CN116953422A - Fault sensing method, device, equipment and medium for neutral point ungrounded system - Google Patents
Fault sensing method, device, equipment and medium for neutral point ungrounded system Download PDFInfo
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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
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2688—Measuring quality factor or dielectric loss, e.g. loss angle, or power factor
- G01R27/2694—Measuring dielectric loss, e.g. loss angle, loss factor or power factor
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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
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/52—Testing for short-circuits, leakage current or ground faults
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- 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
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Abstract
The embodiment of the application discloses a fault sensing method, a device, equipment and a medium of a neutral point ungrounded system, which are used for injecting different-frequency detection current and determining a capacitance value converted from a power distribution network to a ground distributed capacitance to a PT secondary side and a power distribution network to the ground distributed capacitance value; the current signals of the reference frequency are injected to respectively determine the impedance of the power distribution network when the power distribution network operates normally and when a single-phase grounding occurs in the system; further determining the parallel impedance of the capacitance converted from the distribution network to the ground distributed capacitance to the PT secondary side and the grounding transition resistance; determining a dielectric loss tangent value to the ground under a current signal injected with a reference frequency by combining a distributed capacitance value to the ground of the power distribution network; and determining the fault state of the neutral point ungrounded system according to the loss tangent value of the medium to ground. The dielectric loss factor under the reference frequency is detected in real time through the injection current so as to reflect the size of the insulation resistance of the distribution network to the ground, the ground fault can be detected rapidly, and the sensing reliability and sensitivity can be improved by reducing the frequency of the injection current signal.
Description
Technical Field
The application relates to the technical field of detection of power distribution network ground faults, in particular to a fault sensing method, device, equipment and medium of a neutral point ungrounded system.
Background
The high-resistance grounding faults of the distribution network are usually accompanied by the generation of electric arcs, the faults of the distribution lines falling on the ground and overhead insulated wires are usually high-resistance, the active arc extinction and protection equipment cannot sense the faults of the lines, the electric arcs cannot be restrained for a long time, and the overvoltage and leakage current of fault points can cause personal electric shock, forest fire and interphase faults; therefore, the premise of actively suppressing and isolating the ground fault needs to quickly detect the occurrence of the high-resistance fault. Because the distribution line grounding fault arc has larger randomness, the fault characteristics are different from the air discharge in an ideal medium, the physical characteristics are complex, the cathode voltage drop and the anode voltage drop are asymmetric, the zero crossing of the arc current is extinguished, the re-combustion occurs after the zero crossing, the arc anode and the cathode are alternately changed, and the arc resistance is in nonlinear change. In order to accurately detect the high-resistance ground fault, the generation and extinction characteristics of the ground fault arc need to be analyzed, and a sensing method suitable for the high-resistance arc ground fault is provided.
In the prior art, the sensing of the high-resistance fault mainly adopts two methods of passive sensing and active sensing, wherein the passive sensing is used for judging the transient state and steady-state voltage and current characteristic quantity generated before and after the occurrence of the ground fault; the active sensing senses the ground fault through actively injecting power frequency or high frequency signals, extracting and analyzing the fed-back voltage and current characteristics. However, the high-resistance fault sensing method has large calculated amount in engineering application, has defects of sensing reliability, instantaneity and sensitivity, and can only sense the high-resistance fault below 2kΩ in the current engineering application.
Disclosure of Invention
In view of the foregoing, it is necessary to provide a fault sensing method, device, apparatus and medium for a neutral point ungrounded system.
To achieve the above object, a first aspect of the present application provides a fault sensing method for a neutral point-ungrounded ground system, the method comprising:
determining a capacitance value converted from the distribution network to the secondary side of the electromagnetic voltage transformer PT and a distribution network to the ground distributed capacitance value through the injected detection current of the first frequency and the injected detection current of the second frequency;
determining reference power distribution network impedance under the reference frequency current signal and grounding power distribution network impedance under the reference frequency current signal when the power distribution network normally operates and the system is in single-phase grounding through the injected reference frequency current signal;
determining the parallel impedance of the capacitance converted from the power distribution network to the PT secondary side and the grounding transition resistance according to the capacitance value converted from the grounding distribution capacitance to the PT secondary side, the reference power distribution network impedance and the grounding power distribution network impedance;
determining a dielectric loss tangent value to the ground under a current signal injected with a reference frequency according to the parallel impedance of the capacitance of the power distribution network to the ground distributed capacitance converted to the PT secondary side and the ground transition resistance and the power distribution network to the ground distributed capacitance value;
and determining the fault state of the neutral point ungrounded system according to the comparison relation between the dielectric loss tangent value to the ground and the threshold value.
