RU2394249C1 - Method of determining overhead electric power line tower with single-phase earthing and earthing fault - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: current I_e flowing through tower to ground and voltage U_e at tower relative to ground are measured simultaneously. Symptoms of faults of two types are revealed at the tower and signal about fault is generated: at I_e>0 and U_e≤U_ph signal about single-phase earthing, at I_e=0 and U_e.stand.<U_e≤U_ph signal about single-phase tower frame ground connection and earthing circuit fault, where U_e.stand. is normalised voltage at tower relative to ground; U_ph is circuit phase voltage. Particular tower fault is locally recorded and be remote means at dispatcher control station. Note here that fault signal is converted into encoded signal that comprises fault type sign and tower registration number. Said signal is transmitted via communication or radio line. Signal is decoded and fault is registered. Measured current and voltage are also used for calculation of actual tower earthing resistance. In case actual earthing resistance exceeds normalised value signal is generated indicating said fact, tower earthing circuit fault is registered locally and by remote means.

EFFECT: higher validity of pinpointing faulty tower with single-phase short circuits and control over actual tower earthing resistance.

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Description

The invention relates to the electric power industry and can be used in distribution networks with a voltage of 6-35 kV with isolated or compensated neutral, for example, in the oil industry.

There is a method of determining the distance of a single-phase circuit in a three-phase power line (transmission line), which consists in determining the damaged line from all lines of the distribution network, disconnecting it at both ends, and then measuring currents. Using the results of measurements of power line currents and a given line length, determine the distance to the place of damage on overhead power lines by calculation using the formula (see patent RU No. 2186404, class G01R 31/08, 04/04/2001).

The disadvantage of this method is the low accuracy and lack of reliability of finding the place of damage, since the measurement results depend on many factors, including the transition resistance at point 033. In addition, the known method requires a lot of time and labor.

There is a method of determining the distance to the place of a single-phase earth fault in distribution networks, based on the registration of an electrical quantity in emergency mode 033, namely, registration of voltage on the damaged phase at the beginning of the line in the transition process of earth fault and the allocation of the natural frequency of the line along which determine the distance to the circuit (see patent RU No. 2216749, CL G01R 31/08, 03/27/2001).

The disadvantage of this method is the low reliability of finding the place of damage, since the recorded electrical quantity and the allocated frequency significantly depend on the parameters of the lines, especially on the changing phase capacity of the overhead power line.

There is a method of finding the support of an overhead power line with a ground fault, based on the registration of an emergency mode parameter near the overhead power line in the form of electromagnetic field strength due to higher harmonic components of the zero sequence current, i.e. single-phase earth fault current. This method is applied in practice. Based on it, devices of various types have been developed, for example, “Search-1”, “Wave”, “Probe”, “Spectrum”, etc., used in 6-35 kV networks to find OZZ places. A support with damage is found by walking along an overhead power line. The poles with insulation damage readings are several times greater than other poles with the normal condition of insulators and wire fasteners (see AP Kuznetsov. Determination of places of damage on overhead power lines. - M.: Energoatomizdat, 1989). This method is relatively simple.

The disadvantage of this method is the low reliability of determining the support with insulation damage, due to the dependence of the measured and controlled values on the unstable value of the transition resistance at the point of a single-phase circuit, on the changing phase capacitance of the overhead power line, on the random nature of a number of factors affecting the harmonic components of the current of the single-phase circuit. In some cases, it is difficult and even impossible to determine the place of damage. So, if only two lines of approximately the same length leave the substation, then when a ground fault occurs on one of them, zero sequence currents at the beginning of both lines will be almost equal to each other. Therefore, using instruments based on the method of controlling the higher harmonic components of these currents, it will be practically impossible to determine the damaged line and support. A similar situation will be with a larger number of outgoing lines, if two of them have lengths exceeding the total length of the remaining lines. In addition, the known method is time consuming, especially on long power lines. To speed up the search requires several teams of personnel simultaneously working on sections of the line.

