CN111551821A - Power distribution network ground fault identification method, device and equipment - Google Patents
Power distribution network ground fault identification method, device and equipment Download PDFInfo
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Abstract
The invention discloses a method, a device and equipment for identifying a ground fault of a power distribution network, wherein the method comprises the steps of firstly establishing a low-current signal with the same amplitude and frequency conversion injected from a neutral point of the power distribution network, measuring a feedback voltage signal through a voltage transformer, thereby calculating the ground conductance and the ground capacitance of the power distribution network, then calculating the incremental damping rate under each frequency by using the ground conductance and the ground capacitance, further calculating the incremental damping rate generated by a fault transition resistance and superposing the incremental damping rates to carry out fault according to a preset criterion, thereby realizing effective amplification of a fault characteristic quantity, and simultaneously greatly reducing the influence of interference, thereby effectively identifying a high-resistance ground fault. The invention solves the problem of difficult identification of the high-resistance grounding fault of the resonance grounding power distribution network, can make the grounding fault characteristics highlighted, has higher noise resistance and greatly improves the identification capability of the high-resistance grounding fault.
Description
Technical Field
The invention belongs to the field of power distribution network ground fault detection, and particularly relates to a power distribution network ground fault identification method, device and equipment based on multi-frequency incremental damping rate superposition.
Background
The power distribution network goes deep into the user terminal, the operation conditions are complex and changeable, faults are easy to occur, 80% of the faults are about single-phase earth faults, and phase-to-phase faults are formed by the development of single-phase earth faults which are not detected and processed in time. When a high-resistance ground fault (tree fault, incomplete breakdown of an arrester and the like) occurs in a power distribution network, the transition resistance is often up to thousands of ohms, the fault characteristic quantity is very weak, the neutral point displacement voltage is far less than 15% phase voltage of the national standard, the existing ground fault detection method is difficult to detect the high-resistance fault, the fault point transition medium is continuously discharged until the transition resistance is reduced to a detectable range, and then the fault point transition medium can be identified by a detection device, so that the fault expansion can be caused in the period, and the personal equipment safety can be seriously threatened.
In order to realize high-sensitivity identification of single-phase grounding faults of the power distribution network, effective measurement of system ground admittance parameters is required. The existing ground parameter measuring methods comprise a direct method, an indirect method and an injection signal method, wherein the indirect method comprises an external capacitor, an external voltage, a tuning method, a frequency conversion method and the like. The direct method and the indirect method both need to change the primary parameters of the system or the topological structure of the system, are complex to operate, have personal electric shock danger and are not suitable for measuring the system parameters in real time. Therefore, the method can measure the parameters of the power distribution network in real time without being influenced by the system operation mode and high-frequency interference, can finish measurement from the secondary side, does not influence the normal operation of the primary side of the system, and has very important significance in improving the accuracy of fault judgment.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method, a device and equipment for identifying the ground fault of the power distribution network based on multi-frequency incremental damping rate superposition, which can realize high-resistance ground fault identification and improve the identification sensitivity of the ground fault.
