Power CT Disconnection Identification Method

Abstract

A method for identifying CT disconnection in electric power systems relates to the technical field of electric power systems. This method first screens out target points that meet the set conditions from the data sampling points of the electric power data acquisition device in the most recent day, then calculates the CT disconnection threshold based on the acquisition data of these target points, determines whether the electric power line is overcurrent at the current moment according to the calculated CT disconnection threshold, calculates the CT disconnection alarm value based on the real-time three-phase current acquisition values of the electric power data acquisition device, and timely sends out the CT disconnection alarm information according to the calculated CT disconnection alarm value. The identification method provided by the present invention is used for electric power data acquisition.

Description

Technical Field

[0001] The present invention relates to the technology of power systems, and particularly to a technology for identifying power CT disconnection. Background Art

[0002] Power data acquisition devices in power systems all use current transformers (abbreviated as CTs) to acquire current values. Once a current transformer (CT) is disconnected, high voltages will be generated, endangering the safety of equipment and personnel.

[0003] Existing methods for power data acquisition devices to identify CT disconnection are all to manually set a CT alarm current threshold in the device, and send a CT disconnection alarm message when the acquired current exceeds the set CT alarm threshold. This manual setting method is not only time-consuming and laborious, but also the current values of different power lines are different. Therefore, the CT alarm thresholds that need to be set for power data acquisition devices on different power lines are also different, and setting errors are likely to occur, which will lead to incorrect judgment of CT disconnection. Summary of the Invention

[0004] Aiming at the defects existing in the above-mentioned prior art, the technical problem to be solved by the present invention is to provide a power CT disconnection identification method that can adaptively set the CT disconnection alarm value according to the current value of the power line, so as to avoid incorrect judgment of CT disconnection.

[0005] To solve the above technical problem, a power CT disconnection identification method provided by the present invention is characterized in that the specific steps are as follows:

[0006] 1) Assume that the number of daily data sampling times of the power data acquisition device is n times, then there are n data sampling points for the power data acquisition device every day;

[0007] Select n data sampling points of the power data acquisition device on the most recent day to form a sampling point sequence S, and screen out all target points from the sampling point sequence S to form a target point sequence M;

[0008] The rule for screening target points is: for any sampling point k in the sampling point sequence S, if the sampling point k can simultaneously meet Condition 1, Condition 2, and Condition 3, then the sampling point k is defined as a target point;

[0009] Condition 1:

[0010] 1.1×Uaver>U(ka)>0.1×Uaver, and 1.1×Uaver>U(kb)>0.1×Uaver, and 1.1×Uaver>U(kc)>0.1×Uaver;

[0011] Where Uaver is the average value of the three-phase voltage collection values of n sampling points in the sampling point sequence S, U(ka) is the A-phase voltage collection value at sampling point k, U(kb) is the B-phase voltage collection value at sampling point k, and U(kc) is the C-phase voltage collection value at sampling point k;

[0012] Condition 2:

[0013] 1.1×Iaver>I(ka)>0.1×Iaver, and 1.1×Iaver>I(kb)>0.1×Iaver, and 1.1×Iaver>I(kc)>0.1×Iaver;

[0014] Where Iaver is the average value of the three-phase current acquisition values of n sampling points in the sampling point sequence S, I(ka) is the acquisition value of phase A current at sampling point k, I(kb) is the acquisition value of phase B current at sampling point k, and I(kc) is the acquisition value of phase C current at sampling point k;

[0015] Condition 3: At sampling point k, no overcurrent signal occurs in the power line collected by the power data acquisition device;

[0016] 2) Sort the three-phase current collected values of each target point in the target point sequence M from small to large, and then define the phase current collected values arranged in the first 15% position as the CT disconnection threshold value Idz;

[0017] 3) The current data sampling time of the power data acquisition device is defined as time t, and a CT disconnection alarm value flag is set with an initial value of 0;

[0018] 4) Obtaining the three-phase current collection values of the power data collection device at time t;

[0019] If I(ta)≥Idz, or I(tb)≥Idz, or I(tc)≥Idz, go to step 6);

[0020] If I(t)max<I0, set flag=1, otherwise set flag=0;

[0021] in:

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029] Wherein, I(ta) is the value of the phase A current collected by the power data acquisition device at time t, I(tb) is the value of the phase B current collected by the power data acquisition device at time t, and I(tc) is the value of the phase C current collected by the power data acquisition device at time t;

