CN113671315B - ITn power supply insulation fault positioning method based on proportional differential principle - Google Patents
ITn power supply insulation fault positioning method based on proportional differential principle Download PDFInfo
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- 238000004364 calculation method Methods 0.000 claims abstract description 15
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/083—Locating faults in cables, transmission lines, or networks according to type of conductors in cables, e.g. underground
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
Abstract
The application discloses a ITn power supply insulation fault positioning method based on a proportional differential principle, which can be used for carrying out section positioning on a ground insulation fault of a ITn power supply system by measuring the response of a single-frequency alternating current injection signal, so that the maintenance workload of the ITn system is reduced, and the occurrence of important load outage accidents is avoided. The positioning method provided by the application adopts a proportional differential principle, is provided with an injection voltage sensor, adopts a synchronous sampling mode, accurately obtains the resistive component of the injection current, obtains the action component and the braking component of the injection signal in the section through measurement and differential calculation of the resistive component of the injection current, and can position the section where the fault occurs through a proportional braking algorithm. The differential algorithm of the application mainly judges faults by means of the polarity of the current, and effectively relieves the pressure of the calculation precision of the resistive current component.
Description
Technical Field
The application relates to the technical field of ITn power supply system on-line monitoring, in particular to a ITn power supply insulation fault positioning method based on a proportional differential principle.
Background
The International Electrotechnical Commission (IEC) classifies low-voltage power supply systems into three types, namely TT, IT and TN, and TN-C power supply systems are used for a long time in China. With the development of economy, TN-S, TN-C-S, TT and IT power supply systems are widely applied in China.
Because the neutral point of the IT power supply system is not grounded or is grounded through high impedance, the fault current is very small when a single-phase grounding fault occurs, and the IT power supply system can continue to operate for a period of time under the fault condition, so that the power supply reliability is high. IT power supply systems are widely applied in many developed countries, but only in hospitals, mining, metallurgy, ports and other fields.
When the neutral point or the neutral line of the IT power supply system has a ground fault, the fault does not generate any electrical quantity for monitoring, and the IT system becomes a TT or TN system at the moment, if the IT system is not processed in time, the risk of power failure of an important load exists. For this reason, IEC does not recommend that IT power supply systems draw neutral lines, which makes IT difficult to access single phase loads.
In order to ensure the power supply reliability of an IT system, a ground insulation monitoring device is generally configured, so that the ground insulation state of the power supply system can be measured in real time, and when a ground fault occurs, a line can be overhauled in time and the fault can be removed. In a large-scale power supply system, in order to reduce maintenance workload, an insulation monitoring device is generally required to have a fault locating function. The IT system provided with the insulation monitoring equipment has the condition of leading out a neutral line, and can be conveniently connected into a single-phase load, namely a ITn power supply system.
The insulation monitoring equipment generally obtains fault characteristic quantity through an active injection mode, common injection modes comprise direct current injection, ping-pong injection, single-frequency injection and double-frequency injection, and the injection position can be selected from a neutral point of a transformer and an opening triangle of a voltage transformer. The direct current injection method carries out fault discrimination and section positioning through the magnitude of direct current, because the zero drift and the temperature drift of a measuring system are in a direct current frequency band, the measuring precision and the sensitivity of the system are limited, the resolution ratio of the large-caliber through direct current transformer is lower, and the direct current injection method cannot carry out positioning calculation when a high-resistance grounding fault occurs. The ping-pong injection method solves the problems of zero drift and temperature drift of a measurement system by switching the polarity of an injected direct current signal, but the performance is not obviously improved because the direct current response is adopted as a criterion; the double-frequency injection method eliminates the influence of the distributed capacitance of the power supply system on measurement, but has a complex equipment structure, cannot be applied to the topological structure of ring network power supply, and is not applicable to the condition of metallic grounding; the traditional single-frequency injection method is simple in principle, is easily influenced by the distributed capacitance of a power supply system, and is not suitable for a topological structure of ring network power supply because the data of a plurality of current sensors are not comprehensively used.
The proportion differential positioning principle provided by the application is based on a single-frequency injection method of a neutral point of a transformer, and the defects are effectively overcome.
Disclosure of Invention
In order to solve the defects in the prior art, the application aims to provide a ITn power supply insulation fault positioning method based on a proportional differential principle, which is used for obtaining insulation fault characteristic quantity through a single-frequency injection mode of a neutral point of a transformer, extracting a resistive component of alternating current injection current and accurately realizing fault section positioning through differential calculation of a plurality of resistive components.
The application adopts the following technical scheme.
