A DC power supply system grounding fault classification diagnosis method and device

Abstract

A method and device for classifying and diagnosing grounding faults in a DC power supply system, belonging to the technical field of DC power supply systems, solves the problems of large interference and long diagnosis time in existing detection methods of DC power supply systems. The technical solution of the present invention faces different types of grounding of DC power supply systems. First, it is determined whether the bus voltage is reduced, and then a DC leakage detection method is used to detect the branch grounding situation. Finally, a bus grounding diagnosis method combining the balanced resistance method and the DC leakage detection method is designed. When detecting the bus grounding situation, this diagnostic scheme avoids the repeated switching of the control switch in the unbalanced bridge method, reducing interference to the DC power supply system. In addition, since there is no need to calculate the insulation resistance of the positive and negative busbars to the ground, but directly sample the current size on the balanced resistance, the time of the entire fault diagnosis process is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of direct current power supply systems, and relates to a method and device for classifying and diagnosing grounding faults in direct current power supply systems. Background Art

[0002] At present, the DC power supply system is an independent power source. In power plants and substations, the DC power supply system can provide DC power for emergency lighting, AC uninterruptible power supply and emergency lubricating oil pumps in the event of an AC power failure. It is not affected by the generator, factory power consumption and system operation mode, and can continue to provide DC power to the equipment when the external AC power is interrupted.

[0003] The reliability of the DC power supply system plays a vital role in the safe operation of power plants and substations, and is the guarantee of safe operation. Among them, whether the DC bus and its branch loads are grounded correctly is very important for the guarantee of personal safety and the reliable operation of equipment.

[0004] Existing DC power supply system grounding fault classification diagnosis methods, such as the balanced bridge method, require frequent disconnection of each branch, and repeated opening and closing of the switch is prone to failure. In addition, there is a possibility of misjudgment in rainy weather or other special working conditions. The DC differential current method can judge the grounding condition of the branch, but it cannot identify the situation where the positive and negative busbars are grounded at the same time. The unbalanced bridge method can judge the situation where the positive, negative, and two sections of the bus are grounded at the same time, but it requires the switching of two control switches, which will interfere with the DC power supply system.

[0005] The Chinese invention patent application document "Direct Current Bus Grounding Detection Method and Device" with application publication number CN105548798A and application publication date May 4, 2016 adopts the method of detecting the voltage on the direct current bus; judging whether the voltage on the direct current bus is within a preset threshold; if it is judged that the voltage on the direct current bus is not within the preset threshold, determining that the direct current bus is abnormally grounded, solves the problem of complex detection of the grounding condition of the direct current bus in the related art, and further simplifies the detection of the grounding condition of the direct current bus. However, the document does not provide a method for judging whether the bus voltage grounding fault occurs on the positive bus or the negative bus, nor does it detect the grounding condition of the branch load. Summary of the invention

[0006] The purpose of the present invention is to design a method and device for classifying and diagnosing ground faults in a DC power supply system, so as to solve the problems of large interference and long diagnosis time in the existing detection methods of the DC power supply system.

[0007] The present invention solves the above technical problems through the following technical solutions:

[0008] A classification diagnosis method for a DC power supply system grounding fault classification diagnosis device, the DC power supply system grounding fault classification diagnosis device comprising: a positive busbar and a negative busbar of the DC power supply system, balancing resistors R1 and R2, a plurality of current Hall sensors, and a plurality of branch loads; one end of the balancing resistors R1 and R2 are respectively connected to the positive busbar and the negative busbar of the DC power supply system, the other ends of the balancing resistors R1 and R2 are connected together and then grounded, and the balancing resistors R1 and R2 are installed with Hall sensors; the positive and negative poles of each branch load are correspondingly connected to the positive busbar and the negative busbar of the DC power supply system, and each branch load is installed with a Hall sensor;

[0009] The classification diagnosis method comprises the following steps:

[0010] S1. Monitor the voltage between the positive bus and the negative bus of the DC power supply system and the ground. When the voltage between at least one bus and the ground deviates from the standard value, it is determined that a ground fault occurs in the DC power supply system.

