CN112260219B - Single-interval comprehensive protection method for ground fault of power distribution network - Google Patents
Single-interval comprehensive protection method for ground fault of power distribution network Download PDFInfo
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- CN112260219B CN112260219B CN201910965676.7A CN201910965676A CN112260219B CN 112260219 B CN112260219 B CN 112260219B CN 201910965676 A CN201910965676 A CN 201910965676A CN 112260219 B CN112260219 B CN 112260219B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/16—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to fault current to earth, frame or mass
- H02H3/162—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to fault current to earth, frame or mass for ac systems
- H02H3/165—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to fault current to earth, frame or mass for ac systems for three-phase systems
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
- Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
- Y04S10/52—Outage or fault management, e.g. fault detection or location
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Abstract
The invention discloses a single-interval comprehensive protection method for a power distribution network ground fault. Double-frequency sampling is adopted, a low-frequency sampling signal is used for detecting a single-phase earth fault of a large-current grounding system and a single-interval conventional protection function, and a high-frequency sampling signal is converted through a wavelet packet to detect the single-phase earth fault of a small-current grounding system. And (3) the grounding mode of the self-adaptive detection system selects a corresponding criterion to judge the single-phase grounding. The method can be realized in a conventional single-interval comprehensive protection device, solves the problem that the rapid processing of various types of ground faults under different grounding modes is difficult to realize when only a single-interval protection device is configured at present, does not need to be configured with a centralized small-current grounding line selection device, can solve the problem that the wiring of the existing centralized small-current grounding line selection device is complex, effectively simplifies protection configuration and saves investment.
Description
Technical Field
The invention relates to the field of relay protection of a power system, in particular to a single-interval comprehensive protection method for a power distribution network ground fault.
Background
In 3kV-66kV power systems, single-phase grounding is a relatively common type of fault.
For a large-current grounding system, a steady-state zero-sequence overcurrent method is generally adopted to detect a grounding fault at present. When a line has a ground fault, the line is not in instantaneous metallic grounding, but a transition resistor, especially a large transition resistor, exists at a grounding point, so that the grounding current is very small and cannot reach the action value of zero-sequence overcurrent protection, and the protection is often rejected.
For a small-current grounding system, when single-phase grounding occurs, the grounding fault current is very small, and the steady-state zero-sequence overcurrent method is difficult to detect. At present, a centralized grounding line selection device is generally adopted to detect a branch which is grounded, or a small resistor is put into a neutral point after zero sequence overvoltage is detected for a period of time, so that a system grounding mode is changed into a large-current grounding mode, and a stable zero sequence overcurrent protection of a single-interval protection device is used for detecting a grounding fault. The centralized grounding line selection device is adopted, the investment of the device and the cable is required to be increased, the wiring is complex, and the operation and the maintenance are inconvenient. The mode of switching small resistance after the ground fault occurs and increasing the zero sequence current to pass through the fault in the overcurrent protection detection area is adopted, so that on one hand, the fault processing time is prolonged, on the other hand, the ground fault characteristics are changed, and the judgment result of the small current grounding line selection device is interfered.
Disclosure of Invention
The invention aims to provide a single-interval comprehensive protection method for ground faults of a power distribution network, and solves the problem that the rapid processing of various types of ground faults under different grounding modes is difficult to realize only configuring a single-interval protection device at present.