A ITn power supply insulation fault locating method based on a proportional differential principle, the method comprising the steps of:
(1) Configuring an injection power supply and a voltage sensor at a neutral point of a low-voltage side of the transformer, injecting a single-frequency alternating current signal, and measuring the voltage amplitude and the phase of the single-frequency alternating current signal;
(2) Dividing ITn power supply system maintenance sections, configuring current sensors at interfaces of the sections, and synchronously collecting the amplitude and the phase of injection current through the current sensors;
(3) Collecting voltage and current vectors collected at the same moment, and then calculating each resistive component;
(4) Calculating an action current and a braking current according to each resistive component;
(5) The section where the fault occurs is identified based on a predetermined differential operation threshold current and differential proportional brake coefficient.
Further, in the step (2),
the number of the current sensors corresponding to each section may be 1 or more.
Further, in the step (3),
the resistive component is calculated as follows:
I r ＝I*cos(θ)
wherein I is the current amplitude of the current sensor, θ is the current phase of the current sensor minus the voltage phase of the voltage sensor, I r Is a resistive component.
Further, in the step (4),
operating current I dz The calculation formula is as follows, for the sum of all the resistive components:
I dz ＝|∑I ri |
wherein I is ri For each resistive component scalar value.
Further, in the step (4),
braking current I zd The calculation formula is as follows:
I zd ＝I 1 +I 2
wherein I is 1 Is the absolute value of the sum of negative resistive components, I 2 Is the absolute value of the sum of the forward resistive components.
Further, in the step (5),
meanwhile, when the following two conditions are satisfied, the fault can be judged to be located in the section:
I dz >I 0
I dz >I zd *K
wherein I is dz For the action current, I zd For braking current, I 0 The differential action threshold current, K is the differential proportional brake coefficient.
Further, in the step (1),
the injection power supply is connected between the neutral point of the low-voltage side of the transformer and the ground, and single-frequency alternating current signals are injected into the ITn power supply system; the voltage transformer is connected in parallel with two ends of the injection power supply and measures the amplitude and the phase of the voltage of the injection power supply.
Further, in the step (2),
the current sensor is a through type current sensor, and is sleeved on the outgoing cable of each power supply loop, and the four power supply lines ABCN simultaneously pass through the current sensor.
Further, in the step (5),
threshold current I of differential motion 0 The value is the minimum accurate calculated current of the current sensor, namely the value is 2-10 times of the resolution of the resistive component of the current sensor.
Further, in the step (5),
the value range of the differential proportion braking coefficient K is 0-1.
The application has the beneficial effects that compared with the prior art:
the positioning algorithm based on the proportional differential principle judges the section where the fault occurs through the vector of the resistive component, when all the transformers take the current flowing into the section as the positive direction, the differential current is the vector sum absolute value of all the resistive components, and the braking current is the absolute value of the vector sum of the positive polarity current minus the vector sum of the negative polarity current. When the fault in the area is detected, the differential current is equal to the braking current, and when the braking coefficient is smaller than 1, the fault in the area can be reliably identified; the differential current is zero when the out-of-zone fault occurs, and the brake current is the passing current, so that the reliability and the error judgment can be ensured not to occur when the out-of-zone fault occurs. The differential algorithm mainly relies on the polarity of a plurality of currents to judge faults, and the accuracy requirement on current sensor acquisition is low.
The differential algorithm has the characteristic of strong adaptability of network topology, and the sensitivity of the differential algorithm cannot be changed no matter in a star network or a ring network. The same differential algorithm can be used for all the section-related current transformers from 1 to a plurality of section-related current transformers, and the reliability of the algorithm is not affected.
Due to the arrangement of the injection voltage sensor, the resistive component of the injection current can be accurately obtained after the synchronous sampling mode is adopted, so that the influence of the distributed capacitance on positioning is eliminated in principle.
The alternating current injection mode can utilize the existing zero sequence residual current transformer, the cost advantage of the transformer is obvious, and the cost performance is higher than that of the direct current transformer. After the dynamic injection frequency is adopted, the whole cycle sampling of the power frequency interference signal and the injection signal can be realized, the frequency spectrum leakage effect of the effective signal can be avoided, and the interference frequency point can be set to the singular point of the window function, so that the suppression ratio of the interference signal is greatly improved, and the precision requirement of the differential algorithm is met.
Drawings
FIG. 1 is a schematic diagram of a ITn power supply system insulation monitoring device deployment;
FIG. 2 is a schematic diagram of a proportional differential action curve for segment positioning;
FIG. 3 is a flow chart of a differential algorithm of the ground fault current of the ITn power supply system;
FIG. 4 is a schematic diagram of differential segment definitions under different topology conditions;
fig. 5 is a schematic diagram of the positioning of a ground fault section of a ITn power supply system.
