CN113659547B - Power distribution network differential protection data synchronization method and system based on effective zero crossing point - Google Patents

Power distribution network differential protection data synchronization method and system based on effective zero crossing point Download PDF

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CN113659547B
CN113659547B CN202110968156.9A CN202110968156A CN113659547B CN 113659547 B CN113659547 B CN 113659547B CN 202110968156 A CN202110968156 A CN 202110968156A CN 113659547 B CN113659547 B CN 113659547B
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zero
current
sides
crossing point
time
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CN113659547A (en
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邹贵彬
周成瀚
魏秀燕
高厚磊
臧琳冬
温旭辉
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Shandong University
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Shandong University
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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
    • 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
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00006—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment
    • H02J13/00016—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment using a wired telecommunication network or a data transmission bus
    • H02J13/00017—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment using a wired telecommunication network or a data transmission bus using optical fiber
    • 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
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00032—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for
    • H02J13/00036—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for the elements or equipment being or involving switches, relays or circuit breakers
    • H02J13/0004—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for the elements or equipment being or involving switches, relays or circuit breakers involved in a protection system
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • 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
    • Y04S10/20—Systems supporting electrical power generation, transmission or distribution using protection elements, arrangements or systems
    • 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
    • Y04S40/00—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them
    • Y04S40/12—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them characterised by data transport means between the monitoring, controlling or managing units and monitored, controlled or operated electrical equipment
    • Y04S40/124—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them characterised by data transport means between the monitoring, controlling or managing units and monitored, controlled or operated electrical equipment using wired telecommunication networks or data transmission busses

Abstract

The invention belongs to the technical field of power distribution network relay protection, and provides a power distribution network differential protection data synchronization method and system based on an effective zero crossing point. The method comprises the steps of obtaining three-phase current flowing through protection devices on two sides of a protected feeder line; taking the moment when the three-phase current meets the starting criterion of each protection device as corresponding starting moment; respectively calculating the current phasor value of the corresponding side and searching the current zero crossing point of the corresponding side in the historical time direction by taking the starting time of the protection devices at the two sides as the starting time; judging the effectiveness of the zero crossing point according to the interaction information of the protection devices at the two sides; calculating the zero starting time difference of the protection devices at two sides; the zero starting time difference is the time difference between the starting time of the protection device on the corresponding side and the first effective zero crossing point; and constructing a current differential protection criterion containing phase synchronization correction through the current phasor values at two sides and the zero-starting time difference, and if the criterion is met, determining that an intra-area fault occurs.

Description

Power distribution network differential protection data synchronization method and system based on effective zero crossing point
Technical Field
The invention belongs to the technical field of power distribution network relay protection, and particularly relates to a power distribution network differential protection data synchronization method and system based on an effective zero crossing point.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The commonly used three-section type current protection in the traditional power distribution network cannot be suitable for an active power distribution network with high distributed power supply permeability, and a power distribution network protection scheme suitable for distributed power supply access is urgently needed. In order to meet the protection requirement of the active power distribution network, in recent years, researchers have proposed many new protection schemes. A common idea is to apply the longitudinal differential protection, which is already widely used in power transmission lines, to active power distribution networks.
The prior art proposes a positive sequence current fault component-based current differential protection for an active power distribution network. Because the distribution network adopts three-phase reclosing without fault phase selection, the communication traffic can be reduced by adopting the positive sequence component to construct the protection criterion. The prior art also provides a pilot differential protection based on a comprehensive sequence component based on the characteristic that fault current of an inverter-type distributed power supply only contains a positive sequence component. Firstly, judging whether a fault is a symmetrical fault by using a positive-negative sequence current amplitude ratio; and then for symmetric faults and asymmetric faults, constructing a differential protection criterion by using the positive sequence current and the negative sequence current respectively. In the prior art, a virtual multi-terminal current differential protection is provided in consideration of an inverter type distributed power supply which is connected into a feeder line of a power distribution network in a T shape. The method comprises the steps of firstly deducing an active power reference value and a grid-connected point positive sequence voltage of each inversion type distributed power supply according to active power and line impedance at two ends of a line, then estimating the magnitude of output current of each inversion type power supply according to a control strategy, and combining measured currents at two ends of the line to construct virtual multi-terminal current differential protection. The scheme can be suitable for a power distribution network containing a T-connection distributed power supply, and compared with a multi-terminal current differential protection, the cost is lower.
