CN112688284B - Power distribution network differential protection data synchronization method and system based on voltage zero crossing point - Google Patents

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

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CN112688284B
CN112688284B CN202110079115.4A CN202110079115A CN112688284B CN 112688284 B CN112688284 B CN 112688284B CN 202110079115 A CN202110079115 A CN 202110079115A CN 112688284 B CN112688284 B CN 112688284B
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CN112688284A (en
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陈卫
熊宇威
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Huazhong University of Science and Technology
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Abstract

The invention discloses a power distribution network differential protection data synchronization method and system based on voltage zero crossing points, and belongs to the field of power distribution network relay protection. The method comprises the following steps: each protection device continuously samples the current and voltage of the line; each protection device takes the fault occurrence time detected by each protection device as a starting point, searches in the reverse direction of the time sequence, and suspends the search when the sampling time adjacent to the voltage zero crossing point is searched; judging whether the voltage variation trends of the protection devices at the time of pausing the search are the same or not; if yes, entering the next step; otherwise, continuing searching; obtaining a voltage zero crossing point by using the voltage sampling values at the pause searching time and the previous time; and each protection device takes the corresponding voltage zero crossing point as a sampling starting point and performs resampling on the current actual sampling value by combining a set sampling period to obtain a completely synchronous current sampling value sequence. The invention can ensure that the current sampling values of the protection devices at all sides in the differential protection area are completely synchronous, thereby ensuring the safe and stable operation of the power grid.

Description

Power distribution network differential protection data synchronization method and system based on voltage 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 a voltage zero crossing point.
Background
After the power grid fails, each relay protection device in the differential protection area collects current, voltage and other data of each part of the power grid, stores the data in a cache area of the relay protection device in a certain mode, processes sampling value data by using a preset differential protection algorithm, and judges whether the power grid fails or not by comparing the sampling value data with a setting value. The differential protection algorithm compares the amplitude and the phase of the current phasor flowing through two ends of the protected line at the same moment, and judges whether an intra-area fault occurs, so that the differential protection algorithm has higher requirements on whether the electrical quantity data acquired by the protection device are synchronous. The communication condition of the current power distribution network is severe, multi-terminal electric quantity synchronization information is difficult to obtain, and unsynchronized electric quantity data input differential protection algorithm can cause large unbalanced current, so that protection misoperation or refusal operation is caused, and great hidden danger is brought to safe and stable operation of a power grid.
The current solution to the problem of differential protection data synchronization is mainly divided into two directions, a data channel-based synchronization method and a uniform clock-based synchronization method. The synchronization method based on the data channel (also called as a sampling time adjustment method) mainly utilizes the stable and equal time of the data frame in the fiber channel to calculate the data transmission delay, calculates the sampling time of the opposite side data at the local side after receiving the data, compares the sampling time with the local side sampling time, and calculates the time difference, thereby accurately adjusting the local side sampling time and leading the protection devices at the two sides to sample at the same time. The synchronous method based on the uniform clock utilizes the GPS time service system to send pulse per second to the protective devices on two sides of the line at the same time, and the protective devices are decomposed into sampling pulses for sampling, so that the purpose of sampling at the same time is achieved. The synchronization method based on the GPS unified clock has the advantages of high precision, simplicity in implementation and the like, but is not suitable for large-scale use in the aspect of stable performance. The synchronization method based on the data channel has the advantages of simple principle and strong adaptability, but the precondition is that the data transmission delay in the optical fiber channel is determined, so the method is often adopted in a power transmission network, the communication condition of a power distribution network is severe, the factors of economy, feasibility and the like are considered, the wireless communication is often adopted, the data transmission delay of the wireless communication is uncertain, and the data sampling time cannot be estimated by using the channel transmission delay by the protection equipment for receiving data, so the synchronization error is larger.
Disclosure of Invention
Aiming at the defects or the improvement requirements of the prior art, the invention provides a power distribution network differential protection data synchronization method and a power distribution network differential protection data synchronization system based on a voltage zero crossing point, and aims to solve the problem that a data receiving end cannot determine the sampling time of data due to uncertain communication time delay in a power distribution network, so that synchronous sampling of protection devices at two ends of a line cannot be adjusted.