Detailed Description
The application is further described below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present application, and are not intended to limit the scope of the present application.
As shown in fig. 1, a schematic diagram is deployed for an insulation monitoring device of a ITn power supply system, and in order to implement a positioning function of a differential section of a ground fault, an injection power supply, a voltage sensor and a plurality of current sensors need to be configured in the power supply system.
The injection power supply is connected between the neutral point of the low-voltage side of the transformer and the ground, and injects a single-frequency alternating current detection signal into the ITn power supply system. The voltage transformer is connected in parallel with two ends of the injection power supply and measures the amplitude and the phase of the voltage of the injection power supply. The through type current sensor is sleeved on the outgoing cable of each power supply loop, and the four power supply lines of the ABCN simultaneously pass through the current sensor. The current transformer divides the whole ITn power supply system into a plurality of sections, each current sensor and each voltage sensor are synchronously sampled, the calculated current amplitude and the calculated phase are comparable, and the resistive component of each current sensor relative to the voltage sensor can be obtained through vector calculation.
When the ITn power supply system is normal, as the power supply loop has a distributed capacitance C1 to the ground, and the distributed capacitance may have a three-phase imbalance condition, a main power frequency capacitance current flows through each current sensor, and the current is also called a power frequency residual current. The injection current also loops through the distributed capacitance and flows through the current sensor, but the magnitude of the capacitive injection current is typically much smaller than the power frequency residual current due to the injection frequency being below 50 Hz. When the ITn power supply system has a ground fault, the injected power supply can form a loop through the fault resistor R, and the injected current has one more resistive component. When the fault points are located in different sections, the amplitude and the phase of the resistive component in each current sensor are different, and the section where the fault occurs can be accurately determined through a differential algorithm of the resistive component.
Because the power frequency residual current is far greater than the injection current, under the high-resistance grounding condition, the capacitive component in the injection current is far greater than the resistive component, and great interference exists when the penetration type current sensor is used for synchronously extracting the injection resistive component, so that the calculation accuracy of the resistive current component is a key difficulty in system realization. The differential algorithm of the application mainly judges faults by means of the polarity of the current, and effectively relieves the pressure of the calculation precision of the resistive current component.
Fig. 2 is a schematic diagram of a proportional differential motion curve for segment positioning.
The two-section type proportional differential broken line is located in the first quadrant of the coordinate system, the ordinate of the coordinate system is the action current, and the abscissa is the braking current. I 0 Is a differential threshold current, through I 0 The solid line parallel to the horizontal axis is a part of the proportional differential polyline, and the straight line passing through the origin slope K is another part of the proportional differential polyline.
After obtaining two data of the action current and the braking current of the fault section, finding a corresponding point in a coordinate system, when the point is positioned above the proportional differential broken line, the fault occurs in the section, otherwise, the fault occurs outside the section.
Differential threshold current I 0 The value is generally the smallest accurate calculated current of the current sensor, i.e. the value is 2-10 times the resolution of the resistive component of the current sensor. The range of the differential slope K is 0-1, the situation of misjudgment as the fault in the region is easy to occur when the K value is too small, and the region is easy to occur when the K value is too largeThe internal fault is generally 0.5 when it is not recognized.
As shown in fig. 3, a differential algorithm flow chart of the ITn power supply system ground fault current is shown.
The ITn power supply insulation fault positioning method based on the proportional differential principle comprises the following steps:
(1) Configuring an injection power supply and a voltage sensor at a neutral point of a low-voltage side of the transformer, injecting a single-frequency alternating current signal, and measuring the voltage amplitude and the phase of the single-frequency alternating current signal;
(2) Dividing maintenance sections according to the operation and maintenance requirements of a ITn power supply system, configuring current sensors at interfaces of the sections, and synchronously collecting the amplitude and the phase of injection current through the current sensors;
the number of the current sensors corresponding to each section may be 1 or more.
(3) Collecting voltage and current vectors collected at the same moment, and then calculating each current resistance component;
firstly subtracting the voltage phase of the voltage sensor from the current phase of all relevant current sensors in the section to obtain the relative phase angle of the current sensor, and then solving the projection of the current vector in the direction of the voltage vector, namely the resistive component of the current sensor, wherein the calculation formula is as follows:
I r ＝I*cos(θ)
wherein I is the current amplitude of the current sensor, θ is the current phase of the current sensor minus the voltage phase of the voltage sensor, I r The resistive component calculated is a scalar value.