[0030] Wherein, I(t)max is the maximum value among the three-phase current values collected by the power data acquisition device at time t, Ia(t-i) is the value of the phase A current collected by the power data acquisition device at time t-i, Ib(t-i) is the value of the phase B current collected by the power data acquisition device at time t-i, Ic(t-i) is the value of the phase C current collected by the power data acquisition device at time t-i, the time t-i refers to the previous i data sampling times of time t, D is the number of data samplings of the power data acquisition device within the time of 1000 / fHZ, fHZ is the grid frequency of the power line collected by the power data acquisition device, δ is the electrical angle, and δ = 360 / D;

[0031] 5) If flag = 1, then send out a CT disconnection alarm message;

[0032] 6) After waiting for the power data acquisition device to reach the next data sampling time, return to step 3).

[0033] The power CT disconnection recognition method provided by the present invention calculates the CT disconnection threshold according to the historical acquisition data of the most recent day, calculates the CT disconnection alarm value according to the real-time three-phase current acquisition values, and determines whether the CT is disconnected through the calculated CT disconnection threshold and CT disconnection alarm value, so as to automatically adapt to the normal current value of the power line according to the acquisition information without manual setting, thereby avoiding incorrect judgment of CT disconnection, and not affecting the judgment of CT disconnection under the conditions of overload, low voltage, and short circuit, and improving the protection reliability. Specific Embodiments

[0034] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments, but these embodiments do not limit the present invention. Any similar structures and their similar changes using the present invention shall fall within the protection scope of the present invention. The commas in the present invention all represent the relationship of "and", and the English letters in the present invention are case-sensitive.

[0035] A power CT disconnection recognition method provided by an embodiment of the present invention is characterized in that the specific steps are as follows:

[0036] 1) If the number of data sampling times of the power data acquisition device per day is \(n\) times, then there are \(n\) data sampling points of the power data acquisition device per day;

[0037] Select \(n\) data sampling points of the power data acquisition device on the most recent day to form a sampling point sequence \(S\), and screen out all target points from the sampling point sequence \(S\) to form a target point sequence \(M\);

[0038] The rule for screening target points is: for any sampling point \(k\) in the sampling point sequence \(S\), if the sampling point \(k\) can satisfy condition 1, condition 2, and condition 3 at the same time, then the sampling point \(k\) is defined as a target point;

[0039] Condition 1:

[0040] \(1.1\times U_{aver}>U(ka)>0.1\times U_{aver}\), and \(1.1\times U_{aver}>U(kb)>0.1\times U_{aver}\), and \(1.1\times U_{aver}>U(kc)>0.1\times U_{aver}\);

[0041] Where \(U_{aver}\) is the average value of the three-phase voltage acquisition values of the \(n\) sampling points in the sampling point sequence \(S\), \(U(ka)\) is the A-phase voltage acquisition value of the sampling point \(k\), \(U(kb)\) is the B-phase voltage acquisition value of the sampling point \(k\), and \(U(kc)\) is the C-phase voltage acquisition value of the sampling point \(k\);

[0042] Condition 2:

[0043] \(1.1\times I_{aver}>I(ka)>0.1\times I_{aver}\), and \(1.1\times I_{aver}>I(kb)>0.1\times I_{aver}\), and \(1.1\times I_{aver}>I(kc)>0.1\times I_{aver}\);

[0044] Where \(I_{aver}\) is the average value of the three-phase current acquisition values of the \(n\) sampling points in the sampling point sequence \(S\), \(I(ka)\) is the A-phase current acquisition value of the sampling point \(k\), \(I(kb)\) is the B-phase current acquisition value of the sampling point \(k\), and \(I(kc)\) is the C-phase current acquisition value of the sampling point \(k\);

[0045] Condition 3: At the moment of the sampling point \(k\), no overcurrent signal occurs in the power line collected by the power data acquisition device;

[0046] 2) Sort the three-phase current acquisition values of each target point in the target point sequence \(M\) from small to large, and then define the phase current acquisition value at the first 15% position as the CT disconnection threshold \(I_{dz}\);

[0047] 3) Define the current data sampling moment of the power data acquisition device as the \(t\) moment, and set a CT disconnection alarm value \(flag\) with an initial value of 0;

[0048] 4) Obtaining the three-phase current collection values of the power data collection device at time t;

[0049] If I(ta)≥Idz, or I(tb)≥Idz, or I(tc)≥Idz, go to step 6);