The closest method of the same purpose to the claimed invention by the totality of features is a method for determining the support of power lines with damaged insulation, based on the control of the emergency mode parameter in the form of current through the support to the ground (see A. Kuznetsov. Determination of places of damage on overhead power lines . - M .: Energoatomizdat, 1989). This current is controlled by a split-core current transformer. The magnetic core consists of two halves that surround the supporting structure of the reinforced concrete support or the supporting corner of the metal support, i.e. The current-carrying armature of the support is used as the primary winding of a current transformer. A signal element is connected to the secondary winding of this transformer, for example, in the form of a squib and an associated fixing signal flag. This method is implemented in UPI-1 devices used in practice (pointer poles with damaged insulation). This method is adopted as a prototype.

Signs of the prototype, coinciding with the essential features of the claimed invention - control the current through the support to the ground with a good grounding of the support, make local damage fixation.

The disadvantage of this method, adopted as a prototype, is the low reliability of determining supports with insulation damage, due to the fact that the known method is based on monitoring only the current through the support to the ground. However, the absence of current through the support or its very small value (within the insensitivity of the control means) does not mean that there is no insulation damage on the support. If the insulator is damaged, the current will be zero due to a break in the ground circuit of the insulator fittings. The current may be close to zero due to unacceptably high ground resistance of the support due to drying or melting of the soil. In addition, using a current transformer with a detachable "solid" magnetic circuit with a complex form of the bearing structure of the support, it is difficult to control all current-carrying support elements to the ground. It is for this reason that the used devices of the UPI-1 type and similar reliably work only at damage currents of 200-300 A and more and have found application only on power lines with voltage of 110 kV and more.

In networks of 6-35 kV, this well-known method for determining supports with insulation damage can be used only with double (double) earth faults, but also only if the supports are well-grounded.

The complexity of the task of determining the support with insulation damage and a single-phase earth fault in 6-35 kV networks is as follows:

- these networks operate with isolated or compensated neutral, the earth fault current is small and can have values of about 1-10 A, depending on the length of the power transmission line and the neutral mode;

- 033 mode can be long due to failure of protection at the substation or due to uninterrupted power supply requirements of consumers;

- due to the prolonged flow of current through the support to the ground, drying of the soil and a significant increase in the transition resistance of the grounding of the support, especially of the reinforced concrete support, are possible;

- there may be a violation of the integrity of the grounding conductors of the insulator mounting reinforcement, as a result of which damage to the insulator will not cause a short to ground, but a short to the support reinforcement, which will (create) a high potential on the support relative to the ground and the risk of electrical injuries at the support.

The problem to which the claimed invention is directed is to increase the reliability of determining power transmission towers with insulation damage and resulting in two types of single-phase faults (short circuit to the grounded armature of the support and shorting to the armature of the support in the event of grounding failure), and monitoring the excess of the value of the actual grounding resistance of the support over the normalized value.

The problem was solved due to the fact that in the known method for determining the support of an overhead power line with a single-phase circuit and a ground fault, based on the control of the current through the support to the ground with the support being properly grounded and local damage is fixed, the current through the support to the ground is simultaneously monitored I _З and the voltage on the support with respect to ground U _W use current and voltage values for the analysis of an emergency, which is performed by a predetermined algorithm, according to the analysis by the logical neck of lyayut signs of damage to the support and is formed of two kinds of damage signal respectively when _W I> 0 _W and U ≤U _Z.NORM. - signal of a single-phase earth fault; or at I _З = 0 and U _{З. НОРМ.} <U _З ≤U _Ф - signal about a single-phase short circuit to the armature of the support and the malfunction of the ground circuit, where U _{Z. NORM.} - the normalized voltage value on the support relative to the ground; U _Ф - phase voltage of the network, using the generated signal of damage, simultaneously localize the fact of damage of a specific type at the support with damage and remote in the dispatch control point, for which the signal about the type of damage is converted into a coded signal containing a sign of the type of damage and registration number of the support, transmit it over the communication line or over the air to a distance where the signal is decoded and the damage is recorded; and in addition, the measured current and voltage are simultaneously used to calculate the actual grounding resistance of the support, the result is compared with the normalized grounding resistance, and if there is an excess of the actual grounding resistance over the normalized value, they also generate a signal about the excess of grounding resistance and conduct local and remote fixing the fact of a grounding failure of the support.