In order to achieve the technical purpose, the invention adopts the following technical scheme:
a power distribution network ground fault identification method based on multi-frequency incremental damping rate superposition comprises the following steps:
injecting same-amplitude frequency conversion small current signal into power distribution network
Measuring a feedback voltage signal by a voltage transformer
Wherein the subscript i represents the different frequency numbers of the low current signal;
according to equivalent ground admittance computational formula and low current signal of distribution network
And a voltage signal fed back
Calculating the ground electric conduction G and the ground capacitance C when the distribution network generates LC resonance;
the equivalent ground admittance calculation formula of the power distribution network is as follows:
the conditions for generating LC resonance in the power distribution network are as follows:
the earth conductance G and the earth capacitance C when the LC resonance is generated in the distribution network can be obtained by the formulas (1) and (2) as follows:
wherein,
for small current signals injected on the secondary side
A current reduced to the primary side, and
k1calculating a current reduction coefficient;
for voltage signals fed back from the secondary side
A feedback voltage reduced to the primary side, and
k2calculating a voltage normalization coefficient; f. ofiAs a low current signal
L is the equivalent inductance of the arc suppression coil in the power distribution network; i isim、fim、UimRespectively, small current signals injected on the secondary side
Amplitude of (d), small current signal injected at secondary side
Frequency f ofiSecondary side feedback voltage signal
The amplitudes of the two signals respectively represent symbols when the power distribution network generates LC resonance;
the method comprises the steps that the ground conductance and the ground capacitance of the power distribution network when small current signals of each frequency are injected are respectively taken as the ground conductance and the ground capacitance when the power distribution network generates LC resonance; then, the incremental damping rate d at each frequency is calculated according to the following equation (5) and the ground conductance G and the ground capacitance Cdi：
In the formula, g0、rLFor the earth conductance of the distribution network before a fault and the equivalent loss resistance, omega, of the arc suppression coiliAs a low current signal
The angular frequency of (d);
according to the criterion preset by the following formula (6), in the multi-frequency superposition process of different frequency numbers i of frequency conversion from 1 to n, judging whether an inequality in the criterion is met, if so, judging that the power distribution network has a ground fault, if not, judging that the power distribution network is in a three-phase unbalanced state and if not, judging that the power distribution network has a neutral point voltage displacement, and the preset criterion is as follows:
wherein d issetTo a preset damping rate start value, d0Is the inherent damping rate, d, of the distribution networkLAdditional damping ratio for the arc suppression coil, gsetFor setting the transition conductance, n is the number of times of superposition of the multi-frequency incremental damping rate, omegaimFor the LC resonance angular frequency of the distribution network, INT () is a rounding function.
In a more preferable technical scheme, a same-amplitude frequency conversion small current signal is injected
The frequency range of (a) is: f. of0±5Hz，f0Is the power frequency of the power distribution network.
In a more preferable technical scheme, after the incremental damping rate at each frequency is obtained through calculation, the incremental damping rate is reduced to the power frequency angular frequency, and the reduced incremental damping rate d'diComprises the following steps:
the invention also provides a power distribution network ground fault identification device based on multi-frequency incremental damping rate superposition, which comprises the following steps:
a signal injection and feedback module to: injecting same-amplitude frequency conversion small current signal into power distribution network
Measuring a feedback voltage signal by a voltage transformer
Wherein the subscript i represents the different frequency numbers of the low current signal;
a ground admittance parameter calculation module to: according to equivalent ground admittance computational formula and low current signal of distribution network
And a voltage signal fed back
Calculating the ground electric conduction G and the ground capacitance C when the distribution network generates LC resonance;
the equivalent ground admittance calculation formula of the power distribution network is as follows:
the conditions for generating LC resonance in the power distribution network are as follows:
the earth conductance G and the earth capacitance C when the LC resonance is generated in the distribution network can be obtained by the formulas (1) and (2) as follows:
wherein,
for small current signals injected on the secondary side
A current reduced to the primary side, and
k1calculating a current reduction coefficient;
for voltage signals fed back from the secondary side
A feedback voltage reduced to the primary side, and
k2calculating a voltage normalization coefficient; f. ofiAs a low current signal
L is the equivalent inductance of the arc suppression coil in the power distribution network; i isim、fim、UimRespectively, small current signals injected on the secondary side
Amplitude of (d), small current signal injected at secondary side
Frequency f ofiSecondary side feedback voltage signal
The amplitudes of the two signals respectively represent symbols when the power distribution network generates LC resonance;
an incremental damping rate calculation module to: the method comprises the steps that the ground conductance and the ground capacitance of the power distribution network when small current signals of each frequency are injected are respectively taken as the ground conductance and the ground capacitance when the power distribution network generates LC resonance; then, the incremental damping rate d at each frequency is calculated according to the following equation (5) and the ground conductance G and the ground capacitance Cdi：
In the formula, g0、rLFor the earth conductance of the distribution network before a fault and the equivalent loss resistance, omega, of the arc suppression coiliAs a low current signal
The angular frequency of (d);
a fault identification module to: according to the criterion preset by the following formula (6), in the multi-frequency superposition process of different frequency numbers i of frequency conversion from 1 to n, judging whether an inequality in the criterion is met, if so, judging that the power distribution network has a ground fault, if not, judging that the power distribution network is in a three-phase unbalanced state and if not, judging that the power distribution network has a neutral point voltage displacement, and the preset criterion is as follows:
wherein d issetTo a preset damping rate start value, d0Is the inherent damping rate, d, of the distribution networkLAdditional damping ratio for the arc suppression coil, gsetFor setting the transition conductance, n is the number of times of superposition of the multi-frequency incremental damping rate, omegaimFor the LC resonance angular frequency of the distribution network, INT () is a rounding function.