In order to achieve the purpose, the invention adopts the technical scheme that: a single-interval comprehensive protection method for a power distribution network ground fault comprises the following steps:
the method comprises the following steps: sampling in real time by double frequency, collecting three-phase voltage and zero sequence current data of the interval protection installation place, sampling the zero sequence voltage data by three-phase voltageCalculating data, and calculating zero sequence current amplitude I by using low frequency sampling data 0 Calculating zero sequence voltage amplitude U through low-frequency three-phase voltage sampling data 0 And amount of mutation DeltaU 0 ；
Step two: detecting zero sequence voltage amplitude U 0 Whether the system is out of limit or not, if so, judging that the system has a ground fault, and entering a third step;
step three: calculating the transient zero-sequence power direction by using the high-frequency zero-sequence current and zero-sequence voltage data, and calculating the transient zero-sequence power direction if the zero-sequence break variable delta U 0 Exceeds a preset threshold value delta U 0set The transient zero-sequence power direction of the moment points to the fourth quadrant, and the zero-sequence current amplitude I 0 Exceeds a predetermined threshold value I 0set If the grounding system is judged to be a large-current grounding system, the step IV is carried out, otherwise, the grounding system is judged to be a small-current grounding system, and the step V is carried out;
step four: calculating the angle of the steady-state zero-sequence current leading the zero-sequence voltage by using the low-frequency zero-sequence current and zero-sequence voltage data, judging that the current is an internal fault if the current accords with the internal fault characteristics of the large-current grounding system, and resetting if the current is not the internal fault;
step five: take Delta U 0 Decomposing and reconstructing the high-frequency sampling data of each power frequency period before and after the threshold crossing by using a wavelet packet, selecting a frequency band with the maximum energy, judging that the fault is in the region if the transient zero-sequence power direction of the frequency band in the two power frequency periods accords with the fault characteristics in the region of the low-current grounding system, and resetting if the transient zero-sequence power direction of the frequency band in the two power frequency periods does not accord with the fault characteristics in the region of the low-current grounding system.
Further, in the above scheme, the low frequency is greater than 100Hz, and the high frequency is greater than 6000 Hz.
Furthermore, in the scheme, the low-frequency sampling data is used for detecting the single-phase earth fault of the large-current grounding system and the single-interval conventional protection function, and the high-frequency sampling data is converted by the wavelet packet to detect the single-phase earth fault of the small-current grounding system.
Further, in the second step in the above scheme, the zero sequence voltage amplitude U is detected 0 Whether the limit is exceeded is specifically determined as U 0 Whether or not it is greater than a constant value U 0set (ii) a Wherein U is 0set The value range is 5% -20% of the interphase voltage.
Further, in the third step in the above scheme, Δ U 0set The value range is 3% -10% of interphase voltage, I 0set The value range is 5-15% of rated current.
Further, in the fourth step of the scheme, if the zero-sequence current leads the zero-sequence voltage by-165-15 degrees, the fault is judged to be an internal fault.
Further, in the fifth step in the above scheme, if the zero-sequence power direction of the frequency band in the two power frequency cycles is 0-180 °, an intra-area fault is determined.
The invention has the beneficial effects that:
(1) the method can adaptively detect the single-phase earth fault of the protected interval under different earth modes, the longest discrimination time is only one power frequency period, and the aim of rapidly disposing the single-phase earth fault can be achieved.
(2) The invention adopts double-frequency sampling, the low-frequency sampling signal is used for detecting the single-phase earth fault of the heavy-current grounding system and the single-interval conventional protection function, the high-frequency sampling signal is used for detecting the single-phase earth fault of the small-current grounding system through wavelet packet transformation, and the high-sensitivity earth fault detection function is realized on the single-interval protection device.
(3) The method can be realized in a conventional single-interval comprehensive protection device, a centralized small-current grounding line selection device is not required to be configured, the problem that the existing centralized small-current grounding line selection device is complex in wiring can be solved, the protection configuration is effectively simplified, and the investment is saved.
(4) When the system adopts a mode of putting a small resistor into a neutral point after the ground fault occurs, a detection result can be given once before the small resistor is put into the system, the fault processing speed is accelerated, the change of the ground mode is detected in a self-adaptive mode after the small resistor is put into the system, the detection criterion is switched for detection again, and the protection reliability is improved.
Drawings
Fig. 1 is a connection diagram of a single-interval comprehensive protection system for realizing the earth fault of a power distribution network.
Fig. 2 is a zero sequence vector diagram of a ground fault of a large-current grounding system.
Fig. 3(a) zero sequence equivalent network of the low current grounding system ground fault.
Fig. 3(b) zero sequence vector diagram of the earth fault of the small current grounding system.
Fig. 4 is a logic flow diagram of a single-interval comprehensive protection method for ground faults of a power distribution network.
Detailed Description
The invention discloses a single-interval comprehensive protection method for ground faults of a power distribution network, which solves the problem that the ground faults under different grounding modes are difficult to rapidly process when only a single-interval protection device is configured at present.
