CN114498574A - High-frequency impedance differential protection method for high-proportion photovoltaic power distribution network - Google Patents
High-frequency impedance differential protection method for high-proportion photovoltaic power distribution network Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
- H02H7/262—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of switching or blocking orders
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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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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
- H02H7/263—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of measured values
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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Abstract
A high-frequency impedance differential protection method for a photovoltaic power distribution network with a high proportion utilizes a high-frequency component generated by voltage and current mutation of a fault component when a line is in short circuit to obtain a high-frequency impedance, and forms a protection criterion to judge faults inside and outside a region by comparing the relation between the average value of an action high-frequency impedance under a plurality of frequency points and the average value of a brake high-frequency impedance under a plurality of frequency points during fault.
Description
Technical Field
The invention relates to a technology in the field of power grid control, in particular to a high-frequency impedance differential protection method and device for a photovoltaic power distribution network with a high proportion.
Background
After large-scale distributed photovoltaic is connected into a power distribution network, due to the intermittent nature of photovoltaic power generation and the nonlinear relation between output current and grid-connected point voltage, the fault current characteristic is changed, the current protection setting value is difficult to set, and the current protection setting value does not have directionality, so that the current protection cannot meet the protection requirement of the power distribution network containing the photovoltaic. The application of differential protection in a power distribution network is mainly limited by the following three points: firstly, there are more T-junction branches in the distribution network, which has a large impact on the traditional differential protection. Secondly, the inverter control strategy of the grid-connected photovoltaic has large influence on the transient process length of the fault current and the steady-state amplitude and phase angle of the power frequency quantity, so that the transient process time of the power frequency electric quantity is different and the steady-state amplitude is unstable during fault. Thirdly, the differential protection based on the power frequency quantity has higher requirements on the synchronization of the two ends of the line data, and the transformation cost of the differential protection is high. In addition, when the voltage drop of a grid-connected point is serious, the phase-locked loop cannot work normally, the photovoltaic fault current has non-power frequency characteristics, and the protection performance based on the power frequency quantity is unstable. In summary, after the large-scale distributed photovoltaic is connected to the power distribution network, the original protection adaptability of the power distribution network becomes poor, and new protection needs to be provided urgently to meet the protection requirement of the power distribution network containing the high-proportion distributed photovoltaic.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a high-frequency impedance differential protection method for a photovoltaic power distribution network with a high proportion, which only needs to extract data of 5ms before and after the protection starting time, has short data window, rapid action, no need of synchronization of double-end data, small influence by the change of a photovoltaic operation mode and a control strategy thereof, can adapt to the condition that a circuit has T-connection branches, has stronger anti-transition resistance capability and anti-noise interference capability, can correctly and rapidly identify various types of short-circuit faults, and is favorable for the isolation and recovery of power grid faults.
The invention is realized by the following technical scheme:
the invention relates to a high-frequency impedance differential protection method for a photovoltaic power distribution network with a high proportion, which obtains high-frequency impedance by utilizing high-frequency components generated by voltage and current mutation of fault components when a line is short-circuited, and forms a protection criterion to judge faults inside and outside a zone by comparing the relation between the average value of action high-frequency impedance under a plurality of frequency points and the average value of brake high-frequency impedance under a plurality of frequency points during fault, wherein the method specifically comprises the following steps: the measuring device is positioned at the head end of the circuit, namely the protection M side, and at the tail end of the circuit, namely the protection N side, continuously measures fault component voltage, after the time difference of the fault component voltage crosses a threshold value, protection is started, 2.5ms of fault component voltage current before and after the protection starting moment is extracted, frequency spectrum decomposition is carried out to obtain high-frequency impedance, the high-frequency impedance measured through the protection at the head end of the circuit and the high-frequency impedance measured through the protection at the tail end of the circuit are used for obtaining calculation high-frequency impedance and calculating high-frequency impedance, and therefore the judgment of faults in a region is achieved, and tripping signals are sent to the circuit breaker.
The measuring device is as follows: a voltage transformer and a current transformer.
The threshold value is as follows: the difference of the fault component voltage to the time is 0kV/s theoretically when no fault exists, so that the threshold value is set to be 0.1kV/s to ensure a certain margin, and the actual engineering can be adjusted according to the protection reliability.
The judgment of the faults in the area refers to the following steps: when the calculated action high-frequency impedance is larger than the calculated braking high-frequency impedance, judging that the fault is in the area and sending a tripping signal to the breaker; otherwise, it is an out-of-area fault.