(4) Obtaining the action current I of the differential algorithm dz And a braking current I zd ；
After the resistive current component is calculated, the sum of the forward current and the reverse current is calculated respectively, and then the braking current and the action current of the differential algorithm are calculated.
Operating current I dz The calculation formula is as follows, for the sum of all the resistive components:
I dz ＝|∑I ri |
wherein, the liquid crystal display device comprises a liquid crystal display device,I ri resistive component scalar values calculated for each current sensor, I dz Is the action current in the differential algorithm.
Dividing all the resistive components into two types of more than zero and less than zero, respectively summing and taking absolute values:
I 1 ＝|∑I ri | (Iri<0)
I 2 ＝|∑I ri | (Iri>0)
wherein I is ri Resistive component scalar values calculated for each current sensor, I 1 Is the absolute value of the sum of negative resistive currents, I 2 Is the absolute value of the sum of the forward resistive currents.
Braking current I zd Is I 1 And I 2 The sum is that:
I zd ＝I 1 +I 2
wherein I is 1 Is the absolute value of the sum of negative resistive currents, I 2 Is the absolute value of the sum of forward resistive currents, I zd Is the braking current in the differential algorithm.
(5) According to a preset differential threshold current I 0 And the braking coefficient K identifies the section where the fault occurred;
the position of the fault section can be achieved through the position relation of the braking current and the action current relative to the proportional braking broken line.
Meanwhile, when the following two conditions are satisfied, the fault can be judged to be located in the section:
I dz >I 0
I dz >I zd *K
wherein I is dz For the action current, I zd For braking current, I 0 The differential action threshold current, K is the differential proportional brake coefficient.
As shown in fig. 4, a schematic diagram of differential segment definition under different topology conditions is shown.
The current sensor divides the power supply loop into a plurality of sections, a closed area formed by combining any plurality of sections can form a positioning section, and the number of the current sensors corresponding to each section can be 1-N. N may take any integer value greater than 1, but when N is too large, the accumulated error of the resistive current may lead to erroneous decisions of the faulty section, typically N is not greater than 10.
The sections of TA1, TA2, TA3 and TA4 divide the ITn power supply loop into a closed area, and the closed area jointly forms a section 1, wherein the section 1 comprises 3 lines L1, L2 and L3, and the closed area belongs to the multi-terminal differential condition. When any line of the section 1 has a ground fault, the differential algorithm can identify the section 1 as a fault. If it is required to distinguish which fault is specific in the three lines, a current transformer can be added to the head ends of the three lines, i.e. the section 1 is subdivided.
The section 2 belongs to a special section, only comprises one current transformer TA2, and the section 2 only comprises a line L4 and belongs to the single-ended differential condition. Line L5 is also a single-ended differential section, which is formed by TA3 and TA 4.
Each current sensor is forward in the sense of the section, the same current sensor may be defined opposite for different sections, e.g. TA2 is defined opposite for sections 1 and 2, and the effect is different in differential calculation of the two sections.
As shown in fig. 5, a schematic diagram of the positioning of the ground fault section of the ITn power supply system is shown.
When the line L4 fails, TA2 flows through the resistive component I1, and since L4 is located in the single-ended differential section, the action current of the section is equal to the brake current according to the differential algorithm, and the failure section can be identified only by ensuring that the resistive component I1 is greater than the resolution of the current sensor under the condition that the brake coefficient is less than 1. TA1 flows through the reverse polarity resistive component with the same amplitude as TA2, and the action current of the section 1 (comprising the lines L1, L2 and L3) is zero, so that the section 1 can be ensured not to be misjudged.
When line L2 fails, I2 is the resistive component of L2 flowing to the point of failure, and because the relative magnitudes of the impedances of L2 and L3 are not determined, there may be a certain amount of resistive component I3 flowing from L3 to the point of failure, but because I3 flows through TA3 and TA4 simultaneously, and the polarities are opposite, I3 does not generate an action current, which is generated entirely by the resistive component of TA 1. After selecting a proper braking coefficient K, the fault section can be reliably judged.
From the analysis of the two cases, it can be found that the magnitude of the action current is not influenced by the ITn power supply topological structure, the differential algorithm mainly depends on the polarity of the current to realize positioning calculation, and proper braking coefficients are selected to ensure the positioning accuracy.
The application has the beneficial effects that compared with the prior art:
the positioning algorithm based on the proportional differential principle judges the section where the fault occurs through the vector of the resistive component. When all the transformers take the flowing section current as the positive direction, the differential current is the vector sum absolute value of all the resistive components, and the braking current is the absolute value of the positive polarity current vector sum minus the negative polarity current vector sum. When the fault in the area is detected, the differential current is equal to the braking current, and when the braking coefficient is smaller than 1, the fault in the area can be reliably identified; the differential current is zero when the out-of-zone fault occurs, and the brake current is the passing current, so that the reliability and the error judgment can be ensured not to occur when the out-of-zone fault occurs. The differential algorithm mainly relies on the polarity of a plurality of currents to judge faults, and the accuracy requirement on current sensor acquisition is low.
