SU1631469A1 - Method for measuring distance to break in phase line of aerial isolated heutral three-phase power network - Google Patents

Abstract

The invention relates to instrumentation engineering and can be used to determine the distance to the point of phase failure in aerial three-phase electrical networks with insulated neutral. The purpose of the invention is to improve the accuracy of determining the distance to the cliff. Constantly monitor the value of the zero-sequence voltage, determine the increment of the effective value of the zero-sequence voltage of the monitored network relative to its value when it is in good condition, determine and compare among themselves the capacitances of the individual phases of the network, respectively, the earth the controlled network, determine the phase in which there is a break, determine the sign of the time derivative of the zero sequence voltage of the controlled network at the time of the break, depending on The stations connecting the values of the capacitances of the phases of the monitored network and the sign of the time derivative of the zero sequence voltage of the monitored network at the time of the break, determine the distance to the place of the phase break. 2 Il. (L

Description

The invention relates to instrumentation engineering and can be used to determine the distance to the point of phase failure in air three-phase electrical networks with insulated neutral.

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

FIG. 1 shows a block diagram of a device implementing the proposed method; Fig. 2 shows the dependence of the value of the calculated voltage on the distance to the break point for different phases.

The device (figure 1) contains a block

1 isolation of damaged phase, block

2 discontinuity selections, zero sequence voltage extraction unit 3, zero sequence initial value memory storing unit 4, zero sequence current voltage value storing unit 5, zero value derivative derivative sign extraction unit 6, first zero projection element 7, first

8 and the second 9 NAND elements, the I Yu element, the second 11, the third 12, the fourth 13 BAN elements, the block 14,

WITH&

with

4i

0

J1

a subtracting unit 15, first 16 and second 17 units determining a breakage zone, terminals 18 for connecting to a monitored network to which the corresponding inputs of units 1-3 are connected. The first output of block 1 is connected to the first input of the element AND 10, the second input of which is connected to the output of block 2, the first inputs of the element BAN 7, the first 8 and the second 9 elements of NAND, the second input of which is connected to the second input of the element NAND 8 and the second output of block 1, the third input element AND-HE 9 is connected to the first output of block 6, the second output of which is connected to the third input of the element AND-HE 8, the output of which is connected to the first input of the BAN member 11, the second input of which is connected to the output of block 14 , the first and second inputs of which are connected with the corresponding unit inputs 15 and outputs respectively block 5 and block 4, the input of which is connected to the output of the BAN 7, the second input of which is connected to the inputs of blocks 5 and 6 and the output of block 3. The output of the block 15 is connected to the first input of the BAN 12,

0

five

0

five

the output of which is connected to the input of block 17, and the second input is connected to the output of the BAN 13 element, the first and second inputs of which are connected to the outputs of the AND 10 element and the AND-HE element 9, respectively.

FIG. Figure 2 shows the dependences characterizing the relationship between the calculated voltage and the distance to the point of phase failure, respectively, for cases when the capacity of the damaged phase relative to the earth is less than 19 and greater than 20 than the similar capacity of each of the intact phases.

The distance L to the point of break is determined by the formula

L KU0,

where K is the proportionality coefficient determined by the type of network;

U. - rated voltage. The method is carried out as follows.

In the normal operation of a three-phase electrical network, the value of the zero sequence voltage is defined as

p UA (CA + CA.) + iVSSu + Svm) + is (ss. + ce “) m

"° SA (+ Sy- + Syme + SS + Sl

SS + Ss

where ik u

BUT

a, U0 - phase voltage A,

В, С, Сд1, Сд «, С6, С.с, Сс, Сс" - capacities of the network phases

A, B, C relative to the ground before I and after the II place of the cliff.

The direction of the zero sequence voltage vector depends on the ratio of the capacitances. Suppose that, in this electrical network, the capacity of phase A is greater than the capacity of phases B and C:

(Sd + SAP)

CB +

C6

Ss. + C c

Then the vector of this voltage is opposite to the vector of phase voltage of phase A, while the total phase voltage relative to the earth of phase A is reduced by the value UHO, and the voltage of phases B and C

increased by U value

but

This value of Uc0 is memorized in block 4.

When a phase breaks up, for example, A, the current value of the zero sequence voltage is defined as.,

Su + Svm) + is (ss. + Ce “) m

Sim + SS + Sl

SS + Ss

n UftCft + U & (C9 + C8i.) + CA (SS + SS) (2h ot Sd1 + SA “+ St + Ss“ + SsP

Denote by dio VQ ± UHo.

As can be seen from the relation of expressions (1) and (2), the difference can take both positive and negative values. It depends on the ratio of Cd and C, i.e. from the total length of the line to the point of break to the total length of the line beyond the break point. Thus, U0-j; may have three meanings: Uot UWo; U0-t UHO, respectively u.U0 - Of A.U0 0; & U0 0 i.e. the increment of the zero sequence voltage can be either positive or negative.

