Timing method for differential protection device, differential protection device and differential protection system

Abstract

Disclosed is a timing method for a differential protection device, comprising: obtaining multiple current sampling values ​​of a power line and a count value of each current sampling value from a merging unit of the power line, wherein the sampling moment of a current sampling value having a first count value among the multiple current sampling values ​​is the moment of generating a second pulse signal of the merging unit; resampling the multiple current sampling values ​​according to a sampling frequency J point / cycle of the differential protection device to obtain multiple current resampled values, wherein the multiple current resampled values ​​include a reference current resampled value corresponding to the current sampling value having the first count value; performing Fourier transform on the multiple current resampled values ​​to obtain multiple current Fourier values ​​arranged in time, wherein the multiple current Fourier values ​​include a reference current Fourier value corresponding to the sampling moment of the current sampling value having the first count value, and the reference current Fourier value is determined based on the reference current resampled value and J-1 current resampled values ​​arranged before the reference current resampled value in time.

Description

Technical Field

[0001] The present disclosure relates to a timing method for a differential protection device of a power line, a differential protection device for executing the timing method, and a differential protection system including the differential protection device. Background Art

[0002] According to the differential protection principle, the differential protection device needs to obtain current sampling values ​​from each end (two ends or more ends) of the differential protection area, and these current sampling values ​​must be aligned in time. Traditionally, parallel cable communication is used between the process layer and the bay layer of the substation automation system. The differential protection device directly receives the current analog value from the current transformer, and then converts and synchronizes the current analog value using the second pulse signal generated by its satellite positioning module as the reference time. However, with the development of substation automation systems, it has gradually evolved into using process bus communication between its process layer and the bay layer. The differential protection device does not directly receive the current analog value from the current transformer, but receives the current sampling value message from the merging unit via the process bus. In this case, if the differential protection device still synchronizes the time using the second pulse signal generated by its own satellite positioning module as the reference time, there will be a large error, which will pose a great safety risk in situations such as crossing a fault. Summary of the Invention

[0003] In view of the above problems in the prior art, one aspect of the present disclosure provides a timing method for a differential protection device for a power line. The method includes: obtaining a plurality of current sampling values ​​of the power line and a count value of each current sampling value from a merging unit of the power line, wherein the sampling time of the current sampling value with the first count value among the plurality of current sampling values ​​is the time when the second pulse signal of the satellite positioning module of the merging unit is generated; resampling the plurality of current sampling values ​​according to the sampling frequency J points / cycle of the differential protection device to obtain a plurality of current resampled values, wherein the plurality of current resampled values ​​include a reference current resampled value corresponding to the current sampling value with the first count value among the plurality of current sampling values, wherein J is an integer greater than 1; and performing Fourier transform on the plurality of current resampled values ​​to obtain a plurality of current Fourier values ​​arranged in time, wherein the plurality of current Fourier values ​​include a reference current Fourier value corresponding to the sampling time of the current sampling value with the first count value, and the reference current Fourier value is determined based on the reference current resampled value and J-1 current resampled values ​​arranged before it in time.

[0004] Another aspect of the present disclosure provides a differential protection device for a power line. The device includes a communication module, a sampling module, and a timing module. The communication module is configured to obtain multiple current sampling values ​​and a count value of each current sampling value from a merging unit of the power line. The sampling time of the current sampling value with the first count value among the multiple current sampling values ​​is the time when the second pulse signal of the satellite positioning module of the merging unit is generated. The sampling module is configured to resample the multiple current sampling values ​​according to the sampling frequency J points / cycle of the differential protection device to obtain multiple current resampled values. The multiple current resampled values ​​include a reference current resampled value corresponding to the current sampling value with the first count value among the multiple current sampling values, where J is an integer greater than 1. The timing module is configured to perform a Fourier transform on the multiple current resampled values ​​to obtain multiple current Fourier values ​​arranged in time. The multiple current Fourier values ​​include a reference current Fourier value corresponding to the sampling time of the current sampling value with the first count value. The reference current Fourier value is determined based on the reference current resampled value and J-1 current resampled values ​​arranged in time before the reference current resampled value.

[0005] Another aspect of the present disclosure provides a differential protection system for power lines. The system includes a current transformer, a merging unit, and a differential protection device. The current transformer is configured to measure an analog current value of the power line. The merging unit is configured to sample the analog current value to generate multiple raw current sampling values, interpolate the multiple raw current sampling values ​​to obtain multiple current sampling values, and mark each current sampling value with a count value. The sampling time of the current sampling value with a first count value among the multiple current sampling values ​​is the time when the second pulse signal of the satellite positioning module of the merging unit is generated. The differential protection device is used to: obtain multiple current sampling values ​​of the power line and the count value of each current sampling value from the merging unit of the power line; resample the multiple current sampling values ​​according to the sampling frequency J points / cycle of the differential protection device to obtain multiple current resampled values, the multiple current resampled values ​​including a reference current resampled value corresponding to the current sampling value with a count value of the first value among the multiple current sampling values, where J is an integer greater than 1; perform Fourier transform on the multiple current resampled values ​​to obtain multiple current Fourier values ​​arranged in time, the multiple current Fourier values ​​including a reference current Fourier value corresponding to the sampling moment of the current sampling value with a count value of the first value, and the reference current Fourier value is determined based on the reference current resampled value and J-1 current resampled values ​​arranged before it in time. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 It is a schematic diagram of the differential protection principle of power lines;

[0007] Figure 2 This is an example usage scenario diagram of a time synchronization method according to the prior art;

[0008] Figure 3 is a diagram showing an example of a time synchronization method according to the prior art;

[0009] Figure 4 is a diagram of an example usage scenario of a time synchronization method according to an embodiment of the present disclosure;

[0010] Figure 5 is a flowchart of a time synchronization method according to an embodiment of the present disclosure;

[0011] Figure 6 is a schematic diagram of data transformation according to a time synchronization method according to an embodiment of the present disclosure;

[0012] Figure 7 is another example usage scenario diagram of the time synchronization method according to an embodiment of the present disclosure;

[0013] Figure 8 is a schematic block diagram of a differential protection device according to an embodiment of the present disclosure.