In a more preferred technical scheme, the signal injection and feedback module injects the same-amplitude frequency conversion small current signal into the power distribution network
The frequency range of (a) is: f. of0±5Hz，f0Is the power frequency of the power distribution network.
In a more preferred embodiment, the apparatus further includes a normalization module, configured to: after the incremental damping rate at each frequency is obtained through calculation, the incremental damping rate is reduced to the power frequency angular frequency, and the reduced incremental damping rate d'diComprises the following steps:
the invention also provides an apparatus comprising a processor and a memory; wherein: the memory is to store computer instructions; the processor is used for executing the computer instructions stored in the memory, and particularly executing the method of any one of the above method technical schemes.
Advantageous effects
According to the invention, the small current signals with the same amplitude and frequency conversion are injected into the power distribution network as the characteristic signals for detecting the fault, and the incremental damping rates of the power distribution network under a plurality of different frequencies are measured and superposed to amplify the fault characteristics of the high-resistance ground fault reflected in the damping rates, so that the high-resistance ground fault identification is realized, and the sensitivity of the high-resistance ground fault identification is improved. Meanwhile, the invention is not interfered by the high-frequency noise of the system, and the sensitivity of fault identification is further improved.
In addition, when the method for measuring the ground admittance of the power distribution network based on the injection signal considers the actual operation condition, most transformer substations are provided with both a zero sequence voltage transformer (ZEV) and a bus voltage transformer (PT), and if no resonance elimination resistor is arranged on the secondary side of the bus PT, the two PTs in the substation can be used for measurement. When the bus PT is connected with a resonance elimination resistor, the resonance elimination resistor or the external PT needs to be withdrawn, namely, two voltage transformers are additionally arranged from a neutral point of a grounding transformer or a neutral point of a three-phase compensation capacitor bank to measure the pair admittance of the distribution network. The invention has the following advantages: the testing personnel can measure the parameters of the power distribution network in real time by using the voltage transformer without considering the wiring mode of the bus PT group and whether the zero sequence PT is installed or not, the influence of the system operation mode and high-frequency interference is avoided, and the problem of inaccurate measurement caused by PT magnetic saturation is avoided; the measurement can be completed from the secondary side, the normal operation of the primary side of the system is not influenced, and the measurement process is convenient and reliable.
Drawings
Fig. 1 is a zero sequence circuit diagram of an equivalent power distribution network provided by the present invention;
FIG. 2 injection signal equivalent flow loop
FIG. 3 simplified equivalent loop for injecting a signature signal
FIG. 4 feedback voltage signal
FIG. 5 is a fault discrimination flow chart of a ground fault identification method provided by the present invention;
FIG. 6 is a diagram of the single-phase 200 Ω low-impedance ground fault residual current over time obtained after simulation by the present invention;
FIG. 7 is a graph of single-phase 1500 Ω high-resistance ground fault residual current over time obtained after simulation by the present invention;
FIG. 8 is a plot of single phase intermittent arc ground fault point residual current over time as simulated by the present invention;
FIG. 9 is a graph of high resistance ground fault residual current over time for 30db white noise resulting from simulations performed in accordance with the present invention;
Detailed Description
The following describes embodiments of the present invention in detail, which are developed based on the technical solutions of the present invention, and give detailed implementation manners and specific operation procedures to further explain the technical solutions of the present invention.
As shown in fig. 1, the complete transposition (C) is performed for the distribution network in case of single-phase earth faultA＝CB＝CC＝C0，rA＝rB＝rC＝r0) And the load symmetry obtains a zero sequence equivalent circuit of the power distribution network when the earth fault is unexpected, wherein
For neutral point voltage of distribution network, to earth
rLFor arc suppression coil equivalent loss resistance, rdA fault transition resistance; l is the equivalent inductance of the arc suppression coil, and C is 3C0 and is the total earth capacitance of the power distribution network.