[0011] S2. Use the Hall sensor to detect the magnitude of the DC differential current Ii0 of the i-th branch load. If |Ii0|≥Ⅰ yzi , then the i-th branch is determined to be grounded, otherwise the i-th branch is determined to be not grounded; if Ii0>0 is satisfied, then the i-th branch is determined to be positively grounded; if Ii0<0 is satisfied, then the i-th branch is determined to be negatively grounded; where, Ⅰ yzi is the threshold value of the set DC differential current, i=1,2,3...n;

[0012] S3, use the Hall sensor to detect the current size of the two balancing resistors R1 and R2. If the difference current of the two balancing resistors |I R1 -I R2 |≤Ⅰ yzR , then it is determined that the positive and negative busbars are grounded at the same time; if |I R1 -I R2 |>Ⅰ yzR , then it is determined that one of the positive bus and the negative bus is grounded. If I R1 -I R2 >Ⅰ yzR , then it is determined that the negative bus is grounded. If I R2 -I R1 >Ⅰ yzR , then the positive busbar is determined to be grounded; among them, I yzR is the threshold of the differential current flowing through the two balancing resistors, I R1 ,I R2 They are the currents on the two balancing resistors R1 and R2 respectively.

[0013] The technical solution of the present invention faces different types of grounding of DC power supply systems. First, it is determined whether the bus voltage is reduced, then the DC leakage detection method is used to detect the branch grounding situation, and finally a bus grounding diagnosis method combining the balanced resistance method and the DC leakage detection method is designed; when detecting the bus grounding situation, this diagnostic scheme avoids the repeated switching of the control switch in the unbalanced bridge method, reducing the interference to the DC power supply system. In addition, since there is no need to calculate the insulation resistance of the positive and negative busbars to the ground, but directly sampling the current size on the balanced resistance, the time of the entire fault diagnosis process is reduced.

[0014] Furthermore, the calculation method of the ith branch load DC differential current Ii0 described in step S2 is as follows:

[0015] When the load of the i-th branch is positively grounded, the current flows out from the positive bus and flows back to the negative bus in two ways, namely:

[0016] Positive bus → load i → negative bus;

[0017] Positive bus → equivalent transition resistor Rd → balancing resistor R2 → negative bus;

[0018] Therefore Ii + -Ii - =Id=Ii0;

[0019] When the load of the i-th branch is negatively grounded, the current flows out from the positive bus and flows back to the negative bus in two ways, namely:

[0020] Positive bus → load i → negative bus;

[0021] Positive bus → balancing resistor R1 → equivalent transition resistor Rd → negative bus;

[0022] Therefore Ii - -Ii + =Id=-Ii0.

[0023] Among them, Ii+ and Ii- are the currents flowing through the positive and negative poles of the i-th load respectively; Ii0 is the total current of the i-th branch, and Id is the current flowing through the equivalent transition resistor.

[0024] Furthermore, the two balancing resistors in step S3 have a current difference |I R1 -I R2 The calculation method of | is as follows:

[0025] When the positive bus is grounded, due to the shunt effect of R+, I R1 R2 , we get:

[0026]

[0027] ​When the negative bus is grounded, due to R - The shunting effect makes I R1 >I R2 , we get:

[0028]

[0029] When the positive and negative busbars are grounded at the same time, the insulation between the positive and negative poles and the ground is the same, that is, R + =R - , we get:

[0030] I R1 =I R2

[0031] Among them, R+ and R- are the equivalent resistance to ground when the positive bus and negative bus are grounded, respectively. R+ ,I R- They are the currents flowing through the equivalent resistance to ground when the positive bus and negative bus are grounded, R=R1=R2.

[0032] A DC power supply system grounding fault classification diagnosis device, the DC grounding fault classification diagnosis device comprising: a positive busbar and a negative busbar of the DC power supply system, balancing resistors R1 and R2, a plurality of current Hall sensors, and a plurality of branch loads; one end of the balancing resistors R1 and R2 are respectively connected to the positive busbar and the negative busbar of the DC power supply system, the other ends of the balancing resistors R1 and R2 are connected together and then grounded, and the balancing resistors R1 and R2 are installed with Hall sensors; the positive and negative poles of each branch load are correspondingly connected to the positive busbar and the negative busbar of the DC power supply system, and each branch load is installed with a Hall sensor.

