CN112769108A - Zero-sequence current protection dead zone elimination method for neutral point small resistance grounding system of power distribution network - Google Patents

Zero-sequence current protection dead zone elimination method for neutral point small resistance grounding system of power distribution network Download PDF

Info

Publication number
CN112769108A
CN112769108A CN202011645481.3A CN202011645481A CN112769108A CN 112769108 A CN112769108 A CN 112769108A CN 202011645481 A CN202011645481 A CN 202011645481A CN 112769108 A CN112769108 A CN 112769108A
Authority
CN
China
Prior art keywords
current
zero
line
sequence current
grounding
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
CN202011645481.3A
Other languages
Chinese (zh)
Other versions
CN112769108B (en
Inventor
***
刘鹏飞
黄涛
李益群
谢军
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Zhuhai Longguang Power Engineering Co ltd
Zhuhai Feisen Power Technology Co ltd
Original Assignee
Zhuhai Longguang Power Engineering Co ltd
Zhuhai Feisen Power Technology Co ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Zhuhai Longguang Power Engineering Co ltd, Zhuhai Feisen Power Technology Co ltd filed Critical Zhuhai Longguang Power Engineering Co ltd
Priority to CN202011645481.3A priority Critical patent/CN112769108B/en
Publication of CN112769108A publication Critical patent/CN112769108A/en
Application granted granted Critical
Publication of CN112769108B publication Critical patent/CN112769108B/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • 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
    • G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/266—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving switching on a spare supply
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
    • Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
    • Y04S10/52—Outage or fault management, e.g. fault detection or location

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Emergency Protection Circuit Devices (AREA)

Abstract

The invention discloses a method for eliminating a zero-sequence current protection dead zone of a neutral point small-resistance grounding system of a power distribution network, which comprises the following specific steps of: A. a quasi-zero magnetic flux zero-sequence current transformer is adopted to provide neutral points and high-precision zero-sequence current analog quantities of all outgoing lines for a centralized protection device; B. adaptively setting a zero-sequence current protection threshold value and a neutral point current threshold value of an outgoing line; C. after the current of each outgoing line or neutral point exceeds a set threshold, the grounding fault of the line or the bus is judged through a virtual square wave phase comparison criterion, a tripping circuit of a 10kV incoming line switch of the line or the main transformer is started, and the grounding fault is removed through tripping in a setting time limit. The invention judges the grounding fault line based on the phase of the virtual rectangular square wave, can accurately judge the metallic grounding of the line or the bus and the grounding of the high transition resistor, and has enough sensitivity at least when the transition resistor is 5k omega. The method solves the defect that the protection dead zone of the conventional zero-sequence current protection is increased along with the increase of the system capacitance current, and fills the gap of the domestic distribution network small-resistance grounding system.