According to the fault zero sequence equivalent circuit, the residual current can be obtained
Size: :
in the formula: i isgIs residual streamActive component of (1)g＝U0G；ICIs a capacitance current to ground, IC＝3ωC0U0；ILIs the inductance current of the arc suppression coil; d is the damping rate of the distribution network system, Ig/ICGenerally expressed in percent; v is the detuning degree of the resonant grounded power distribution network, v ═ IC-IL)/ICAlso generally expressed in percentage, and v ═ 1-K, K is the harmonic of the resonant grounded distribution network.
As can be seen from the formula (7), the residue remains
Is related to the damping rate d and the detuning degree v of the distribution grid system. Because the arc suppression coil is generally set to operate close to the resonance point and v is a fixed value, the damping rate of the system can be accurately measured and calculated according to the residue
And effectively identifying the running state of the power distribution network. Therefore, the embodiment of the invention provides fault identification for the grounding of the power distribution network based on the principle.
When a 10kV power distribution network normally operates, the damping rate of an overhead line is about 3% -5%, and the damping rate of a line can reach 8% -10% when the line is insulated and affected by tide; the damping rate of the cable line is small, about 2% -4%, and can increase to 10% when the insulation is aged. Because the parameters of the power distribution networks with different scales are greatly different, the damping rate setting value d of the power distribution network with the fault is identified under the general conditionset20%, and the ground fault transition resistance is about 200-400 omega; damping rate setting value d of power distribution networkset15%, the resistance of the transition resistor is about 400-600 Ω. The identification method of the high-resistance grounding single-frequency damping rate with the transition resistance larger than 1000 omega or even higher fails. Aiming at the technical problem, the invention provides a power distribution network earth fault identification method based on multi-frequency incremental damping rate superposition, which accumulates the incremental damping rates generated by fault transition resistance by injecting small current signals with multiple frequencies so as to highlight the fault characteristics, thereby improving the single-phase earth fault of high-resistance transition resistanceAnd (5) identifying the rows.
The technical solution of the present invention is explained below by examples.
The method for identifying the ground fault of the power distribution network based on the multi-frequency incremental damping rate superposition, as shown in fig. 5, includes the following steps:
step S10, injecting the same amplitude frequency conversion small current signal into the power distribution network
Measuring a feedback voltage signal by a voltage transformer
Wherein the subscript i represents the different frequency numbers of the low current signal;
the frequency conversion means that the frequency of the small current signal changes with time, specifically, the frequency of the small current signal is changed each time and maintained for a period of time, and then the next frequency increase is performed, that is, the small current signal of another frequency is injected.
And measuring the fed back voltage signal while injecting a small current signal, wherein the measurement is carried out by adopting a zero sequence voltage transformer of the power distribution network. Wherein, the equivalent circulation loop for injecting small current signal is shown in FIG. 2, and the frequency of the small current is fiThe corresponding damping rate of the distribution network can be expressed as shown in the following formula (8):
in the formula: i isiRIs the real part of the injected current; i isiCIs the imaginary part of the injected current αiThe phase angle difference between the injected current signal and the feedback voltage, namely the power angle of the injected small current signal; omegaiIs the angular frequency of the injected small current signal.
Step S20, according to the equivalent admittance to ground calculation formula of the distribution network and the small current signal
And voltage information of feedbackNumber (C)
And calculating the ground electric conduction G and the ground capacitance C when the LC resonance occurs in the power distribution network.
In the context of figure 2, it is shown,
for small current signals injected on the secondary side
A current reduced to the primary side, and
k1calculating a current reduction coefficient;
for voltage signals fed back from the secondary side
A feedback voltage reduced to the primary side, and
k2the voltage reduction coefficient is obtained. L is1Is primary side leakage inductance, L 'of a voltage transformer inside an arc suppression coil'2The value of the secondary side leakage inductance is reduced to the value of the primary side due to L1、L′2The inductance is far smaller than the equivalent inductance L of the arc suppression coil, so the influence of the primary and secondary side leakage inductances of the voltage transformer on the measurement can be ignored. Thereby, an injection frequency f to the distribution network as shown in fig. 3 is obtainediA simplified equivalent loop of a low current signal. And the equivalent earth admittance calculation formula of the distribution network obtained from fig. 3 is:
wherein, the equivalent inductance L of arc suppression coil in the distribution network can be set according to the gear and obtain.