Although the current differential protection has high reliability and sensitivity in a power distribution network containing a high-permeability distributed power supply, the data synchronization of two sides of a line must be ensured when the methods are applied. In the power transmission line, a ping-pong algorithm or a GPS time synchronization is usually adopted to ensure data synchronization on both sides. The ping-pong algorithm needs a special data channel, and the conventional power distribution network mostly adopts a communication mode of a multiplex optical fiber to reduce the cost; when the GPS time is synchronized, a GPS signal receiver needs to be additionally arranged at each protection installation position, however, the power distribution network has the characteristics of multiple nodes and multiple branches, and if the GPS receiver needs to be arranged at each node, the investment cost of the power distribution network is greatly increased. Therefore, current differential protection is limited by cost factors and is difficult to popularize and apply in a power distribution network.
The prior art provides a power distribution network current differential protection data synchronization scheme based on fault signal self-synchronization. According to the scheme, the feeder line of the power distribution network is considered to be short, and the protection devices on two sides of the line can detect fault signals at the same time after a fault occurs, so that the devices respectively use the time when the measured current reaches a starting threshold as reference time to realize synchronous calculation of data on two sides. The scheme does not depend on a special data channel and additional synchronous equipment, and has higher economical efficiency. However, when the fault location is far from the load side or the fault point has a large transition resistance, the measured current in the load-side protection device needs to reach the start threshold with a long delay. At this time, the difference between the synchronous reference time of the devices on the two sides in the scheme is large, and the reliability of the current differential protection is seriously influenced.
The inventor finds that the existing data synchronization scheme for power distribution network differential protection needs to be provided with additional equipment or is greatly influenced by a fault detection algorithm, and a data synchronization scheme which does not need to be provided with additional synchronization equipment and has high reliability does not exist.
Disclosure of Invention
In order to solve the technical problems in the background art, the invention provides a power distribution network differential protection data synchronization method and system based on effective zero crossing points, which only use current information, do not depend on GPS signals and special data channels, are suitable for power distribution networks with relatively low investment cost, are not influenced by a fault detection algorithm, and can still reliably ensure data synchronization at two sides when the transition resistance of a fault point is large.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a power distribution network differential protection data synchronization method based on effective zero crossing points, which comprises the following steps:
acquiring three-phase current flowing through protection devices on two sides of a protected feeder line;
taking the moment when the three-phase current meets the starting criterion of each protection device as corresponding starting moment;
respectively calculating the current phasor value of the corresponding side and searching the current zero crossing point of the corresponding side in the historical time direction by taking the starting time of the protection devices at the two sides as the starting time;
judging the effectiveness of the zero crossing point according to the interaction information of the protection devices at the two sides;
calculating the zero starting time difference of the protection devices at two sides; the zero starting time difference is the time difference between the starting time of the protection device on the corresponding side and the first effective zero crossing point;
and constructing a current differential protection criterion containing phase synchronization correction through the current phasor values at two sides and the zero-starting time difference, and if the criterion is met, determining that an intra-area fault occurs.
The second aspect of the present invention provides a power distribution network differential protection data synchronization system based on effective zero crossing points, which includes:
the three-phase current acquisition module is used for acquiring three-phase current flowing through the protection devices on the two sides of the protected feeder line;
the starting time determining module is used for taking the time when the three-phase current meets the starting criterion of each protection device as the corresponding starting time;
the current phasor calculation and zero crossing point searching module is used for respectively calculating the current phasor value of the corresponding side and searching the current zero crossing point of the corresponding side in the historical time direction by taking the starting time of the protection devices at the two sides as the starting time;
the zero crossing point effectiveness judging module is used for judging the effectiveness of the zero crossing point according to the interaction information of the protection devices at the two sides;
the zero starting time difference calculation module is used for calculating the zero starting time difference of the protection devices at two sides; the zero starting time difference is the time difference between the starting time of the protection device on the corresponding side and the first effective zero crossing point;
and the fault judgment module is used for constructing a current differential protection criterion containing phase synchronization correction through the current phasor values at two sides and the zero-starting time difference, and if the criterion is met, determining that an intra-area fault occurs.
A third aspect of the present invention provides a computer readable storage medium, on which a computer program is stored, which program, when being executed by a processor, realizes the steps of the method for synchronizing the differential protection data of a power distribution network based on effective zero-crossing points as described above.
A fourth aspect of the present invention provides a computer device, which includes a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method for synchronizing differential protection data of a power distribution network based on effective zero-crossing points as described above.
Compared with the prior art, the invention has the beneficial effects that:
(1) the method realizes data synchronization by using the current zero crossing point before the faults on two sides, and is not influenced by a fault detection algorithm; the method is suitable for the power distribution network based on the Ethernet multiplexing optical fiber communication, does not need a special data channel and additional time synchronization equipment, and is high in economy and easy to realize;
(2) the invention fully retains the good performance of current differential protection, has higher sensitivity, quick action and absolute selectivity under various fault conditions, and can be better suitable for an active power distribution network with complex operation modes in principle; the protection method has the advantages of simple and clear principle, accurate identification and easy engineering realization.
Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.
Fig. 1 is a schematic diagram of a simple active power distribution network according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of current waveforms at two sides when the start delay at the load side is longer according to the embodiment of the present invention;
FIG. 3 is a schematic diagram of an invalid zero crossing point according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a simulation model of an active power distribution network according to an embodiment of the present invention;
fig. 5 is an overall flowchart of a power distribution network differential protection data synchronization method based on an effective zero crossing point according to an embodiment of the present invention.
Detailed Description
The invention is further described with reference to the following figures and examples.
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
Example one
Referring to fig. 5, the method for synchronizing differential protection data of a power distribution network based on an effective zero crossing point provided in this embodiment specifically includes the following steps:
step 1: and acquiring three-phase current flowing through the protective devices on two sides of the protected feeder line.
Step 2: and taking the moment when the three-phase current meets the starting criterion of each protection device as the corresponding starting moment.
In the embodiment, the phase current sudden change amount is used as the starting criterion for detecting whether the fault occurs.
Taking the simple active power distribution network shown in fig. 1 as an example, when a fault occurs inside the feeder MN, the phase currents measured at both sides of the feeder MN may change abruptly. Because the length of a feeder line of a power distribution network is short (generally less than 20 kilometers), and the propagation time of fault electromagnetic waves on the feeder line is extremely short (less than 0.1 millisecond), the protection devices on the M side and the N side can be approximately considered to simultaneously feel fault signals, and the protection devices on the two sides calculate electric quantities related to protection by taking the respective protection starting time (the fault occurrence time identified by the protection devices) as reference time, so that synchronous calculation of data on the two sides can be realized.
However, the protection start time in the above fault data self-synchronization scheme is not the true fault occurrence time, but the time when the device measures the current that meets the protection start criterion. For the protection device started by adopting the phase current sudden change amount, the starting time delay is inevitable. The starting criterion of the phase current abrupt change commonly used in the protection device is as follows:
||i(k)-i(k-N)|-|i(k-N)-i(k-2N)||≥KSIN
wherein i (K) represents the phase current sampling value of the kth sampling point, N is the number of sampling points in a power frequency period, KSTo start the threshold coefficient, INIs the rated current.
It can be known from this criterion that the delay of the protection start depends on the speed of change of the amplitude of the phase current after the fault. When an out-of-range fault occurs, the current flowing through the protection devices on the two sides can be regarded as the same penetrating current flowing to a fault point, and even if time delay exists, the fault data self-synchronizing scheme can still ensure synchronous calculation of data on the two sides because the time delay is the same; when an in-zone fault occurs, the currents flowing through the protection devices on the two sides have independence, and the amplitude of the short-circuit current on the two sides of the feeder line is related to factors such as fault position, fault type, transition resistance and distributed power supply output. Because the short-circuit current that the system power supply provided is great, system side protection can start fast. The load side fault current is relatively small, if a fault point is far away from the load side or a large transition resistor is included, the starting time delay of the load side protection device is long, the starting time difference of the devices on the two sides is further large, and the reliability of the current differential protection adopting the fault data self-synchronization scheme is reduced.
Fig. 2 is a diagram of a fault current waveform when the load-side (N-side) start-up delay is long. T in the figure0Indicating the actual time of occurrence of the fault, tdIndicating the protection device activation time and subscripts M and N respectively indicate the location of the protection device.
As can be seen from fig. 2, after the fault occurs, the current waveform of the M side has a large abrupt change, so that the M side protection device can be started quickly; the sudden change of the current on the N side is not obvious, the sudden change of the current cannot reach a starting threshold in a short time after the fault, and the N side protection device cannot be started until the current approaches the next wave crest. At this time, the start delay difference between the M-side protection device and the N-side protection device is about 9.5 milliseconds, and if the conventional fault data self-synchronization scheme is adopted, the synchronization error causes a phase angle error of about 171 degrees, which seriously affects the reliability of the current differential protection.
The reason why the zero-crossing point of the current before the fault is searched in the method of the embodiment is that compared with the current waveform after the fault with larger randomness, the current waveforms on both sides before the fault are completely symmetrical by neglecting the measurement error, and therefore, the corresponding time of the zero-crossing point is consistent. In FIG. 2, t1And t2Respectively, the self-fault occurrence time t0The first and second forward zero crossings correspond to the time instants. If both side protection devices are given t1And the synchronous calculation of the data on the two sides can be realized for reference time.