Description

Zero-sequence current protection dead zone elimination method for neutral point small resistance grounding system of power distribution network
Technical Field
The invention relates to the field of zero sequence current protection of a 10 kV-20 kV power distribution network neutral point through a small resistance grounding system, in particular to a grounding fault initial end (t)1,t2]The maximum instantaneous value of the interval zero-sequence current forms a virtual square wave phase comparison criterion, so that the grounding zero-sequence current protection of the high transition resistance is realized, and the zero-sequence current protection dead zone is eliminated.
Background
In large and medium-sized cities in China, 10-20kV distribution lines all adopt cable lines, system capacitance current can often reach hundreds of amperes and even thousands of amperes, even single-circuit line capacitance current can reach hundreds of amperes, and a low-resistance grounding mode (10 omega resistance is adopted mostly) is correspondingly adopted for a neutral point. And setting according to the maximum unbalanced current of the line when the fault of the external ground of the hidden area occurs. A medium-loop supply mode often appears in operation, the capacitance current of each loop can be changed at any time, so that the maximum unbalanced current is not a definite value, usually 40-60A is taken, the setting value of some 20kV systems is as high as 150A, and when the transition resistance is more than 65-134 omega, the zero-sequence current is less than a starting set value, so that a protection dead zone is formed. Because the neutral point equipment is stably selected according to short-time dynamic heat, the protection and the refusal inevitably form great threats to power equipment and personal safety. The zero sequence current protection research subject suitable for high-transition resistance grounding and elimination of the protection dead zone continues continuously, but only stays in a simulation test stage, and an ideal solution is not provided so far.
The publication number CN105140897B discloses a protection method suitable for a single-phase earth fault of a small-resistance earth system, which adopts zero-sequence voltage as a braking quantity, adaptively adjusts a setting value of zero-sequence current, and can give consideration to both the sensitivity of metallic earth and the reliability of high-resistance earth protection. The patent gives a minimum action setting value Iset.min3A-10A; zero sequence current setting value I of the illustrated casesetExample 5ATaking the corresponding bus zero sequence setting voltage U0The action process of the criterion is described as 1.3 × 5A × 10 Ω ═ 65V. The criterion has the following problems: 1) the neutral point of a small-resistance grounding system mostly uses a 10 omega resistor, the maximum grounding current is usually about 700A, the maximum grounding current is regarded as the upper measurement limit of a zero-sequence current transformer, the lowest current transformer with the rated current of 600A is selected, and the minimum current setting value I in the illustrated case isset.minWhen the zero-sequence current transformer is 5A, the zero-sequence current transformer accounts for 0.83% of a rated value, no matter the zero-sequence current transformer is a measurement stage or a protection stage, the boundary of the minimum accurate working current can not be reached, the unbalanced current in normal operation can not be detected, and the measurement error is in an uncontrollable range. 2) Zero-sequence voltage is an indirect representation of zero-sequence current, U0＝I0Z0Here Z0Is the equivalent zero-sequence impedance at the back of the bus, is a fixed value and has no relation with the transition resistance, and the patent gives the inflection point voltage Ures.gThe voltage measuring range of the residual voltage defined by DL/T726 is far beyond 1.3 × 5 × 10 which is 65V and occupies 1.12% of the rated value, and the measuring error is within an uncontrollable range. Therefore, the current-voltage analog cannot be linearly converted, and the subsequent operation logic will not be referred to. 3) When the high transition resistance forms micro grounding current, zero-crossing arc quenching phenomenon exists, so that the standard sinusoidal current waveform obtained by simulation or artificial field test with fixed transition resistance can not conform to the actual grounding current with high transition resistance and the action behavior of the protection device. In addition, the voltage quantity is increased according to the criterion, and the criterion is influenced by the disconnection of a voltage circuit, so that the calculation is complex, the reliability is reduced, and a lot of troubles are brought to the operation and maintenance. Standing at the user's position to change the thinking, this patent cannot be implemented. 4) Any digital simulation model does not count the influence of the nonlinear transmission process of the electric quantity on the operation result, and the simulation result cannot form a practical product. The patent is a paper of national science fund funding project (51477184) and science and technology project (GZHKJ00000020) of the national south China Power grid Limited liability company, the case sets the starting current to be 4A, the zero sequence voltage of the braking inflection point is 133V (accounting for 2.3 percent of the rated value), the measurement error of the residual voltage is not taken into consideration, and the correct action of the transition resistance of 900 ohms can be realized on a simulation modelNo case of on-site run-on evidence is seen.
