CN107632235B - Device and method for identifying fault line of low-resistance grounding system - Google Patents
Device and method for identifying fault line of low-resistance grounding system Download PDFInfo
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- CN107632235B CN107632235B CN201710601071.0A CN201710601071A CN107632235B CN 107632235 B CN107632235 B CN 107632235B CN 201710601071 A CN201710601071 A CN 201710601071A CN 107632235 B CN107632235 B CN 107632235B
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Abstract
The invention discloses a device and a method for identifying a fault line of a small-resistance grounding system, which belong to the field of power systems and comprise an analog quantity acquisition and conversion circuit, a central processing unit and an output control circuit, wherein the analog quantity acquisition circuit comprises an ADC1 module for acquiring system zero-sequence voltage and an ADC2 module for acquiring line zero-sequence current, the central processing unit is used for receiving data of the analog quantity acquisition and conversion circuit and carrying out data calculation, and controlling the output control circuit according to a calculation result, and the output control circuit comprises a trip outlet and an alarm outlet; the identification method comprises the steps that a, an analog quantity acquisition conversion circuit acquires system zero-sequence voltage and line zero-sequence current; b, the central processing unit receives the data of the analog quantity acquisition and conversion circuit and performs data calculation; and c, identifying the fault line according to the calculation result, and outputting a control circuit to control the fault line to trip and alarm. The invention solves the problem of identifying the high-resistance grounding fault line and accurately judges the fault line.
Description
Technical Field
The invention relates to the field of power systems, in particular to a fault line identification device and a fault line identification method.
Background
The neutral point is grounded through a small resistor, so that the overvoltage of a non-fault phase during single-phase grounding fault can be effectively reduced, and arc light overvoltage and some resonance overvoltage are eliminated; the zero sequence current protection can be adopted to quickly select a fault line, and a fault point is cut off by instant tripping, so that the single-phase earth fault is prevented from developing into an interphase fault; the duration of the single-phase earth fault is controlled within a few seconds, so that the electric shock probability of personnel can be obviously reduced, and the personal safety is improved. Therefore, in the major urban areas with developed economy in China, the neutral point is popularized and applied in a grounding mode of a small resistor.
According to the related regulations of the current power industry, the criterion of zero-sequence current protection in a small-resistance grounding system is a zero-sequence current amplitude, the starting fixed value of the amplitude must avoid the capacitance current of the line, and theoretical analysis and practice prove that the method cannot identify high-resistance grounding. Taking the power grids of 10kV and 20kV in Guangzhou as an example, the zero-sequence current setting value is 60A, and the transition resistance which can be endured by the 10kV and 20kV systems is about 40 Ω and 80 Ω respectively by calculating according to the sensitivity of 2. And the human body resistance is about 1500 omega, if a 10kV system generates human body electric shock, the fault current is about 3.8A and is far less than a protection constant value, the protection is not started, but the current is far more than the safe current which can be born by a human body. Therefore, the neutral point is grounded through a small resistor, and the problems that high-resistance grounding faults such as disconnection grounding and the like are difficult to identify and the protection sensitivity is insufficient are faced, and the application effect of the small resistor is greatly influenced.
The invention patent application with the application number of 201611066976.4 is published by the national intellectual property office of 5/10/2017, the Fourier is adopted to calculate the angle value between the zero-sequence voltage and the zero-sequence current, the method is obviously superior to the current amplitude method, but the application range is insufficient: the method is only suitable for stable ground fault analysis, and in the case of arc grounding or intermittent ground fault, the frequency spectrum range of zero sequence voltage and zero sequence current is wide, and the method has the characteristic of frequency spectrum continuity and is not suitable for Fourier calculation, so the method has obvious limitation.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a device and a method for identifying a fault line of a low-resistance grounding system, which solve the problem of identifying a high-resistance grounding fault line and accurately judge the fault line.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
the utility model provides an identification means of fault line of small resistance grounding system, includes analog acquisition converting circuit, central processing unit and output control circuit, analog acquisition circuit is including the ADC1 module that is used for the zero sequence voltage of collection system and the ADC2 module that is used for gathering circuit zero sequence current, central processing unit is used for receiving analog acquisition converting circuit's data and carries out data calculation, controls output control circuit according to the calculated result, and output control circuit contains trip outlet and warning outlet.