And step 3: and respectively calculating the current phasor value of the corresponding side and searching the current zero crossing point of the corresponding side in the historical time direction by taking the starting time of the protection devices at the two sides as the starting time.
Wherein, the principle of the step 3 is as follows: the existing distribution network fault data self-synchronization scheme considers that after a distribution network feeder fault occurs, protection devices on two sides of the same feeder section can be approximately considered to be capable of simultaneously sensing fault signals, and therefore starting time t of the protection devices is useddAs a reference time for the two-sided data synchronization calculation.
And eliminating invalid zero-crossing points through zero-crossing point time difference, and recording the corresponding time of the first two valid zero-crossing points of the protection devices at the two sides.
The process of eliminating the invalid zero crossing point through the zero crossing point time difference is as follows:
recording the corresponding time of the first two zero-crossing points found from the starting moment to the historical time direction as t1And t2；
Calculating t1And t2Time difference T of12If T is12Equal to the time corresponding to half cycle, the first two zero-crossing points are both effective zero-crossing points;
if T12The time corresponding to the second zero crossing point is recorded as the invalid zero crossing point if the time is not equal to the time corresponding to the half cyclet1And the time corresponding to the third zero-crossing point is recorded as t2；
Recalculate t1And t2Until the time difference equals the time corresponding to half a cycle, at which time t1And t2The corresponding zero crossing points are the first two effective zero crossing points.
The principle of eliminating invalid zero-crossing points by the zero-crossing point time difference is as follows:
according to the scheme, the time corresponding to the first zero-crossing point before the fault occurs is used as the reference time, but the real fault occurrence time t cannot be known by the protection device in reality0Only from the device start-up time tdThe zero crossings are looked forward. If at t0And tdZero crossing point exists between, then from tdThe first zero crossing found forward is actually located after the fault occurs, and the zero crossings at both sides cannot be synchronized at this time, so the zero crossings must be eliminated.
The scheme is used for judging the fault occurrence time t0Defining the front zero-crossing point as effective zero-crossing point, and defining the fault occurrence time t0The latter zero crossing is defined as an invalid zero crossing. FIG. 3 is a typical current waveform plot with invalid zero crossings. It can be seen from fig. 3 that the protection device is started from the N-side at time td.NThe first two zero-crossing points found forward are both at t0After time, they belong to invalid zero crossings; the third zero crossing point is at t0Previously, it is the first effective zero crossing, and its corresponding time can be used as a reference time to realize the synchronous calculation of the data on both sides.
The invalid zero-crossing point in fig. 3 is caused by that the local current waveform at the zero-crossing point is not monotonous due to high-frequency oscillation after the fault, and the time difference between them is short; however, since the period of the zero crossing of the current is half cycle (when the power frequency of the system is 50Hz, the half cycle is 10 ms) in normal operation, the time difference between two effective zero-crossing points should be half cycle, as shown by t in FIG. 21And t2As shown.
Invalid zero crossings can thus be excluded by this feature, in particular: self-device start time tdLooking forward for zero crossingAnd calculating the time difference between the zero-crossing points until a group of zero-crossing points with half cycle time difference are found, considering the zero-crossing points as the first two effective zero-crossing points and recording the corresponding time t1And t2。
And 4, step 4: and judging the effectiveness of the zero crossing point according to the interactive information of the protection devices at the two sides.
In a specific implementation, the mutual information of the two-side protection devices includes a starting time, a zero-crossing time, a current slope polarity and a current phasor value.
Specifically, the process of judging the effectiveness of the zero-crossing point is as follows:
comparing the current slope polarities at the first zero-crossing points on the two sides, wherein if the polarities of the zero-crossing points on the two sides are opposite, the zero-crossing points are effective;
if the current slope polarities of the two sides are the same, an invalid zero-crossing point exists on the side with the lower fault current amplitude, and the zero-crossing point corresponding to the second zero-crossing point time is taken as the first valid zero-crossing point on the side.