In order to achieve the above object, the present invention provides a power distribution network differential protection data synchronization method based on voltage zero crossing point, which includes:
s1, continuously sampling line current and voltage by each relay protection device in a differential protection area to obtain a continuously updated voltage and current data time sequence;
s2, each protection device takes the fault occurrence time detected by each protection device as a starting point, searches in the reverse direction of the time sequence, and suspends the search when the sampling time adjacent to the voltage zero crossing point is searched;
s3, judging whether the voltage variation trends of the protection devices at the time of pausing the search are the same or not; if yes, go to step S4; if not, each protection device continues to search in the reverse direction of the time sequence;
s4, each protection device constructs a Lagrange interpolation function by taking the voltage sampling values of the pause searching time and the last time as nodes respectively, and obtains a voltage zero-crossing point time scale;
and S5, each protection device takes the corresponding voltage zero-crossing time scale as a sampling starting point respectively, and resampling the current actual sampling value of each protection device by combining a set sampling period to obtain a current sampling value sequence of each protection device which is completely synchronous.
Further, in step S2, specifically,
for each protection device p, taking the fault occurrence time as a starting point, and sampling the voltage at the fault occurrence time
Figure BDA0002908433980000021
And the last time voltage sampling value
Figure BDA0002908433980000022
Performing product operation;
if it is
Figure BDA0002908433980000031
Then search window is formed
Figure BDA0002908433980000032
Become into
Figure BDA0002908433980000033
Performing product operation on the voltage sampling values in the search window again until the multiplication result of the voltage sampling values corresponding to the adjacent sampling moments is less than 0, and suspending the search; wherein P is 1,2, …, P; p represents the total number of protection devices in the differential protection zone.
Further, in step S3, specifically,
for each protection device p, the search time will be suspended
Figure BDA0002908433980000034
Corresponding voltage sampling value and last moment
Figure BDA0002908433980000035
Carrying out difference operation on corresponding voltage sampling values to obtain
Figure BDA0002908433980000036
Multiplying the difference operation results corresponding to the protection devices;
if it is
Figure BDA0002908433980000037
The voltage variation trends of the protection devices at the moment of pausing the search are different, and the protection devices continue to search in the reverse direction of the time sequence; if it is
Figure BDA0002908433980000038
The voltage variation tendencies of the respective protection devices at the time of suspension of the search are the same, and the process proceeds to step S4.
Further, in step S4, specifically,
for each protection device p, in order to
Figure BDA0002908433980000039
For the nodes, a Lagrange interpolation function L (t) is constructed:
Figure BDA00029084339800000310
let L (t) be 0 to obtain the time scale of zero crossing point of interpolation function voltage
Figure BDA00029084339800000311
Further, in step S5, specifically,
for each protection device p, in order to
Figure BDA00029084339800000312
As a resampling start point, a set time TsResampling for a sampling period, resampling point time scales
Figure BDA00029084339800000313
According to the resampling point time scale tpnAdjacent current actual sampling values
Figure BDA00029084339800000314
Obtaining the side weight sampling point t by linear interpolationpnCurrent value at time:
Figure BDA00029084339800000315
thereby obtaining p-fold sampling value sequence { i'p1,…i′pn,…,i′pN}; where N is 1, …, N represents the number of actual sampling points.
Further, in step S1, specifically,
each protection device in the differential protection zone is respectively according to the sampling period TsSampling the current and voltage of the line, and storing the sampled current and voltage into different buffer areas of the protection device respectively to obtain a time sequence i1、i2...ixAnd u1、u2...uxUpdating the time sequence in the cache region once every sampling; wherein, the length of the time sequence of the buffer area is x.
In general, the above technical solutions contemplated by the present invention can achieve the following advantageous effects compared to the prior art.
The invention considers that the voltage zero crossing points with the same change trend of the protection devices at each side in the differential protection area have the same time, and obtains the time scales of the resampling points of the protection devices according to the voltage zero crossing points with the same change trend, and then calculates the sampling values of the time of each resampling point by using a linear difference method, so that the current sampling values of the protection devices at each side in the differential protection area are completely synchronous, and the safe and stable operation of a power grid is ensured.