[0014] Figure 9 is a schematic block diagram of a differential protection system according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0015] The present disclosure will be described in detail below with reference to exemplary embodiments of the present disclosure. However, the present disclosure is not limited to the embodiments described herein and may be implemented in many different forms. The described embodiments are intended only to make the present disclosure thorough and complete and to fully convey the concept of the present invention to those skilled in the art. The features of the various described embodiments may be combined or replaced with each other unless expressly excluded or should be excluded based on the context.

[0016] Unless otherwise defined, technical or scientific terms used in this disclosure should have the same general meaning as those generally understood by persons skilled in the art in the art to which this disclosure pertains. The terms "first," "second," and similar terms used in this disclosure do not denote any order, quantity, or importance, but are merely used to distinguish different components.

[0017] Figure 1 It is a schematic diagram of the differential protection principle of power lines.

[0018] refer to Figure 1 The principle of differential protection of power line L is to determine whether the differential current of power line L is zero, that is, whether the vector sum of currents I1 and I2 at both ends of power line L is zero, to determine whether the differential protection action of power line L should be triggered (for example, causing the associated circuit breaker to trip, etc.).

[0019] For example, whether the differential protection action of the power line L should be triggered can be determined based on the following criteria:

[0020] For I bias s2 , when |I diff |>k1|I bias |+I s1 When triggered;

[0021] For I bias >I s2 , when |I diff |>k2|I bias |-(k2-k1)I s2 +I s1 When triggered;

[0022] in:

[0023] is the bias current of the power line L, that is, the mean of the scalar sum of the currents at both ends of the power line L;

[0024] I diff =I1+I2, which is the differential current of the power line L, i.e., the vector sum of the currents at both ends of the power line L;

[0025] k1 and k2 are bias percentages;

[0026] I s1 , I s2 The values ​​of k1 and k2 can be selected according to the actual situation of the power line L. Here, I1 and I2 refer to the fundamental components of the currents I1 and I2 at both ends of the power line L, respectively.

[0027] Figure 1 The protection area shown for a power line L with two ends is for example only; protection areas with more ends are also possible. For example, if one side of the protection area is a busbar substation, and the other side includes multiple branch substations, the differential protection device for the busbar substation needs to consider the total vector sum of the current information on this side and the current information of the substations on the other side to determine whether to trigger differential protection for the protection area.

[0028] Figure 2 This is an example usage scenario diagram of a time synchronization method according to the prior art.

[0029] As mentioned above, the time synchronization method according to the prior art is applicable to a substation automation system in which the process layer and the bay layer are connected via parallel cables. Figure 2 The substations at the A and B ends of the power line L shown in FIG. 1 belong to such a substation automation system.

[0030] like​ Figure 2 As shown, at end A, the current transformer CT1 serves as a process layer device of the substation automation system at end A, which measures the current analog quantity at end A. The differential protection device R1 serves as an interval layer device of the substation automation system at end A, which receives the current analog quantity from the current transformer CT1 via a parallel cable, and then processes the current analog quantity at end A according to the synchronization method of the prior art to convert it into the synchronized current digital quantity at end A. The arrangement of end B is similar to that of end A, and the differential protection device R1 also processes the current analog quantity at end B according to the synchronization method of the prior art to convert it into the synchronized current digital quantity at end B. The differential protection devices R1 and R2 exchange each other's synchronized current digital quantities via the communication channel CH, and then according to Figure 1 The differential protection principle shown makes a differential protection decision on whether to take differential protection action.

[0031] The differential protection devices R1 and R2 have a satellite positioning module that can receive the reference time source of timing systems such as the Global Positioning System (GPS), BeiDou System (BDS), Galileo System and GLONASS System, correct their own time based on the reference time source, and generate a pulse per second (PPS) signal per second.

[0032] Figure 3 is a diagram illustrating an example of a time synchronization method according to the related art.

[0033] According to the prior art time synchronization method, Figure 1 The method is performed by the differential protection devices R1 and / or R2 in the differential protection device. For example, the method can be summarized as follows: In the first step, the differential protection device R1 receives a current analog value from the current transformer CT1; in the second step, the differential protection device R1 samples the current analog value to obtain current sampling values; in the third step, the differential protection device R1 uses the pulse per second (PPS) signal generated by its own satellite positioning module as a reference time and performs a Fourier transform on the obtained current sampling values ​​to obtain multiple current Fourier values.

[0034] refer to Figure 3 , which shows an example of a time synchronization method according to the prior art. In the first step, the differential protection device R1 receives the current analog value from the current transformer CT1, such as Figure 3As shown in the curve 310, the current analog quantity is a sine wave. In the second step, the differential protection device R1 samples the current analog quantity according to its sampling frequency. Taking the power frequency of 50Hz and the sampling frequency of 48 points / cycle as an example, the differential protection device R1 obtains 48 current sampling values ​​per cycle, and obtains 2400 current sampling values ​​per second. If needed, interpolation or other methods can be used to ensure that the sampling time of one current sampling value in every 2400 current sampling values ​​is the generation time of the PPS signal generated by the satellite positioning module of the differential protection device R1. As shown in the diagram 320, the current sampling value S i The sampling time is the generation time of the first PPS signal of the satellite positioning module of the differential protection device R1, t pps1 , current sampling value S i+4000 The sampling time is the generation time of the second PPS signal of the satellite positioning module of the differential protection device R1. pps2 In the third step, the differential protection device R1 generates its own PPS signal at the time t pps1 and t pps2 As the reference time, every 6 current sampling values ​​are taken to perform a Fourier transform on 48 consecutive current sampling values, and the current sampling values ​​S i ~S i+3999 The corresponding current Fourier value DFT0~DFT 399 and the current sampling value S i+4000 ~S i+7999 Corresponding DFT 400 ~DFT 799 Since the generation time of two adjacent PPS signals is t pps1 and t pps2 If the interval between them is 1s, then the moments when two adjacent current Fourier values ​​are aligned are 2.5ms apart in time.