The principle of verifying the validity of the zero crossing point from the integrated information of the two-sided devices is:
in addition to the invalid zero-crossings shown in fig. 3, there is also an invalid zero-crossing caused by the protection device being activated too slowly, which usually occurs on the load side, as indicated by the dots in fig. 2. The time difference between the dot in fig. 2 and the previous zero crossing is 10.22 ms, which is close to half a cycle, and since a certain margin should be kept when using the time difference of the zero crossing to determine the valid zero crossing, the invalid zero crossing may not be excluded in step 3. The ineffective zero-crossing caused by the slow start of the load side device is only one at most, and the ineffective zero-crossing can be eliminated by using the current slope polarities at the zero-crossing points on the two sides. In FIG. 2, t1The polarity of the slope of the current at the M side is negative, the polarity of the slope of the current at the N side is positive, and the two are opposite; and the slope polarity of the current at the N-side at the invalid zero-crossing point indicated by the dot is negative and the same as the slope polarity of the first valid zero-crossing point at the M-side. In addition, if there is a large start-up delay on the load side, the fault current amplitude should be much smaller than the system side current. Therefore, the validity of the zero crossing point can be verified by using the integrated information of the two-side device, specifically: ratio ofAt t for the two-sided arrangement1If the current slope polarities at the moment are the same, the situation that an invalid zero crossing point exists on the load side is indicated; if invalid zero-crossing points exist, comparing the magnitude of the fault current amplitude in the data at the two sides, regarding the side with smaller amplitude as a load side, and regarding t in the load side2And the zero crossing point corresponding to the moment is regarded as the first effective zero crossing point.
And 5: calculating the zero starting time difference of the protection devices at two sides; the zero-starting time difference is the time difference between the starting time of the protection device on the corresponding side and the first effective zero-crossing point.
Step 6: and constructing a current differential protection criterion containing phase synchronization correction through the current phasor values at two sides and the zero-starting time difference, and if the criterion is met, determining that an intra-area fault occurs.
The two side protection devices respectively start at the time t when calculating the current phasordFor reference time, taking the failure shown in FIG. 2 as an example, the M-side and N-side devices are respectively given td.MAnd td.NAnd calculating the fault current phasor for the initial moment, wherein the calculated current phasor has a large synchronization error, and the phase synchronization compensation needs to be carried out on the fault current phasor when a current differential protection criterion is constructed.
Defining the time difference between the starting time of the protection device and the first effective zero crossing point as the zero-starting time difference, taking fig. 2 as an example, the zero-starting time differences at two sides are respectively Td.MAnd Td.N. Because the corresponding time of the first effective zero-crossing points on the two sides is consistent, the zero-starting time difference can reflect the starting time difference of the protection devices on the two sides. The current differential protection criterion containing the phase synchronization compensation can be constructed through the zero-starting time difference of the devices on the two sides as follows:
Figure BDA0003224669950000101
in the formula (I), the compound is shown in the specification,
Figure BDA0003224669950000102
and
Figure BDA0003224669950000103
current phasor values, K, at both sides of the protected sectionrelTo a reliability factor, e-jAs a rotation factor, Δ TdThe zero-starting time difference between the side and the opposite side, taking the side M as an example, is Delta Td＝Td.N-Td.M。
In the current differential protection criterion, the phasor of the current on the opposite side rotates by a certain angle according to the zero-starting time difference of the two sides, and the angle can compensate the phase synchronization error caused by the inconsistency of the starting time of the devices on the two sides.
An 8-node active power distribution network model is built by utilizing electromagnetic transient simulation software PSCAD/EMTDC, and the power distribution network differential protection data synchronization scheme based on the effective zero crossing point provided by the invention is verified:
1) simulation model
The structure of the simulation model is shown in FIG. 4. The model adopts a neutral point to be directly grounded, the system reference voltage is 10.5kV, and the transformer capacity is 100 MVA; B. l and C represent bus, load and parallel capacitor, respectively; s represents a switch, and a protection device is arranged at each switch; DG represents a distributed power supply, and DGs at 4 positions in the model are all photovoltaic power supplies, wherein the capacity of DG2 is 4MW, and the capacities of the rest DGs are all 2 MW; the total load of the system is (24+ j0.12) MVA; feeder B1B2、B2B3Has a length of 4km, a feeder B5B6、B7B8The length of the feeder line is 8km, the lengths of the other feeder lines are all 6km, and the impedance Z of the feeder line in unit length is (0.38+ j0.45) omega/km; failure point f1-f3Respectively located at the middle point and fault point f of the feeder line4-f6Are respectively positioned on the feeder B3B410%, 50% and 90% from the head end.
2) Simulation verification
a) Precision of the data synchronization scheme provided by the implementation
Because the existing fault self-synchronization scheme mainly has a large synchronization error when the transition resistance is high, and the synchronization scheme based on the effective zero crossing point can solve the problem, the simulation experiment sets a series of phase-A grounding faults containing large transition resistance at different fault points, and calculates the synchronization errors of the synchronization scheme provided by the embodiment and the existing fault self-synchronization scheme, and the result is shown in table 1. Since the load-side protection device has a long activation delay when a fault including a large transient resistance occurs, the fault initial phase angle in table 1 is the angle of the load-side a-phase current at the time of the fault. When calculating the synchronization error, the calculation step of the simulation model is 10 mus (corresponding to a frequency of 100kHz), and the sampling frequency of the protection device is assumed to be 10kHz, i.e. one point is extracted in every 10 sampling points at equal intervals to calculate the synchronization error.