The publication number CN108776284B discloses a single-phase ground fault protection method for a low-resistance grounding system based on zero-sequence current comparison, which compares all current amplitudes or phases, wherein the amplitude of a certain outgoing line is more than 10 times larger than the amplitudes of other outgoing lines, and determines that the certain outgoing line is a ground fault line, and if the certain outgoing line does not exist, determines that the bus is a ground fault. To obtain high transition resistance zero sequence current protection sensitivity, amplitude starting current IsetThe zero-sequence current protection circuit is arranged between 1A and 2A, and the simulation can realize the correct zero-sequence current protection action with the transition resistance of 1000 omega. The patent is introduced in the national science foundation funding project (51477184) and the scientific and technological top of Guangdong electric network finite responsibility company (031300KK52160023), and phase comparison criteria are added in the project, namely a comprehensive protection method. In fact: 1) if the ratio of the long line to the short line is greater than 10, it is impossible to distinguish whether the line is grounded or the bus is grounded: 2) the specific difference and the angular difference are 2 equivalent elements for calibrating the measurement precision, the difference between the specific difference and the angular difference is a coefficient, the angular difference (or the specific difference) is definitely not qualified as long as the specific difference (or the angular difference) is unqualified, and when the amplitude of the grounding current and the amplitude of the capacitor current of a sound line are out of the minimum accurate working current of the zero sequence current transformer, the real data of the angular difference cannot be determined. The ratio difference is just the name interchanging, and has no essential difference, and the defects are the same as those described in the patent.
Publication number CN108899879B discloses a grounding protection method for a low-resistance grounding system based on zero-sequence current projection coefficients. The principle is the same as the active component method of the ground line selection criterion, and is completely the same as the amplitude comparison and phase comparison principle of the second patent, and the absolute value comparison of the triangular hook, strand and string of the voltage (or current) is converted into a trigonometric function for comparison, only the permutation of the operation sign is needed, and the content is not changed. The criterion describes: by taking the resistance current of the neutral point as a reference, the angular difference of approximately 90 degrees exists between the capacitance current of the sound circuit and the resistance current of the neutral point resistance, and the projection coefficient (namely cosine value) is close to zero; when the high resistance is grounded, the zero sequence current of the fault line is basically an active component, the maximum included angle between the zero sequence current and the neutral point resistance current is very small, the projection coefficient (namely the secant value) is slightly larger than 1, and the ground fault line is judged;and when the projection coefficient is not larger than 1 (namely, secant value), judging the bus grounding fault. Simulation of example parameters: direct trip fault acquisition of system sound line capacitance current 45AsetThe neutral point ground resistance is 10 Ω, 40A. Starting value I based on high transition resistance criterionSThe measured value of the capacitor current of the healthy line is 0.00005A-0.215A, which is not within the accurate working current range of the zero sequence current transformer. The method is completely consistent with research articles of science and technology projects (521532170037) of national power grid Hubei Power saving Limited company and research articles of national science fund funding projects (51477184), has special marks, and is more ideal when the protection threshold starting value is set within the range of 1-2A. The drawbacks are as described in the first patent mentioned above.
The national science foundation fundament project (51477184) also provides high-sensitivity step-type zero-sequence overcurrent protection of a small-resistance grounding system, and the original zero-sequence current and grounding transformer protection of the circuit are cut into multiple sections to form step-type protection with multiple fixed values and multiple time limits. Starting from the reduction of the starting current, the zero sequence current of the line is set to be 3A (which is 0.5% of the rated current of the zero sequence current transformer), the principle of which is completely the same as the three patents, and the zero sequence current amplitude comparison criterion is still adopted: and if the ratio of the zero sequence current of the outgoing line to the neutral point current is greater than 1, the outgoing line is a grounding fault line, and if the ratio of the zero sequence current of the outgoing line to the neutral point current is not greater than 1, the outgoing line is grounded through a bus. The starting current of the lowest section is reduced, the action time limit is increased, and the uninterrupted matching of the upper and lower stages of the line protection and the grounding transformer protection is realized. The current setting value is 3A, the simulation test can meet the requirement of correct action when the transition resistance is 1500 omega and the field test grounding current is 5.99A (equivalent to the transition resistance 954 omega), and the results do not exceed the three patents. The setting value is 3A, and only accounts for 0.5 percent of the rated current of the current transformer, the measurement error is uncontrollable, and the inherent defects are the same as the content of the first patent and cannot be overcome.