[0035] The differential protection device R2 at the B end also uses the generation time of its own satellite positioning module PPS signal as the reference time and generates the current Fourier value in a similar way. The current information generated by each of them is exchanged via the communication channel CH. The current information includes the current Fourier value and the time when the current Fourier value is aligned. The differential protection devices R1 and R2 can then generate the current Fourier value according to the current Fourier value. Figure 1 The differential protection principle shown calculates the differential current at the target moment.

[0036] However, the time synchronization method according to the prior art is not applicable to a substation automation system that adopts process bus communication, such as a substation automation system that complies with the IEC61850-9-2 standard.

[0037] Figure 4 2 is an example usage scenario diagram of the time synchronization method according to an embodiment of the present disclosure.

[0038] refer to Figure 4 ,At the A and B ends of the power line L, both use ,substation automation systems that use process bus communication.

[0039] At end A, current transformer CT1, a process-layer device in the substation automation system at end A, measures the analog current at end A. Merging unit 401, a key component of the interface between the process and bay layers of the substation automation system at end A, connects one end to current transformer CT1 via a parallel cable. It receives the analog current at end A measured by current transformer CT1 and processes it into a current sampling value message. Its other end connects to differential protection device 402, a bay-layer device, via a process bus and transmits the current sampling value message to it.

[0040] At end B, similar to end A, current transformer CT2 measures the analog current at end B. Merging unit 403 receives the analog current at end B measured by current transformer CT2 via a parallel cable, processes the analog current into a current sampling value message, and then transmits the sampled value message to differential protection device 404 via a process bus.

[0041] and Figure 2 The difference is that in Figure 4 The merging unit 401 is introduced into the usage scenario, and the transmission between the merging unit 401 and the differential protection device 402 does not rely on parallel cables but on process buses, which causes a large transmission delay that cannot be ignored for differential protection. Moreover, since the process bus is susceptible to many interference factors, the transmission delay is also unstable. If the differential protection devices 402 and 404 still use Figure 3 The timing method shown here can result in a discrepancy between the time at which the current Fourier transform values ​​are aligned and the time at which the corresponding current values ​​are collected. This in turn leads to incorrect differential current calculations. In situations where the current amplitude varies significantly over a short period of time (e.g., during a fault), this can cause the differential protection device to make erroneous differential protection decisions. In light of this, the present disclosure proposes a timing method applicable to substation automation systems with merging units that utilize process bus communication.

[0042] Figure 4 The differential protection devices 402 and 404 in the embodiment of the present disclosure execute the synchronization method according to the embodiment of the present disclosure to convert the sampled values ​​into the synchronized current Fourier values. After the differential protection devices 402 and 404 exchange the synchronized current Fourier values ​​generated by each other via the communication channel CH, they can Figure 1 The differential protection principle shown here can be used to make correct differential protection decisions.

[0043] The merging units 401 and 403 and the differential protection devices 402 and 402 all include the satellite positioning module as described above for receiving a reference time source of a timing system such as GPS, BDS, Galileo or GLONASS and generating a PPS signal.

[0044] The following combination Figure 5 and Figure 6 A time synchronization method according to an embodiment of the present disclosure is described.

[0045] Figure 5 is a flowchart of a time synchronization method according to an embodiment of the present disclosure. Figure 6 3 is a schematic diagram of data transformation according to the time synchronization method of an embodiment of the present disclosure.

[0046] refer to Figure 5 According to an embodiment of the present disclosure, the time synchronization method 500 includes steps S510 to S530. The time synchronization method 500 can be performed by the differential protection device 402 and / or 404. The differential protection device 402 is used as an example for description.

[0047] In step S510, the differential protection device 402 obtains multiple current sampling values ​​of the power line L and the count value of each current sampling value from the merging unit 401. The sampling time of the current sampling value whose count value is the first value among the multiple current sampling values ​​is the generation time of the PPS signal of the satellite positioning module of the merging unit 401.

[0048] Figure 6 The diagram 610 in FIG. 4 shows an example of a current sampling value obtained by the merging unit 401 by sampling the current analog quantity measured by the current transformer CT1. ppsh , t ppsi , t ppsj and t ppsk They represent the hth PPS signals PPS generated successively by the satellite positioning modules of the merging unit 401. h , the i-th PPS signal PPS i , the jth PPS signal PPS j and the kth PPS signal PPS k The merging unit 401 samples N current sampling values ​​per second. For example, at the i-th PPS signal PPS i The generation time t ppsi and the jth PPS signal PPS j The generation time t ppsj There are N current sampling values ​​X arranged between i,0 ~X i,N-1 , where X i,0 is the PPS signal PPS in the i-th i The generation time tppsi The current sampling value of the sample. N is an integer greater than 1.

[0049] Here, depending on the sampling control mode between the merging unit 401 and the current transformer CT1, the original current sampling value obtained by the merging unit 401 sampling the current analog value may not contain the sampling time exactly being the generation time t of each PPS signal. ppsh , t ppsi , t ppsj and t ppsk The merging unit 401 can implement the current sampling value as shown in Figure 610 by performing operations such as interpolation on the original current sampling value, with the sampling time being the generation time t of each PPS signal. ppsh , t ppsi , t ppsj and t ppsk Since the interpolation operation is a well-known technique in the art and in order to avoid blurring the present disclosure, the present disclosure does not describe this operation in detail.

