SU1666988A1 - Device for locating faults in isolated neutral systems - Google Patents

Abstract

The invention relates to instrumentation engineering and can be used to determine the distance to the damage site in electric networks with insulated neutral. The purpose of the invention is to improve the accuracy of determining the distance to the damage. When a short circuit occurs, the selector 24 of the faulty phase is triggered and connects the inputs of the measurement unit 25 to the outputs of the first 18 and fourth 21 filtering nodes. Measurement unit 25 thus forms two voltages, one of which is proportional to the circuit current, and the second, the reactive component of the current of the first generator 1. The measurement results go to calculation unit 26, where the distance to the fault site is determined. From the output of the calculating unit 26, the information signal is fed to the display unit 27. 1 il.

Description

The invention relates to a measuring and control technique and can be used to determine the distance to the damage site in electric networks with insulated neutral.

The purpose of the invention is to improve the accuracy of determining the distance to the damage.

The drawing shows the functional diagram of the device.

The device contains the first 1, second 2 and third 3 sinusoidal current generators (audio frequency), block 4 connection, the first 5, the second 6 and the third 7 thyristor keys, the first 8, the second 9 and the third 10 AC chokes, the first 11, the second 12 and third 13 control modules of the triac keys, the zero sequence voltage sensor 14, the first 15, the second 16 and the third 17 current sensors, the first 18, the second 19, the third 20, the fourth 21, the fifth 22, and the sixth 23 Units, selector 24 of the damaged phase, measurement block 25, calculation block 26 and block 27 indications, feedback voltage sensor 28, sawtooth voltage generator 29, nonlinear element 30, adjustable 31 and constant 32 resistors, high-speed analog switch 33 with normally closed 34 and normally open 35 contacts, amplitude detector 36, zero-organ 37, a control pulse shaper 38, a controlled network 39 and terminals 40 for connecting a control object, the first, second and third inputs of unit 4 are connected to the corresponding terminals 40, the first outputs of each of generators 1-3 are connected to a common bus, The second output of the generator 1 is inductively coupled to the sensor 15 and connected to the first output of the block 4, the second output of the generator 2 is inductively coupled to the sensor 16 and connected to the second output of the block 4, the second output of the generator 3 is inductively coupled to the sensor 17 and connected to the third the output of block 4, the first terminals of the first 15, second 16 and third 17 sensors are connected to a common bus, the output of block 25 is connected to the input of block 26, the output of which is connected to the input of block 27, the first terminals of the first 8, second 9 and third 10 chokes are connected to shared bus, the second output throttle 8 is connected via key 5 to the second output of the generator 1 and the first output of block 4, the second output of the throttle 9 is connected via key 6 to the second output of the generator 2 and to the second output of the block 4, the second output of the third throttle 10 is connected through the third switch 7 to the second output of the generator 3 and with the third output of block 4,

The second terminals of the first 15, second 16 and third 17 sensors are connected to the inputs of the first 18, second 19 and third 20 nodes, the outputs of which are connected to the first inputs of the respective blocks 11, 12 and 13, and respectively the first, second and third inputs of the selector 24, the inputs of the fourth 21, fifth, 22 and sixth 23 nodes are connected to the second outputs of the first 1, second 2 and third 3 generators, respectively, and the outputs of these nodes are connected to the second inputs of the corresponding blocks 11, 12 and 13, respectively, with the fourth, fifth and sixth entrances voter 24, third entry blo5 Cove 11. 12 and 13 are connected to respective outputs of the sensor 14, the zero-sequence voltage, and the blocks 11, 12 and outputs 13 connected to the control inputs of the respective keys 5, 6 and 7,

0 while the first and second outputs of the voters 24 are connected respectively with the first and second inputs of the block 25.

The first input of the feedback voltage sensor 28 is connected to the first input.

