Direct current loop insulation fault discrimination method

Abstract

The invention discloses a direct-current circuit insulation fault judgment method, which comprises the following steps of: measuring circuit load impedance in a direct-current circuit for multiple times according to a measurement period, and respectively measuring the circuit load impedance in the direct-current circuit for multiple times within 5 minutes, 30 minutes and three continuous 30 minutes according to preset first, second and third alarm thresholds of grounding insulation impedance, so as to judge the insulation fault of the direct-current circuit. Short window judgment, long window judgment and trend judgment of grounding type insulation damage faults are realized respectively; according to a preset first alarm threshold value and a preset second alarm threshold value of inter-core insulation impedance, main judgment and short window judgment of the inter-core insulation damage fault are achieved respectively in combination with the inter-core impedance measured for multiple times within 10 minutes and five continuous 2 minutes, and fluctuation judgment of the inter-core insulation damage fault is conducted in combination with the inter-core impedance measured for a single time.

Description

Technical Field

[0001] The present invention relates to the field of DC circuit insulation fault detection methods, in particular to a DC circuit insulation fault determination method. Background Art

[0002] Currently, substations of 220kV and below are unmanned, and substations of 500kV and above are less manned and are transitioning to unmanned operation. These have put forward higher requirements on the operation and maintenance of substation secondary systems.

[0003] The DC secondary circuit is the "cardiovascular system" of a substation's secondary equipment. Failures in this circuit can cause secondary system failure and even threaten the safe operation of the entire power grid. In recent years, there have been numerous incidents of insulation failure in DC system cables, leading to the shutdown of protective devices.

[0004] At present, the unbalanced bridge method is widely used at home and abroad to measure the insulation resistance of the DC circuit. By switching two or more switches to form an unbalanced bridge, the insulation resistance of the positive and negative DC bus to the ground is calculated based on the voltage value at both ends of the input resistor. Figure 1 The following is the schematic diagram of the unbalanced bridge insulation monitoring circuit, where R1 and R2 form a balanced bridge, R is the unbalanced bridge cut-in resistor, and R + and R - are the insulation resistance of DC positive and negative bus cables to ground respectively. Switch S + 、S - Periodically invest separately, when S + When the resistor R1 is put into operation, the voltage is U + 、When S - When the resistor R2 is put into operation, the voltage is U - , the positive and negative parent voltages are U m , we can get the equation shown in formula 1, and then we can get R shown in formula 2 + and R - The calculation formula can be used to determine whether the insulation resistance of the positive and negative bus cables to the ground has decreased. Formula 1 and Formula 2 are as follows:

[0005]

[0006] However, the existing unbalanced bridge method has the following problems:

[0007] 1. The simple size judgment based on insulation resistance is often interfered by the signal within the station. Alarm based on a single measurement result is inevitably accompanied by a large number of false alarms.

[0008] 2. To prevent false alarms, the insulation resistance alarm setting can only be adjusted to a conservative value. Due to the conservative setting, the alarm will not be issued until the circuit insulation is severely damaged, missing the opportunity to discover the circuit fault in advance, and there is a delay in the alarm.

[0009] 3. Insufficient research on the resistance characteristics of short circuits between core wires makes it sometimes impossible to determine faults between core wires.

[0010] 4. Insulation fault detection is inefficient. R+ and R- represent the insulation condition of the DC busbar to ground. Even with the addition of a feeder inspection function (such as a low-current injection method), it can only locate the feeder trunk line of the feeder panel, not the branches that feed out of the panel cabinet. Summary of the Invention

[0011] The present invention provides a method for distinguishing insulation faults in a DC circuit to solve the problems of the prior art unbalanced bridge method, such as false alarms, hysteresis, inability to distinguish insulation faults between core wires, and inability to locate branches fed back from a panel cabinet.

[0012] In order to achieve the above object, the technical solution adopted by the present invention is:

[0013] A method for determining insulation faults in a DC circuit, wherein the DC circuit is composed of positive and negative DC busbars and a load, is provided. The process is as follows:

[0014] Measure the loop load impedance in the DC circuit multiple times with a measurement cycle of 30 seconds;

[0015] Set the first alarm threshold R of the ground insulation resistance set,1 , based on the impedance first alarm threshold R set,1 Make the following judgment:

[0016] If the average value of all loop load impedances measured multiple times within 5 minutes is less than or equal to the first alarm threshold of ground insulation impedance R set,1 , and the maximum value of all loop load impedances measured multiple times within 5 minutes is less than or equal to 2 times the first alarm threshold R of the ground insulation impedance set,1 , it is determined that there is a grounding type insulation damage fault and an alarm is immediately issued;

[0017] Otherwise, it is determined that there is no grounding type insulation damage fault and no alarm is given.