The starting criterion is as follows: when the circuit operates normally, the fault voltage component does not exist or is very small, and the time difference is almost 0; at the moment of a fault, the voltage of a fault component suddenly changes, the time difference is obviously increased, and the characteristic can be used for constructing an M-side starting criterion:
|duMdt | > epsilon and the N-side start criterion: | duNDt | > ε, wherein: u. ofMAnd uNThe instantaneous values of fault component voltages of the M side and the N side are respectively, the grounding impedance relay uses the fault component phase voltages, the interphase impedance relay uses the fault component line voltages, epsilon is a threshold value, and the value of epsilon is to ensure that the protection is reliably started when the slightest fault occurs in a region and a certain margin is reserved.
The protection criterion is as follows: calculating the high frequency impedance of the motion
And calculating the brake high frequency impedance
Wherein: zr JFor calculating the high-frequency impedance of motion, Zres JIn order to calculate the braking high-frequency impedance,
and
for action and braking high-frequency impedance of selected frequency, n is the number of selected frequency points, fiFor the frequency of the selected frequency point, when the internal fault occurs, the action high-frequency impedance is larger than the brake high-frequency impedance, and the external fault is just opposite, so that the protection identification criterion is constructed as follows:
wherein: k is a reliability coefficient, which varies with different requirements on reliability in actual engineering, but the reliability coefficient must be greater than 1, and preferably the reliability coefficient is 1.2.
The calculated action high-frequency impedance Zr JAnd calculating the braking high-frequency impedance Zres JThe action high-frequency impedance and the braking high-frequency impedance are obtained by the mean value under different frequency points, and the action high-frequency impedance ZrAnd braking high frequency impedance ZresThe calculation formulas are respectively as follows: zr＝|ZM+ZN|，Zres＝|ZM-ZNL, wherein: zMMeasuring high-frequency impedance, Z, for protection of MNTo protect N, the high frequency impedance is measured.
The identification criterion needs to adopt actions and braking high-frequency impedance under a plurality of frequency points for calculation, namely the calculated action high-frequency impedance Z is obtainedr JAnd calculating the braking high-frequency impedance Zres JThe selection of the multiple frequency points should follow a frequency selection principle, specifically:
1) the lower limit is a frequency determined by the following formula, only satisfying
The impedance is constant in the frequency distribution type photovoltaic high frequency, the distribution type photovoltaic is approximate to a linear element, wherein: c is the filter capacitance, CDCIs a DC side capacitor of the inverter, L1The filter is a power grid side inductor;
2) according to the sampling theorem, the upper limit should be less than half the sampling frequency, i.e.:
wherein: f. ofsIs the sampling frequency.
3) The frequency resolution of the spectrogram obtained by Fourier decomposition is determined by a data window and is as follows:
wherein: f. ofiAnd fjFor selected frequency point frequency, z is any integer, tsIs the data window length.
The frequency points are preferably 2200Hz, 2600Hz, 3000Hz, 3400Hz and 3800 Hz.
Technical effects
The method integrally solves the problem that the existing power frequency protection of the power distribution network is influenced by the photovoltaic operation mode and the inverter control and can not correctly identify the faults inside and outside the area;
compared with the prior art, the method only needs to extract data of 5ms, which is 2.5ms before and after the fault, so as to perform fault identification, the protection action is rapid, the data of two ends does not need to be synchronous, the method is not influenced by a distributed photovoltaic operation mode and a control strategy, the method can adapt to the condition that a circuit has T connection, and the accurate identification of the fault position can be realized under the condition that a power distribution network contains high-proportion distributed photovoltaic.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a schematic diagram of a 10kV ring network type power distribution network according to an embodiment;
FIG. 3 is a schematic diagram illustrating the metallic short-circuit identification result inside and outside the MN region of the circuit according to the embodiment;
in the figure: the solid line is braking high-frequency impedance, the dotted line is action high-frequency impedance, the circle is braking high-frequency impedance at the selected frequency, and the cross is action high-frequency impedance at the selected frequency;
FIG. 4 is a schematic diagram of the simulation result of the inside and outside short circuit recognition in the AB area of the circuit according to the embodiment;
in the figure: the solid line is braking high-frequency impedance, the dotted line is action high-frequency impedance, the circle is braking high-frequency impedance at the selected frequency, and the cross is action high-frequency impedance at the selected frequency;
FIG. 5 is a schematic diagram illustrating three-phase short circuit fault identification in different photovoltaic operation modes according to an embodiment;
in the figure: the solid line is braking high-frequency impedance, the dotted line is action high-frequency impedance, the circle is braking high-frequency impedance at the selected frequency, and the cross is action high-frequency impedance at the selected frequency;
fig. 6 is a schematic diagram illustrating three-phase short circuit identification under different photovoltaic control strategies according to an embodiment.
In the figure: the solid line is braking high-frequency impedance, the dotted line is action high-frequency impedance, the circle is braking high-frequency impedance of the selected frequency, and the cross is action high-frequency impedance of the selected frequency.