Further, the determining, by the injected detection current of the first frequency and the injected detection current of the second frequency, the capacitance value of the power distribution network to ground distributed capacitance converted to the PT secondary side and the power distribution network to ground distributed capacitance includes:
according to the detection current of the first frequency and the detection current of the second frequency, respectively determining a first power distribution network impedance of the power distribution network under the detection current of the first frequency and a second power distribution network impedance of the power distribution network under the detection current of the second frequency;
determining a capacitance value converted from the distribution network to the ground distributed capacitance to the PT secondary side according to the first distribution network impedance and the second distribution network impedance;
obtaining PT transformation ratio;
and determining the distribution network ground distributed capacitance value according to the PT transformation ratio and the capacitance value converted from the distribution network ground distributed capacitance to the PT secondary side.
Further, the determining, according to the detected current of the first frequency and the detected current of the second frequency, a first power distribution network impedance of the power distribution network under the detected current of the first frequency and a second power distribution network impedance of the power distribution network under the detected current of the second frequency respectively specifically includes:
at the detection current of the first frequency, according to the formulaDetermining a first power distribution network impedance;
at the detection current of the second frequency, according to the formulaDetermining a second power distribution network impedance;
wherein f 1 A frequency Z outputted by the detection current source under the detection current of the first frequency 21 For the first distribution network impedance,for detecting the voltage across the current source at the detection current of the first frequency, < >>Detecting an output current of the power supply at a detection current of a first frequency; f (f) 2 The frequency Z of the output of the detection current source under the detection current of the second frequency 22 For the second distribution network impedance, < >>For detecting the voltage across the current source at the second frequency of the detection current, ">To detect the output current of the power supply at the second frequency, j is an imaginary unit, R 2 Is PT DC resistance and line resistance R L The resistance value is converted to PT secondary side, L 2 The PT leakage inductance and the line inductance are converted into the inductance value of the PT secondary side, C S2 And converting the distributed capacitance of the power distribution network to the capacitance value of the PT secondary side.
Further, determining, according to the first power distribution network impedance and the second power distribution network impedance, a capacitance value of the power distribution network to ground distributed capacitance converted to a PT secondary side specifically includes:
according to the formulaDetermining an imaginary part of the first distribution network impedance;
according to the formulaDetermining an imaginary part of the second distribution network impedance;
according to the formulaDetermining a capacitance value of the power distribution network to be converted into a PT secondary side by the distributed capacitance to the ground;
Im Z21 for the imaginary part, im, of the impedance of the first distribution network Z22 Is the imaginary part of the second distribution network impedance.
Further, determining the power distribution network ground distributed capacitance value according to the PT transformation ratio and the capacitance value converted from the power distribution network ground distributed capacitance to the PT secondary side specifically includes:
according to the formulaDetermining a distributed capacitance value of the power distribution network to the ground; wherein C is S And the capacitance value is distributed for the power distribution network to the ground, and n is PT transformation ratio.
Further, the determining, by the injected current signal of the reference frequency, a reference power distribution network impedance under the current signal of the reference frequency when the power distribution network operates normally and a ground power distribution network impedance under the current signal of the reference frequency when the system is in single-phase grounding specifically includes;
according to the formulaDetermining a reference power distribution network impedance;
according to the formulaDetermining the impedance of a grounded power distribution network;
wherein,,for reference frequency->Injecting current into the current source, ">Is the voltage at two ends of the current source during normal operation; the impedance parallel is denoted by// and, and (2)>To the voltage across the current source at ground fault, R d2 The transition resistance to ground translates to the resistance on the secondary side of PT.
Further, determining the parallel impedance of the capacitance converted from the distributed capacitance to the PT secondary side of the power distribution network to the ground and the grounding transitional resistance according to the capacitance value converted from the distributed capacitance to the PT secondary side, the reference power distribution network impedance and the grounding power distribution network impedance, wherein the method specifically comprises the following steps of;
according to the formulaDetermining the parallel impedance of a capacitor converted from the distribution network to the PT secondary side and the grounding transition resistance;
wherein Z is f02 To eliminate R 2 、L 2 The capacitance C of the affected distribution network to the ground distributed capacitance to the PT secondary side S2 And a ground transition resistance R d2 Is a parallel impedance of (c).