Drawings
Fig. 1 is a schematic diagram of a circuit MN and a protection device according to the present invention;
FIG. 2 is a schematic diagram of the cache update and the detection of pointer movement according to the present invention;
FIG. 3 is a schematic diagram of the zero crossing point of the same trend of the detected voltage according to the present invention;
FIG. 4 is a schematic of current resampling based on voltage zero crossings in accordance with the present invention;
FIG. 5 is a flow chart of a data synchronization method according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides a power distribution network differential protection data synchronization method based on voltage zero crossing points, which takes 2 sets of relay protection devices in a differential protection area as an example, and is installed at two sides of a protected line MN, and the line and the protection device are shown in figure 1, and concretely comprises the following steps:
s1: and 2 sets of relay protection devices are arranged in the differential protection area, sampling is continuously carried out according to sampling intervals respectively, and the time sequence of the electric quantity data in the cache of the protection devices on two sides of the line MN is updated. The fault starting element detects the occurrence of a fault, records a time sequence in a cache region at the moment of the occurrence of the fault, and starts to search in the reverse direction of the time sequence by taking the detected moment of the occurrence of the fault as a reference for protection at each side;
the relay protection device collects the voltage and the current of two ends of a protected line to obtain a current and voltage sampling value sequence { i } on two sides of the lineM},{iNAnd { u }M},{uNAt sampling period TsAnd sampling N points in each power frequency period. Respectively stored in the buffer area of the respective protection device, the time sequence length of the buffer area is x, i1、i2...ixAnd u1、u2...ux. Updating the time sequence in the buffer area once every sampling, adopting first-in-firstThe principle is that all data in the buffer area are sequentially shifted to the left by one bit, the leftmost data is removed, and the latest sampling value is stored in the rightmost buffer area, as shown in fig. 2.
Meanwhile, the relay protection device utilizes the sampled data in the cache region to detect faults. As known from the half-wave fourier algorithm, the sampled signal can be developed by fourier techniques, and is represented as:
Figure BDA0002908433980000051
the calculation formula of the sine term coefficient and the cosine term coefficient is as follows:
Figure BDA0002908433980000052
Figure BDA0002908433980000053
taking the M-side sampling value as an example, will
Figure BDA0002908433980000054
The time sequence of a half period is used as a time window, and the amplitude of the fundamental wave at the current moment can be obtained
Figure BDA0002908433980000055
When the amplitude of the fundamental wave is greater than K times the amplitude of the rated current, the fault-detecting element is activated, i.e.
Figure BDA0002908433980000061
Wherein INAnd starting a fault detection element for rated current, wherein K is generally 1.2-1.3 according to engineering experience. Recording the sampling value of the buffer area in the protection device at the moment when the fault occurs, taking the moment when the fundamental wave amplitude exceeds the setting value as a search starting point, namely taking the last sampling value of the buffer area at the moment when the fault occurs as the search starting point, and pointing the last element u by the detection moment pointer kxAnd starts to move in the reverse direction of the time sequence. The manner of detecting the occurrence of the fault at the N side is the same.
S2: and taking the fault occurrence moment as a starting point, and multiplying the voltage sampling value at the moment by the voltage sampling value at the previous moment by the relay protection devices at the two sides of the circuit respectively. If the result is greater than 0, continuing to search in the reverse direction of the time sequence, and if the result is less than 0, temporarily stopping searching;
for the M side, if
Figure BDA0002908433980000062
When the zero crossing point of the voltage does not appear, the time sequence is searched in the reverse direction continuously, the pointer at the current detection moment moves forward by one bit and changes x into x-1, namely the detection time window is changed from
Figure BDA0002908433980000063
Become into
Figure BDA0002908433980000064
And performing product operation on the sampling values in the time window again until the multiplication result of the two sampling values in the time window is less than 0, indicating that the voltage zero crossing point appears, pausing the detection, and recording the current detection time pointer as kMAs shown in fig. 3.
For the same reason, for the N side, if
Figure BDA0002908433980000065
Then the searching is continued to the reverse direction of the time sequence, the pointer at the current detection time is moved forward by one bit, and is changed from x to x-1, namely the detection time window is changed from
Figure BDA0002908433980000066
Become into
Figure BDA0002908433980000067
Performing product operation on the sampling values in the time window again until the multiplication result of the two sampling values in the time window is less than 0, detecting and suspending, and recording the current detection time pointer as kNAs shown in fig. 3.
