Low voltage overcurrent protection delay calculation method

Abstract

The application discloses a low-voltage overcurrent protection delay calculation method and relates to the technical field of power systems.The method selects current data collected by a target device in the latest one month as sample data, screens four appropriate sampling points as target points from the sample data, calculates the running current value and the no-load current value of the target device by using the screened target points and the data between the target points, and dynamically adjusts the protection action delay length of the target device according to the running current value, the no-load current value and the current collection value of the target device.The method provided by the application is used for the overcurrent protection mechanism of low-voltage electrical devices in power systems.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power systems, in particular to a low-voltage overcurrent protection delay calculation method. BACKGROUND

[0002] Low-voltage electrical equipment is provided in the low-voltage power supply circuit (low voltage refers to a voltage below 400V) of a power system, and overcurrent protection is a measure to protect the safety of low-voltage electrical equipment.

[0003] In order to avoid the disturbance of instantaneous current triggering the overcurrent protection mechanism (such as the instantaneous current when the low-voltage electrical equipment starts will be significantly higher than the rated current), the overcurrent protection mechanism will delay for a certain period of time when detecting overcurrent condition, and if the overcurrent condition still exists after the delay, the overcurrent protection action will be taken.

[0004] The current values of low-voltage electrical equipment under load working condition and no-load working condition are different, but in the existing overcurrent protection mechanism of low-voltage electrical equipment, the overcurrent protection delay time is a fixed value (such as 1ms), which cannot dynamically adjust the protection delay time according to the equipment operating condition, and is prone to misoperation due to fault judgment error. SUMMARY

[0005] In view of the defects in the prior art, the technical problem to be solved by the present application is to provide a low-voltage overcurrent protection delay calculation method which can dynamically adjust the overcurrent protection delay time according to the real-time operating condition of the equipment, thereby avoiding the misoperation of the overcurrent protection mechanism.

[0006] In order to solve the above technical problems, the low-voltage overcurrent protection delay calculation method provided by the present application is characterized in that the specific steps are as follows:

[0007] 1) Set the low-voltage electrical equipment in the power system to be calculated as the target device, select the current data collected in the last month as the sample data, and arrange the sampling points of each current data in the sample data in order from near to far according to the collection time sequence;

[0008] 2) Select 4 sampling points as target points from the sample data, and the selection rule of the target points is: for any 4 sampling points N, M, K, J in the sample data, if the 4 sampling points can meet conditions 1, 2 and 3 at the same time, the 4 sampling points are defined as target points;

[0009] Condition 1:

[0010] 4 sampling points are sequentially N, M, K and J from near to far according to the collection time sequence, wherein the sampling point N is the n-th sampling point in the sample data, the sampling point K is the k-th sampling point in the sample data, the sampling point M is the m-th sampling point in the sample data, and the sampling point J is the j-th sampling point in the sample data;

[0011] wherein the time interval between the sampling points N and M is at least 12 hours, the time interval between the sampling points J and K is at least 12 hours, and the number of sampling points between the sampling points M and K is more than 10 and less than 5000;

[0012] Condition 2:

[0013] and I(n)≥In / 20, and I(m-1)≥In / 20;

[0014] wherein, which means that the current collection value of each sampling point in the interval [m, n) is less than In / 20, the interval [m, n) includes the sampling point M and the sampling points between the sampling points M and N, In is the rated current value of the target device, I(n) is the current collection value of the sampling point N, and I(m-1) is the current collection value of the (m-1)-th sampling point in the sample data;

[0015] Condition 3:

[0016] and (I(k)≤In / 20||I(k)≥1.2×In), and (I(j-1)≤In / 20||I(j-1)≥1.2×In);

[0017] wherein, which means that the current collection value of each sampling point in the interval [j, k) is greater than In / 20 and less than 1.2×In, the interval [j, k) includes the sampling point J and the sampling points between the sampling points J and K, In is the rated current value of the target device, I(k) is the current collection value of the sampling point K, and I(j-1) is the current collection value of the (j-1)-th sampling point in the sample data;