Detailed Description
As shown in fig. 2, for the rationality of verifying the high-frequency impedance differential protection of the photovoltaic power distribution network with a high ratio, the 10kV ring network type power distribution network adopting the low-current grounding mode in this embodiment includes: A. b, M, N, distributed photovoltaic is connected with the protection N back side bus and the T access line AB through the special line, the rated capacity of the distributed photovoltaic power supply is 8MVA, the distributed photovoltaic power supply is in the unit power factor operation state when in normal operation, and the control of inhibiting negative sequence current is adopted. The peak load capacity is 2MVA, and the power factor is 0.85. The switch cabinets are all provided with switch station terminal equipment, data communication can be achieved, and the data sampling frequency is 10 kHz.
As shown in fig. 1, this embodiment specifically includes the following steps:
step 1: and calculating the voltage difference value of the fault components at two ends of the line at the minimum sampling interval.
Step 2: and if the voltage difference value meets the starting criterion, starting protection, and turning to the step 3, otherwise, returning to the step 1.
And step 3: and respectively extracting 5ms data of 2.5ms before and after the starting time for the fault component voltage and the fault component current of the M side and the N side, and performing frequency spectrum decomposition to obtain fault high-frequency voltage and fault high-frequency current.
And 4, step 4: the M and N sides calculate the high frequency impedance, respectively.
And 5: and if the high-frequency impedances of the M side and the N side exist, the step 6 is carried out, otherwise, the step 1 is returned.
Step 6: and obtaining action high-frequency impedance and braking high-frequency impedance through the high-frequency impedances of the M side and the N side.
And 7: and determining the selected frequency through a frequency selection principle, thereby obtaining a calculated action high-frequency impedance and a calculated brake high-frequency impedance.
And 8: and (4) identifying the fault position by calculating action high-frequency impedance and brake high-frequency impedance, if the fault is an in-zone fault, sending a tripping signal to the two-side protection, and otherwise, returning to the step 1.
As can be seen from FIG. 3, according to the method of this embodiment, when a metallic short circuit occurs in the MN line area (k1), outside the forward direction area (k2), and outside the reverse direction area (k3), the operating high-frequency impedance Z is calculated at the time of an in-area faultr JGreater than the calculated braking high-frequency impedance Zres JMultiplying by a reliability factor k, identifying positiveConfirming; calculating the action high-frequency impedance Z at the time of an out-of-range faultr JLess than the calculated braking high-frequency impedance Zres JAnd multiplying by a reliability coefficient k to identify the correct data.
The fault recognition of the protection scheme according to the embodiment is shown in fig. 4 when a metallic short circuit occurs inside and outside the AB region of the line in the presence of a T connection. As can be seen, the calculated operating high frequency impedance Z at the time of an in-zone faultr JGreater than the calculated braking high-frequency impedance Zres JMultiplying by a reliability coefficient k; calculating high-frequency impedance Z of motion during fault outside forward and reverse directionsr JLess than the calculated braking high-frequency impedance Zres JAnd multiplying by a reliable coefficient k, identifying correctly when faults occur inside and outside the area, and protecting the circuit to be suitable for the T connection condition of the circuit.
Distributed photovoltaic at 0.5PNFig. 5 shows the case of fault recognition when a metallic three-phase short circuit occurs inside and outside the MN region of the line during power output and offline. The photovoltaic adopts a control strategy of inhibiting active fluctuation and reactive fluctuation, and when a metallic three-phase short circuit occurs outside a MN region of a line, the fault identification condition is shown in figure 6. As can be seen from the figure, the identification results are correct, and the photovoltaic operation mode and the control strategy are protected from being influenced.
Simulation results show that the high-frequency impedance differential protection of the high-proportion photovoltaic power distribution network is applied to the high-proportion distributed photovoltaic power distribution network, and the fault identification and isolation capability of the power distribution network can be effectively improved.
In conclusion, the protection strategy is not influenced by the control of the photovoltaic inverter, can adapt to the T connection condition of the protected line, and can meet the problem of poor protection adaptability of the high-proportion distributed photovoltaic power distribution network.
The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (9)
1. A high-frequency impedance differential protection method for a photovoltaic power distribution network with a high proportion is characterized in that high-frequency impedance is obtained by utilizing high-frequency components generated by sudden changes of voltage and current of fault components when a line is in short circuit, and by comparing the relation between the average value of action high-frequency impedance under a plurality of frequency points and the average value of brake high-frequency impedance under a plurality of frequency points during fault, the internal and external faults of a protection criterion distinguishing area are formed, and the method specifically comprises the following steps: the measuring device is positioned at the head end of the circuit, namely the protection M side, and the measuring device is positioned at the tail end of the circuit, namely the protection N side, and continuously measures fault component voltage, after the time difference of the fault component voltage exceeds a threshold value, protection is started, and 2.5ms of fault component voltage current before and after the protection starting time is extracted for frequency spectrum decomposition to obtain high-frequency impedance, and the high-frequency impedance measured by the protection at the head end of the circuit and the high-frequency impedance measured by the protection at the tail end of the circuit are used for calculating the high-frequency impedance and calculating the high-frequency impedance, so that the fault judgment in a region is realized, and a tripping signal is sent to the circuit breaker.