[0050] The merging unit 401 transmits each sampled value to the differential protection device 402 in the form of a sampled value message (e.g., a message format conforming to the IEC 61850-9-2 standard). Each sampled value message includes a tag SmpCnt (hereinafter referred to as SC) indicating a count value of the sampled value, and the count value is labeled in units of N current sampled values ​​included between the generation times of two consecutive PPS signals. The N current sampled values ​​included between the generation times of two consecutive PPS signals are referred to herein as a current sampled value set. The multiple current sampled values ​​include at least one current sampled value set, and the count values ​​of the N current sampled values ​​in each current sampled value set are labeled in chronological order from 0 to N-1, with the first value of the count value being 0.

[0051] For example, as shown in diagram 610, the horizontal axis represents the time of the merging unit 401, and the vertical axis represents the current sampling values ​​obtained by the merging unit 401. Taking the power frequency as 50 Hz and the sampling frequency of the merging unit as 80 points / cycle as an example, the merging unit 401 samples 4000 current sampling values ​​per second, that is, N = 4000. The i-th current sampling value set includes the current sampling values ​​arranged in the i-th PPS signal PPS i The generation time t ppsi and the jth PPS signal PPS j The generation time t ppsj N current sampling values ​​X between i,0 ~X i,3999 , their count values ​​are SC i,0 ~SC i,3999Similarly, the jth current sampling value set following the ith current sampling value set includes the current sampling value set arranged in the jth PPS signal PPS j The generation time t ppsj and the kth PPS signal PPS k The generation time t ppsk N current sampling values ​​X between j,0 ~X j,3999 , their count values ​​are SC j,0 ~SC j,3999 .

[0052] Figure 6 Graph 620 in FIG shows an example of current sampling values ​​received by the differential protection device 402 from the merging unit 401. The horizontal axis of graph 620 represents the time of the differential protection device 401, and the vertical axis represents the current sampling values ​​received by the differential protection device 401. The differential protection device 402 receives the sampling value message generated by the merging unit 401 via the process bus. This transmission process may have a large transmission delay, resulting in, for example, the differential protection device 402 receiving the SC with the first value of the count value in the i-th current sampling value set. i,0 Current sampling value X i,0 Time t i,0 The satellite positioning system of the differential protection device 402 generates the i-th PPS signal PPS i The generation time t ppsi Distance Δt i,delay ; SC receiving the first value of the count value in the j-th current sampling value set j,0 Current sampling value X j,0 The receiving time t j,0 The jth PPS signal PPS of the satellite positioning system of the differential protection device 402 j Time t ppsj Distance Δt j,delay In some examples, the merging unit 401 can transmit the sample value message in real time, but the transmission delay is unstable due to the interference factors that the process bus transmission is susceptible to. The time interval Δt i,delay and time interval Δt j,delay Not necessarily equal.

[0053] In step S520, the differential protection device 402 resamples the multiple current sampling values ​​according to its sampling frequency J points / cycle (J is an integer greater than 1) to obtain multiple current resampled values, wherein the multiple current resampled values ​​include a reference current resampled value corresponding to the current sampling value having a count value of the first value among the multiple current sampling values.

[0054] Because the sampling frequency of differential protection device 402 is often different from the sampling frequency of merging unit 401, differential protection device 402 needs to resample multiple current sampled values. The resampling method can be linear interpolation or other methods to generate M current resampled values ​​per second. After resampling, the current resampled value corresponding to the current sampled value with the first count value is used as the reference current resampled value.

[0055] Figure 6 The diagram 630 in FIG. 6 is an example of a plurality of current resampled values ​​obtained by the differential protection device 402 resampling the current sampled values ​​in FIG. 620. The horizontal axis of FIG. 630 represents the time of the differential protection device 402, and the vertical axis represents the current resampled values ​​obtained by the differential protection device 401. Since the time for the differential protection device 402 to perform the resampling operation is negligible relative to the calculation accuracy of the differential current, the time for the differential protection device 401 to perform the resampling operation is not considered in FIG. 630. As shown in FIG. 630, taking the power frequency of 50 Hz and the sampling frequency of the differential protection device 402 of J = 48 points / cycle as an example, after resampling, M = 2400 current resampled values ​​are formed per second. For example, the current resampled value Y i,0 To Y i,2399 .

[0056] The M current resampled values ​​corresponding to a current sampled value set are referred to herein as a current resampled value set. The multiple resampled values ​​obtained by resampling by differential protection device 402 include at least one current resampled value set, which corresponds one-to-one with at least one current sampled value set shown in diagram 620. The first current resampled value in each current resampled value set serves as the aforementioned reference current resampled value.

[0057] As shown in diagram 630, the i-th current resampled value set includes the current sampled value set X corresponding to the i-th current resampled value set. i,0 ~X i,3999 2400 current resampled values ​​Y i,0 ~Y i,2399 , and the first current resampled value Y i,0 The current sampling value X with the count value being the first value i,0 Correspondingly, as the reference current resampled value of the i-th current resampled value set. The j-th current resampled value set immediately following the i-th current resampled value set includes the current resampled value set corresponding to the j-th current resampled value set X j,0 ~X j,3999 2400 current resampled values ​​Y j,0 ~Y j,2399 , and the first current resampled value Y j,0 The current sampling value X with the count value being the first value j,0Correspondingly, it serves as the reference current resampled value of the j-th current resampled value set.

[0058] In addition, depending on the requirements for differential current calculation accuracy, the differential protection device 402 may resample the current sampling value more than once. For example, considering the requirements of further noise reduction, filtering or reducing the amount of calculation, the current sampling value may be resampled multiple times.

[0059] In step S530, a Fourier transform is performed on the multiple current resampled values ​​to obtain a plurality of current Fourier values ​​arranged in time, the plurality of current Fourier values ​​including a reference current Fourier value corresponding to a sampling moment of the current sampling value having a count value of the first value, and the reference current Fourier value is determined based on the reference current resampled value and J-1 current resampled values ​​arranged before it in time.