Further, the capacitance is converted into PT secondary according to the power distribution network to the groundThe parallel impedance of the side capacitor and the grounding transition resistance and the distribution network ground distribution capacitance value determine the dielectric loss tangent value to the ground under the current signal of the injection reference frequency, and the method specifically comprises the following steps: according to the formulaDetermining a dielectric loss tangent to ground at a current signal injected at a reference frequency; wherein omega 0 Is to inject a current source with a frequency f 0 Corresponding angular frequency, delta f0 Is Z f02 Residual angle of impedance angle, I n Is a single-phase grounding transition resistance.
Further, determining a fault state of the neutral point ungrounded system according to the comparison relation between the dielectric loss tangent value to ground and the threshold value, including:
determining a dielectric loss tangent to ground at a current signal at a reference frequency;
if the dielectric loss tangent value to the ground is larger than the threshold value, the neutral point non-grounding system has a grounding fault;
and if the dielectric loss tangent value to the ground is smaller than or equal to the threshold value, the neutral point is not grounded, and the system normally operates.
To achieve the above object, a second aspect of the present application provides a fault sensing apparatus for a neutral point ungrounded system, comprising:
the control unit is used for determining the capacitance value converted from the distribution network to the ground distributed capacitance to the secondary side of the electromagnetic voltage transformer PT and the distribution network to the ground distributed capacitance value through the injected detection current of the first frequency and the injected detection current of the second frequency;
the control unit is also used for determining the reference power distribution network impedance under the current signal of the reference frequency when the power distribution network normally operates and the grounding power distribution network impedance under the current signal of the reference frequency when the system is in single-phase grounding through the injected current signal of the reference frequency;
the control unit is further used for determining the parallel impedance of the capacitance converted from the power distribution network to the PT secondary side and the grounding transition resistance according to the capacitance value converted from the grounding distributed capacitance to the PT secondary side, the reference power distribution network impedance and the grounding power distribution network impedance;
the control unit is further used for determining a dielectric loss tangent value to the ground under a current signal injected with a reference frequency according to the parallel impedance of the capacitance of the power distribution network to the ground distributed capacitance converted to the PT secondary side and the ground transition resistance and the power distribution network to the ground distributed capacitance value;
and the fault judging unit is used for determining the fault state of the neutral point non-grounding system according to the comparison relation between the dielectric loss tangent value to the ground and the threshold value.
To achieve the above object, a third aspect of the present application provides a computer device comprising a memory and a processor, the memory storing a computer program which, when executed by the processor, causes the processor to perform the steps of the method according to the first aspect.
To achieve the above object, a fourth aspect of the present application provides a computer-readable storage medium storing a computer program, which when executed by a processor causes the processor to perform the steps of the method according to the first aspect.
The embodiment of the application has the following beneficial effects:
according to the application, different-frequency detection current is injected into the power distribution network through the electromagnetic voltage transformer between the neutral point and the ground of the power distribution network, so that the capacitance value converted from the power distribution network to the ground distributed capacitance to the secondary side of the electromagnetic voltage transformer PT and the power distribution network to the ground distributed capacitance are determined; detecting dielectric loss tangent value tg delta of power distribution network under current signal of reference frequency in real time through current signal of injected reference frequency f0 ，tgδ f0 Reflects the size of the insulation resistance of the distribution network to the ground, when tg delta f0 And when the set threshold value is exceeded, judging that the power distribution network has a ground fault. The sensing method provided by the application judges the ground fault through the dielectric loss tangent value, and has the advantages of smaller calculated amount, higher sensitivity and more meeting engineering application requirements.
Drawings
In order to more clearly illustrate the embodiments of the application or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Wherein:
FIG. 1 is a flow diagram of a fault sensing method for a neutral ungrounded system in one embodiment;
FIG. 2 is an equivalent zero sequence loop diagram of a fault sensing device of a neutral point ungrounded system in one embodiment;
FIG. 3 is an equivalent simplified zero sequence loop diagram of a fault sensing device of a neutral ungrounded system in one embodiment;
fig. 4 is a graph showing a change in dielectric loss tangent of a fault sensing device of a neutral point ungrounded system upon a ground fault in one embodiment.
Fig. 5 is a schematic structural diagram of a ground fault sensing device of a neutral point ungrounded system in an embodiment.