[0033] The advantages of the present invention are:

[0034] The technical solution of the present invention faces different types of grounding of DC power supply system. First, it determines whether the bus voltage is reduced, then uses the DC leakage detection method to detect the branch grounding situation, and finally proposes a bus grounding diagnosis method that combines the balanced resistance method and the DC leakage detection method; when detecting the bus grounding situation, this diagnostic scheme avoids the repeated switching of the control switch in the unbalanced bridge method, reducing the interference to the DC power supply system. In addition, since there is no need to calculate the insulation resistance of the positive and negative bus to the ground, but directly sample the current size on the balanced resistance, the time of the entire fault diagnosis process is reduced. The diagnosis type is more comprehensive; the balanced resistance method and the DC leakage detection method are combined, and the Hall element is innovatively added to the balanced resistance to detect the differential current, which can accurately diagnose DC grounding in various situations including bus positive grounding, bus negative grounding, bus positive and negative grounding, and branch grounding; the diagnosis speed is improved; when detecting the bus grounding situation, since the Hall element is installed, the differential current can be directly compared, and there is no need to collect multiple variables and then solve the equation to calculate the positive and negative bus resistance to the ground, which improves the diagnosis speed of the whole process. The diagnostic process is more stable; for the case of simultaneous grounding of double busbars, compared with the unbalanced resistance method, there is no need to repeatedly switch on and off the control switch, which reduces the interference to the DC power supply system during the diagnostic process and enhances the stability of the diagnostic process. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural schematic diagram of a grounding fault classification diagnosis device for a DC power supply system of the present invention;

[0036] Figure 2 and 3 are the equivalent circuits of the positively grounded and negatively grounded loads of the i-th branch respectively;

[0037] Figure 4 , Figure 5 and Figure 6 These are the equivalent circuits when the positive busbar is short-circuited to the ground, the negative busbar is short-circuited to the ground, and the positive and negative busbars are short-circuited to the ground at the same time;

[0038] Figure 7 The present invention is a flow chart of a classification diagnosis method of a DC grounding fault classification diagnosis device. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0041] Embodiment 1

[0042] like Figure 1 As shown, a DC power supply system grounding fault classification diagnosis device includes: a positive bus +KM, a negative bus -KM of the DC power supply system, balancing resistors R1 and R2, i+1 current Hall sensors CT0, CT1, ... CT i , i branch loads; where i=1, 2, 3…; one end of the balancing resistors R1 and R2 are respectively connected to the positive bus +KM and the negative bus -KM of the DC power supply system, the other ends of the balancing resistors R1 and R2 are connected together and then grounded, and the balancing resistors R1 and R2 are installed with Hall sensors; the positive and negative poles of each branch load are correspondingly connected to the positive bus +KM and the negative bus -KM of the DC power supply system, and a Hall sensor is installed on each branch load.

[0043] like Figure 2 and 3 As shown, they are the equivalent circuits of the positive and negative grounding of the i-th branch load. In the figure, I+ and I- are the currents flowing through the balancing resistors R1 and R2 respectively; Ii+ and Ii- are the currents flowing through the positive and negative poles of the i-th load respectively; Ii0 is the total current of the i-th branch, R+ and R- are the equivalent resistance to ground when the positive and negative busbars are grounded respectively, and Rd is the equivalent transition resistance when the i-th branch load is positively grounded or negatively grounded.

[0044] like Figure 2 As shown in the figure, when the load of the i-th branch is positively grounded, the current flows out from the positive bus and flows back to the negative bus in two ways, namely:

[0045] Positive bus → load i → negative bus;

[0046] Positive bus → equivalent transition resistor Rd → balancing resistor R2 → negative bus;

[0047] Therefore Ii + -Ii - =Id=Ii0.

[0048] like Figure 3 As shown, when the i-th branch load is negatively grounded, the current flows out from the positive bus and flows back to the negative bus in two ways, namely:

[0049] Positive bus → load i → negative bus;

[0050] Positive bus → balancing resistor R1 → equivalent transition resistor Rd → negative bus;

[0051] Therefore Ii - -Ii +=Id=-Ii0.

[0052] In summary, different branch grounding types can be distinguished by simply judging the polarity of the current difference flow Ii0 flowing into the positive and negative electrodes of the load i.

[0053] like Figures 4 to 6 As shown, the equivalent circuit when the positive bus is short-circuited to the ground, the negative bus is short-circuited to the ground, and the positive and negative bus are short-circuited to the ground at the same time, selects the balancing resistor R1=R2=R.

[0054] like Figure 4 As shown, when the positive bus is grounded, due to the shunt effect of R+, I R1 R2 , we can deduce:

[0055]

[0056] At this point, it can be seen that when the positive bus is grounded, if it is necessary to ensure that the differential current on the balancing resistor on the positive bus is maintained at a large level, it is only necessary to ensure that the value of the balancing resistor is large enough to ensure its current diversion effect.

[0057] like Figure 5 As shown, when the negative bus is grounded, due to R - The shunting effect makes I R1 >I R2 , we can deduce:

[0058]

[0059] At this point, it can be seen that when the negative bus is grounded, if it is necessary to ensure that the differential current on the balancing resistor on the negative bus is maintained at a large level, it is only necessary to ensure that the value of the balancing resistor is large enough to ensure its current diversion effect.