[0018] Furthermore, the second alarm threshold value R of the ground insulation impedance is set. set,2 , R set,1 ﹤R set,2 , when the first alarm threshold R based on the ground insulation impedance set,1 When it is determined that there is no grounding insulation damage fault, the second alarm threshold R set,2 Make the following judgment:

[0019] If the average value of the integrated results of all loop load impedances measured multiple times within 30 minutes is less than or equal to the second alarm threshold of ground insulation impedance R set,2, it is determined that there is a grounding type insulation damage fault. If the grounding type insulation damage fault judgment conditions are always met for a period of time, an alarm will be issued after the period of time;

[0020] Otherwise, it is determined that there is no grounding type insulation damage fault and no alarm is given.

[0021] Furthermore, the third alarm threshold of ground insulation impedance R is set. set,3 , R set,2 ﹤R set,3 , when the second alarm threshold R based on the ground insulation impedance set,2 When it is determined that there is no grounding insulation damage fault, the third alarm threshold R of the grounding insulation impedance is used. set,3 Make the following judgment:

[0022] If within three consecutive 30-minute periods, the average of the integrated results of all loop load impedances measured multiple times in the first 30 minutes is less than or equal to the third alarm threshold of ground insulation impedance R set,3 If the average value of the integral results of all loop load impedances measured multiple times within the second 30 minutes is less than or equal to the average value of the integral results of all loop load impedances measured within the first 30 minutes, and the average value of the integral results of all loop load impedances measured multiple times within the third 30 minutes is less than or equal to the average value of the integral results of all loop load impedances measured multiple times within the second 30 minutes, then it is determined that a grounding type insulation damage fault exists. If the grounding type insulation damage fault judgment conditions are always met for a period of time, an alarm will be issued after that period of time.

[0023] Otherwise, it is determined that there is no grounding type insulation damage fault and no alarm is given.

[0024] Furthermore, the first alarm threshold value R of the insulation resistance between cores is set. setpp,1 , based on the first alarm threshold R of the insulation resistance between cores setpp,1 Make the following judgment:

[0025] If the average value of the integrated results of all inter-core impedances measured multiple times within 10 minutes is less than or equal to the first alarm threshold R setpp,1 , it is determined that there is an inter-core insulation damage fault and an alarm is immediately issued;

[0026] Otherwise, it is determined that there is no inter-core insulation damage fault and no alarm is given.

[0027] Furthermore, the first alarm threshold value R of the insulation resistance between cores is set. setpp,1 , based on the first alarm threshold R of the insulation resistance between cores setpp,1 Make the following judgment:

[0028] If, within five consecutive 2-minute periods, the average value of the integrated results of all inter-core impedance measurements taken multiple times within a certain 2-minute period is the smallest, and the average value of the integrated results of all inter-core impedance measurements taken multiple times within the smallest 2-minute period is less than or equal to 0.8 times the second alarm threshold R of the inter-core insulation resistance, the alarm will be raised. setpp,2 , it is determined that there is an inter-core insulation damage fault and an alarm is immediately issued;

[0029] Otherwise, it is determined that there is no inter-core insulation damage fault and no alarm is given.

[0030] Furthermore, the second alarm threshold value R of the insulation resistance between cores is set. setpp,2 , based on the second alarm threshold R of the insulation resistance between cores setpp,2 Make the following judgment:

[0031] When the variance of the inter-core impedance measured in a single time is greater than or equal to R setpp,2 , it is judged that there is a core-to-core insulation damage fault. If the core-to-core insulation damage fault judgment condition is always met for a period of time, an alarm will be issued after the period of time;

[0032] Otherwise, it is determined that there is no inter-core insulation damage fault and no alarm is given.

[0033] The present invention can realize the precise positioning of insulation faults, can meet the needs of on-site insulation fault identification, has the advantages of accurate and timely alarm, can accurately judge the insulation faults between core wires, and can accurately locate the branch insulation faults re-fed in the panel cabinet. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a measurement principle diagram of the existing unbalanced bridge method.

[0035] Figure 2 This is a schematic diagram of the principle of judging a grounding type insulation damage fault in an embodiment of the present invention.