5 of the control unit 11, and the second input with the second input of the control unit 11 and with the input of the sawtooth generator 29. The output of the feedback voltage sensor 28 is connected to the input of the non-linear element 30 and with an adjustable resistor 31.

The device works as follows.

In the normal operation of the electrical network with open thyristor switches 5-7, the current of each of the three generators 1-3 closes in two parallel circuits: one part of the current lci flows through its own capacitance Ci

0 phase relative to the earth, and the other part of this current ILI - through the appropriate thyristor key 5, 6 or 7 and the AC choke 8, 9 or 10.

The currents lei and In create in magnetic circuits

5 current sensors 15-17, the corresponding magnetic fluxes, and due to the fact that these currents are out of phase with each other, the magnetic flux created by the current lci is compensated by the magnetic flux created by the current ILI. During adjustment of the device, change the equivalent inductive resistance of each drossel by adjusting the angles of control of the thyristor switches 5-7, using

5 control units 11-13 achieve that the inductive currents of the chokes fully compensate for the corresponding capacitive currents.

During operation, with possible changes in the currents lci, caused by changes in the proper capacitances of the wires due to on-line switching or other reasons, the currents ILI and maintaining the equality In ILI are controlled by blocks 11-13 of the control automatically.

Due to the equality of the currents la and ILI, the resulting magnetic fluxes generated in the magnetic cores of each current sensor are zero, and therefore there is no EMF in the secondary windings of the sensors in normal mode.

The permissibility of the equivalent inductive resistance of chokes of an alternating current about the angle of control of the thyristor switches 11-13 is described by the expression

Me. (2g $ - sin 2tti), (1)

where the inductive resistance of the corresponding choke is 8, 9, or 10 when the thyristor keys are shorted; Kloi 2л11 | ;

f- frequency generators;

LI is the inductance of the corresponding chokes when the thyristor keys are shorted;

(T (is the control angle of the corresponding thyristor key 5. 6 or 7.

When the control angle changes (X from O to / 2, the resistance of kl changes from oo to moi

The inductance of the LI chokes is chosen based on

A.Lol 1 / (2jrf С | max), (2)

where Syaks is the maximum possible wire capacity of the corresponding phase of the electrical network relative to the earth.

The value of Syaks can be determined experimentally or with the maximum length of max electrical network known in each particular case using the formula

C | max Coi max. (3)

where Coi is the specific capacity of the cable of the corresponding phase of the electrical network relative to the ground.

When a single-phase ground fault occurs through a transition resistance, for example, the first phase of the electrical network, the current of the first generator 1 changes. In this case, the current 1E flowing through the circuit is added to the existing current ci and li.i: generator 1 - connection unit 4 - active and inductive resistances of the section of the first phase of the line to the point of damage - transitional resistance to earth - first generator 1.

The magnetic flux generated by this current in the magnetic core of the first 15 sensors

five

0

current, is uncompensated, which leads to the appearance in the secondary winding of this sensor EMF E. proportional to the current circuit

5E k13, (4)

where k is the proportionality coefficient, which is the same for all current sensors and determined by their design parameters and magnetic core material.

0 EMF E is lagging behind the voltage of the generator Uri, given its own angle of current sensors of 90 °, by an angle

H 9QP + a,

where a is the phase angle between voltage Uri and current 13;

- ° ОЈ-г & - 6

where LO is the specific inductance of the wire;

1X is the distance to the place of single-phase ground closure:

r0 is the specific resistance of the wire;

RM is the active transitional resistance in the place of single-phase ground fault.

Based on the foregoing, information on the distance to the single-phase ground fault, provided that the current is lei compensated by current, gives the partial separation of the reactive component of the first generator voltage (Ui 1 sin (H - 90 °) by EMF E.

In accordance with this, when a single-phase ground fault occurs, the selector 24 of the damaged phase is triggered, and after a predetermined time delay (if the damage persists), connects the inputs of the measurement unit 25 to the outputs of the first 18 and fourth 21 filtering sites.