Detailed Description
The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
In an embodiment of the present application, referring to fig. 1, fig. 1 is a flow chart of a fault sensing method of a neutral point ungrounded system in an embodiment, and the fault sensing method of the neutral point ungrounded system includes steps S110 to S150.
In an embodiment of the application, fig. 2 shows an equivalent zero sequence loop diagram of a fault sensing means of a neutral point ungrounded system, wherein,to detect a current source; i H Distributing capacitance to the ground for the distribution network; i n Is a single-phase grounding transition resistance; n is the neutral point of the distribution system, and the voltage of the point is set as +.>PT is an electromagnetic voltage transformer, one side of PT, which is connected with a neutral point of a power distribution network, is a primary side, and the transformation ratio is n; r is R L The direct current resistor is a system line direct current resistor; l is the system line inductance.
And neglecting the excitation impedance of the PT, and looking into the PT from the PT secondary side, so as to obtain an equivalent simplified zero sequence loop diagram of the fault sensing device of the neutral point ungrounded system shown in fig. 3.
Referring to fig. 3, in the drawing,to detect a current source; r is R 2 Is PT DC resistance and line resistance R L A resistor converted to the PT secondary side; l (L) 2 Converting PT leakage inductance and line inductance into PT secondary side inductance; c (C) S2 Converting the distributed capacitance of the power distribution network to the capacitance of the PT secondary side; r is R d2 The transition resistance to ground translates to the resistance on the secondary side of PT. C (C) S2 And I H The calculation relation between the two is as follows: c (C) S2 ＝n 2 C S ，I n And R is d2 The calculation relation between the two is as follows: r is R d2 ＝R d /n 2 。
Step S110, determining a capacitance value converted from the distribution network to the ground distributed capacitance to the secondary side of the electromagnetic voltage transformer PT and a distribution network to the ground distributed capacitance value through the injected detection current of the first frequency and the injected detection current of the second frequency;
further, step S110 specifically includes steps S210 to S240.
Step S210, according to the detected current of the first frequency and the detected current of the second frequency, respectively determining a first power distribution network impedance of the power distribution network under the detected current of the first frequency and a second power distribution network impedance of the power distribution network under the detected current of the second frequency;
step S220, determining, according to the first power distribution network impedance and the second power distribution network impedance, a capacitance value of the power distribution network to ground distributed capacitance converted to the PT secondary side.
Further, in a specific embodiment, when the power distribution network is operating normally, i.e. the ground transition resistance R d2 Infinity, the detection current source outputs a detection current f with a first frequency 1 And a detection current f of a second frequency 2 Measuring a detection current f at a first frequency 1 Voltage at the lower partA detection current f of a second frequency 2 Lower voltage->Then there are:
at the detection current of the first frequency, according to the formulaDetermining a first power distribution network impedance;
at the detection current of the second frequency, according to the formulaDetermining a second power distribution network impedance;
wherein f 1 A frequency Z outputted by the detection current source under the detection current of the first frequency 21 For the first distribution network impedance,for detecting the voltage across the current source at the detection current of the first frequency, < >>Detecting an output current of the power supply at a detection current of a first frequency; f (f) 2 The frequency Z of the output of the detection current source under the detection current of the second frequency 22 For the second distribution network impedance, < >>For detecting the voltage across the current source at the second frequency of the detection current, ">To detect the output current of the power supply at the second frequency, j is an imaginary unit, R 2 Is PT DC resistance and line resistance R L The resistance value is converted to PT secondary side, L 2 The PT leakage inductance and the line inductance are converted into the inductance value of the PT secondary side, C S2 And converting the distributed capacitance of the power distribution network to the capacitance value of the PT secondary side.
From Z above 21 、Z 22 Are equal in real parts and all have the value R 2 Values. The upper imaginary parts are respectively set as Im Z21 And Im Z22 In a specific embodiment, then, according to the formulaDetermining an imaginary part of the first distribution network impedance;
according to the formulaDetermining an imaginary part of the second distribution network impedance;
combining the two formulas into an equation set, and solving to obtain:and determining the capacitance value of the power distribution network, which is converted to the PT secondary side, from the ground distributed capacitance.
In step S230, the PT transformation ratio is obtained, specifically, the transformation ratio may be obtained by a nameplate, or detected.