[0060] As shown in diagram 640, the obtained multiple current Fourier values ​​may include at least one current Fourier value set, for example, the i-th current Fourier value set includes the current resampled values ​​Y arranged in time. i,0 ~Y i,M-1 DFT of G current resampled values i,0 ~DFT i,G-1 , where DFT i,0 is the resampled value Y corresponding to the reference current i,0 The current Fourier value is also the current sampling value X corresponding to the first value of the count value i,0 The current Fourier value of the i-th current Fourier value set is used as the reference current Fourier value of the i-th current Fourier value set; the j-th current Fourier value set includes the current resampling values ​​Y arranged in time. j,0 ~Y j,M-1 DFT of G current resampled values j,0 ~DFT j,G-1 , where DFTj i,0 is the resampled value Y corresponding to the reference current j,0 The current Fourier value is also the current sampling value X corresponding to the first value of the count value j,0 The current Fourier value of is used as the reference current Fourier value of the j-th current Fourier value set; and so on.

[0061] According to the Fourier transform principle, for multiple current resampled values ​​obtained with a resampling frequency of J points / cycle, a Fourier transform can be performed on J consecutive current resampled values ​​every K current resampled values. Then the number of current Fourier values ​​contained in each Fourier value set is The symbols Indicates rounding down, G is usually an integer.

[0062] The differential protection device 402 obtaining the multiple current Fourier values ​​includes obtaining each current Fourier value set in at least one current Fourier value set.

[0063] Next, we can obtain the DFT of the Fourier value set of the i-th current. i,0 ~DFT i,G-1 Take the following example to illustrate how to perform Fourier transform.

[0064] First, obtain the first current Fourier value DFT in the i-th current Fourier value set i,0 As shown in FIG640, taking J as 48 points / cycle as an example, the reference current resampling value Y of the i-th current resampling value set is i,0 and the 47 current resampled values ​​arranged before it in time, namely Y h,2353 ~Y i,0 , as the transformation object, perform Fourier transform to obtain the first current Fourier value DFT i,0 Since the first current Fourier value DFT i,0 and the reference current resampled value Y i,0 Correspondingly, the reference current resampled value Y i,0 The current sampling value X with the count value being the first value i,0 Correspondingly, therefore, the first current Fourier value DFT i,0 The current sampling value X with the count value being the first value i,0 Correspondingly, it serves as the reference current Fourier value of the i-th current Fourier value set.

[0065] Then, obtain the second current Fourier value DFT in the i-th current Fourier value set i,1 As shown in FIG640, taking K as 6 as an example, the transformation object of the first current Fourier value, ie, Y h,2353 ~Y i,0 , 48 current resampled values ​​are obtained by shifting 6 current resampled values ​​backward in time, Y h,2359 ~Y i,6 , as the transformation object of the second current Fourier value, perform Fourier transform, and obtain the second current Fourier value DFT i,1 .

[0066] Then, obtain the second current Fourier value DFT with i,1 Similarly, the 48 current resampled values ​​obtained by shifting the transformation object of the previous current Fourier value backward in time by 6 current resampled values ​​are used as the transformation object of the next current Fourier value, and Fourier transform is performed to obtain the third to Gth current Fourier value DFTs in sequence. i,2 ~DFT i,399 .

[0067] All current Fourier values ​​corresponding to the graph 630 can be obtained in the same way.

[0068] In addition, when the differential protection device 402 resamples the current sample value multiple times, J is the sampling frequency of the last resampling.

[0069] Thus, according to the timing method of the embodiment of the present disclosure, the first current Fourier value in each current Fourier value set in the acquired current Fourier values, such as DFT i,0 , DFT j,0 , as the reference current Fourier value, respectively with each current sampling value of the first value, such as X i,0 、X j,0 , corresponding to. And each count value is the current sampling value of the first value, such as X i,0 、X j,0 , respectively, are the PPS signals of the satellite positioning module of the merging unit, such as PPS i 、PPS j , the generation time t PPSi , t PPSi Correspondingly, therefore, the first current Fourier value as the reference current Fourier value, such as DFT i,0 , DFT j,0 Respectively with the corresponding PPS signal PPS i 、PPS j The generation time is aligned.

[0070] The timing method according to an embodiment of the present disclosure may further include step 540 of marking the time of each of the multiple current Fourier values ​​obtained so that the obtained values ​​are transmitted to an external device for use in calculating the differential current. The external device may be, for example, the differential protection device 404 at the other end of the power line L or another device that collects current information from both ends A and B of the power line L. Marking the time of each of the multiple current Fourier values ​​obtained includes marking the time of each current Fourier value in each set of current Fourier values.

[0071] The following is the DFT of the Fourier value of the i-th current i,0 ~DFT i,G-1 This section gives an example of how to mark a moment.

[0072] First, mark the time of the reference current Fourier value in the i-th current Fourier value set. As mentioned above, each first current Fourier value DFT as the reference current Fourier value i,0 , DFT j,0 Respectively with the corresponding PPS signal PPS i 、PPS jaligned with the generation time. Therefore, as shown in FIG. 640, the time of the first current Fourier value in the i-th current Fourier value set (i.e., the reference current Fourier value) is marked as the corresponding PPS signal PPS i of the generation time t PPSi .

[0073] Then, mark the times of the second to the G-th current Fourier values in the i-th current Fourier value set. Mark the time of the Q-th (2 < Q ≤ G) current Fourier value in the current Fourier value set as the time of the reference current Fourier value plus (Q - 1)*Δt, where Δt = (duration of one cycle) / (J / K). For example, taking the power frequency of 50 Hz, the resampling frequency J of the differential protection device 402 is 48 points / cycle, and taking 48 consecutive current resampling values every K = 6 current resampling values to calculate one current Fourier value as an example, the time of the second current Fourier value in the i-th current Fourier value set is marked as t PPSi + 2.5 ms, and the time of the third current Fourier value is marked as t PPSi + 5 ms, and so on.