1 The voltages at the outputs of the filtering units 18 and 21 are directly proportional, respectively, to the EMF E of the first 5 current sensor 15 and the voltage Uri of the first generator 1. The measurement unit 25 from these voltages generates two other voltages, one of which, taking into account expression (4) is proportional to the current Ij of the closed loop and the second to the reactive component of the first generator 1.

The measurement results are received in the block 26 of calculations, which by them calculates the distance to the single-phase closure ne the earth taking into account the expression (4) - (6) using the formula

. to Vri sin (M -90 °), „

, x-2 P7E- (7)

five

0

five

The result of the calculation is transmitted to the display unit 27, which represents it in digital form on the display board.

When a single-phase short circuit to earth of another phase of the electrical network, the device operates in a similar way.

Compensation of capacitive currents lei during a single-phase ground fault is achieved by the fact that when it occurs at the first voltage surge at the output of the zero-sequence voltage sensor 14, the control blocks 11-13 fix the values of the control angles that take place at this time, and then If the damage is permanent, these angles remain unchanged. In this connection, the inductive currents will also not change. But, since they, up to the occurrence of damage, are equal to the corresponding capacitive currents (compensate them), then, in the presence of a single-phase ground fault, the indicated equalities are preserved in all phases, including the damaged one.

We consider the operation of the control keys 11–13 with the thyristor keys on the example of the first block 11. The control angle of the thyristor key 5 depends on the level of the control voltage, which, during normal operation of the electrical network, enters the second input of the zero-body 37 through a normally closed contact 34 high-speed analog key 33 directly from the nonlinear element 30.

During adjustment of the device, the level of this voltage is manually adjusted by varying the resistance of the adjustable resistor 31 so that the voltage at the output of the first 18 filter-breaker unit, and consequently, at the output of the feedback voltage sensor 28, becomes zero ( in this case, the current Id is fully compensated by the current 1c).

If during operation the current lei changes in magnitude, for example, decreases for any reason, this results in a DC voltage proportional to the geometric sum of the currents lei and ILL at the output of the feedback voltage sensor 28. Moreover, this will be positive, since in this case the total current of generator 1 lags behind its output voltage by 90 ° due to the fact that more ICL The occurrence of this positive voltage at the output of feedback sensor 28 leads to an increase in the constant voltage the input of the nonlinear element 30, which causes a decrease in its resistance. As a result, the level of the control voltage and the angle of the control of the thyristor switch 5 are reduced. When reducing the angle of control in

According to expression (1), a proportional increase in the equivalent resistance of the first alternating current throttle 8 occurs and the current ILI decreases. Ultimately, it becomes equal to the new value of the capacitive current IGI.

If, however, the capacitive current lei increases for some reason, the control angle also increases due to the appearance of a negative constant

5 is the voltage at the output of the feedback voltage sensor 28. As a result, taking into account (1), the current 1c increases and again becomes equal to ICL

So in normal mode

0 of the electrical network operation, the control angle is automatically controlled (l. And due to this, the lei and ILL currents are maintained equal when a single-phase ground fault occurs on the first surge of zero-sequence voltage, a signal appears at the output of the zero-voltage sensor 14 high-speed analog

0, the key 33 opens the normally closed contact 34 and closes the normally open contact 35. At the same time, the amplitude detector 36 detects the voltage value that at a given moment of time stands out on the resistance of the nonlinear element 30. As the voltage released on the resistance of the nonlinear element 30 during a single phase ground fault, always more than

0 in normal operation of the electrical network (due to the fact that the closing current is inductive in nature and it is much larger than the total current lei + ILI at ILI Id), then, taking into account the principle of operation of the amplitude detector 36. control voltage at single phase The circuit remains constant in magnitude and equal to the voltage detected by the amplitude detector. Therefore, the angle of control also remains unchanged and equal to the value that was at the time of the occurrence of a single-phase ground fault.