The sensitivity of the protection device to high-transition resistance grounding is improved, the starting current is only one way, but the starting current is limited by the technical performance of the zero-sequence current transformer, the zero-sequence current transformer cannot be too low and only lingers above 10A, and all research results and patents do not put the minimum accurate working current of the zero-sequence current transformer at the head and only stay in a digital simulation stage which cannot reflect the nonlinear characteristics of the current transformer.
The research and development group actually measures the unbalanced voltage of 20 neutral points of the city area through a small-resistance grounding system 10kV bus, the range is 0.5V-1.5V (0.5% -1.5% of a rated value), the normal zero-sequence current of the neutral points is calculated to be 2.9A-8.7A, and reference data is provided for setting the current threshold of the neutral points.
The grounding line selection prototype of the research group is in spot test operation in a ring network in DY region, and is matched with another patent of the applicant: a wide-linearity high-precision open-close structure zero-sequence current transformer (patent number 2020112228419) successfully acquires 0.2A instantaneous ground fault and accumulates experience for a system which is grounded at a neutral point through a small resistor.
Disclosure of Invention
The invention aims to provide a method for eliminating a zero-sequence current protection dead zone of a power distribution network neutral point small-resistance grounding system, which overcomes the major defect that the existing zero-sequence current protection of a neutral point through the small-resistance grounding system has the dead zone and provides a method based on a grounding fault initial end (t)1-t2]The maximum instantaneous value of the interval zero-sequence current forms a virtual square wave phase comparison criterion, so that the high-transition resistance grounding zero-sequence current protection is realized, and a zero-sequence current protection dead zone is eliminated.
In order to solve the technical problems, the invention adopts the following technical scheme:
the invention provides a method for eliminating a zero-sequence current protection dead zone of a neutral point small-resistance grounding system of a power distribution network, which is characterized by comprising the following specific steps of:
A. a quasi-zero magnetic flux zero-sequence current transformer is adopted to provide neutral points and high-precision zero-sequence current analog quantities of all outgoing lines for a centralized protection device;
B. self-adaptive setting outgoing line zero sequence current protection threshold IL.setAnd neutral point current increment threshold delta IB.set；
C. After the current of each outgoing line or neutral point exceeds a set threshold, the grounding fault of the line or the bus is judged through a virtual square wave phase comparison criterion, a tripping circuit of a 10kV incoming line switch of the line or the main transformer is started, and the grounding fault is removed through tripping in a setting time limit.
Preferably, the zero sequence current protection threshold I of the outgoing line in the step BL.set＝KkIL.bp.max(ii) a In the formula: i isL.bp.max-measuring a line maximum unbalance current peak value; kk-a reliability factor; neutral point current increment threshold delta IB.set＝1A。
Preferably, the working current range of the quasi-zero flux zero sequence current transformer in the step A is 20 mA-1000A.
Preferably, the determination content in step C is: let t1To the time of occurrence of a ground fault, t2For the effective current cut-off time, the waveform width Δ t is t2-t11.5ms, and interval [ t [ ]1，t2]The maximum current value and a time axis form a virtual square wave, the circuit is judged as a grounding fault circuit on one side of the time axis, a circuit switch is tripped out after the time delay of tII (tI + delta t), and the tI is the original time-limited quick-break time; all virtual square waves are arranged on one side of a time axis, a bus grounding fault is judged, the main transformer incoming line switch is tripped through the original tII + delta t time delay, and meanwhile, the backup protection of the line switch is realized.
Preferably, the interval [ t ]I，t2]The maximum value of the current is the grounding initial point t1And (3) superposition of the zero sequence current at the moment and the instantaneous amplitude of the original unbalanced current.