[0074] In addition, as mentioned above, in some examples, due to the instability of the transmission delay between the merging unit 401 and the differential protection unit 402, the time interval Δt in FIG. 620 i,delay and the time interval Δt j,delay are not necessarily equal, which may result in different numbers G of current Fourier values in different current Fouriers.

[0075] Referring to FIG. 620, the time interval Δt i,delay and the time interval Δt j,delay are not necessarily equal. In other words, the time interval between the reception times of two current sampling values with the first value in two adjacent current sampling value sets received by the differential protection device 402, such as t j,0 - t i,0 , is not necessarily 1 second. For example, when Δt j,delay > Δt i,delay , t j,0 - t i,0 is greater than 1 second. When Δt j,delay < Δt i,delay , t j,0 - t i,0 is less than 1 second, which may cause the number G of current Fourier values in the corresponding current Fourier value set to change.

[0076] Taking the power frequency of 50 Hz and the resampling frequency of the differential protection device 402 as J = 48 points / cycle as an example, when Δt j,delay ≥ Δti,delay , thus t j,0 -t i,0 ≥1 second, the differential protection device 402 is at time t i,0 Calculate the first Fourier value DFT in the i-th current Fourier value set i,0 Then, calculate the second Fourier value DFT every 6 resampled values i,1 , and so on, until the DFT is calculated i,399 , then wait for time t j,0 The arrival of the first Fourier value DFT of the j-th current Fourier value set is calculated j,0 Thus, the number G of current Fourier values ​​in the i-th current Fourier value set is 400.

[0077] However, at Δt j,delay <Δt i,delay , thus t j,0 -t i,0 If the time is less than 1 second, it is possible that the differential protection device 402 has not yet calculated the last one or more current Fourier values ​​in the i-th current Fourier value set when it has received the current sampling value with the first count value in the j-th current Fourier value set. In this case, the differential protection device 402 stops calculating the last one or more current Fourier values ​​in the i-th current Fourier value set and immediately calculates the first current Fourier value DFT in the j-th current Fourier value set. j,0 Thus, the number G of current Fourier values ​​in the i-th current Fourier value set is less than 400.

[0078] Using the time synchronization method described above according to an embodiment of the present disclosure, the differential protection device 402 can obtain current information I1 at terminal A of the power line L. This current information I1 includes the Fourier transform value of the current at terminal A marked with the alignment time. This current information can be sent to an external device for use in calculating the differential current of the power line L.

[0079] Compared with the timing method according to the prior art, the timing method 500 according to the embodiment of the present disclosure does not calculate the current Fourier value based on the PPS signal generated by the satellite positioning module of the differential protection device itself as the reference time, but takes into account the transmission delay between the merging unit and the differential protection device, and aligns the current Fourier value to the collection time of the current value corresponding to the current Fourier value based on the current sampling value of SmpCnt=0 received by the differential protection device from the merging unit.

[0080] As a result, the timing accuracy of the current Fourier value is improved, and the reliability of the differential current value calculated based on the current Fourier value is enhanced. In the case of large changes in current amplitude in a short period of time (for example, crossing a fault, etc.), it can avoid making erroneous differential protection decisions due to a large error between the calculated differential current and the actual differential current.

[0081] Figure 7 FIG. 4 is another example usage scenario diagram of the time synchronization method according to an embodiment of the present disclosure.

[0082] The time synchronization method 500 according to the embodiment of the present disclosure described above is also applicable to Figure 7 The scene shown. Figure 7 , the A end of the power line L and Figure 4 The A end has the same arrangement as the Figure 2 The B end has the same arrangement. The differential protection device 402 at the A end executes the synchronization method 500 according to the embodiment of the present disclosure to obtain the current information I1 of the A end after synchronization, I1 including the current Fourier value of the A end marked with the alignment moment. The differential protection device R2 at the B end executes the above-mentioned combination Figure 2 The synchronization method according to the prior art described above obtains the synchronized current information I2 of the terminal B, which includes the Fourier value of the current at the terminal B marked with the alignment time. After exchanging the current information I1 and I2 via the communication channel CH, the differential protection device 402 and R2 can calculate the differential current of the power line L, thereby Figure 1 The differential protection principle shown here can be used to make correct differential protection decisions.

[0083] Figure 8 is a schematic block diagram of a differential protection device according to an embodiment of the present disclosure.

[0084] refer to Figure 8 , according to the differential protection device 800 of the embodiment of the present disclosure (for example, it can be Figure 4 401, 402) include a communication module 801, a sampling module 802 and a time synchronization module 803.

[0085] The communication module 801 is used to obtain multiple current sampling values ​​of the power line and the count value of each current sampling value from the merging unit of the power line L. The sampling time of the current sampling value whose count value is the first value among the multiple current sampling values ​​is the generation time of the second pulse (PPS) signal of the first satellite positioning system module of the merging unit.

[0086] The sampling module 802 is used to resample multiple current sampling values ​​according to the sampling frequency J point / cycle of the differential protection device to obtain multiple current resampled values, and the multiple current resampled values ​​include a reference current resampled value corresponding to the current sampling value whose count value is the first value among the multiple current sampling values.

[0087] The timing module 803 is used to perform Fourier transform on multiple current resampled values ​​to obtain multiple current Fourier values ​​arranged in time, the multiple current Fourier values ​​include a reference current Fourier value corresponding to the sampling moment of the current sampling value whose count value is the first value, and the reference current Fourier value is determined based on the reference current resampled value and J-1 current resampled values ​​arranged before it in time.

[0088] In addition, the differential protection device 402 may further include a satellite positioning module 804 (not shown in the figure) for receiving a reference time source of a timing system and generating a PPS signal.