This embodiment is as followsStep S10, injecting same amplitude frequency conversion small current signal into power distribution network
The voltage signal fed back by the post-measurement power distribution network is shown in fig. 4, the amplitude of the feedback voltage signal is maximum when 5.425s is taken, which shows that the total ground-to-ground capacitance of the power distribution network and the arc suppression coil inductance generate non-power frequency parallel resonance, and the resonance frequency fimIs 54.25Hz, corresponding to which the system admittance to ground is minimal. According to the formula (9), the conditions for generating LC resonance in the distribution network are as follows:
from the equations (9) and (10), the ground-to-ground conductor G and the ground-to-ground capacitor C when the LC resonance occurs in the distribution network can be obtained as follows:
wherein, Iim、fim、UimRespectively, small current signals injected on the secondary side
Amplitude of (d), small current signal injected at secondary side
Frequency f ofiSecondary side feedback voltage signal
The amplitudes of the two signals respectively represent symbols when the power distribution network generates LC resonance;
step S30, the earth conductance and the earth capacitance of the power distribution network when injecting the small current signal of each frequency are both valued as the earth conductance and the earth capacitance when the power distribution network generates LC resonance; then according toThe incremental damping rate d at each frequency is calculated by the following equation (13) for the ground conductance G and the ground capacitance Cdi：
In the formula (d)0i、dLiFrequency f of small current signal injected into distribution networkiThe inherent damping rate and the additional damping rate of the arc suppression coil are obtained; g0、rLThe equivalent loss resistances omega of the earth conductance and the arc suppression coil before the fault of the power distribution networkiAs a low current signal
The angular frequency of (c).
Because the compensation capacity of the arc suppression coil is expressed as QL＝ILUphSo that the frequency of the small current signal can be expressed in the form of a percentage value as fiActive loss P of time arc suppression coili：
I.e. PiThe ratio of the active current of the arc suppression coil to the inductive current or the ratio of the inductive reactance to the equivalent loss resistance. The increment damping rate of the joint type (13) and the formula (14) is as follows:
step S40, according to the criteria preset by the following formula (16), in the multi-frequency superposition process of different frequency numbers i of frequency conversion from 1 to n, judging whether inequality in the criteria is met, if yes, judging that the power distribution network has a ground fault, if not, judging that the power distribution network is in a three-phase unbalanced state and if neutral point voltage displacement occurs, and the preset criteria are as follows:
wherein d issetTo a preset damping rate start value, d0Is the inherent damping rate, d, of the distribution networkLAn additional damping rate for the arc suppression coil; gsetFor setting the transition conductance, the change is made to the form of the transition resistance rdsetIndicating the expected measured transition resistance value; n is the superposition frequency of the multi-frequency incremental damping rate, the value of the superposition frequency is influenced by the resistance value of the maximum transition resistor expected to be measured, and when the common transition resistor is 1k omega, n is 2 or 3; omegaimFor the LC resonance angular frequency of the distribution network, INT () is a rounding function.
In the embodiment, the small current signals with the same amplitude and frequency conversion are injected into the power distribution network to serve as the characteristic signals for detecting the faults, and the incremental damping rates of the power distribution network under a plurality of different frequencies are measured and overlapped to amplify the fault characteristics of the high-resistance ground fault reflected in the damping rates, so that the high-resistance ground fault identification is realized, and the sensitivity of the high-resistance ground fault identification is improved. Meanwhile, the invention is not interfered by the high-frequency noise of the system, and the sensitivity of fault identification is further improved.
From the formula (16), it can be known that the incremental damping rate of the distribution network is changed when the small current signal is injected into the distribution network, so that in a more preferred embodiment, the frequency of the injected small current signal is as close to the power frequency as possible, that is, the injection of the same-amplitude frequency-conversion small current signal is limited
The frequency range of (a) is: f. of0±5Hz，f0Is the power frequency of the power distribution network. Therefore, the influence of small current signal injection on the power distribution network can be eliminated to the greatest extent, and the identification degree of the power distribution network fault is further improved.
As can be seen from the foregoing, since the ground admittance when the LC resonance occurs in the power distribution network is the smallest, when calculating the incremental damping rate for each frequency, the ground-to-ground conductor G and the ground-to-ground capacitor C when the LC resonance occurs in the power distribution network are used, but these values are different from the actual values, so that the incremental damping rates calculated from the ground-to-ground conductor G and the ground-to-ground capacitor C are also different. To reduce the effect of the deviation and to improve the fault discrimination, the invention, in a more preferred embodiment, is implemented in a computerAfter the incremental damping rate under each frequency is obtained, the formula is followed
And (4) reducing the frequency to the power frequency angular frequency, and then carrying out fault identification on the power distribution network according to a formula (16) in step S40.