Step S240, determining a distribution network ground distributed capacitance value according to the PT transformation ratio and the capacitance value converted from the distribution network ground distributed capacitance to the PT secondary side;
in a specific embodiment, through C S2 And C S The calculated relation between: c (C) S2 ＝n 2 C s The distributed capacitance value C of the distribution network to the ground can be calculated S 。
Step S120, determining reference power distribution network impedance under the current signal of the reference frequency and ground power distribution network impedance under the current signal of the reference frequency when the system is in single-phase grounding during normal operation of the power distribution network through the injected current signal of the reference frequency;
further, the step S120 specifically includes:
according to the formulaDetermining reference power distribution network impedance under a current signal injected with reference frequency when the power distribution network normally operates;
according to the formulaDetermining the impedance of a grounded distribution network under a current signal injected with a reference frequency when the system is in single-phase grounding;
wherein f 0 As a reference to the frequency of the reference,injecting current into the current source, ">Is the voltage at two ends of the current source during normal operation; the impedance parallel is denoted by// and, and (2)>To the voltage across the current source at ground fault, R d2 The transition resistance to ground translates to the resistance on the secondary side of PT.
Step S130, determining the parallel impedance of the capacitance of the distribution network, which is converted to the PT secondary side, and the grounding transition resistance according to the capacitance value, the reference distribution network impedance and the grounding distribution network impedance of the distribution network, which are converted to the PT secondary side;
further, step S130 specifically includes:
according to the formulaDetermining the parallel impedance of a capacitor converted from the distribution network to the PT secondary side and the grounding transition resistance;
wherein Z is f02 To eliminate R 2 、L 2 The capacitance C of the affected distribution network to the ground distributed capacitance to the PT secondary side S2 And a ground transition resistance R d2 Is a parallel impedance of (c).
Step S140, determining a dielectric loss tangent value to the ground under a current signal injected with a reference frequency according to the parallel impedance of the capacitance of the power distribution network to the PT secondary side and the grounding transition resistance;
further, step S140 specifically includes: the concept of dielectric loss tangent is introduced, the system insulation is destroyed by the ground fault of the distribution line, the loss is increased by the ground transition resistance, and the distribution network is at the reference frequency f 0 The following dielectric loss tangent values were:
wherein omega 0 Is to inject a current source with a frequency f 0 Corresponding angular frequency, delta f0 Is Z f02 Residual angle of impedance angle, R d Is a single-phase grounding transition resistance. From this formula, tg delta f0 Reference frequency f injected with current source 0 And distribution network ground distributed capacitance value C S Inversely proportional. tg delta f0 Reflects the magnitude of the leakage resistance of the distribution network to the ground, and when tg delta f0 When the power distribution network is increased to a certain value, the occurrence of the ground fault of the power distribution network can be judged.
Step S150, determining a fault state of the neutral point non-grounding system according to the comparison relation between the dielectric loss tangent value to the ground and the threshold value; in an embodiment of the application, tgδ f0 Reflects the size of the insulation resistance of the distribution network to the ground, when tg delta f0 When the threshold value is exceeded, the power distribution network can be judged to have the ground fault, and the threshold value is generally 0.01-0.2. This is exemplified by 0.05 in the present application.
Further, the step S150 specifically includes:
determining a dielectric loss tangent to ground at a current signal at a reference frequency;
if the dielectric loss tangent value to the ground is larger than the threshold value, the neutral point non-grounding system has a grounding fault;
and if the dielectric loss tangent value to the ground is smaller than or equal to the threshold value, the neutral point is not grounded, and the system normally operates.
By adopting the technical scheme of the embodiment, the sensitivity of detecting the ground fault is improved, whether the single-phase ground fault occurs in the system can be rapidly judged, and the calculation is simpler
Referring to fig. 4, fig. 4 is a graph of a change of dielectric loss tangent of a fault sensing device of a neutral point ungrounded system in a ground fault, assuming that the neutral point ungrounded system of a 10kV distribution network has a capacitance current of 1A-100A and a ground transition resistance of 1kΩ -100 kΩ, according to the following conditionsObtaining a current source injection reference frequency f 0 Tg delta at 8Hz f0 The variation is shown.
It can be seen that under the condition of a certain ground fault transition resistance, the larger the capacitance current of the distribution network is, tg delta is f0 The smaller; under the condition of a certain capacitance current of the distribution network, the larger the grounding transition resistance is, tg delta is f0 The smaller; capacitive current and ground fault resistance with tgδ f0 Is decreased by an increase in (c). Reference frequency f of current source injection signal 0 Preferably, a low frequency value is adopted to detect the increase of capacitance resistance formed by the power supply, and the same grounding transition resistance is at the frequency f 0 The following tg delta f0 The fault perception sensitivity is improved.