Signs of the proposed method, distinctive from the method of the prototype, at the same time control the current through the support to the ground I _Z and the voltage on the support relative to the ground U _З ; controlled values of current and voltage are used to analyze the emergency situation on the support, which is carried out according to a given algorithm; according to the results of the analysis, the signs of damage on the support of two types are logically detected and a signal about the damage is generated, respectively: for I _З > 0 and U _З ≤U _{З. НОРМ.} - signal of a single-phase earth fault; or at I _З = 0 and U _З.norm. <U _З ≤U _Ф (where U _{З. НОРМ.} - normalized voltage value on the support relative to the ground; U _Ф - phase voltage of the network) - a signal about a single-phase short circuit to the support arm and ground circuit malfunctions; carry out, using the generated signal of damage, simultaneously local recording the fact of damage of a particular type at the support with damage and remote at the control center, for which the signal about the type of damage is converted into a coded signal containing the sign of the type of damage and the registration number of the support in the code; transmit a signal over a communication line or over a radio channel to a distance where they decode the signal and fix the damage; the measured current and voltage are simultaneously used to calculate the value of the actual grounding resistance of the support; the result obtained is compared with the normalized value of the grounding resistance, and by the presence of an excess of the actual grounding resistance over the normalized value, a signal is generated about the excess of the grounding resistance and local and remote fixation of the fact of a grounding failure of the support is carried out.

When analyzing the known technical solutions, the applicant did not reveal a set of features that distinguish the claimed technical solution from the prototype, leading to an increase in the reliability of identifying power transmission towers with damage to the electrical network. Also, the use for the purpose of determining the support of power lines with damage at the same time as the current through the support to the ground and the voltage on the support relative to the ground was not revealed. Therefore, we can conclude that the claimed technical solution meets the criteria of "novelty" and "inventive step".

The proposed method for determining the support of an overhead power line with damage is illustrated by the functional block diagram shown in the drawing. The diagram shows:

1 - the support of an overhead power line, on which damage in the form of single-phase faults of two types is monitored, as well as a possible grounding failure of the support;

2 - a flexible current sensor, which surrounds the support and control the current through the support to the ground;

3 - measuring electrode, which is placed in the ground near the support at a distance of 15-20 m and use it using an insulated conductor to control the voltage on the support relative to the ground;

4 - measuring insulated conductor, which is laid from the reinforcement of the insulators and is used to control the voltage on the support;

5 - measurement and logic module, where, using controlled current and voltage values, an emergency analysis is carried out, signs are identified and a logical conclusion is made about the type of damage on the support of two types and, accordingly, signals are generated to fix the facts of damage to a specific type;

6 - division block, where the value of the actual grounding resistance of the support is calculated;

7 - an element where the actual grounding resistance of the support is compared with a standardized value and subject to R _{Z. FACT.} > R _{Z. NORM.} . norms, form at the output a signal about a failure of grounding of the support;

8 is a block for local recording of facts of damage on a support, where damage signals are converted into light or other signals for personnel;

9 is a block where damage signals on a support are converted into an encoded telemetric or radio signal containing signs of damage in the code and the registration number of the support;

10 is a communication line through which an encoded signal is transmitted in the form of a wired, fiber optic line or radio channel;

11 is a block for remote recording of facts of damage on the supports of the distribution network lines, where the signals coming through all communication lines are decoded and converted for centralized dispatch control.

The method is as follows.