[0018] 3) calculating the running current value and the no-load current value of the target device, and the calculation formula is:

[0019]

[0020]

[0021] wherein, Is is the running current value of the target device, Ir is the no-load current value of the target device, and I(i) is the current collection value of the i-th sampling point in the sample data;

[0022] 4) Set the protection action delay time length Tt of the target device;

[0023] 5) Define the current data sampling time of the target device as t, if I(t)>Is, go to step 6), otherwise go to step 7); wherein I(t) is the current collection value of the target device at t;

[0024] 6) Calculate the protection delay coefficient Cos at t, and update the value of the protection action delay time length Tt of the target device as Tt / Cos, and the calculation formula of the protection delay coefficient Cos is:

[0025] Cos=((I(t)-Ir) / (Is-Ir)) 0.02

[0026] 7) Wait for the target device to reach the next current data sampling time, and return to step 5).

[0027] The low-voltage overcurrent protection delay calculation method provided by the application calculates the running current value and the no-load current value of the low-voltage electrical device according to the historical collection data, and then calculates the overcurrent protection delay time length according to the real-time current value, the running current value and the no-load current value of the low-voltage electrical device, so that the overcurrent protection delay time length can be dynamically adjusted according to the real-time working condition of the device, thereby avoiding the misoperation of the overcurrent protection mechanism. DETAILED DESCRIPTION

[0028] The technical solutions of the application are further described in detail below in combination with specific embodiments, but the embodiments are not used to limit the application, and any similar structure and similar changes thereof shall be included in the protection scope of the application, the dots in the application represent the relationship of sum, and the English letters in the application are case-sensitive.

[0029] The low-voltage overcurrent protection delay calculation method provided by the embodiment of the application has the following characteristics:

[0030] 1) Set the low-voltage electrical device to be calculated for low-voltage overcurrent protection delay in the power system as a target device, select the current data collected in the last month of the target device as sample data, and arrange the sampling points (collect current data once at each sampling point) of each current data in the sample data in order from near to far according to the collection time sequence;

[0031] 2) Select four sampling points as target points from the sample data, and the selection rule of the target points is that: for any four sampling points N, M, K and J in the sample data, if the four sampling points can simultaneously satisfy condition 1, condition 2 and condition 3, the four sampling points are defined as target points;

[0032] Condition 1:

[0033] 4 sampling points are sequentially N, M, K, J from near to far according to the collection time sequence, wherein the sampling point N is the n th sampling point in the sample data, the sampling point K is the k th sampling point in the sample data, the sampling point M is the m th sampling point in the sample data, and the sampling point J is the j th sampling point in the sample data;

[0034] Wherein, the time interval between sampling points N and M is at least 12 hours, the time interval between sampling points J and K is at least 12 hours, and the number of sampling points between sampling points M and K is more than 10 and less than 5000;

[0035] Condition 2:

[0036] And I(n)≥In / 20, and I(m-1)≥In / 20;

[0037] In the formula, It means that the current collection value of each sampling point in the interval [m, n) is less than In / 20, the interval [m, n) includes the sampling point M and the sampling points between the sampling points M and N, In is the rated current value of the target device, I(n) is the current collection value of the sampling point N, and I(m-1) is the current collection value of the m-1 th sampling point in the sample data;

[0038] Condition 3:

[0039] And (I(k)≤In / 20||I(k)≥1.2×In), and (I(j-1)≤In / 20||I(j-1)≥1.2×In);

[0040] In the formula, It means that the current collection value of each sampling point in the interval [j, k) is greater than In / 20 and less than 1.2×In, the interval [j, k) includes the sampling point J and the sampling points between the sampling points J and K, In is the rated current value of the target device, I(k) is the current collection value of the sampling point K, and I(j-1) is the current collection value of the j-1 th sampling point in the sample data;

[0041] 3) Calculate the running current value and the no-load current value of the target device, and the calculation formula is:

[0042]

[0043]

[0044] In the formula, Is is the running current value of the target device, Ir is the no-load current value of the target device, and I(i) is the current collection value of the i th sampling point in the sample data;

[0045] 4) Set the target device protection action delay time Tt, the initial value of Tt is usually determined according to the load type of the electrical device, and the typical value is 1000ms;

[0046] 5) Define the current current data sampling time of the target device as t time, if I(t)>Is, go to step 6), otherwise go to step 7); wherein I(t) is the current collection value of the target device at t time;

[0047] 6) Calculate the protection delay coefficient Cos at t time, and update the value of the protection action delay time Tt of the target device to Tt / Cos, and the calculation formula of the protection delay coefficient Cos is:

[0048] Cos=((I(t)-Ir) / (Is-Ir)) 0.02

[0049] 7) Wait for the target device to reach the next current data sampling time, and return to step 5).

[0050] The embodiment of the application can dynamically adjust the over-current protection delay time according to the real-time working condition of the device, so as to avoid the misoperation of the over-current protection mechanism, automatically avoid the action interval during the start of the device, and not affect the fault judgment under the short circuit condition.

Claims

1. A method for calculating a low-voltage overcurrent protection delay, characterized in that The specific steps are as follows: 1) Set the low-voltage electrical equipment to be calculated in the power system as the target equipment, select the current data collected in the last month as the sample data, and arrange the sampling points of each current data in the sample data in order from near to far according to the collection time sequence; 2) Select four sampling points as target points from the sample data, and the selection rule of the target points is: for any four sampling points N, M, K, J in the sample data, if the four sampling points can meet conditions 1, 2 and 3 at the same time, the four sampling points are defined as target points; Condition 1: The four sampling points are N, M, K, J in order from near to far according to the collection time sequence, wherein the sampling point N is the nth sampling point in the sample data, the sampling point K is the kth sampling point in the sample data, the sampling point M is the mth sampling point in the sample data, and the sampling point J is the jth sampling point in the sample data; Wherein, the time interval between the sampling points N and M is at least 12 hours, the time interval between the sampling points J and K is at least 12 hours, and the number of sampling points between the sampling points M and K is more than 10 and less than 5000; Condition 2: and I(n) > In / 20, and I(m-1) > In / 20; In the formula, It is referred to that the current collection value of each sampling point in the interval range of [m, n) is less than In / 20, the interval range of [m, n) contains the sampling point M and the sampling points between the sampling points M and N, In is the rated current value of the target device, I(n) is the current collection value of the sampling point N, and I(m-1) is the current collection value of the m-1th sampling point in the sample data. Condition 3: and (I(k) < In / 20 || I(k) > 1.2 x In), and (I(j-1) < In / 20 || I(j-1) > 1.2 x In); In the formula, It is referred to that the current collection value of each sampling point in the interval range of [j, k) is greater than In / 20 and less than 1.2*In, the interval range of [j, k) contains the sampling point J and the sampling points between the sampling points J and K, In is the rated current value of the target device, I(k) is the current collection value of the sampling point K, and I(j-1) is the current collection value of the j-1th sampling point in the sample data. 3) Calculate the running current value and no-load current value of the target equipment, and the calculation formula is: Wherein, Is is the running current value of the target equipment, Ir is the no-load current value of the target equipment, and I(i) is the current collection value of the ith sampling point in the sample data; 4) Set the protection action delay time Tt of the target equipment; 5) Define the current current data sampling time of the target equipment as t time, if I(t)>Is, go to step 6), otherwise go to step 7); wherein I(t) is the current collection value of the target equipment at t time; 6) Calculate the protection delay coefficient Cos at t time, and update the value of the protection action delay time Tt of the target equipment to Tt / Cos, and the calculation formula of the protection delay coefficient Cos is: Cos = ((I(t) - Ir) / (Is - Ir)) 0.02 7) Wait for the target equipment to reach the next current data sampling time, and return to step 5).

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