The invention has the beneficial effects that: the phase based on the virtual square wave is used for judging the grounding fault line, the current threshold value is 40-60 times smaller than the existing setting value, the line or bus metal grounding and the high transition resistance grounding can be accurately judged, and at least when the transition resistance is 5k omega, enough sensitivity is provided. The method solves the defect that the protection dead zone of the conventional zero-sequence current protection is increased along with the increase of the system capacitance current, and fills the gap of the domestic distribution network small-resistance grounding system.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a single-phase grounding equivalent circuit diagram of a system in which a neutral point is grounded through a small resistor;
FIG. 2 is a flow chart of a starting-end effective waveform current direction-based criterion provided by the present invention;
fig. 3 is a recording diagram of the ring network point grounding fault provided by the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
The specific implementation process of the invention is as follows:
A. the zero-sequence current transformer of the quasi-zero magnetic flux line provides current analog quantity for the centralized protection device;
B. adaptively setting a line current starting threshold according to the maximum unbalanced current of the hidden line;
IL.set＝KkIL.bp.max
in the formula: i isL.bp.max-measuring a line maximum unbalance current peak value; kk-a reliability factor; the length and asymmetry of each outgoing line are different, the magnitude and direction of the unbalanced current in operation are different, the unbalanced voltage of the system and the randomness of the mutual supply mode are added, and the unbalanced current I in normal operationL.bpThe superposition result of the grounding current and the unbalanced current always develops in the increasing direction once the outgoing line has a ground fault, the threshold is obtained by self-adaption to simplify and be practical, and IL.set＝KkIbp.maxReliability coefficient, take Kk2, according to the longest lengthThe self capacitance current of the outgoing line is estimated by 30A, the maximum unbalance current does not exceed 0.45A, and I can be selectedL.set＝0.9A；
The neutral point current is the sum of the phase quantity of a system phase-to-earth asymmetric capacitor, a three-phase magnetic circuit of a system, an asymmetric circuit and the unbalanced current of the system, the unbalanced current in normal operation is about between 2.9A and 8.7A and is in a relatively stable state, and the unbalanced current is insensitive to the change of the unbalanced current of each line, so that the neutral point adopts the instantaneous current increment as a threshold value, and the delta I isB.set1A, ensuring enough sensitivity when a high transition resistor is grounded and not needing to be matched with a line current threshold;
C. when the current of the line or the neutral point exceeds a starting threshold value, protection is started, and the initial end [ t ] of the line grounded is taken1，t2]Interval current maximum value, waveform width Δ t ═ t (t)2-t1) The virtual square wave is formed by 1.5ms and a time axis, so that enough current transient component leading criteria can be ensured, accurate grounding information is further amplified, and reliability and anti-interference strength can be enhanced for a healthy line with small capacitance current; the only virtual square wave on one side of the time axis is judged as a grounding fault line through tII(tITime, + Δ t, (t)I-original time-limited quick-off time) time-delayed tripping of the line switch; all the virtual square waves are arranged on one side of the time axis, and the bus grounding fault is judged according to the original tIIAnd + delta t is delayed, the main transformer incoming line switch is tripped, and meanwhile, the backup protection of the line switch is realized.
Further, the working current range of the quasi-zero magnetic flux zero sequence current transformer in the step A is 20 mA-1000A; the angular difference is less than 1 deg. and the specific difference is less than 0.5%. The unbalanced current and the maximum grounding current of the line of the small-resistance grounding system can be accurately measured.
Further, the interval [ t ]I，t2]The maximum value of the current is the grounding initial point t1The superposition of instantaneous amplitude of zero-sequence current and original unbalanced current at moment, especially the high-resistance earth fault current is very small, and the auxiliary amplitude is close to the self unbalanced current amplitude, so that the interval [ t ] can be increased by times1，t2]Maximum current value, ensuring that the virtual square wave is determined by leading the transient componentThe accurate grounding information is further amplified, and meanwhile, the reliability and the anti-interference strength can be enhanced, so that the method is very favorable for a healthy line with small capacitance current.
Example 2
FIG. 1 is a single-phase grounding equivalent circuit of a neutral point through a small-resistance grounding system; in the figure: r is1Transition resistance, ifFault line ground current, C1～Cn-three-phase equivalent capacitance of healthy circuit of transformer substation iC.1～iC.n-robust line capacitance current, r2Neutral low resistance. The L-grounding is changed into an equivalent inductor, an M-bus and a G-ground. Equation (1) always holds regardless of whether it is instantaneously grounded, intermittent arc grounded, or permanently grounded;
if(t)＝ir(t)+iC(t)……(1)
in the formula if(t) -ground current of the fault line; i.e. ir(t) -the current of the neutral point resistance,
Figure BDA0002881065910000081
iC(t) -capacitive current of healthy line of the system, apparently