The first embodiment is as follows:
in the embodiment, the connection of the ground fault single-interval comprehensive protection system of the power distribution network is realized as shown in fig. 1, and the ground fault single-interval comprehensive protection device is connected with a bus three-phase voltage transformer and a zero-sequence current transformer of the interval and is used for completing the acquisition of bus three-phase voltage and zero-sequence current of the interval; and judging the existence of the ground fault, judging the fault in the area and removing the fault according to the collected bus voltage and zero sequence current.
The embodiment of the single-interval comprehensive protection method for the ground fault of the power distribution network comprises the following steps:
the method comprises the following steps: sampling with double frequency in real time, wherein the low frequency is more than 100Hz, the high frequency is more than 6000Hz, collecting three-phase voltage and zero-sequence current data at the interval protection installation position, calculating the zero-sequence voltage data from the three-phase voltage sampling data, and calculating the zero-sequence current amplitude I by using the low frequency sampling data 0 Calculating zero sequence voltage amplitude U through low-frequency three-phase voltage sampling data 0 And amount of mutation DeltaU 0 。
Step two: detecting zero sequence voltage amplitude U 0 Whether it exceeds the limit, if it is larger than the fixed value U 0set Judging that the system has a ground fault, and entering a third step; otherwise, resetting is carried out. Wherein, U 0set The value range can be 5% -20% of the interphase voltage.
Step three: calculating the transient zero-sequence power direction by using the high-frequency zero-sequence current and zero-sequence voltage data, and calculating the transient zero-sequence power direction if the zero-sequence break variable delta U 0 Exceeds a preset threshold value delta U 0set The transient zero-sequence power direction of the moment points to the fourth quadrant, and simultaneously zero-sequence powerAmplitude of flow I 0 Exceeds a predetermined threshold value I 0set If not, the grounding system is judged to be a low-current grounding system, and the step five is entered. Wherein, Delta U 0set The value range can be 3% -10% of interphase voltage, I 0set 5 to 15 percent of rated current can be obtained.
Step four: and calculating the angle of the steady-state zero-sequence current leading the zero-sequence voltage by using the low-frequency zero-sequence current and zero-sequence voltage data, judging that the current is an internal fault if the current accords with the internal fault characteristics of the large-current grounding system, and resetting if the current is not consistent with the internal fault characteristics. The criterion of the fault characteristics in the large-current grounding system area adopted in the embodiment is as follows: and if the zero-sequence current leads the zero-sequence voltage by-165-15 degrees, judging that the fault is an internal fault.
Step five: taking Delta U 0 Decomposing and reconstructing the high-frequency sampling data of each power frequency period before and after the threshold crossing by using a wavelet packet, selecting a frequency band with the maximum energy, judging that the fault is in the region if the transient zero-sequence power direction of the frequency band in the two power frequency periods accords with the fault characteristics in the region of the low-current grounding system, and resetting if the transient zero-sequence power direction of the frequency band in the two power frequency periods does not accord with the fault characteristics in the region of the low-current grounding system. The criterion of the fault characteristics in the small current grounding system area adopted in the embodiment is as follows: and if the zero sequence power direction of the frequency band in the two power frequency periods is 0-180 degrees, judging that the frequency band is an intra-area fault.
The principle of the scheme is as follows:
in a large current grounding system (such as a neutral point directly grounded or grounded through a small resistor), both the zero sequence voltage and the zero sequence current are 0 when the system is in normal operation. If the earth fault occurs, the zero-sequence power supply is at a fault point, and the zero-sequence voltage of the fault point is the highest. The zero sequence current is generated by zero sequence voltage and flows to the ground from a fault point through a line and a neutral point. The vector diagram of the zero sequence voltage and the zero sequence current of the large-current grounding system is shown in fig. 2. In FIG. 2
And
the included angle of the zero-sequence current path is beta, and the beta is equal to the zero-sequence impedance angle of the zero-sequence current path. The zero sequence impedance of the large-current grounding system is inductive,so the direction of the transient zero-sequence power at the moment of grounding points to the fourth quadrant. Generally, when influence of ground loop resistance (neutral point grounding resistance and fault point transition resistance) is not considered, the zero sequence impedance angle of the system is taken as 75 degrees, and the zero sequence impedance angle is selected after the fault is stable
The 180-degree area with the direction as the center is an in-area judgment area, and as shown by a slash area in figure 2, the in-area judgment of the invention can be a zero-sequence current advanced zero-sequence voltage-165-15-degree area.