[0089] Since it has been combined Figure 5 and Figure 6 The process of the differential protection devices 402 and 404 executing the time synchronization method 500 according to the embodiment of the present disclosure has been described in detail, and will not be repeated here to avoid repetition.

[0090] Figure 9 is a schematic block diagram of a differential protection system 900 according to an embodiment of the present disclosure.

[0091] refer to Figure 9 According to an embodiment of the present disclosure, the differential protection system 900 includes: Figure 2 、 Figure 4 , the current transformer CT1 or CT2 in Figure 7, such as Figure 4 、 Figure 7 The merging unit 401 or 403 in Figure 8 The differential protection device 800 in FIG.

[0092] Current transformers are used to measure the analog value of the current in the power line.

[0093] The merging unit is used to sample the current analog value to generate multiple original current sampling values, and interpolate the multiple original current sampling values ​​to obtain multiple current sampling values, and mark a count value for each current sampling value, and the sampling time of the current sampling value with the first count value among the multiple current sampling values ​​is the generation time of the second pulse signal of the satellite positioning module of the merging unit.

[0094] The differential protection device is used to: obtain multiple current sampling values ​​of the power line and the count value of each current sampling value from a merging unit, the sampling moment of the current sampling value with the first count value among the multiple current sampling values ​​is the generation moment of the second pulse signal of the merging unit; resample the multiple current sampling values ​​according to the sampling frequency J point / cycle of the differential protection device to obtain multiple current resampled values, the multiple current resampled values ​​include a reference current resampled value corresponding to the current sampling value with the first count value among the multiple current sampling values; perform Fourier transform on the multiple current resampled values ​​to obtain multiple current Fourier values ​​arranged in time, the multiple current Fourier values ​​include a reference current Fourier value corresponding to the sampling moment of the current sampling value with the first count value, and the reference current Fourier value is determined based on the reference current resampled value and J-1 current resampled values ​​arranged before it in time.

[0095] Since it has been combined Figure 5 and Figure 6 The process of how the current transformer CT1 , the merging unit 401 and the differential protection device 402 cooperate to implement the time synchronization method 500 according to the embodiment of the present disclosure is described in detail, and will not be repeated here to avoid repetition.

[0096] The timing method, differential protection device, and differential protection system according to the disclosed embodiments consider the impact of transmission delays caused by the transmission of sampled value messages between the process layer and bay layer of a substation automation system via a process bus on the calculation of the differential current on power line L. These methods are suitable for timing synchronization in substation automation systems that utilize process bus communication. The current sampling value (SmpCnt = 0) received by the differential protection device from the merging unit is used as a reference to align the current Fourier transform values ​​and the sampling times of the corresponding current values. This improves the accuracy of differential current calculation and significantly benefits electrical system safety.

[0097] Those skilled in the art should understand that the above-mentioned specific embodiments are merely examples and not limitations, and that various modifications, combinations, partial combinations and replacements may be made to the embodiments of the present disclosure according to design requirements and other factors. As long as they are within the scope of the attached claims or their equivalents, they fall within the scope of rights to be protected by the present disclosure.

Claims

1. A timing method for a differential protection device of a power line, comprising: Acquire, from a merging unit of the power line, a plurality of current sampling values ​​of the power line and a count value of each current sampling value, wherein a sampling moment of a current sampling value having a first count value among the plurality of current sampling values ​​is a moment at which a pulse-per-second signal of a satellite positioning module of the merging unit is generated; resampling the multiple current sampling values ​​according to a sampling frequency J points / cycle of the differential protection device to obtain multiple current resampled values, the multiple current resampled values ​​including a reference current resampled value corresponding to the current sampling value having a count value of the first value, where J is an integer greater than 1; as well as A Fourier transform is performed on the multiple current resampled values ​​to obtain a plurality of current Fourier values ​​arranged in time, the plurality of current Fourier values ​​including a reference current Fourier value corresponding to a sampling moment of a current sampling value having a count value of a first value among the multiple current sampling values, and the reference current Fourier value is determined based on the reference current resampled value and J-1 current resampled values ​​arranged before the reference current resampled value in time.

2. The time synchronization method according to claim 1, wherein: The multiple current sampling values ​​include at least one current sampling value set, each current sampling value set in the at least one current sampling value set includes N current sampling values ​​located between the generation moments of two second pulse signals, the count values ​​of the N current sampling values ​​are marked as 0 to N-1 in chronological order, and the first value is 0, where N is an integer greater than 1.

3. The time synchronization method according to claim 2, wherein: The multiple current resampled values ​​include at least one current resampled value set corresponding one-to-one to the at least one current resampled value set, each current resampled value set in the at least one current resampled value set includes M current resampled values, and the first current resampled value in each current resampled value set serves as the reference current resampled value, where M is an integer greater than 1.

4. The time synchronization method according to claim 3, wherein: The multiple current Fourier values ​​include at least one current Fourier value set, each current Fourier value set in the at least one current Fourier value set includes G current Fourier values, and the first current Fourier value in each current Fourier value set serves as the reference current Fourier value, where G is an integer greater than 1.

5. The time synchronization method according to claim 4, wherein: Performing Fourier transform on the multiple current resampled values ​​to obtain multiple current Fourier values ​​arranged in time includes: Obtaining each current Fourier value set in the at least one current Fourier value set, wherein obtaining each current Fourier value set comprises: Performing Fourier transform on the reference current resampled value and J-1 current resampled values ​​arranged before it in time as transformation objects of the reference current Fourier value in the current Fourier value set, so as to obtain the first current Fourier value in the current Fourier value set as the reference current Fourier value; and Sequentially performing Fourier transform G-1 times on J current resampled values ​​obtained by shifting the transformation object of the previous current Fourier value backward in time by K current resampled values ​​as the transformation object of the next current Fourier value, so as to sequentially obtain second to Gth current Fourier values ​​in the current Fourier value set; Among them, the And the Indicates rounding down M / K.