S3: when the multiplication results of the sampling values at two sides of the line MN are both smaller than 0, namely the voltage zero crossing points are searched at two sides of the MN, the two-side protection device carries out difference operation on the sampling value at the time of pausing the search in S2 and the sampling value at the previous time, if the signs of the difference results at the two sides are different, the two-side protection device continues to search in the opposite direction of the time sequence, and if the signs are the same, the time scales of the two sides at the current time and the previous time and the voltage sampling value at the corresponding time are recorded;
taking the M side as an example, the current side is used to detect the time pointer kMCorresponding voltage sampling value, corresponding to a time (k-1) on the sideMBy differential operation of voltage samples, i.e.
Figure BDA0002908433980000071
The N side is treated in the same way to obtain
Figure BDA0002908433980000072
And transmitting the differential operation result of the M side to the N side, and transmitting the differential operation result of the N side to the M side. Multiplying the two differential operation results if
Figure BDA0002908433980000073
Then continuing to search in the reverse direction of the time sequence; if it is
Figure BDA0002908433980000074
The routine proceeds to S4, and the time stamps of the present time and the previous time are recorded
Figure BDA0002908433980000075
Voltage sampling value corresponding to time
Figure BDA0002908433980000076
Figure BDA0002908433980000077
t0
S4: constructing a Lagrange interpolation function by taking the voltage sampling values of the pause search time and the previous time of the current side as nodes on two sides of the line respectively, solving a voltage zero-crossing time scale, and considering the voltage zero-crossing time scales solved by the sides as the same time actually;
for the M side, the
Figure BDA0002908433980000078
For the node, construct the Lagrangian interpolation function L (t)
Figure BDA0002908433980000079
Let L (t) be 0, the time scale of the zero crossing point of the interpolation function voltage can be solved
Figure BDA00029084339800000710
For the N side, with
Figure BDA00029084339800000711
Constructing a Lagrangian interpolation function L' (t) for the nodes
Figure BDA00029084339800000712
Let L' (t) be 0, the time scale of the zero crossing point of the interpolation function voltage can be solved
Figure BDA00029084339800000713
The invention considers that the zero crossing points of the voltages with the same trend on each side are the same, namely
Figure BDA00029084339800000714
S5: the two sides of the circuit are respectively provided with t0For the starting point of sampling, TsAnd resampling the current sampling value sequence of each side for a sampling period to obtain the current sampling value sequence with two completely synchronous sides.
For the M side, t0As a resampling start point, TsResampling for a sampling period, resampling point time scale tn＝t0+nTs. Find the resampling point time scale tnAdjacent current actual sampling value
Figure BDA00029084339800000715
The side weight sampling point t can be obtained by linear interpolationnThe value of the time of day is shown in fig. 4.
Figure BDA0002908433980000081
Thereby obtaining an M side weight sampling value sequence { i'M}。
For the N side, t0As a resampling start point, TsResampling for a sampling period, resampling point time scale tn＝t0+nTs. Find the resampling point time scale tnAdjacent current actual sampling value
Figure BDA0002908433980000082
The side weight sampling point t can be obtained by linear interpolationnThe value of the time of day is shown in fig. 4.
Figure BDA0002908433980000083
Thereby obtaining an N-side weight sampling value sequence { i'N}。
According to the data synchronization method of the present invention, the complete process is shown in fig. 5, and the current sampling values of the protection devices on both sides of the line MN can be completely synchronized, i.e., { i'M},{i′NThe method is completely synchronous in time, and provides a solid foundation for the calculation and accurate action of the differential protection criterion.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (7)

1. A power distribution network differential protection data synchronization method based on voltage zero crossing points is characterized by comprising the following steps:
s1, continuously sampling line current and voltage by each relay protection device in a differential protection area to obtain a continuously updated voltage and current data time sequence;
s2, each protection device takes the fault occurrence time detected by each protection device as a starting point, searches in the reverse direction of the time sequence, and suspends the search when the sampling time adjacent to the voltage zero crossing point is searched;
s3, judging whether the voltage variation trends of the protection devices at the time of pausing the search are the same or not; if yes, go to step S4; if not, each protection device continues to search in the reverse direction of the time sequence;
s4, each protection device constructs a Lagrange interpolation function by taking the voltage sampling values of the pause searching time and the last time as nodes respectively, and obtains a voltage zero-crossing point time scale;
and S5, each protection device takes the corresponding voltage zero-crossing time scale as a sampling starting point respectively, and resampling the current actual sampling value of each protection device by combining a set sampling period to obtain a current sampling value sequence of each protection device which is completely synchronous.