In order to verify the reliability of the method for identifying the ground fault of the power distribution network based on the multi-frequency admittance measurement, a 10kV resonance grounding power distribution network model shown in figure 1 is built in PSCAD/EMTDC simulation software. The parameters are set as shown in table 1, and the simulation analysis and verification of the low-resistance earth fault, the high-resistance earth fault and the arc grounding fault are carried out.
Meter 110 kV distribution network ground parameter
Neutral point voltage deviation is caused by single-phase earth faults of the power distribution network, and the size of residual current of fault points is influenced by the resistance value of the transition resistor. The simulation sets a ground fault at 0.05 second, and the waveforms of the low-resistance ground, high-resistance ground and arc ground faults are shown in fig. 6-8.
The transient characteristic is obvious when the low-resistance earth fault occurs, the earth fault can be effectively identified by collecting the transient characteristic signal, but the method is easily interfered by system noise when the earth fault is grounded through high impedance or the arc high-resistance earth fault occurs, and the fault transient signal is difficult to be effectively captured. The results of the ground fault identification based on the multi-frequency admittance measurements are shown in table 2. For different starting values d respectivelysetAnd simulating different transition resistances and different fault distance conditions, and calculating by a formula (16) to obtain a fault identification condition and a transition resistance range.
TABLE 2 identification results under different fault conditions
As can be seen from table 2, in different fault situations, the high-resistance fault cannot be identified by measuring the damping rate parameter under a single frequency, and the high-resistance ground fault detection is realized by amplifying the characteristics of the high-resistance ground fault by adopting a multi-frequency incremental damping rate superposition detection method; by setting different transition resistance and setting value rsetAnd a starting value dsetA large number of simulations are carried out, and results show that the method can effectively judge the single-phase earth fault with the transition resistance of 3k omega, and the theoretical analysis result is verified.
TABLE 3 Fault identification results with noise
In order to verify that the method provided by the present disclosure is not affected by the switching frequency of the power electronics and the system noise, the paper superimposes gaussian white noise with different decibels in the simulation, fig. 9 shows that the neutral point voltage has shifted in a normal state when the residual current of the high-resistance ground fault is 30db white noise, and the fault identification result is shown in table 3. Because the method is used for processing the steady-state characteristic parameters, the influence of system interference is small. When 30db white Gaussian noise exists in the system, the ground fault with the transition resistance of 3k omega can still be effectively judged.
The invention also provides an embodiment of a device for identifying the ground fault of the power distribution network based on the superposition of the multi-frequency incremental damping rates, which corresponds to the implementation of the method and comprises the following steps:
a signal injection and feedback module to: injecting same-amplitude frequency conversion small current signal into power distribution network
Measuring a feedback voltage signal by a voltage transformer
Wherein the subscript i represents the different frequency numbers of the low current signal;
a ground admittance parameter calculation module to: calculating formula according to equivalent ground admittance of power distribution network and small powerStream signal
And a voltage signal fed back
Calculating the ground electric conduction G and the ground capacitance C when the distribution network generates LC resonance;
the equivalent ground admittance calculation formula of the power distribution network is as follows:
the conditions for generating LC resonance in the power distribution network are as follows:
the earth conductance G and the earth capacitance C when the LC resonance is generated in the distribution network can be obtained by the formulas (1) and (2) as follows:
wherein,
for small current signals injected on the secondary side
A current reduced to the primary side, and
k1calculating a current reduction coefficient;
for voltage signals fed back from the secondary side
A feedback voltage reduced to the primary side, and
k2calculating a voltage normalization coefficient; f. ofiAs a low current signal
L is the equivalent inductance of the arc suppression coil in the power distribution network; i isim、fim、UimRespectively, small current signals injected on the secondary side
Amplitude of (d), small current signal injected at secondary side
Frequency f ofiSecondary side feedback voltage signal
The amplitudes of the two signals respectively represent symbols when the power distribution network generates LC resonance;
an incremental damping rate calculation module to: the method comprises the steps that the ground conductance and the ground capacitance of the power distribution network when small current signals of each frequency are injected are respectively taken as the ground conductance and the ground capacitance when the power distribution network generates LC resonance; then, the incremental damping rate d at each frequency is calculated according to the following equation (5) and the ground conductance G and the ground capacitance Cdi：
In the formula, g0、rLFor the earth conductance of the distribution network before a fault and the equivalent loss resistance, omega, of the arc suppression coiliAs a low current signal
The angular frequency of (d);
a fault identification module to: according to the criterion preset by the following formula (6), in the multi-frequency superposition process of different frequency numbers i of frequency conversion from 1 to n, judging whether an inequality in the criterion is met, if so, judging that the power distribution network has a ground fault, if not, judging that the power distribution network is in a three-phase unbalanced state and if not, judging that the power distribution network has a neutral point voltage displacement, and the preset criterion is as follows:
wherein d issetTo a preset damping rate start value, d0Is the inherent damping rate, d, of the distribution networkLAdditional damping ratio for the arc suppression coil, gsetFor setting the transition conductance, n is the number of times of superposition of the multi-frequency incremental damping rate, omegaimFor the LC resonance angular frequency of the distribution network, INT () is a rounding function.