[0036] Figure 3 This is a schematic diagram of the principle of judging inter-core insulation damage faults in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the accompanying drawings and examples.

[0038] This embodiment discloses a method for determining insulation faults in a DC circuit. The DC circuit is composed of positive and negative DC busbars and a load. The method process of this embodiment is as follows:

[0039] Step 1: Measure the loop load impedance in the DC circuit multiple times with a measurement cycle of 30 seconds.

[0040] In this embodiment, by detecting the DC circuit core current I land bus voltage U, from which the loop load impedance R can be calculated l , the loop load impedance R l The changing trajectory of can represent the insulation condition of the loop to the ground and the insulation condition between the cores.

[0041] In this embodiment, the bus voltage U can be obtained by directly detecting the voltage between the positive and negative DC bus bars.

[0042] In this embodiment, the DC circuit core current I l The current signal is converted into a voltage signal by inserting a sampling resistor in series in the detection circuit. The voltage signal is then input into the first-level isolation amplifier. The output signal of the first-level isolation amplifier is then converted into a signal within a reasonable range by the second-level amplifier and then enters the AD chip. The DC circuit core current I is collected by the AD chip. l The use of a first-stage isolated op amp effectively isolates the input current signal from the final output signal. The input and output power supplies of the first-stage isolated op amp are also isolated, using separate DC-DC modules for power supply. This prevents any impact on the existing channels on the AD chip. Furthermore, a voltage stabilization circuit is designed at the input front end of the first-stage isolated op amp to prevent front-end circuit anomalies (such as a disconnected sampling resistor, causing strong current to enter the op amp or AD chip) from damaging the board or causing false alarms.

[0043] Therefore, the DC circuit core current I is measured multiple times according to the set 30s measurement cycle. l , bus voltage U, and then the loop load impedance R can be calculated each time l .

[0044] Step 2: Determine whether the grounding type insulation damage fault or the core-to-core type insulation damage fault is caused.

[0045] Grounding type insulation damage fault refers to the insulation damage of the cable core wire that is connected to the ground or the insulation drop fault on the cable shielding layer and armoring layer that is connected to the ground. When judging the grounding type insulation damage fault, the first alarm threshold of the grounding insulation impedance R is pre-set. set,1 , Ground insulation resistance second alarm threshold R set,2 , Ground insulation resistance third alarm threshold R set,3 , and there is R set,1 ﹤R set,2 ﹤R set,3 , based on the pre-set ground insulation impedance alarm threshold, the grounding type insulation damage fault is judged, including short window judgment, long window judgment, and trend judgment, such as Figure 2 As shown, the process is as follows:

[0046] (A1) Based on the impedance first alarm threshold R set,1 , perform the following short window judgment:

[0047] If the average value of all loop load impedances measured multiple times within 5 minutes is less than or equal to the first alarm threshold of ground insulation impedance R set,1 , and the maximum value of all loop load impedances measured multiple times (a total of 10 times) within 5 minutes is less than or equal to 2 times the first alarm threshold R of the ground insulation resistance set,1 , it is determined that there is a grounding type insulation damage fault, and an alarm is immediately issued. The short window judgment of the grounding type insulation damage fault is based on the following formula:

[0048]

[0049] Among them, R l,t is the loop load impedance of any single measurement at time t.

[0050] Otherwise, it is determined that there is no grounding type insulation damage fault and no alarm is given.

[0051] (A2) When the first alarm threshold R set,1 When it is determined that there is no grounding insulation damage fault, the second alarm threshold R set,2 Perform the following long window judgment:

[0052] If the average value of the integral results of all loop load impedances measured multiple times (60 times in total) within 30 minutes is less than or equal to the second alarm threshold of ground insulation impedance R set,2 , it is determined that there is a grounding type insulation damage fault. If the grounding type insulation damage fault judgment condition is always met within a period of time, an alarm will be triggered after the period of time. In this embodiment, the period of time is set to 10 minutes. The long window judgment basis for the grounding type insulation damage fault is shown in the following formula:

[0053]

[0054] Otherwise, it is determined that there is no grounding type insulation damage fault and no alarm is given.