TABLE 1 synchronization error calculation results of the conventional self-synchronization scheme and the synchronization scheme proposed in the present invention
Figure BDA0003224669950000121
As can be seen from Table 1, for a single-phase earth fault with a large transition resistance, the existing fault self-synchronization scheme will have a synchronization error of millisecond level when f is1When the A phase grounding fault containing 40 omega transition resistance occurs at a point, the maximum synchronization error can reach 6.1ms, the corresponding phase error is 109.8 degrees at the moment, and the reliability of the current differential protection is seriously influenced. For the data synchronization scheme based on the effective zero-crossing point, which is proposed in this embodiment, since the synchronization reference of the data on both sides is the first zero-crossing point before the fault, not the starting time of the protection device, the synchronization error is very small, and the maximum error does not exceed 1 microsecond. The synchronization scheme provided by the embodiment is not affected by a fault detection algorithm in principle, and the error of the synchronization scheme is derived from the error caused by estimating the zero-crossing time by discrete sampling points and is far smaller in value than the error of the existing self-synchronization scheme. Synchronization errors on the order of microseconds are insignificant for current differential protection.
b) Effectiveness of current differential protection based on synchronization scheme provided by the invention
In order to verify the effectiveness of the current differential protection based on the synchronization scheme provided in this embodiment, different types of faults are set at different fault points, and the simulation results are shown in tables 2 to 4. Sensitive in view of current differential protection constructed using positive sequence fault componentsThe current phasor value in the table adopts a positive sequence fault component; in addition, the reliability coefficient K in the braking currentrelIs 0.5.
TABLE 2 f5Simulation result of point occurrence of different types of metallic faults
Figure BDA0003224669950000122
Figure BDA0003224669950000131
TABLE 3 f5Simulation result of A-phase grounding fault with different transition resistances occurring at point
Figure BDA0003224669950000132
TABLE 4 f4-f6Simulation result of A-phase grounding fault with 70 omega transition resistance occurring at point
Figure BDA0003224669950000133
In Table 2 are shown at f5The points set simulation results for different types of metallic faults. It can be seen from table 2 that when different types of metallic faults occur, both protection devices can be started quickly, Δ T, because both sides can detect a large fault currentdThe value of (d) is 0. At the moment, phase synchronization errors do not need to be compensated, and the current differential protection based on the existing fault data self-synchronization can also correctly identify faults in the area.
In Table 3 is shown at f5And setting a simulation result of the A-phase grounding fault containing 20-80 omega transition resistance at the point. As can be seen from table 3, as the resistance value of the transition resistor increases, the magnitude of the fault current detected by the devices on both sides decreases. Since the load-side current itself is small, the load-side protection device is activated when the transition resistance increasesThe time delay will be increased, which causes the calculated value of the current phasors at two sides to have larger synchronization error, and further causes the sensitivity of the current differential protection based on the existing fault self-synchronization to be reduced and even refused. Taking the simulation result when the transition resistance is 80 Ω as an example, the starting time of the load-side protection device at this time lags behind the system side by 4.1ms, and the phase difference of the fault current on both sides is 163.6 °. When both side protection devices calculate the fault current phasor with reference to the respective start-up time, there will be a phase synchronization error of 73.8 ° on both sides. Because the current differential protection criterion provided by the invention can compensate the phase according to the zero starting time difference of the two sides, the phase difference of the two sides after compensation is 89.8 degrees, the differential current and the braking current of the protection criterion are respectively 20.4A and 10.2A, and the fault can be reliably and sensitively identified. If the phase compensation is not carried out, the differential current and the braking current calculated according to the traditional current differential protection criterion are respectively 11.4A and 13.2A, and the protection will be refused because the differential current is smaller than the braking current.
In Table 4 is shown at f4-f6The point sets the simulation result of the phase-A grounding fault with 70 omega transition resistance. As can be seen from table 4, the closer the fault location is to the system-side protection device, the larger the fault current on the system side is, the smaller the fault current on the load side is, and the larger the difference in the start time between the protection devices on both sides is. However, no matter the fault occurs at any position of the protected line, the phase synchronization error caused by the starting delay difference of the protection device can be compensated, the differential current in the current differential protection criterion is more than twice of the brake current, and the protection can reliably and sensitively identify the fault. Because the load side protection device is started slowly due to the fact that fault resistance is large, the current differential protection based on the existing fault self-synchronizing scheme can have the situation of insufficient sensitivity and even failure. With f6For example, when a point fault occurs, the differential current and the braking current calculated according to the conventional current differential protection criterion are respectively 12.5A and 13.7A, and the protection is refused.