In a small current grounding system (such as an ungrounded system and a grounding system through an arc suppression coil), when the system normally operates, the zero sequence voltage and the zero sequence current are both 0. If the earth fault occurs, the zero sequence power supply is at a fault point, and the zero sequence voltage of the fault point is the highest. Because the neutral point is not effectively grounded, the grounding current is very small, and in addition, if the system is grounded through a compensated arc suppression coil, after the grounding fault is stabilized, the zero sequence current of the fault branch circuit has the same characteristics as the non-fault branch circuit, so that the grounding fault can not be judged by adopting a steady-state zero sequence overcurrent method. As shown in fig. 3(a), at the transient moment of the ground fault, the capacitance currents of all the non-fault branches flow into the fault branch from the bus through the earth and the ground fault point, and then flow to the bus from the line of the fault branch, and the transient zero-sequence power direction of the fault line is opposite to that of the non-fault branch. When a ground fault of the low-current grounding system occurs instantaneously, the transient zero-sequence power is mainly capacitive reactive power, as shown in fig. 3(b), the power direction is 0-180 degrees, and the transient zero-sequence power can be properly deflected to the second quadrant in consideration of the influence of resistance.
Example two:
in the second embodiment of the single-interval comprehensive protection method for the ground fault of the power distribution network, a single-interval comprehensive protection device for the ground fault is connected with a bus three-phase voltage transformer and a zero-sequence current transformer at the interval and is used for completing the collection of the bus three-phase voltage and the zero-sequence current at the interval; and judging the existence of the ground fault, judging the fault in the area and removing the fault according to the collected bus voltage and zero sequence current.
In the present embodiment, the voltage transformer is used onceThe value of 10kV, the secondary rated value of 100V and the transformation ratio of the branch zero-sequence transformer of 50/1, the zero-sequence voltage is fixed value U 0set Set to 15V, zero sequence voltage break variable delta U 0set Set to 5V, zero sequence over-current definite value I 0set The setting is 0.1A, and the fixed values are all secondary values.
The ground fault detection comprises the steps of data acquisition and processing, fault starting, ground mode judgment and in-zone judgment, the logic is as shown in figure 4, specifically,
the method comprises the following steps: real-time dual-frequency sampling, wherein the low frequency is 1.2kHz, the high frequency is 9.6kHz, three-phase voltage and zero-sequence current data of the interval protection installation part are collected, the zero-sequence voltage data is obtained by calculating the three-phase voltage sampling data, and the zero-sequence current amplitude I is calculated by using the low-frequency sampling data 0 Calculating the amplitude U of the zero-sequence voltage through the low-frequency three-phase voltage sampling data 0 And amount of mutation DeltaU 0 ；
Step two: detecting zero sequence voltage amplitude U 0 If it is greater than the constant value U 0set Judging that the system has a ground fault, and entering a third step; u in this example 0set The value is 15V.
Step three: calculating the transient zero-sequence power direction by using the high-frequency zero-sequence current and zero-sequence voltage data, and calculating the transient zero-sequence power direction if the zero-sequence break variable delta U 0 Over a constant value Δ U 0set The transient power direction of the moment points to the fourth quadrant, and the zero sequence current amplitude I 0 Exceeding a constant value I 0set If the grounding system is judged to be a large-current grounding system, the step IV is carried out, otherwise, the grounding system is judged to be a small-current grounding system, and the step V is carried out; wherein, Delta U 0set The value is 5V, I 0set The value is 0.1A.