On each support 1 of the power transmission line, the emergency mode parameters are simultaneously monitored: current through the support 1 to the ground I _З and the voltage on the support 1 relative to the ground U _З. To control a relatively small current, for example, 1-30 A, which is typical for 6-35 kV networks with overhead power lines, a flexible current sensor 2 is used, which surrounds the bearing structure of the support 1 of any shape with minimal gaps. To control the voltage at the support 1, a measuring electrode 3 is used, which is placed in the soil at a distance of 15-20 m from the support 1 and is used in measurements as a point of zero ground potential. The second point for voltage measurements is: on reinforced concrete supports - the place of connection of the reinforcement fasteners of insulators with the grounding conductor of the support; on metal supports - any point of the supporting structure. Controlled electrical quantities I _З and U _З are supplied to the inputs of module 5 and the inputs of block 6. In module 5, using the values of current I _З and voltage U _З , an emergency analysis is carried out according to a given algorithm, and signs of damage are identified on the support of two types:

1) if a current of a certain value I _З > 0 flows through the support to the ground and at the same time the voltage across the support relative to the ground is small, for example, does not exceed U _З ≤U _{З. НОРМ.} = 10-300 V (where U _{Z. NORM.} Is the normalized voltage value on the support relative to the ground), then the coincidence of conditions I _З > 0 and U _З ≤U _{З. НОРМ.} - this is a sign of damage to the support of the first type, namely, a single-phase earth fault;

2) if there is no current through the support (or its value is small within the sensitivity of the current sensor), i.e. I _З = 0 and at the same time the voltage value on the support is large and is within U _{З. НОРМ.} <U _З ≤U _Ф (where U _Ф is the phase voltage of the network), then the coincidence of conditions I _З = 0 and U _{З. НОРМ.} <U _З ≤U _Ф - this is a sign of damage to the support of the second type, namely, a single-phase short circuit to the support armature in the event of a ground fault.

Based on the revealed characteristic, a logical conclusion is made about the type of damage on the support 1 and, accordingly, a signal is generated about the specific damage at the first or second outputs of module 5. For example, if the current through the support is I _З = 1 ÷ 10 A and at the same time the voltage on the support will be U _З = 10 ÷ 100 V, then under the condition that R _{З. НОРМ.} = 0 m (other values of R _З.norm. And, accordingly, U _{З are} possible), a logical conclusion follows about the first type of damage: on the support 1 the insulation is damaged (in the form of overlap or destruction of the insulator or otherwise), a single-phase earth fault through the valve supports 1 with good grounding. The signal of the first type of damage appears only at the first output of module 5.

In another case, if the current through the support I _З = 0 or has a negligible value and at the same time the voltage across the support will be U _{З. НОРМ.} <U _З ≤U _Ф , i.e. in magnitude can be close to the phase voltage of the network, then a logical conclusion follows about the second type of damage: on the support 1, the insulation is damaged, a single-phase short circuit occurs on the fittings that are in contact with the support, however, in the ground circuit of the insulator reinforcement there is an open or ground resistance of the support unacceptably large. In this case, the signal of the second type of damage appears only on the second output of module 5.

The signal from the first output of module 5 is fed to the first input of block 8 and, accordingly, of block 9.

In block 8, this signal is converted into a light signal or into a signal for changing the color or position of the blinker, or into another signal, and thereby local indication and fixing of damage on the support is carried out in the form of a single-phase earth fault. In block 9, the same signal is converted into an encoded telemetric or radio signal. Then the encoded signal is transmitted via a communication line or radio channel to the centralized control station 11. Here, the received signal is decoded and the damage is remotely recorded on the pole in the form of a single-phase earth fault and the registration number of this pole 1.

Similarly, the signal from the second output of module 5 is fed to the second input of block 8 and, accordingly, of block 9.