When the single-phase closure is eliminated5, the high-speed analog switch 33 switches to ground and the initial state and the control unit 11 again goes into the tracking mode and automatic current compensation ICL

The second 12 and third 13 thyristor key control units 6 and 7 operate in a similar way.

Claims (2)

Claims 1. A device for specifically referring to a fault in an electrical | | / their network with insulated neutral, comprising terminals for connecting a control unit, an attachment unit, first. the second and third sinusoidal current generators, the first, second and third current sensors, made in the form of an annular magnet with a two-pin secondary winding located on it, a damaged phase selector, a measuring unit, a calculating unit and a display unit, the first, second and third the inputs of the connection block are connected to the corresponding terminals for connection to the control object, the first outputs of each of the three sinusoidal current generators are connected to the common bus, the second output of the first sinusoidal current generator is inductively coupled to the first current sensor and connected to the first output of the connection unit, the second output of the second sinusoidal current generator is inductively coupled to the second current sensor and connected to the second output of the connection unit, the second output of the third sinusoidal current generator is inductively connected to the third current sensor and connected to the third output of the connection unit; the first terminals of the first, second and third current sensors are connected to the bus; the output of the measuring unit is connected to the input of the calculation unit, the output of which is connected It is not connected with the input of the display unit, which is due to the fact that, with a chain of accuracy improvement, it is determined the distance to the place of damage, it introduced three alternating current chokes, three thyristor switches, three thyristor control switches, six filtering units, the first outputs of the first, second and third AC chokes are connected to the common bus, the second output of the first throttle through the first thyristor switch is connected to the second output of the first generator of sinusoidal current and the first output of the accessory unit, the second output of the second connection through the second thyristor the key is connected to the second output of the second sinusoidal current generator and the second output of the attachment unit, the second output of the throttle is connected via a third thyristor switch to the second output m of the third generator of sinusoidal current and the third output of the connection block, the second terminals of the first, second and second sensors the scale is connected to the inputs of the first, second and third filter developing nodes, the outputs of the first, second and third filtering nodes of the solenoid 5 with the first inputs of the corresponding thyristor key control units and the first, second and third inputs of the damaged phase selector, inputs the fourth, fifth, and 0 of the sixth filtering and erecting nodes are connected to the second outputs of the first, second, and third generators of sinusoidal current, respectively, and the outputs of these nodes are r, the second inputs the corresponding block control of the thyristor keys and respectively the fourth, fifth and sixth inputs of the damaged phase selector; the third inputs of the control modules of the thyristor keys are connected to the corresponding outputs of the zero-sequence voltage sensor, and the outputs of the control units are connected to the control inputs of the corresponding thyristor - key, with the first and second The 5 outputs of the damaged phase selector are connected respectively to the first and second terminals of the measuring unit. 2. The device pop 1, characterized in that the thyristor control unit 0 key contains voltage feedback sensor, sawtooth generator, adjustable and constant resistors, nonlinear element, high-speed analog switch with normal 5 closed and normally open contacts, an amplitude detector, a zero-organ and a control pulse shaper, the first input of the feedback voltage sensor connected to the first input 0 of the control unit, and the second input is with the second input of the control unit and with the input of the sawtooth generator, the output of which is connected to the first input of the zero organ, the output of the feedback voltage sensor is connected to the input of the nonlinear element and through an adjustable resistor with a positive the source of a constant voltage source, the first output of the nonlinear element is connected via normal 0 is a closed contact of a fast analog switch with a second input of a zero-organ, and through a normally open contact with an input of an amplitude detector, and through a constant resistor with a positive pole of a constant voltage source, the second output of a nonlinear element is connected to a common bus source constant voltage, control input of high-speed analog switch is connected to the third input of the unit 11166698812 control, the output of the amplitude detector of the control pulse generator, the output is connected to the third input of the zero-body, which is connected to the output of the control unit. The output of the zero-body is connected to the input of the formula.