According to the simulation results, the fault data synchronization scheme based on the effective zero crossing point can improve the synchronization precision of the existing fault self-synchronization scheme from millisecond level to microsecond level, and can meet the requirement of current differential protection of the power distribution network under various fault conditions; in addition, the current differential protection based on the data synchronization scheme can correctly identify the fault section under various fault conditions, particularly when a ground fault with large transition resistance occurs, the load side protection device is started slowly at the moment, so that the reliability of the differential protection based on the existing fault self-synchronization scheme is reduced, but the current differential protection scheme provided by the invention can still reliably and sensitively identify the fault.
Example one
In the embodiment, the characteristics of multiple nodes and multiple branches of the power distribution network and the adoption of multiplex optical fiber communication are considered, and a scheme for synchronizing the differential protection data of the power distribution network based on the effective zero crossing point is provided. The PSCAD simulation result shows that the data synchronization scheme provided by the invention has higher synchronization precision under various fault conditions, and the current differential protection scheme containing phase synchronization compensation can reliably and sensitively identify faults. Especially when a ground fault with large transition resistance occurs, the scheme is not influenced by a fault detection algorithm, and the reliability of differential protection can still be ensured. In addition, the differential protection data synchronization scheme provided by the invention only utilizes current information at two sides, a GPS signal receiver is not required to be additionally arranged at each protection installation position, a special data channel is not required, and the cost of the current differential protection of the power distribution network can be greatly reduced.
Example two
The embodiment provides a power distribution network differential protection data synchronization system based on an effective zero crossing point, which specifically comprises the following modules:
the three-phase current acquisition module is used for acquiring three-phase current flowing through the protection devices on the two sides of the protected feeder line;
the starting time determining module is used for taking the time when the three-phase current meets the starting criterion of each protection device as the corresponding starting time;
the current phasor calculation and zero crossing point searching module is used for respectively calculating the current phasor value of the corresponding side and searching the current zero crossing point of the corresponding side in the historical time direction by taking the starting time of the protection devices at the two sides as the starting time;
the zero crossing point effectiveness judging module is used for judging the effectiveness of the zero crossing point according to the interaction information of the protection devices at the two sides;
the zero starting time difference calculation module is used for calculating the zero starting time difference of the protection devices at two sides; the zero starting time difference is the time difference between the starting time of the protection device on the corresponding side and the first effective zero crossing point;
and the fault judgment module is used for constructing a current differential protection criterion containing phase synchronization correction through the current phasor values at two sides and the zero-starting time difference, and if the criterion is met, determining that an intra-area fault occurs.
It should be noted that, each module in the present embodiment corresponds to each step in the first embodiment one to one, and the specific implementation process is the same, which is not described herein again.
EXAMPLE III
The present embodiment provides a computer readable storage medium, on which a computer program is stored, which program, when being executed by a processor, implements the steps of the method for synchronizing the differential protection data of a power distribution network based on effective zero-crossing points as described above.
Example four
The present embodiment provides a computer device, which includes a memory, a processor and a computer program stored in the memory and executable on the processor, and the processor executes the program to implement the steps of the method for synchronizing the differential protection data of the power distribution network based on the effective zero-crossing points as described above.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of a hardware embodiment, a software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by a computer program, which can be stored in a computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. The storage medium may be a magnetic disk, an optical disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), or the like.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (7)

1. A power distribution network differential protection data synchronization method based on effective zero crossing points is characterized by comprising the following steps:
acquiring three-phase current flowing through protection devices on two sides of a protected feeder line;
taking the moment when the three-phase current meets the starting criterion of each protection device as corresponding starting moment;
respectively calculating the current phasor value of the corresponding side and searching the current zero crossing point of the corresponding side in the historical time direction by taking the starting time of the protection devices at the two sides as the starting time;
judging the effectiveness of the zero crossing point according to the interaction information of the protection devices at the two sides;
the process of judging the effectiveness of the zero crossing point is as follows:
comparing the current slope polarities at the first zero-crossing points on the two sides, wherein if the polarities of the zero-crossing points on the two sides are opposite, the zero-crossing points are effective;
if the current slope polarities at the two sides are the same, an invalid zero-crossing point exists at the side with lower fault current amplitude, and the zero-crossing point corresponding to the second zero-crossing point time is taken as a first valid zero-crossing point at the side;
calculating the zero starting time difference of the protection devices at two sides; the zero starting time difference is the time difference between the starting time of the protection device on the corresponding side and the first effective zero crossing point;
constructing a current differential protection criterion containing phase synchronization correction through current phasor values at two sides and zero-starting time difference, and if the criterion is met, determining that an intra-area fault occurs;
the current differential protection criterion containing the phase synchronization correction is as follows:
Figure FDA0003540964510000011
in the formula (I), the compound is shown in the specification,
Figure FDA0003540964510000012
and
Figure FDA0003540964510000013
current phasor values, K, at both sides of the protected sectionrelTo a reliability factor, e-jIn order to be a factor of rotation,△Tdthe zero starting time difference between the side and the opposite side;
the interactive information of the protection devices on the two sides comprises starting time, zero crossing time, current slope polarity and current phasor value.