6. The timing method according to claim 5, further comprising marking a time instant of each of the plurality of current Fourier values, comprising: For each set of current Fourier values: Marking the time of the reference current Fourier value in the current Fourier value set as the sampling time of the current sampling value whose corresponding count value is the first value; The time instant of the Qth current Fourier value in the current Fourier value set is marked as the time instant of the reference current Fourier value plus (Q-1)*Δt, where Q is an integer greater than 1 and not greater than G, and Δt=(duration of 1 cycle) / (J / K).

7. The time synchronization method according to claim 5, wherein: Obtaining each current Fourier value set also includes: In response to receiving a current sampling value whose count value corresponding to the reference current Fourier value of the subsequent current Fourier value set of the current Fourier value set is a first value, stopping acquiring the current Fourier values ​​that have not yet been acquired in the current Fourier value set, and instead acquiring the reference current Fourier value of the subsequent current Fourier value set.

8. The time synchronization method according to claim 7, further comprising: The plurality of current Fourier values ​​are sent to an external device for use in calculating a differential current of the power line.

9. The time synchronization method according to claim 1, wherein: The satellite positioning module includes a positioning module based on the global positioning system or a positioning module based on the Beidou positioning system.

10. The time synchronization method according to claim 1, wherein: The multiple current sampling values ​​are obtained by interpolating original current sampling values ​​generated by sampling current analog values ​​of the power line by the merging unit, and the current analog values ​​are measured by a current transformer of the power line.

11. A differential protection device for a power line, comprising: a communication module, configured to obtain, from a merging unit of the power line, a plurality of current sampling values ​​of the power line and a count value of each current sampling value, wherein a sampling moment of a current sampling value having a first count value among the plurality of current sampling values ​​is a moment when a second pulse signal of a satellite positioning module of the merging unit is generated; a sampling module, configured to resample the plurality of current sampling values ​​according to a sampling frequency J point / cycle of the differential protection device to obtain a plurality of current resampled values, the plurality of current resampled values ​​including a reference current resampled value corresponding to a current sampling value having a first count value among the plurality of current sampling values; a timing module, configured to perform Fourier transform on the multiple current resampled values ​​to obtain a plurality of current Fourier values ​​arranged in time, wherein the multiple current Fourier values ​​include a reference current Fourier value corresponding to a sampling moment of a current sampling value having a count value of a first value among the multiple current sampling values, and the reference current Fourier value is determined based on the reference current resampled value and J-1 current resampled values ​​arranged before the reference current resampled value in time, where J is an integer greater than 1.

12. The differential protection device according to claim 11, wherein: The multiple current sampling values ​​include at least one current sampling value set, each current sampling value set in the at least one current sampling value set includes N current sampling values ​​located between the generation moments of two second pulse signals, the count values ​​of the N current sampling values ​​are marked as 0 to N-1 in chronological order, and the first value is 0, where N is an integer greater than 1.

13. The differential protection device according to claim 12, wherein: The multiple current resampled values ​​include at least one current resampled value set corresponding one-to-one to the at least one current resampled value set, each current resampled value set in the at least one current resampled value set includes M current resampled values, and the first current resampled value in each current resampled value set serves as the reference current resampled value, where M is an integer greater than 1.

14. The differential protection device according to claim 13, wherein: The multiple current Fourier values ​​include at least one current Fourier value set, each current Fourier value set in the at least one current Fourier value set includes G current Fourier values, and the first current Fourier value in each current Fourier value set serves as the reference current Fourier value, where G is an integer greater than 1.

15. The differential protection device according to claim 14, wherein: The timing module performs Fourier transform on the plurality of current resampled values ​​by acquiring each current Fourier value set in the at least one current Fourier value set, and acquires each current Fourier value set by performing the following operations: Performing Fourier transform on the reference current resampled value and J-1 current resampled values ​​arranged before it in time as transformation objects of the reference current Fourier value in the current Fourier value set, so as to obtain a first current Fourier value in the current Fourier value set as the reference current Fourier value; as well as Sequentially performing Fourier transform G-1 times on J current resampled values ​​obtained by shifting the transformation object of the previous current Fourier value backward in time by K current resampled values ​​as the transformation object of the next current Fourier value, so as to sequentially obtain the second to Gth current Fourier values ​​in the current Fourier value set, in, And the Indicates rounding down M / K.

16. The differential protection device according to claim 15, wherein: The timing module is further configured to mark the time of each of the multiple current Fourier values ​​by performing the following operations: Marking the time of the reference current Fourier value in the current Fourier value set as the sampling time of the current sampling value whose corresponding count value is the first value; The time instant of the Qth current Fourier value in the current Fourier value set is marked as the time instant of the reference current Fourier value plus (Q-1)*Δt, where Q is an integer greater than 1 and not greater than G, and Δt=(duration of 1 cycle) / (J / K).

17. The differential protection device according to claim 15 or 16, wherein: The timing module stops acquiring the current Fourier values ​​that have not yet been acquired in the current Fourier value set in response to the communication module receiving a current sampling value with a count value corresponding to the reference current Fourier value of the subsequent current Fourier value set of the current Fourier value set being a first value, and instead acquires the reference current Fourier value of the subsequent current Fourier value set. 18 . The differential protection device according to claim 17 , wherein the communication module is further configured to send the plurality of current Fourier values ​​to an external device for use in calculating the differential current of the power line.

19. A differential protection system for a power line, comprising: a current transformer, used to measure an analog value of a current in the power line; a merging unit, configured to sample the current analog value to generate a plurality of original current sampling values, interpolate the plurality of original current sampling values ​​to obtain a plurality of current sampling values, and mark each current sampling value with a count value, wherein a sampling moment of a current sampling value having a first count value among the plurality of current sampling values ​​is a generation moment of a second pulse signal of a satellite positioning module of the merging unit; A differential protection device according to any one of claims 11 to 18.

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