[0055] (A3) When the second alarm threshold R set,2 When it is determined that there is no grounding insulation damage fault, the third alarm threshold R of the grounding insulation impedance is set,3 Make the following trend judgments:

[0056] If within three consecutive 30-minute periods, the average of the integral results of all loop load impedances measured multiple times (a total of 60 times) in the first 30 minutes is less than or equal to the third alarm threshold of ground insulation impedance R set,3If the average of the integral results of all loop load impedances measured multiple times within the second 30 minutes is less than or equal to the average of the integral results of all loop load impedances measured within the first 30 minutes, and the average of the integral results of all loop load impedances measured multiple times within the third 30 minutes is less than or equal to the average of the integral results of all loop load impedances measured multiple times within the second 30 minutes, then it is determined that a grounding type insulation damage fault exists. If the grounding type insulation damage fault judgment condition is consistently met for a period of time, an alarm is triggered after the period of time. In this embodiment, the period of time is set to 10 minutes. The trend judgment of the grounding type insulation damage fault is based on the following formula:

[0057]

[0058] Otherwise, it is determined that there is no grounding type insulation damage fault and no alarm is given.

[0059] Inter-core insulation damage fault refers to the fault phenomenon in which the insulation performance between the insulation layers between two cores is reduced. When judging the inter-core insulation damage fault, the first alarm threshold value R of the inter-core insulation impedance is pre-set. setpp,1 , the second alarm threshold of the insulation resistance between cores R setpp,2 , based on the pre-set inter-core insulation impedance alarm threshold, the inter-core insulation damage fault is judged, including main judgment, short window extreme value judgment, and fluctuation judgment, such as Figure 3 As shown, the process is as follows:

[0060] (B1) Based on the first alarm threshold R of the insulation resistance between cores setpp,1 Make the following main judgment:

[0061] If the average value of all inter-core impedance integration results of multiple measurements (20 times in total) within 10 minutes is less than or equal to the first alarm threshold R setpp,1 , it is determined that there is an inter-core insulation damage fault and an alarm is immediately issued. The main judgment basis for the inter-core insulation damage fault is shown in the following formula:

[0062]

[0063] Otherwise, it is determined that there is no inter-core insulation damage fault and no alarm is given.

[0064] Among them, R pp,t is the inter-core impedance of a single measurement.

[0065] (B2) Based on the first alarm threshold R of the insulation resistance between cores setpp,1 Perform the following short window extreme value judgment:

[0066] If the impedance R between all cores is measured multiple times (4 times in total) within five consecutive 2-minute periods, pp,tThe mean value of the integration result is the smallest, and the minimum inter-core impedance R pp,t The mean of the integral results is less than or equal to 0.8 times the second alarm threshold R of the inter-core insulation resistance. setpp,2 , it is determined that there is an inter-core insulation damage fault and an alarm is immediately triggered. The short window extreme value judgment of the inter-core insulation damage fault is based on the following formula:

[0067]

[0068] Otherwise, it is determined that there is no inter-core insulation damage fault and no alarm is given.

[0069] (B3) Based on the second alarm threshold R of the core insulation resistance setpp,2 The following volatility judgment is made:

[0070] When the single measurement of the core impedance R pp,t The variance is greater than or equal to R setpp,2 , indicating that the inter-core impedance of a single measurement fluctuates violently. This may be due to an intermittent discharge channel in the inter-core insulation. In this case, an inter-core insulation damage fault is determined to exist. If the inter-core insulation damage fault judgment condition is consistently met for a period of time, an alarm is triggered after the period. In this embodiment, the period is set to 10 minutes. The volatility of the inter-core insulation damage fault is based on the following formula:

[0071]

[0072] Among them, R pp,t Recorded as a time series, Var() represents R pp,t The variance of .

[0073] Otherwise, it is determined that there is no inter-core insulation damage fault and no alarm is given.

[0074] The preferred embodiments of the present invention are described in detail above with reference to the accompanying drawings. The embodiments described in the present invention are merely descriptions of the preferred embodiments of the present invention and do not limit the concept and scope of the present invention. The various specific technical features described in the above specific embodiments can be combined in any suitable manner unless there is any contradiction. Such combinations should also be regarded as the contents disclosed in this disclosure as long as they do not violate the concept of the present invention. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0075] The present invention is not limited to the specific details of the above-mentioned embodiments. Within the scope of the technical concept of the present invention and without departing from the design concept of the present invention, various modifications and improvements made to the technical solution of the present invention by those skilled in the art should fall within the scope of protection of the present invention. The technical contents for which protection is sought in the present invention have been fully recorded in the claims.