The differential algorithm has the characteristic of strong adaptability of network topology, and the sensitivity of the differential algorithm cannot be changed no matter in a star network or a ring network. The same differential algorithm can be used for all the section-related current transformers from 1 to a plurality of section-related current transformers, and the reliability of the algorithm is not affected.
Due to the arrangement of the injection voltage sensor, the resistive component of the injection current can be accurately obtained after the synchronous sampling mode is adopted, so that the influence of the distributed capacitance on positioning is eliminated in principle.
The alternating current injection mode can utilize the existing zero sequence residual current transformer, the cost advantage of the transformer is obvious, and the cost performance is higher than that of the direct current transformer. After the dynamic injection frequency is adopted, the whole cycle sampling of the power frequency interference signal and the injection signal can be realized, the frequency spectrum leakage effect of the effective signal can be avoided, and the interference frequency point can be set to the singular point of the window function, so that the suppression ratio of the interference signal is greatly improved, and the precision requirement of the differential algorithm is met.
While the applicant has described and illustrated the embodiments of the present application in detail with reference to the drawings, it should be understood by those skilled in the art that the above embodiments are only preferred embodiments of the present application, and the detailed description is only for the purpose of helping the reader to better understand the spirit of the present application, and not to limit the scope of the present application, but any improvements or modifications based on the spirit of the present application should fall within the scope of the present application.
Claims (6)
1. ITn power supply insulation fault positioning method based on proportional differential principle is characterized by comprising the following steps:
(1) Configuring an injection power supply and a voltage sensor at a neutral point of a low-voltage side of the transformer, injecting a single-frequency alternating current signal, and measuring the voltage amplitude and the phase of the single-frequency alternating current signal;
(2) Dividing ITn power supply system maintenance sections, configuring current sensors at interfaces of the sections, and synchronously collecting the amplitude and the phase of injection current through the current sensors;
(3) Collecting voltage and current vectors collected at the same moment, and then calculating each resistive component; the resistive component is calculated as follows:
I r =I*cos(θ)
wherein I is the current amplitude of the current sensor, θ is the current phase of the current sensor minus the voltage phase of the voltage sensor, I r Is a resistive component;
(4) Calculating an action current and a braking current according to each resistive component; operating current I dz The calculation formula is as follows, for the sum of all the resistive components:
I dz =||
wherein I is ri Scalar values for each resistive component; braking current I zd The calculation formula is as follows:
I zd = I 1 +I 2
wherein I is 1 Is the absolute value of the sum of negative resistive components, I 2 Is the absolute value of the sum of the forward resistive components;
(5) Identifying a section where a fault occurs according to a preset differential action threshold current and a differential proportion braking coefficient; meanwhile, when the following two conditions are satisfied, the fault can be judged to be located in the section:
I dz >I 0
I dz > I zd *K
wherein I is dz For the action current, I zd For braking current, I 0 The differential action threshold current, K is the differential proportional brake coefficient.
2. The method for locating a ITn power supply insulation fault based on the proportional differential principle as claimed in claim 1, wherein in said step (2),
the number of the current sensors corresponding to each section may be 1 or more.
3. The method for locating a ITn power supply insulation fault based on the proportional differential principle as claimed in claim 1, wherein in said step (1),
the injection power supply is connected between the neutral point of the low-voltage side of the transformer and the ground, and single-frequency alternating current signals are injected into the ITn power supply system; the voltage sensor is connected in parallel with two ends of the injection power supply and measures the amplitude and the phase of the voltage of the injection power supply.
4. The method for locating a ITn power supply insulation fault based on the proportional differential principle as claimed in claim 1, wherein in said step (2),
the current sensor is a through type current sensor, and is sleeved on the outgoing cable of each power supply loop, and the four power supply lines ABCN simultaneously pass through the current sensor.
5. The method for locating a ITn power supply insulation fault based on the proportional differential principle as claimed in claim 1, wherein in said step (5),
threshold current I of differential motion 0 The value is the minimum accurate calculated current of the current sensor, namely the value is 2-10 times of the resolution of the resistive component of the current sensor.
6. The method for locating a ITn power supply insulation fault based on the proportional differential principle as claimed in claim 1, wherein in said step (5),
the value range of the differential proportion braking coefficient K is 0-1.
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