The smaller the reference frequency, the same limit value is selected, so that the sensing range can be enlarged, the reference frequency is generally 1 Hz-20 Hz, and the application takes 8Hz as an example.
When the power distribution network operates normally, tg delta f0 Near zero, the current source injection reference frequency is f 0 =8 Hz, in dielectric loss increment Δtgδ f0 =0.05 is the ground fault determination limit, and when the distribution network dielectric loss tangent variation exceeds this value, single-phase grounding occurs. When the calculated capacitance current is 100A, the high-resistance grounding fault of 7kΩ and below can be perceived. As the capacitance current decreases, the range of the perceived ground transition resistance increases, and when the capacitance current is below 50A, the voltage across the capacitor is reducedHigh resistance ground faults of 14k omega and below are sensed, high resistance ground faults of 24k omega and below are sensed when the capacitance current is below 30A, and high resistance ground faults of 72k omega and below are sensed when the capacitance current is below 10A.
According to the specification of overvoltage protection and insulation fit of the national standard GB/T50064 alternating current electric device, the capacitance current of the distribution network is more than 10A, and an arc suppression coil is adopted for grounding, so that the high-resistance fault sensing method provided by the application has higher sensitivity. Clearly, the current source injection frequency is 8Hz, and the dielectric loss tangent delta tgdelta delta of the distribution network is detected in real time f0 =0.05, the ground fault of the system 24kΩ of which the neutral point is not grounded can be effectively detected, and engineering application requirements are met.
In an embodiment of the present application, referring to fig. 5, fig. 5 is a schematic structural diagram of a fault sensing device of a neutral point ungrounded system in an embodiment, where the fault sensing device of the neutral point ungrounded system includes: a control unit 102 and a failure judgment unit 104.
The control unit 102 is configured to determine a capacitance value converted from the distribution network to the ground distributed capacitance to the secondary side of the electromagnetic voltage transformer PT and a distribution network to the ground distributed capacitance value through the injected detection current of the first frequency and the injected detection current of the second frequency; the specific function and process of the control unit 102 also refer to step S110.
The control unit 102 is further configured to determine, through the injected current signal of the reference frequency, a reference power distribution network impedance under the current signal of the reference frequency when the power distribution network operates normally and a ground power distribution network impedance under the current signal of the reference frequency when the system is in single-phase grounding; the specific function and process of the control unit 102 also refer to step S120.
The control unit 102 is further configured to determine the parallel impedance of the capacitance of the power distribution network converted to the PT secondary side and the ground transition resistance according to the capacitance value converted to the PT secondary side of the power distribution network, the reference power distribution network impedance, and the ground power distribution network impedance; the specific function and process of the control unit 102 also refer to step S130.
The control unit 102 is further configured to determine a dielectric loss tangent value to the ground under a current signal injected with a reference frequency according to the parallel impedance of the capacitance of the power distribution network to the ground distributed capacitance converted to the PT secondary side and the ground transition resistance and the power distribution network to the ground distributed capacitance value; the specific function and process of the control unit 102 also refer to step S140.
A fault judging unit 104 configured to determine a fault state of the neutral point non-grounded system according to a comparison relationship between the dielectric loss tangent value to ground and a threshold value; the specific function and processing of the failure determination unit 104 is also referred to step S150.
By adopting the technical scheme of the embodiment, the method is suitable for a system with a neutral point not grounded in a power distribution network, and can rapidly judge whether the system has single-phase grounding faults or not, and the sensitivity is higher and more reliable.
In one embodiment, a computer device is provided, comprising a memory and a processor, the memory storing a computer program that, when executed by the processor, causes the processor to perform the steps of the method embodiments described above.
In one embodiment, a computer-readable storage medium is provided, storing a computer program that, when executed by a processor, causes the processor to perform the steps of the method embodiments described above.
Those skilled in the art will appreciate that all or part of the processes in the methods of the above embodiments may be implemented by a computer program for instructing relevant hardware, where the program may be stored in a non-volatile computer readable storage medium, and where the program, when executed, may include processes in the embodiments of the methods described above. Any reference to memory, storage, database, or other medium used in embodiments provided herein may include non-volatile and/or volatile memory. The nonvolatile memory can include Read Only Memory (ROM), programmable ROM (PROM), electrically Programmable ROM (EPROM), electrically Erasable Programmable ROM (EEPROM), or flash memory. Volatile memory can include Random Access Memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms such as Static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double Data Rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous Link DRAM (SLDRAM), memory bus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), among others.