2. The method for synchronizing the differential protection data of the power distribution network based on the effective zero-crossing points according to claim 1, wherein the ineffective zero-crossing points are eliminated through a zero-crossing point time difference, and the corresponding time of the first two effective zero-crossing points of the protection devices at two sides is recorded.
3. The method for power distribution network differential protection data synchronization based on effective zero-crossing points according to claim 2, wherein the process of excluding the ineffective zero-crossing points through the zero-crossing point time difference is as follows:
recording the corresponding time of the first two zero-crossing points found from the starting moment to the historical time direction as t1And t2；
Calculating t1And t2Time difference T of12If T is12Equal to the time corresponding to half cycle, the first two zero-crossing points are both effective zero-crossing points;
if T12The time which is not equal to the time corresponding to the half cycle is determined, the first zero crossing point is an invalid zero crossing point, and the time corresponding to the second zero crossing point is recorded as t1And the time corresponding to the third zero-crossing point is recorded as t2；
Recalculate t1And t2Until the time difference equals the time corresponding to half a cycle, at which time t1And t2The corresponding zero crossing points are the first two effective zero crossing points.
4. The method for synchronizing the differential protection data of the power distribution network based on the effective zero-crossing points as claimed in claim 1, wherein the phase current jump is used as a starting criterion for detecting whether the fault occurs.
5. A power distribution network differential protection data synchronization system based on effective zero crossing points is characterized by comprising:
the three-phase current acquisition module is used for acquiring three-phase current flowing through the protection devices on the two sides of the protected feeder line;
the starting time determining module is used for taking the time when the three-phase current meets the starting criterion of each protection device as the corresponding starting time;
the current phasor calculation and zero crossing point searching module is used for respectively calculating the current phasor value of the corresponding side and searching the current zero crossing point of the corresponding side in the historical time direction by taking the starting time of the protection devices at the two sides as the starting time;
the zero crossing point effectiveness judging module is used for judging the effectiveness of the zero crossing point according to the interaction information of the protection devices at the two sides;
the process of judging the effectiveness of the zero crossing point is as follows:
comparing the current slope polarities at the first zero-crossing points on the two sides, wherein if the polarities of the zero-crossing points on the two sides are opposite, the zero-crossing points are effective;
if the current slope polarities at the two sides are the same, an invalid zero-crossing point exists at the side with lower fault current amplitude, and the zero-crossing point corresponding to the second zero-crossing point time is taken as a first valid zero-crossing point at the side;
the zero starting time difference calculation module is used for calculating the zero starting time difference of the protection devices at two sides; the zero starting time difference is the time difference between the starting time of the protection device on the corresponding side and the first effective zero crossing point;
the fault judgment module is used for constructing a current differential protection criterion containing phase synchronization correction through current phasor values at two sides and zero-starting time difference, and if the criterion is met, the current differential protection criterion is regarded as an in-zone fault;
the current differential protection criterion containing the phase synchronization correction is as follows:
Figure FDA0003540964510000031
in the formula (I), the compound is shown in the specification,
Figure FDA0003540964510000032
and
Figure FDA0003540964510000033
current phasor values, K, at both sides of the protected sectionrelTo a reliability factor, e-jAs a rotation factor, Δ TdThe zero starting time difference between the side and the opposite side;
the interactive information of the protection devices on the two sides comprises starting time, zero crossing time, current slope polarity and current phasor value.
6. A computer-readable storage medium, on which a computer program is stored, which program, when being executed by a processor, carries out the steps of the method for synchronization of differential protection data of a power distribution network based on effective zero crossings as claimed in any one of the claims 1 to 4.
7. Computer arrangement comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the processor when executing the program performs the steps in the method for synchronization of differential protection data of a power distribution network based on effective zero crossings as claimed in any of the claims 1 to 4.
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