In a more preferred embodiment of the apparatus, the signal injection and feedback module injects the same-amplitude frequency-conversion small-current signal into the distribution network
The frequency range of (a) is: f. of0±5Hz，f0Is the power frequency of the power distribution network.
In a more preferred embodiment of the apparatus, the apparatus further comprises a normalization module configured to: after the incremental damping rate at each frequency is obtained through calculation, the incremental damping rate is reduced to the power frequency angular frequency, and the reduced incremental damping rate d'diComprises the following steps:
the present invention also provides an apparatus embodiment comprising a processor and a memory; wherein: the memory is to store computer instructions; the processor is configured to execute the computer instructions stored in the memory, and in particular, to perform the method of any of the above method embodiments.
The above embodiments are preferred embodiments of the present application, and those skilled in the art can make various changes or modifications without departing from the general concept of the present application, and such changes or modifications should fall within the scope of the claims of the present application.
Claims (7)
1. A power distribution network ground fault identification method based on multi-frequency incremental damping rate superposition is characterized by comprising the following steps:
injecting same-amplitude frequency conversion small current signal into power distribution network
Measuring a feedback voltage signal by a voltage transformer
Wherein the subscript i represents the different frequency numbers of the low current signal;
according to equivalent ground admittance computational formula and low current signal of distribution network
And a voltage signal fed back
Calculating the ground electric conduction G and the ground capacitance C when the distribution network generates LC resonance;
the equivalent ground admittance calculation formula of the power distribution network is as follows:
the conditions for generating LC resonance in the power distribution network are as follows:
the earth conductance G and the earth capacitance C when the LC resonance is generated in the distribution network can be obtained by the formulas (1) and (2) as follows:
wherein,
for small current signals injected on the secondary side
A current reduced to the primary side, and
k1calculating a current reduction coefficient;
for voltage signals fed back from the secondary side
A feedback voltage reduced to the primary side, and
k2calculating a voltage normalization coefficient; f. ofiAs a low current signal
L is the equivalent inductance of the arc suppression coil in the power distribution network; i isim、fim、UimRespectively, small current signals injected on the secondary side
Amplitude of (d), small current signal injected at secondary side
Frequency f ofiSecondary side feedback voltage signal
The amplitudes of the two signals respectively represent symbols when the power distribution network generates LC resonance;
the method comprises the steps that the ground conductance and the ground capacitance of the power distribution network when small current signals of each frequency are injected are respectively taken as the ground conductance and the ground capacitance when the power distribution network generates LC resonance; then, the incremental damping rate d at each frequency is calculated according to the following equation (5) and the ground conductance G and the ground capacitance Cdi：
In the formula, g0、rLFor the earth conductance of the distribution network before a fault and the equivalent loss resistance, omega, of the arc suppression coiliAs a low current signal
The angular frequency of (d);
according to the criterion preset by the following formula (6), in the multi-frequency superposition process of different frequency numbers i of frequency conversion from 1 to n, judging whether an inequality in the criterion is met, if so, judging that the power distribution network has a ground fault, if not, judging that the power distribution network is in a three-phase unbalanced state and if not, judging that the power distribution network has a neutral point voltage displacement, and the preset criterion is as follows:
wherein d issetTo a preset damping rate start value, d0Is the inherent damping rate, d, of the distribution networkLAdditional damping ratio for the arc suppression coil, gsetFor setting the transition conductance, n is the number of times of superposition of the multi-frequency incremental damping rate, omegaimFor the LC resonance angular frequency of the distribution network, INT () is a rounding function.
