence voltage is connected to the second section of the busbars of the supply substation, and the output is connected to the input of the second industrial frequency filter, to the output of which through The second phase-shifting unit and the second comparator, the first input of the second logical element AND, is connected, the input of the first threshold organ is connected to the output of the first measuring transformer of voltage of zero sequence, and its output serves as the output of the first signal about ground fault, the input of the second threshold organ is connected to the output of the second measuring voltage transformer of zero sequence, and its output serves as the output of the second signals about ground fault, the outputs of the first and second filter in industrial frequency, through the first and second matching elements are connected to the first and second inputs of the adder, respectively, the output of the adder through the third and fourth comparators is connected to the second inputs of the first and second logic elements And, respectively, the outputs of which are connected to the inputs of the first and second signaling elements, respectively, the inputs the third and fourth threshold organs are connected to current transformers included in the circuit of high-resistance grounding resistors, and their first outputs are connected respectively with the first conclusions of the first and second operating plates, the second outputs of the third and fourth threshold organs are connected to the inputs of the first and second time delay elements, the outputs of which serve as the outputs of the signals to trip the corresponding switches, the inputs of the n zero sequence current sensors are included respectively in the neutral wire of the current transformers protected lines, and their outputs through series-connected third filters of industrial frequency, fifth comparators, third logical elements And, the first converters drivers of rectangular pulses to sawtooth voltage, sixth comparators, pulse expanders, fourth logical elements AND, second converters of rectangular pulses to sawtooth voltage, seventh comparators and actuators are connected to the first outputs of the third operational plates, the second outputs of which serve as outputs of signals for switching off the corresponding protected lines , the inputs of the third and fourth signaling elements are connected respectively to the outputs of the fourth logical elements And and is organs, the first terminals of n resistors are connected to the positive bus of the power supply, and their second terminals are combined with the anode terminals of the corresponding diodes and connected to the second inputs of the fourth logical elements AND, the cathode terminals of the diodes belonging to the protection lines connected to the first section of the busbars are connected to the second terminal of the first operational strip, and the cathode terminals of the diodes belonging to the protection lines connected to the second section of the busbars are connected to the second terminal of the second operational strip, the second the strokes of the third elements And belonging to the protections of the lines connected to the first section of the busbars are connected to the output of the first logical element And, and the second inputs of the third elements And belonging to the protections of the lines connected to the second section of the busbars are connected to the output of the second logical element And, and the main outputs of the device health check unit are connected to the inputs of the first, second and fifth comparators and the first adder input, the additional output of the device health check unit is connected to the second sum input ora.

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