Claims

1. A method for determining insulation faults in a DC circuit, wherein the DC circuit is composed of positive and negative DC busbars and a load, characterized in that: The process is as follows: Measure the loop load impedance in the DC circuit multiple times with a measurement cycle of 30 seconds; Set the first alarm threshold R of the ground insulation resistance set,1 , based on the impedance first alarm threshold R set,1 Make the following judgment: If the average value of all loop load impedances measured multiple times within 5 minutes is less than or equal to the first alarm threshold of ground insulation impedance R set,1 , and the maximum value of all loop load impedances measured multiple times within 5 minutes is less than or equal to 2 times the first alarm threshold R of the ground insulation impedance set,1 , it is determined that there is a grounding type insulation damage fault and an alarm is immediately issued; Otherwise, it is determined that there is no grounding type insulation damage fault and no alarm is given.

2. A DC circuit insulation fault determination method according to claim 1, characterized in that: Set the second alarm threshold R of the ground insulation resistance set,2 , R set,1 ﹤R set,2 , when the first alarm threshold R based on the ground insulation impedance set,1 When it is determined that there is no grounding insulation damage fault, the second alarm threshold R set,2 Make the following judgment: If the average value of the integrated results of all loop load impedances measured multiple times within 30 minutes is less than or equal to the second alarm threshold of ground insulation impedance R set,2 , it is determined that there is a grounding type insulation damage fault. If the grounding type insulation damage fault judgment conditions are always met for a period of time, an alarm will be issued after the period of time; Otherwise, it is determined that there is no grounding type insulation damage fault and no alarm is given.

3. A DC circuit insulation fault determination method according to claim 2, characterized in that: Set the third alarm threshold R of the ground insulation resistance set,3 , R set,2 ﹤R set,3 , when the second alarm threshold R based on the ground insulation impedance set,2 When it is determined that there is no grounding type insulation damage fault, the third alarm threshold R of the grounding insulation impedance is used. set,3 Make the following judgment: If within three consecutive 30-minute periods, the average of the integrated results of all loop load impedances measured multiple times in the first 30 minutes is less than or equal to the third alarm threshold of ground insulation impedance R set,3 If the average value of the integral results of all loop load impedances measured multiple times within the second 30 minutes is less than or equal to the average value of the integral results of all loop load impedances measured within the first 30 minutes, and the average value of the integral results of all loop load impedances measured multiple times within the third 30 minutes is less than or equal to the average value of the integral results of all loop load impedances measured multiple times within the second 30 minutes, then it is determined that a grounding type insulation damage fault exists. If the grounding type insulation damage fault judgment conditions are always met for a period of time, an alarm will be issued after that period of time. Otherwise, it is determined that there is no grounding type insulation damage fault and no alarm is given.

4. A DC circuit insulation fault determination method according to claims 1-3, characterized in that: Set the first alarm threshold R of the insulation resistance between cores setpp,1 , based on the first alarm threshold R of the insulation resistance between cores setpp,1 Make the following judgment: If the average value of the integrated results of all inter-core impedances measured multiple times within 10 minutes is less than or equal to the first alarm threshold R setpp,1 , it is determined that there is an inter-core insulation damage fault and an alarm is immediately issued; Otherwise, it is determined that there is no inter-core insulation damage fault and no alarm is given.

5. A method for determining DC circuit insulation fault according to claims 1-3, characterized in that: Set the first alarm threshold R of the insulation resistance between cores setpp,1 , based on the first alarm threshold R of the insulation resistance between cores setpp,1 Make the following judgment: If, within five consecutive 2-minute periods, the average value of the integrated results of all inter-core impedance measurements taken multiple times within a certain 2-minute period is the smallest, and the average value of the integrated results of all inter-core impedance measurements taken multiple times within the smallest 2-minute period is less than or equal to 0.8 times the second alarm threshold R of the inter-core insulation resistance, the alarm will be raised. setpp,2 , it is determined that there is an inter-core insulation damage fault and an alarm is immediately issued; Otherwise, it is determined that there is no inter-core insulation damage fault and no alarm is given.

6. A method for determining DC circuit insulation fault according to claims 1-3, characterized in that: Set the second alarm threshold R of the insulation resistance between cores setpp,2 , based on the second alarm threshold R of the insulation resistance between cores setpp,2 Make the following judgment: When the variance of the inter-core impedance measured in a single time is greater than or equal to R setpp,2 , it is judged that there is a core-to-core insulation damage fault. If the core-to-core insulation damage fault judgment condition is always met for a period of time, an alarm will be issued after the period of time; Otherwise, it is determined that there is no inter-core insulation damage fault and no alarm is given.

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