2. The high-frequency impedance differential protection method for the photovoltaic power distribution network with the high proportion as claimed in claim 1, wherein the threshold value is as follows: 0.1 kV/s.
3. The high-frequency impedance differential protection method for the photovoltaic power distribution network with the high proportion as claimed in claim 1, wherein the judgment of the fault in the area is as follows: when the calculated action high-frequency impedance is larger than the calculated braking high-frequency impedance, judging that the fault is in the area and sending a tripping signal to the breaker; otherwise, it is an out-of-area fault.
4. The high-frequency impedance differential protection method containing the high-proportion photovoltaic power distribution network according to claim 1, wherein the starting criterion is as follows: when the circuit operates normally, the fault voltage component does not exist or is very small, and the time difference is almost 0; at the moment of a fault, the voltage of a fault component suddenly changes, the time difference is obviously increased, and the characteristic can be used for constructing an M-side starting criterion: | duMDt | > epsilon and the N-side start criterion: | duNDt | > ε, where: u. ofMAnd uNFor M-side and N-side instantaneous values of fault component voltage, respectively, for use in a grounded impedance relayAnd the phase voltage of the fault component is used, the voltage of the fault component is used by the interphase impedance relay, epsilon is a threshold value, and the value of epsilon is to ensure that the protection is reliably started when the slightest fault occurs in the area and a certain margin is reserved.
5. The high-frequency impedance differential protection method containing the high-proportion photovoltaic power distribution network according to claim 1, wherein the protection criterion is as follows: calculating the high frequency impedance of the motion
And calculating the brake high frequency impedance
Wherein: zr JIn order to calculate the high-frequency impedance of the motion,
in order to calculate the braking high-frequency impedance,
and
for action and braking high frequency impedance of selected frequency, n is the number of selected frequency points, fiFor the frequency of the selected frequency point, when the internal fault occurs, the action high-frequency impedance is larger than the brake high-frequency impedance, and the external fault is just opposite, so that the protection identification criterion is constructed as follows:
wherein: k is the reliability coefficient.
6. The method for high frequency impedance differential protection in connection with a high percentage of photovoltaic power distribution networks of claim 5 wherein the reliability factor is 1.2.
7. The high ratio of claim 5The high-frequency impedance differential protection method of the photovoltaic power distribution network is characterized in that the high-frequency impedance Z of the calculation action is calculatedr JAnd calculating the braking high frequency impedance
The action high-frequency impedance and the braking high-frequency impedance are obtained by the mean value under different frequency points, and the action high-frequency impedance Zr＝|ZM+ZNI, braking high frequency impedance Zres＝|ZM-ZNL, wherein: zMMeasuring high-frequency impedance, Z, for protection of MNTo protect N, the high frequency impedance is measured.
8. The high-frequency impedance differential protection method for the photovoltaic power distribution network with the high proportion as claimed in claim 5, wherein the high-frequency impedance of the calculated action is obtained by calculating the action and braking high-frequency impedance at a plurality of frequency points according to the identification criterion
And calculating the brake high frequency impedance
The selection of the multiple frequency points should follow a frequency selection principle, specifically:
1) the lower limit is a frequency determined by the following formula, only satisfying
The impedance is constant in the frequency distribution type photovoltaic high frequency, the distribution type photovoltaic is approximate to a linear element, wherein: c is the filter capacitance, CDCIs a DC side capacitor of the inverter, L1The filter is a power grid side inductor;
2) according to the sampling theorem, the upper limit should be less than half the sampling frequency, i.e.:
wherein: f. ofsIs the sampling frequency;
3) the frequency resolution of the spectrogram obtained by Fourier decomposition is determined by a data window and is as follows:
wherein: f. ofiAnd fjFor selected frequency point frequency, z is any integer, tsIs the data window length.
9. The high-frequency impedance differential protection method containing the high-proportion photovoltaic power distribution network of any one of the preceding claims, wherein the multiple frequency points are 2200Hz, 2600Hz, 3000Hz, 3400Hz and 3800 Hz.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115085164A (en) * | 2022-07-25 | 2022-09-20 | 华北电力大学 | Wind field outbound interactive protection method and system |
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| Title |
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| 晁晨栩等: "含高比例光伏配电网的高频阻抗差动保护", 《中国电机工程学报》, pages 2 - 4 * |
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| CN115085164A (en) * | 2022-07-25 | 2022-09-20 | 华北电力大学 | Wind field outbound interactive protection method and system |
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