2. According toThe method of claim 1, wherein the same amplitude variable frequency low current signal is injected
The frequency range of (a) is: f. of0±5Hz，f0Is the power frequency of the power distribution network.
3. The method of claim 1, wherein after the incremental damping rate at each frequency is calculated, the incremental damping rate is reduced to the power frequency angular frequency, and the reduced incremental damping rate d is obtainedd′iComprises the following steps:
4. the utility model provides a distribution network earth fault identification device based on stack of multifrequency increment damping rate which characterized in that includes:
a signal injection and feedback module to: injecting same-amplitude frequency conversion small current signal into power distribution network
Measuring a feedback voltage signal by a voltage transformer
Wherein the subscript i represents the different frequency numbers of the low current signal;
a ground admittance parameter calculation module to: according to equivalent ground admittance computational formula and low current signal of distribution network
And a voltage signal fed back
Calculating the ground electric conduction G and the ground capacitance C when the distribution network generates LC resonance;
the equivalent ground admittance calculation formula of the power distribution network is as follows:
the conditions for generating LC resonance in the power distribution network are as follows:
the earth conductance G and the earth capacitance C when the LC resonance is generated in the distribution network can be obtained by the formulas (1) and (2) as follows:
wherein,
for small current signals injected on the secondary side
A current reduced to the primary side, and
k1calculating a current reduction coefficient;
for voltage signals fed back from the secondary side
A feedback voltage reduced to the primary side, and
k2calculating a voltage normalization coefficient; f. ofiAs a low current signal
L is the equivalent inductance of the arc suppression coil in the power distribution network; i isim、fim、UimRespectively, small current signals injected on the secondary side
Amplitude of (d), small current signal injected at secondary side
Frequency f ofiSecondary side feedback voltage signal
The amplitudes of the two signals respectively represent symbols when the power distribution network generates LC resonance;
an incremental damping rate calculation module to: the method comprises the steps that the ground conductance and the ground capacitance of the power distribution network when small current signals of each frequency are injected are respectively taken as the ground conductance and the ground capacitance when the power distribution network generates LC resonance; then, the incremental damping rate d at each frequency is calculated according to the following equation (5) and the ground conductance G and the ground capacitance Cdi：
In the formula, g0、rLFor the earth conductance of the distribution network before a fault and the equivalent loss resistance, omega, of the arc suppression coiliAs a low current signal
The angular frequency of (d);
a fault identification module to: according to the criterion preset by the following formula (6), in the multi-frequency superposition process of different frequency numbers i of frequency conversion from 1 to n, judging whether an inequality in the criterion is met, if so, judging that the power distribution network has a ground fault, if not, judging that the power distribution network is in a three-phase unbalanced state and if not, judging that the power distribution network has a neutral point voltage displacement, and the preset criterion is as follows:
wherein d issetTo a preset damping rate start value, d0Is the inherent damping rate, d, of the distribution networkLAdditional damping ratio for the arc suppression coil, gsetFor setting the transition conductance, n is the number of times of superposition of the multi-frequency incremental damping rate, omegaimFor the LC resonance angular frequency of the distribution network, INT () is a rounding function.
5. The apparatus of claim 4, wherein the signal injection and feedback module injects a same amplitude frequency-converted small current signal into the power distribution network
The frequency range of (a) is: f. of0±5Hz，f0Is the power frequency of the power distribution network.
6. The apparatus of claim 4, further comprising a normalization module to: after the incremental damping rate at each frequency is obtained through calculation, the incremental damping rate is reduced to the power frequency angular frequency, and the reduced incremental damping rate d'diComprises the following steps:
7. an apparatus comprising a processor and a memory; wherein: the memory is to store computer instructions; the processor is configured to execute the computer instructions stored by the memory, in particular to perform the method according to any one of claims 1 to 3.
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