[0050] If I(t)max<I0, set flag=1, otherwise set flag=0;

[0051] in:

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059] Where I(ta) is the current value of phase A collected by the power data acquisition device at time t, I(tb) is the current value of phase B collected by the power data acquisition device at time t, and I(tc) is the current value of phase C collected by the power data acquisition device at time t;

[0060] Where, I(t)max is the maximum value of the three-phase current values collected by the power data acquisition device at time t, Ia(ti) is the current value of phase A collected by the power data acquisition device at time ti, Ib(ti) is the current value of phase B collected by the power data acquisition device at time ti, Ic(ti) is the current value of phase C collected by the power data acquisition device at time ti, time ti refers to the i data sampling moments before time t, D is the number of data sampling times of the power data acquisition device within 1000 Hz / fHZ, fHZ is the grid frequency of the power line collected by the power data acquisition device, and the typical value of fHZ is 50 Hz or 60 Hz, δ is the electrical angle, δ = 360 / D;

[0061] 5) If flag = 1, a CT disconnection alarm message is issued;

[0062] 6) Wait for the power data acquisition device to arrive at the next data sampling time, and then return to step 3).

Claims

1. A method for identifying the disconnection of a power CT, characterized in that, The specific steps are as follows: 1) Assume that the number of data sampling times of the power data acquisition device per day is n times, then there are n data sampling points of the power data acquisition device per day; Select n data sampling points of the power data acquisition device on the most recent day to form a sampling point sequence S, and screen out all target points from the sampling point sequence S to form a target point sequence M; The rule for screening target points is: for any sampling point k in the sampling point sequence S, if the sampling point k can simultaneously meet Condition 1, Condition 2, and Condition 3, then the sampling point k is defined as a target point; Condition 1: 1.1×Uaver>U(ka)>0.1×Uaver, and 1.1×Uaver>U(kb)>0.1×Uaver, and 1.1×Uaver>U(kc)>0.1×Uaver; In the formula, Uaver is the average value of the three-phase voltage acquisition values of the n sampling points in the sampling point sequence S, U(ka) is the A-phase voltage acquisition value of the sampling point k, U(kb) is the B-phase voltage acquisition value of the sampling point k, and U(kc) is the C-phase voltage acquisition value of the sampling point k; Condition 2: 1.1×Iaver>I(ka)>0.1×Iaver, and 1.1×Iaver>I(kb)>0.1×Iaver, and 1.1×Iaver>I(kc)>0.1×Iaver; In the formula, Iaver is the average value of the three-phase current acquisition values of the n sampling points in the sampling point sequence S, I(ka) is the A-phase current acquisition value of the sampling point k, I(kb) is the B-phase current acquisition value of the sampling point k, and I(kc) is the C-phase current acquisition value of the sampling point k; Condition 3: At the moment of the sampling point k, there is no overcurrent signal occurring in the power line collected by the power data acquisition device; 2) Sort the three-phase current acquisition values of each target point in the target point sequence M from small to large, and then define the phase current acquisition value in the first 15% position as the CT disconnection threshold Idz; 3) Define the current data sampling moment of the power data acquisition device as the t moment, and set a CT disconnection alarm value flag with an initial value of 0; 4) Obtain the three-phase current acquisition values of the power data acquisition device at the t moment; If I(ta)≥Idz, or I(tb)≥Idz, or I(tc)≥Idz, then go to step 6); If I(t)max<I0, then set flag = 1, otherwise set flag = 0; Where: In the formula, I(ta) is the A-phase current value collected by the power data acquisition device at the t moment, I(tb) is the B-phase current value collected by the power data acquisition device at the t moment, and I(tc) is the C-phase current value collected by the power data acquisition device at the t moment; Wherein, I(t)max is the maximum value among the three-phase current values collected by the power data acquisition device at time t, Ia(t-i) is the A-phase current value collected by the power data acquisition device at time t-i, Ib(t-i) is the B-phase current value collected by the power data acquisition device at time t-i, Ic(t-i) is the C-phase current value collected by the power data acquisition device at time t-i, the time t-i refers to the previous i data sampling moments of time t, D is the number of data sampling times of the power data acquisition device within 1000 / fHZ time, fHZ is the grid frequency of the power line collected by the power data acquisition device, δ is the electrical angle, and δ = 360 / D; 5) If flag = 1, then send out a CT disconnection alarm message; 6) After waiting for the power data acquisition device to reach the next data sampling moment, return to step 3).

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