Figure BDA0002881065910000082
According to the law of changing paths, at the moment of grounding, the voltages at two ends of the system phase-ground capacitor cannot be suddenly changed, and t is set1Is the moment of earthing, i.e. uMG(t1)＝u0(t1) =0, unbalance current of line itself at t1The time is short-circuited and the discharge is carried out to the ground; while the neutral branch (inductor L + resistive branch r)2) Current cannot change abruptly ir(t1) Grounding occurs at t ═ 01Time of day, formula (1) is rewritten into formula (3)
Figure BDA0002881065910000083
Equation (3) shows that the fault line is at ground t1Time of dayThe current of the transformer is equal to the capacitance current of a system sound line, and the direction of the current of the system sound line is opposite to that of the current of each line;
the ground current of the faulty line depends only on the size of the transition resistance. Get r1When the current is 5k omega, the current I is obtainedfAnd 1.15A means that the minimum accurate working current effective value of the zero sequence current transformer of the fault line must be less than 1.15A. The current is superposed with the minimum unbalanced current of the neutral point in operation to calculate the minimum zero sequence voltage of the bus side
Figure BDA0002881065910000084
KkReliability factor, take Kk1.2. The capacitance current of the low-resistance grounding system is usually over 100A, the length of the outgoing line is long or short, if the average estimation is carried out according to 10 outgoing lines, the capacitance current of a sound line is about 10A, according to U0.minThe capacitive current of the healthy line was calculated to be about 60 mA. Therefore, the margin when the minimum accurate working current of the zero-sequence current transformer is 20mA is considered to be enough to adapt to the zero-sequence current protection of the low-resistance grounding system.
Example 2
Fig. 2 shows the action logic of the criterion. Because the minimum accurate working current of the quasi-zero magnetic flux is extremely low, the maximum unbalanced current in all outgoing lines can be accurately measured, the protection starting value is set in a self-adaptive mode, and the initial end [ t ] of the line grounding is taken1，t2]The maximum value of interval current and the time axis form a virtual square wave, and the only one on one side of the time axis is judged as a grounding fault line through tII(tITime, + Δ t, (t)I-original time-limited quick-off time) time-delayed tripping of the line switch; all initial end waveforms are on one side of a time axis, and bus grounding faults are judged according to original tIIAnd + delta t is delayed, the main transformer incoming line switch is tripped, and meanwhile, the backup protection of the line switch is realized.
Example 3
Referring to fig. 3, a grounding fault oscillogram of a branch circuit of a grounding line selection prototype of the zero-flux zero-sequence current transformer at a DY looped network point is extracted, the grounding fault duration is 45ms, the grounding moment is near a voltage peak value, and the current is effective by considering the error of an original point coordinate during small currentValue approximation
Figure BDA0002881065910000091
Calculating the transition resistance
Figure BDA0002881065910000092
The quasi-zero flux current transformer is proved to be successful in field operation.
In the method, each circuit has unbalanced current, the unbalanced current output by the cable-through type zero-sequence current transformer has zero-sequence property, and the grounding moment u is instantaneousMG(t1)＝u0(t1) 0, the unbalanced current of the line itself is at tIThe time is short-circuited and the discharge is carried out to the ground; and particularly, the high-resistance grounding fault current is extremely small, and the boosting amplitude value is possibly close to the peak value of the self unbalanced current, so that the method is extremely favorable for the direction of the virtual square wave.
The method is matched with a specially-made quasi-zero magnetic flux zero-sequence current transformer, and all grounding current characteristics of a small-resistance grounding system are covered by using high-precision and wide-linear technical indexes, so that the high-transition-resistance grounding zero-sequence current protection of at least 5k omega or below can be realized.
The error special check meter for testing the quasi-zero flux zero sequence current transformer to measure the micro current has the measurement precision of one hundred thousand. By taking a noninductive standard resistor as a reference, 20mA on the primary side passes through a current transformer, secondary output + I/U conversion enters analog quantity of A/D, the angular difference is 27.7', the specific difference is 0.17%, and the interference of an hour hand effect on a distribution network non-effective grounding system can be thoroughly eliminated. The quasi-zero magnetic flux zero sequence current transformer adopts a graded amplification circuit, and the micro current adopts a high amplification factor operational amplifier circuit which is matched with an A/D chip.
The quasi-zero flux zero-sequence current transformer in the present invention refers to a transformer with a primary current having a small measurement error in the range of 20 mA-1000A, but is much more accurate than a common transformer, and approximately considers that there is no error.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims (5)