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The foregoing examples illustrate only a few embodiments of the application and are described in detail herein without thereby limiting the scope of the application. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the application, which are all within the scope of the application. Accordingly, the scope of protection of the present application is to be determined by the appended claims.
Claims (12)
1. A method of fault perception of a neutral point ungrounded ground system, the method comprising:
determining a capacitance value converted from the distribution network to the secondary side of the electromagnetic voltage transformer PT and a distribution network to the ground distributed capacitance value through the injected detection current of the first frequency and the injected detection current of the second frequency;
determining reference power distribution network impedance under the reference frequency current signal and grounding power distribution network impedance under the reference frequency current signal when the power distribution network normally operates and the system is in single-phase grounding through the injected reference frequency current signal;
determining the parallel impedance of the capacitance converted from the power distribution network to the PT secondary side and the grounding transition resistance according to the capacitance value converted from the grounding distribution capacitance to the PT secondary side, the reference power distribution network impedance and the grounding power distribution network impedance;
determining a dielectric loss tangent value to the ground under a current signal injected with a reference frequency according to the parallel impedance of the capacitance of the power distribution network to the ground distributed capacitance converted to the PT secondary side and the ground transition resistance and the power distribution network to the ground distributed capacitance value;
and determining the fault state of the neutral point ungrounded system according to the comparison relation between the dielectric loss tangent value to the ground and the threshold value.
2. The fault sensing method of a neutral point ungrounded system according to claim 1, wherein determining the capacitance value of the distribution network to ground distributed capacitance converted to the PT secondary side and the distribution network to ground distributed capacitance value by injecting the detection current of the first frequency and the detection current of the second frequency comprises:
according to the detection current of the first frequency and the detection current of the second frequency, respectively determining a first power distribution network impedance of the power distribution network under the detection current of the first frequency and a second power distribution network impedance of the power distribution network under the detection current of the second frequency;
determining a capacitance value converted from the distribution network to the ground distributed capacitance to the PT secondary side according to the first distribution network impedance and the second distribution network impedance;
obtaining PT transformation ratio;
and determining the distribution network ground distributed capacitance value according to the PT transformation ratio and the capacitance value converted from the distribution network ground distributed capacitance to the PT secondary side.
3. The fault sensing method of a neutral point ungrounded system according to claim 2, wherein the determining the first distribution network impedance of the distribution network at the first frequency of the detected current and the second distribution network impedance of the distribution network at the second frequency of the detected current according to the first frequency of the detected current and the second frequency of the detected current respectively specifically includes:
at the detection current of the first frequency, according to the formulaDetermining a first power distribution network impedance;
at the detection current of the second frequency, according to the formulaDetermining a second power distribution network impedance;
wherein f 1 The frequency of the output of the current source is detected under the detection current of the first frequency, Z 21 For the first distribution network impedance,for detecting the voltage across the current source at the detection current of the first frequency, < >>Detecting an output current of the power supply at a detection current of a first frequency; f (f) 2 The frequency Z of the output of the detection current source under the detection current of the second frequency 22 For the second distribution network impedance, < >>For detecting the voltage across the current source at the second frequency of the detection current, ">To detect the output current of the power supply at the second frequency, j is an imaginary unit, R 2 Is PT DC resistance and line resistance R L The resistance value is converted to PT secondary side, L 2 The PT leakage inductance and the line inductance are converted into the inductance value of the PT secondary side, C S2 And converting the distributed capacitance of the power distribution network to the capacitance value of the PT secondary side.
4. A method for sensing a fault in a neutral point ungrounded system according to claim 3, wherein determining a capacitance value of the distribution network to ground distributed capacitance converted to a PT secondary side according to the first distribution network impedance and the second distribution network impedance specifically includes:
according to the formulaDetermining an imaginary part of the first distribution network impedance;
according to the formulaDetermining an imaginary part of the second distribution network impedance;
according to the formulaDetermining a capacitance value of the power distribution network to be converted into a PT secondary side by the distributed capacitance to the ground;
Im Z21 for the imaginary part, im, of the impedance of the first distribution network Z22 Is the imaginary part of the second distribution network impedance.