2. The method for power distribution network differential protection data synchronization based on voltage zero-crossing points as claimed in claim 1, wherein step S2 is specifically,
for each protection device p, taking the fault occurrence time as a starting point, and sampling the voltage at the fault occurrence time
Figure FDA0003382305870000011
And the last time voltage sampling value
Figure FDA0003382305870000012
Performing product operation;
if it is
Figure FDA0003382305870000013
Then search window is formed
Figure FDA0003382305870000014
Become into
Figure FDA0003382305870000015
Performing product operation on the voltage sampling values in the search window again until the multiplication result of the voltage sampling values corresponding to the adjacent sampling moments is less than 0, and suspending the search; wherein P is 1,2, …, P; p represents the total number of protection devices in the differential protection zone.
3. The method for power distribution network differential protection data synchronization based on voltage zero-crossing points as claimed in claim 2, wherein step S3 is specifically,
for each protection device p, the search time will be suspended
Figure FDA0003382305870000016
Corresponding voltage sampling value and last moment
Figure FDA0003382305870000021
Carrying out difference operation on corresponding voltage sampling values to obtain
Figure FDA0003382305870000022
Multiplying the difference operation results corresponding to the protection devices;
if it is
Figure FDA0003382305870000023
The voltage variation trends of the protection devices at the moment of pausing the search are different, and the protection devices continue to search in the reverse direction of the time sequence; if it is
Figure FDA0003382305870000024
The voltage variation tendencies of the respective protection devices at the time of suspension of the search are the same, and the process proceeds to step S4.
4. The method for power distribution network differential protection data synchronization based on voltage zero-crossing points as claimed in claim 3, wherein the step S4 is specifically,
for each protection device p, in order to
Figure FDA0003382305870000025
For the nodes, a Lagrange interpolation function L (t) is constructed:
Figure FDA0003382305870000026
let L (t) be 0 to obtain the time scale of zero crossing point of interpolation function voltage
Figure FDA0003382305870000027
5. The method for power distribution network differential protection data synchronization based on voltage zero-crossing points as claimed in claim 4, wherein the step S5 is specifically,
for each protection device p, in order to
Figure FDA0003382305870000028
As a resampling start point, a set time TsResampling for a sampling period, resampling point time scales
Figure FDA0003382305870000029
According to the resampling point time scale tpnAdjacent current actual sampling values
Figure FDA00033823058700000210
Method for obtaining p resampling point time scale t of protection device by linear interpolationpnCurrent value of (d):
Figure FDA00033823058700000211
thereby obtaining p-fold sampling value sequence { i'p1,…i′pn,…,i′pN}; where N is 1, …, N represents the number of actual sampling points.
6. The method for power distribution network differential protection data synchronization based on voltage zero-crossing points according to any one of claims 1-5, wherein step S1 is specifically,
each protection device in the differential protection zone is respectively according to the sampling period TsSampling the current and voltage of the line, storing the sampled current and voltage into different buffer areas of the protection device respectively to obtain current data time sequences i1、i2...ixAnd voltage data time series u1、u2...uxUpdating the time sequence in the cache region once every sampling; wherein, the length of the time sequence of the buffer area is x.
7. A distribution network differential protection data synchronization system based on voltage zero crossing points is characterized by comprising: a computer-readable storage medium and a processor;
the computer-readable storage medium is used for storing executable instructions;
the processor is used for reading executable instructions stored in the computer readable storage medium and executing the power distribution network differential protection data synchronization method based on voltage zero-crossing points according to any one of claims 1 to 6.
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