The technical scheme of the identification method of the invention is further improved as follows: the method comprises the following steps:
a, an analog quantity acquisition conversion circuit acquires system zero-sequence voltage and line zero-sequence current;
b, the central processing unit receives the data of the analog quantity acquisition and conversion circuit and performs data calculation;
and c, identifying the fault line according to the calculation result, and outputting a control circuit to control the fault line to trip and alarm.
The technical scheme of the identification method of the invention is further improved as follows: and b, sequentially caching the sampled data of the zero sequence current signals in the step a in a data cache region.
The technical scheme of the identification method of the invention is further improved as follows: the calculation method of the data calculation in the step b comprises the following steps:
the active component P and the non-active component Q are calculated according to equations (1) and (2),
wherein u ist-the zero-sequence voltage of the system,
it-zero sequence current of a certain outgoing line,
t is the period of the system voltage;
after each or several power frequency cycles, the result of the multiplication and then the accumulation is respectively Pi、QiCalculating a fault characteristic value K by the formula (3)i，
Finally, judging whether the line has faults or not according to the fault characteristic value KiIf the value is larger than the starting fixed value, the fault is judged to be fault, and the fault characteristic value KiAnd judging that no fault exists when the starting constant value is less than the starting constant value.
The technical scheme of the identification method of the invention is further improved as follows: the starting fixed value can be set according to line parameters, and the value is generally 1.5-2.5.
Due to the adoption of the technical scheme, the invention has the technical progress that:
the core problem solved by the invention is the identification of the high-resistance grounding fault line, the ratio of zero-sequence active component to non-active component is used as the fault characteristic value Ki of the line as the criterion, and the method has three natural advantages: firstly, the fault characteristic value is slightly influenced by the grounding transition resistance; secondly, when the small resistor is put into use, the zero sequence active component of the fault line is far larger than the zero sequence reactive component, and the zero sequence active component of the non-fault line is far smaller than the zero sequence reactive component, so that the two components are obviously different; thirdly, the algorithm of the invention adopts real-time integration, signal caching and forward phase-shifting integration algorithm, and is little affected by fault waveform distortion, so the algorithm of the invention has high sensitivity and high accuracy.
Drawings
Fig. 1 is a schematic block diagram of the apparatus of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following examples:
as shown in fig. 1, an apparatus for identifying a fault line of a low-resistance grounding system includes an analog quantity acquisition and conversion circuit, a central processing unit and an output control circuit, where the analog quantity acquisition circuit includes an ADC1 module for acquiring a zero-sequence voltage of the system and an ADC2 module for acquiring a zero-sequence current of the line, the central processing unit is configured to receive data of the analog quantity acquisition and conversion circuit and perform data calculation, and control the output control circuit according to a calculation result, and the output control circuit includes a trip outlet and an alarm outlet, and is connected to OUT1 and OUT2 in fig. 1 respectively.