Consider the case when the capacitance of phase A relative to the earth is greater than the analogous capacitances of the remaining intact phases.

dU0

For this mode, we have

dt

0

Thus, the true increment (in this case, a decrease) of the zero sequence voltage

determines the distance to the point of break, i.e. in the first zone, it is necessary to recalculate the fall value for the distance to the injury site. The device in this case works as follows. The zero sequence voltage before the failure U 0 is remembered in block 4, after the break UQ-J; memorized in block 5, block 2 selects the type of damage (in this case it is open, not short to ground), block 1 fixes on which of the phases the damage occurred (in this case on phase A). At the first output of block 1, a signal appears, which is fed to the input of the second element NAND 9 and the input of the first NAND 8. As it is given. dU0 ±

In the case, the sign of the derivative is r-negative. A signal appears at the output of block 6, which is fed to the input of the second element AND-NOT 9. At the input of the element AND-HE 9 there is a signal from the breakaway selection unit 2. Since there is a signal at all three inputs of the NAND 9 element, the signal at its output is zero, therefore the signal at the enable input of the fourth element BAN 13 is absent. At the inputs of subtraction unit 15, there are signals from block 4 () and from block 5 (Uot), at the output of block 15 we have a signal proportional to (U0fc-it0), T ° e °, which in this case corresponds to the distance to the point of rupture. The signal from the output of block 15 through the third element BANGE 12 (since there is no signal at its prohibiting input goes to block 17, in which the distance to the break is calculated).

If there is a break on the line, when the capacity of the damaged phase is less than 5 than the capacities of the remaining phases, we have

dU0

dt

- 0. In this case, the increment

the zero sequence voltage does not determine the distance to the point of damage, since the initial value of the voltage of the bullet sequence decreased to zero (

U

To

- and on curve 19, fig), and then increased (zone ab in curve 19, figure 2). Therefore, to determine the true location of damage, it is necessary to determine (UHO + U0 - (-), then recalculate it to the distance to

damage sites. The implementation of this mode is carried out as follows. At the output of block 6 there is no signal, dUa the inverter is (.- 0), therefore at the output

of the second element NAND 9 there is a signal which, through the fourth element BAN 13, goes to the prohibiting input of the third element BAN 12. There is no signal at the enable input of the fourth element BAN 13 13 because the other phase is damaged, therefore block 17 does not work. At the output of block 6 there is a signal, since

Ј., „.

At the input of the element IS-HE 8 there is a signal from block 1, at the second input 0 from block 3, at the third input is from block 6, therefore the signal at the output of the first element IS-NOT 8 is zero. In block 14, the value of 11c0 and U0 {-, the sum signal via the second

5, the BANCH element 11 is fed to block 16, in which the distance to the break point is calculated.

When the phase is broken, for example, B, whose capacity is less than the capacity of phase A,

Q, the current value of the zero-sequence voltage is also greater than IO in any case. The curve of the change in U 0. (. Depending on the length of the broken portion of phase B is shown in Fig. 2

(curve 20). Derivative

dU dt

 0

regardless of the point of rupture, therefore, in this case, it is possible to recalculate the value of the increment U0 - | - UMO to the place of the rupture.

The implementation in this case is as follows.

The signal from the second output of block 1 for the extraction of the damaged phase does not reach the first inputs of the I-EE elements 8 and 9, therefore the signal from block 14 does not pass through the second element BAN 11. At the output of the second element

The NAND 9 signal is equal to one, but the prohibiting input of the fourth element BAN 13 has a signal from the AND 10 element, therefore the output of the fourth element BAN 13 is equal to

to zero. The signal from block 15, which in this case is proportional to U0 -) .- - UHQ, goes to the second block 17, in which the distance to the break is determined.

Claims (4)

1. A method for determining the distance to a phase break in air three-phase electric networks with insulated neutral, which consists in measuring the value of the effective voltage value of the zero sequence of the monitored network, recording the moment of phase failure, determining the increment of the value of the current voltage value zero sequence in relation to its value in the good condition of the monitored network and determine the distance to the point of phase failure using the formula L KU0, where L is the distance to the break point; U0 is the rated voltage; K is the proportionality coefficient determined by the type of network, characterized in that, in order to increase the accuracy of determining the distance to the point of phase failure, the values of the capacities of the damaged and intact phases of the monitored network relative to the ground are determined and compared, the damaged phase of the monitored network is determined, the sign of the time derived voltage is determined zero the sequence of the monitored network at the time of the break, according to the ratio between certain values of the capacitances of the phases of the monitored network and the sign of the time derivative of the voltage zero sequence STI controlled network at the time of breakage was determined value of the calculated voltage. 2. The method according to claim 1, characterized in that in the event of a phase failure, the capacitance of which relative to the earth is greater than each of the quantities of similar capacitances of the intact phases, and the time derivative of the zero sequence voltage is a positive value, as the calculated voltage 5, select the sum of the effective value of the voltage of the zero sequence of the monitored network until the moment of interruption and the increment of this voltage at the moment of interruption. 03. Method of claim 1, characterized in that in the event of a phase failure, the capacitance of which relative to the earth is less than the capacitance of the intact phases, the zero-sequence voltage increment is chosen as the calculated voltage. 4. The method of pop. 1, differing from Q and with the fact that in the event of a phase failure, the capacitance of which relative to the earth is greater than each of the values of the analogous capacitances of the intact phases, and the time derivative of the zero sequence voltage is 5 value, as the calculated voltage, choose the voltage increment zero, the sequence. 18 QQO "G UJ LU-HI 1