Step four: calculating the angle of the steady-state zero-sequence current leading zero-sequence voltage by using the low-frequency zero-sequence current and zero-sequence voltage data, judging that the current is an internal fault if the current is-165-15 degrees, and resetting if the current is not-165-15 degrees;
step five: taking Delta U 0 Decomposing and reconstructing the used high-frequency sampling data in each power frequency period before and after the threshold crossing by using a wavelet packet, selecting a frequency band with the maximum energy, judging as an intra-area fault if the zero sequence power direction of the frequency band in the two power frequency periods is 0-180 degrees, and resetting if the zero sequence power direction of the frequency band in the two power frequency periods is not 0-180 degrees.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (3)
1. A single-interval comprehensive protection method for a power distribution network ground fault is characterized by comprising the following steps:
the method comprises the following steps: sampling with double frequency in real time, collecting three-phase voltage and zero-sequence current data at the interval protection installation position, calculating the zero-sequence voltage data from the three-phase voltage sampling data, and calculating zero-sequence current amplitude I by using the low-frequency sampling data 0 Calculating zero sequence voltage amplitude U through low-frequency three-phase voltage sampling data 0 And amount of mutation DeltaU 0 ；
Step two: detecting zero sequence voltage amplitude U 0 Whether the system is out of limit or not, if so, judging that the system has a ground fault, and entering a third step; the zero sequence voltage amplitude value U is detected 0 Whether the crossing of the limit is specific to judge U 0 Whether or not it is greater than a constant value U 0set (ii) a Wherein U is 0set The value range is 5% -20% of the interphase voltage;
step three: calculating the transient zero-sequence power direction by using the high-frequency zero-sequence current and zero-sequence voltage data, and calculating the transient zero-sequence power direction if the zero-sequence break variable delta U 0 Exceeds a predetermined threshold value delta U 0set The transient zero-sequence power direction of the moment points to the fourth quadrant, and the zero-sequence current amplitude I 0 Exceeds a predetermined threshold value I 0set If the grounding system is judged to be a large-current grounding system, the step IV is carried out, otherwise, the grounding system is judged to be a small-current grounding system, and the step V is carried out; wherein, Delta U 0set The value range is 3% -10% of interphase voltage, I 0set The value range is 5% -15% of rated current;
step four: calculating the angle of the leading zero-sequence voltage of the steady-state zero-sequence current by using the low-frequency zero-sequence current and zero-sequence voltage data, if the characteristic of the fault in the large-current grounding system is met, namely the zero-sequence current leads the zero-sequence voltage by-165-15 degrees, judging the fault in the zone, and otherwise, resetting the fault;
step five: take Delta U 0 Decomposing and reconstructing the high-frequency sampling data of each power frequency period before and after the threshold crossing by using a wavelet packet, selecting a frequency band with the maximum energy, if the transient zero-sequence power direction of the frequency band in the two power frequency periods accords with the fault characteristics in the small current grounding system, namely the zero-sequence power direction of the frequency band in the two power frequency periods is 0-180 degrees, judging the fault in the region, and if not, resetting the fault.
2. The method according to claim 1, wherein the double-frequency sampling is performed, wherein the low frequency is greater than 100Hz, and the high frequency is greater than 6000 Hz.
3. The method for single-interval comprehensive protection of the ground fault of the power distribution network according to claim 1, wherein the low-frequency sampled data is used for detecting a single-phase ground fault of the large-current grounding system and a single-interval conventional protection function, and the high-frequency sampled data is subjected to wavelet packet transformation and then is used for detecting the single-phase ground fault of the small-current grounding system.
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| CN104779594A (en) * | 2015-04-27 | 2015-07-15 | 西安热工研究院有限公司 | Inter-phase short circuit and single-phase grounding comprehensive protection method for small-current grounding power system |
| CN107144762A (en) * | 2017-04-20 | 2017-09-08 | 广西电网有限责任公司电力科学研究院 | A kind of distribution net work earthing fault localization method based on Small Electric Current Earthing And Routing Device |
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| CN104779594A (en) * | 2015-04-27 | 2015-07-15 | 西安热工研究院有限公司 | Inter-phase short circuit and single-phase grounding comprehensive protection method for small-current grounding power system |
| CN107144762A (en) * | 2017-04-20 | 2017-09-08 | 广西电网有限责任公司电力科学研究院 | A kind of distribution net work earthing fault localization method based on Small Electric Current Earthing And Routing Device |
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