5. The method for sensing faults in a neutral point ungrounded system according to claim 4, wherein determining a distribution network ground distributed capacitance value from the PT transformation ratio and the capacitance value of the distribution network ground distributed capacitance converted to a PT secondary side specifically comprises:
according to the formulaDetermining a distributed capacitance value of the power distribution network to the ground; wherein C is S And the capacitance value is distributed for the power distribution network to the ground, and n is PT transformation ratio.
6. The fault sensing method of a neutral point ungrounded system according to any of claims 1-5, wherein the determining the reference distribution network impedance under the reference frequency current signal when the distribution network is operating normally and the grounded distribution network impedance under the reference frequency current signal when the system is single-phase grounded by the injected reference frequency current signal specifically comprises;
according to the formulaDetermining a reference power distribution network impedance;
according to the formulaDetermining the impedance of a grounded power distribution network;
wherein f 0 As a reference to the frequency of the reference,injecting current into the current source, ">Is the voltage at two ends of the current source during normal operation; the impedance parallel is denoted by// and, and (2)>To the voltage across the current source at ground fault, R d2 The transition resistance to ground translates to the resistance on the secondary side of PT.
7. The fault sensing method of the neutral point ungrounded system according to claim 6, wherein determining the parallel impedance of the capacitance of the distribution network to ground distributed capacitance to the PT secondary side and the ground transition resistance according to the capacitance value of the distribution network to ground distributed capacitance to the PT secondary side, the reference distribution network impedance, and the ground distribution network impedance specifically comprises;
according to the formulaDetermining the parallel impedance of a capacitor converted from the distribution network to the PT secondary side and the grounding transition resistance;
wherein Z is f02 To eliminate R 2 、L 2 The capacitance C of the affected distribution network to the ground distributed capacitance to the PT secondary side S2 And a ground transition resistance R d2 Is a parallel impedance of (c).
8. The fault sensing method of a neutral point ungrounded system according to claim 7, wherein determining a dielectric loss tangent value to ground under a current signal injected with a reference frequency according to a parallel impedance of a capacitance of a power distribution network to ground distributed capacitance converted to a capacitance of a PT secondary side and a ground transition resistance and a power distribution network to ground distributed capacitance value specifically comprises: according to the formulaDetermining a dielectric loss tangent to ground at a current signal injected at a reference frequency; wherein omega 0 Is to inject a current source with a frequency f 0 Corresponding angular frequency, delta f0 Is Z f02 Residual angle of impedance angle, R d Is a single-phase grounding transition resistance.
9. The method of claim 8, wherein determining the fault condition of the neutral point-ungrounded system based on the comparison between the dielectric loss tangent to ground and the threshold value comprises:
determining a dielectric loss tangent to ground at a current signal at a reference frequency;
if the dielectric loss tangent value to the ground is larger than the threshold value, the neutral point non-grounding system has a grounding fault;
and if the dielectric loss tangent value to the ground is smaller than or equal to the threshold value, the neutral point is not grounded, and the system normally operates.
10. A fault sensing device for a neutral point ungrounded system, the device comprising:
the control unit is used for determining the capacitance value converted from the distribution network to the ground distributed capacitance to the secondary side of the electromagnetic voltage transformer PT and the distribution network to the ground distributed capacitance value through the injected detection current of the first frequency and the injected detection current of the second frequency;
the control unit is also used for determining the reference power distribution network impedance under the current signal of the reference frequency when the power distribution network normally operates and the grounding power distribution network impedance under the current signal of the reference frequency when the system is in single-phase grounding through the injected current signal of the reference frequency;
the control unit is further used for determining the parallel impedance of the capacitance converted from the power distribution network to the PT secondary side and the grounding transition resistance according to the capacitance value converted from the grounding distributed capacitance to the PT secondary side, the reference power distribution network impedance and the grounding power distribution network impedance;
the control unit is further used for determining a dielectric loss tangent value to the ground under a current signal injected with a reference frequency according to the parallel impedance of the capacitance of the power distribution network to the ground distributed capacitance converted to the PT secondary side and the ground transition resistance and the power distribution network to the ground distributed capacitance value;
and the fault judging unit is used for determining the fault state of the neutral point non-grounding system according to the comparison relation between the dielectric loss tangent value to the ground and the threshold value.
11. A computer device comprising a memory and a processor, the memory storing a computer program that, when executed by the processor, causes the processor to perform the steps of the method of any of claims 1 to 9.
12. A computer readable storage medium storing a computer program which, when executed by a processor, causes the processor to perform the steps of the method of any one of claims 1 to 9.
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