1. The method for eliminating the zero sequence current protection dead zone of the neutral point small resistance grounding system of the power distribution network is characterized by comprising the following specific steps of:
A. a quasi-zero magnetic flux zero-sequence current transformer is adopted to provide neutral points and high-precision zero-sequence current analog quantities of all outgoing lines for a centralized protection device;
B. self-adaptive setting outgoing line zero sequence current protection threshold IL.setAnd neutral point current threshold Δ IB.set；
C. After the current of each outgoing line or neutral point exceeds a set threshold, the grounding fault of the line or the bus is judged through a virtual square wave phase comparison criterion, a tripping circuit of a 10kV incoming line switch of the line or the main transformer is started, and the grounding fault is removed through tripping in a setting time limit.
2. The method for eliminating zero sequence current protection dead zone of the neutral point small resistance grounding system of the power distribution network according to claim 1, wherein the zero sequence current protection threshold I of the outgoing line in the step B isL.set＝KkIL.bp.max(ii) a In the formula: i isL.bp.max-measuring a line maximum unbalance current peak value; kk-a reliability factor; neutral point current increment threshold delta IB.set＝1A。
3. The method for eliminating the zero sequence current protection dead zone of the neutral point small resistance grounding system of the power distribution network according to claim 1, wherein the working current range of the quasi-zero flux zero sequence current transformer in the step A is 20 mA-1000A.
4. The method for eliminating the zero sequence current protection dead zone of the distribution network neutral point small resistance grounding system according to claim 1, wherein the criterion content in the step C is as follows: let t1To the time of occurrence of a ground fault, t2For the effective current cut-off time, the waveform width Δ t is taken as t2-t11.5ms, and interval [ t [ ]1，t2]The maximum current value and the time axis form a virtual rectangular square wave, and the only one on one side of the time axis is judged as a grounding fault line through tII(tI+ Δ t) time delay tripping off the line switch, tIThe original time-limited quick-break time is set; all the virtual rectangular square waves are arranged on one side of the time axis, and the bus grounding fault is judged according to the original tIIAnd + delta t is delayed, the main transformer incoming line switch is tripped, and meanwhile, the backup protection of the line switch is realized.
5. The method for eliminating zero sequence current protection dead zone of neutral point low resistance grounding system of power distribution network according to claim 4, wherein the interval [ t ] is1，t2]The maximum value of the current is the grounding initial point t1And (3) superposition of the zero sequence current at the moment and the instantaneous amplitude of the original unbalanced current.
CN202011645481.3A 2020-12-31 2020-12-31 Zero-sequence current protection dead zone elimination method for neutral point small resistance grounding system of power distribution network Active CN112769108B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202011645481.3A CN112769108B (en) 2020-12-31 2020-12-31 Zero-sequence current protection dead zone elimination method for neutral point small resistance grounding system of power distribution network