Because the zero sequence voltage and the zero sequence current are often seriously distorted in the grounding process, and aiming at the capacitive property of a zero sequence loop, the invention adopts a signal cache and a forward phase shift integral algorithm for calculating the non-active component simply, conveniently and in real time: firstly, sampling zero sequence voltage and zero sequence current at the same time; sequentially buffering the sampled data of the zero sequence current signal in a sufficiently large data buffer area; thirdly, the zero sequence voltage signal sampling data is respectively multiplied with the zero sequence current signal data which are simultaneously engraved and the cached 1/4 zero sequence current signal data at the previous moment of the power frequency period, and the products are respectively defined as pij、qijRespectively accumulating the products with the last product; fourthly, after each or a plurality of power frequency periods, the result of the multiplication and the accumulation is respectively Pi、Qi(ii) a Calculating and defining Pi、QiIs a faultCharacteristic value Ki. The specific identification method comprises the following steps:
a, an analog quantity acquisition conversion circuit acquires system zero-sequence voltage and line zero-sequence current;
b, the central processing unit receives the data of the analog quantity acquisition and conversion circuit and performs data calculation;
the data calculation method comprises the following steps:
the active component P and the non-active component Q are calculated according to equations (1) and (2),
wherein u ist-the zero-sequence voltage of the system,
it-zero sequence current of a certain outgoing line,
t is the period of the system voltage;
after each or several power frequency cycles, the accumulated result is Pi、QiCalculating a fault characteristic value K by the formula (3)i，
c, identifying the fault line and the fault characteristic value K according to the calculation resultiIf the value is larger than the starting fixed value, the fault is judged to be fault, and the fault characteristic value KiIf the starting constant value is smaller than the starting constant value, the starting constant value without faults can be set according to line parameters, and the value is generally 1.5-2.5. And finally, the output control circuit controls the tripping and alarming of the fault line.
The core problem solved by the invention is the identification of the high-resistance grounding fault line, the ratio of zero-sequence active component to non-active component is used as the fault characteristic value Ki of the line as the criterion, and the method has three natural advantages: firstly, the fault characteristic value is slightly influenced by the grounding transition resistance; secondly, when the small resistor is put into use, the zero sequence active component of the fault line is far larger than the zero sequence reactive component, and the zero sequence active component of the non-fault line is far smaller than the zero sequence reactive component, so that the two components are obviously different; thirdly, the algorithm of the invention adopts real-time integration, signal caching and forward phase-shifting integration algorithm, and is little affected by fault waveform distortion, so the algorithm of the invention has high sensitivity and high accuracy.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.
Claims (3)
1. A method for identifying a fault line of a low-resistance grounding system is characterized by comprising the following steps: the identification device comprises an analog quantity acquisition conversion circuit, a central processing unit and an output control circuit, wherein the analog quantity acquisition circuit comprises an ADC1 module for acquiring system zero-sequence voltage and an ADC2 module for acquiring line zero-sequence current, the central processing unit is used for receiving data of the analog quantity acquisition conversion circuit and performing data calculation, the output control circuit is controlled according to a calculation result, and the output control circuit comprises a trip outlet and an alarm outlet;
the identification method comprises the following steps:
a, an analog quantity acquisition conversion circuit acquires system zero-sequence voltage and line zero-sequence current;
b, the central processing unit receives the data of the analog quantity acquisition and conversion circuit and performs data calculation;
the data calculation method comprises the following steps:
the active component P and the non-active component Q are calculated according to equations (1) and (2),
wherein u ist-the zero-sequence voltage of the system,
it-zero sequence current of a certain outgoing line,
t is the period of the system voltage;
after each or several power frequency cycles, the result of the multiplication and then the accumulation is respectively Pi、QiCalculating a fault characteristic value K by the formula (3)i，
Finally, judging whether the line has faults or not according to the fault characteristic value KiIf the value is larger than the starting fixed value, the fault is judged to be fault, and the fault characteristic value KiIf the value is less than the starting fixed value, judging that no fault exists;
and c, identifying the fault line according to the calculation result, and outputting a control circuit to control the fault line to trip and alarm.
2. The method for identifying a faulty wire of a low-resistance grounding system according to claim 1, wherein: and b, sequentially caching the sampled data of the zero sequence current signals in the step a in a data cache region.
3. The method for identifying a faulty wire of a low-resistance grounding system according to claim 1, wherein: the starting fixed value can be set according to line parameters, and the value is generally 1.5-2.5.
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