This corresponds to the second type of damage on the support 1. All operations in block 8 and in block 9 occur in the same way as in the first type of damage. However, in this case both in block 8 and in the point of supervisory control 11, the second type of damage is fixed on the support 1, namely, a single-phase circuit to the armature of the support 1 in case of ground failure.

In block 6, the magnitude of the actual grounding resistance of the support 1 is calculated by dividing the magnitude of the input signals, i.e. get the value of R _{Z. FACT.} = U _З / I _З (Ohm). In element 7, the actual grounding resistance of the support is compared with a standardized value and only if R _{З. FACT.} > R _{Z. NORM.} form at the output of element 7 a signal about a grounding failure of the support 1.

This signal is fed to the third input of block 8 and, accordingly, block 9.

In block 8, this signal is converted into a light or other signal and in this way local indication and fixing of the grounding failure of the support 1 is carried out. In block 9, this same signal is converted into an additional sign of the encoded signal of damage on the support 1. Then, the encoded signal is transmitted to the central control room control 11. Here, after decoding the signal, they simultaneously remotely record both damage on the support 1 in the form of a single-phase circuit and a grounding failure of the support 1.

For the practical implementation of the proposed method for determining the support of an overhead power line with damage, known functional elements and devices can be used. As a current sensor 2 through the support 1, you can use a current transformer with a flexible magnetic circuit or apply a flexible current sensor, for example, in the form of a Rogowski torus. In function module 5, analog or digital measurement and logic elements can be used. In block 6, for the division operation, you can also use analog or digital elements. In block 8, it is advisable to use low-power neon or similar indicators for the light display of controlled damage. Known functional elements and devices can also be used to convert signals about damage to the support and grounding failure of the support, encoding and decoding of signals.

An advantage of the invention is that from a large number of supports of overhead power lines of a distribution network of 6-35 kV, it is possible to quickly and reliably determine the specific support on which a single-phase fault occurred, moreover, the fault is of two types. In the first type of single-phase fault, the method simultaneously provides control over the excess of the actual grounding resistance of the support over the normalized value. This, in turn, will allow you to quickly turn off the power line with damage or, if the shutdown is impractical under the condition of uninterrupted power supply, quickly perform actions to ensure safety at the place of damage, to carry out repair work.

In addition, remote detection of the support with damage allows you to identify and damaged from the group of power lines of the distribution network and, therefore, provide protection against single-phase faults with absolute selectivity. A reliable definition of a support with damage reduces the time and labor required to find a support in the electric network, reduces the likelihood and danger of electrical injuries to a damaged support, and increases the safety and reliability of power supply to consumers.

Claims (1)

A method for determining the support of an overhead power transmission line with a single-phase circuit and a ground fault, based on monitoring the current through the support to the ground with proper grounding of the support and local fixation of damage, characterized in that the current through the support to the ground _IZ and the voltage across the support relative to the ground U are simultaneously monitored _C , use the values of current and voltage to analyze the emergency, which is carried out according to a given algorithm, according to the results of the analysis, the signs of damage on the support of two types and form a signal of damage, respectively: for I _З > 0 and U _З ≤U _Ф - a signal about a single-phase earth fault; or at I _З = 0 and U _З.norm <U _З ≤U _Ф - a signal about a single-phase short circuit to the armature of the support and a fault in the ground circuit, where U _З.norm. - the normalized voltage value on the support relative to the ground; U _Ф - phase voltage of the network, using the generated signal of damage, simultaneously localize the fact of damage of a specific type at the support with damage and remote in the dispatch control point, for which the signal about the type of damage is converted into a coded signal containing a sign of the type of damage and registration number of the support, transmit it over the communication line or over the air to a distance where the signal is decoded and damage is fixed; and in addition, the measured current and voltage are simultaneously used to calculate the actual grounding resistance of the support, the result is compared with the normalized value of the grounding resistance, and by the presence of an excess of the actual grounding resistance over the normalized value, they also generate a signal about the excess of grounding resistance and produce local and remote fixing the fact of a grounding failure of the support.