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202011645481.3A CN112769108B (en) 2020-12-31 2020-12-31 Zero-sequence current protection dead zone elimination method for neutral point small resistance grounding system of power distribution network

Publications (2)

Publication Number Publication Date
CN112769108A true CN112769108A (en) 2021-05-07
CN112769108B CN112769108B (en) 2023-04-18

Family

ID=75698797

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202011645481.3A Active CN112769108B (en) 2020-12-31 2020-12-31 Zero-sequence current protection dead zone elimination method for neutral point small resistance grounding system of power distribution network

Country Status (1)

Country Link
CN (1) CN112769108B (en)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102608483A (en) * 2012-02-22 2012-07-25 北京航空航天大学 Direction diagnosing system of grounded fault of small current grounded distribution system
CN106199341A (en) * 2016-08-31 2016-12-07 山东电安电气有限公司 Faulty line recognition methods under a kind of single-phase fault ground connection operating mode and device
CN111474494A (en) * 2020-03-20 2020-07-31 南京南瑞继保工程技术有限公司 High-resistance grounding fault detection method and device of small-resistance grounding system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102608483A (en) * 2012-02-22 2012-07-25 北京航空航天大学 Direction diagnosing system of grounded fault of small current grounded distribution system
CN106199341A (en) * 2016-08-31 2016-12-07 山东电安电气有限公司 Faulty line recognition methods under a kind of single-phase fault ground connection operating mode and device
CN111474494A (en) * 2020-03-20 2020-07-31 南京南瑞继保工程技术有限公司 High-resistance grounding fault detection method and device of small-resistance grounding system

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
郑沛光: "基于零序电流比较的小电阻接地***接地故障保护", 《理论算法》 *

Also Published As

Publication number Publication date
CN112769108B (en) 2023-04-18

Similar Documents

Publication Publication Date Title
Nam et al. A modeling method of a high impedance fault in a distribution system using two series time-varying resistances in EMTP
CN103809070B (en) The direction earth-fault detecting method and device carried out based on three-phase current change
CN103226176B (en) A kind of wire selection method for power distribution network single phase earthing failure
CN103207352B (en) Route selection impedance magnitude characteristic is utilized to realize wire selection method for power distribution network single phase earthing failure
CN110703040B (en) Distribution network single-phase earth fault positioning method based on fault phase and non-fault phase current mutation difference
E. Wilson, Gary A. Zevenbergen, Daniel L. Mah, A. Jay Murphy Calculation of transmission line parameters from synchronized measurements
WO2013007051A1 (en) Residual-variable-based line selection method for small current grounding
WO2011012015A1 (en) Fault line selection method for small current grounding system of distribution network
CN103207354B (en) Maximum line selection coefficient principle based single-phase earth fault line selection method for power distribution network
CN105842583A (en) Distribution network single-phase grounding section positioning method based on fault phase voltage and current abrupt change
CN103018627A (en) Adaptive fault type fault line detection method for non-effectively earthed system
CN107192883B (en) A kind of resonant earthed system high resistance earthing fault transition resistance discrimination method
CN109975653B (en) 10kV distribution line fault location method
CN107329044A (en) A kind of wire selection method for power distribution network single phase earthing failure based on electric arc transient state component
CN109406953A (en) One kind is suitable for containing with bus loop power distribution network earth fault line selection method
Xu et al. Ground distance relaying algorithm for high resistance fault
Suonan et al. A novel single-phase adaptive reclosure scheme for transmission lines with shunt reactors
CN112769108B (en) Zero-sequence current protection dead zone elimination method for neutral point small resistance grounding system of power distribution network
CN110703128B (en) Power distribution network single-phase earth fault phase selection method based on grey correlation analysis
Czapp et al. Verification of safety in low-voltage power systems without nuisance tripping of residual current devices
CN112234579A (en) Injection type stator grounding protection method and system of large hydraulic generator
Zubić et al. Managing post-fault oscillation phenomenon in compensated MV-networks
CN112531659B (en) Protection method for fixed value self-optimization of power distribution zero sequence current
Heavey et al. RMS measuring principles in the application of protective relaying and metering
Soliman et al. On-line estimation of transformer model parameters

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
GR01 Patent grant
GR01 Patent grant