[0060] like Figure 6 As shown in the figure, when the positive and negative busbars are grounded at the same time, it is considered that the insulation between the positive and negative electrodes and the ground is the same, that is, R + =R - , since R=R1=R2, we can deduce:

[0061] I R1 =I R2

[0062] In summary, the threshold I of the difference current flowing through the two balancing resistors is set yzR , different busbar grounding types can be distinguished.

[0063] like Figure 7 As shown, a DC power supply system grounding fault classification diagnosis method includes the following steps:

[0064] ​(1) First, monitor the voltage between the positive bus and negative bus of the DC power supply system and the ground. When at least one bus voltage deviates from the standard value, for example, |U + -U N+ |≥5% or |U - -U N- |≥5%, it is determined that a ground fault has occurred in the DC power supply system; where |U + -U N+ |and|U - -U N- |Represent the positive and negative bus voltages to ground of the DC power supply system respectively.

[0065] (2) The Hall sensor is used to detect the magnitude of the DC differential current Ii0 of the i-th branch load. If |Ii0|≥Ⅰ yzi , then the i-th branch is determined to be grounded, otherwise the i-th branch is determined to be not grounded; if Ii0>0 is satisfied, then the i-th branch is determined to be positively grounded; if Ii0<0 is satisfied, then the i-th branch is determined to be negatively grounded; where, Ⅰ yzi is the threshold value of the set DC differential current, i=1,2,3...n;

[0066] (3) A Hall sensor is used to detect the current on the two balancing resistors R1 and R2. R1 -I R2 |≤Ⅰ yzR , then it is determined that the two busbars are grounded at the same time; if |I R1 -I R2 |>Ⅰ yzR , then it is determined that one of the positive bus and the negative bus is grounded. If I R1 -I R2 >Ⅰ yzR , then it is determined that the negative bus is grounded. If I R2 -I R1 >Ⅰ yzR , then the positive busbar is determined to be grounded; among them, I yzR is the threshold of the differential current flowing through the two balancing resistors, I R1 ,I R2 They are the currents on the two balancing resistors R1 and R2 respectively.

[0067] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A classification diagnosis method for a DC power supply system grounding fault classification diagnosis device, characterized in that: The DC power supply system grounding fault classification diagnosis device comprises: a positive busbar and a negative busbar of the DC power supply system, balancing resistors R1 and R2, a plurality of current Hall sensors, and a plurality of branch loads; one end of the balancing resistors R1 and R2 are respectively connected to the positive busbar and the negative busbar of the DC power supply system, the other ends of the balancing resistors R1 and R2 are connected together and then grounded, and the balancing resistors R1 and R2 are installed with Hall sensors; the positive and negative poles of each branch load are correspondingly connected to the positive busbar and the negative busbar of the DC power supply system, and each branch load is installed with a Hall sensor; The classification diagnosis method comprises the following steps: S1. Monitor the voltage between the positive bus and the negative bus of the DC power supply system and the ground. When the voltage between at least one bus and the ground deviates from the standard value, it is determined that a ground fault occurs in the DC power supply system. S2. Use the Hall sensor to detect the magnitude of the DC differential current Ii0 of the i-th branch load. If |Ii0|≥Ⅰ yzi , then the i-th branch is determined to be grounded, otherwise the i-th branch is determined to be not grounded; if Ii0>0 is satisfied, then the i-th branch is determined to be positively grounded; if Ii0<0 is satisfied, then the i-th branch is determined to be negatively grounded; where, Ⅰ yzi is the threshold value of the set DC differential current, i=1,2,3...n; The calculation method of the DC differential current Ii0 of the i-th branch load is as follows: When the load of the i-th branch is positively grounded, the current flows out from the positive bus and flows back to the negative bus in two ways, namely: Positive bus → load i → negative bus; Positive bus → equivalent transition resistor Rd → balancing resistor R2 → negative bus; Therefore Ii + -Ii - =Id=Ii0; When the load of the i-th branch is negatively grounded, the current flows out from the positive bus and flows back to the negative bus in two ways, namely: Positive bus → load i → negative bus; Positive bus → balancing resistor R1 → equivalent transition resistor Rd → negative bus; Therefore Ii - -Ii + =Id=-Ii0; Among them, Ii+ and Ii- are the currents flowing through the positive and negative electrodes of the i-th load respectively; Ii0 is the total current of the i-th branch, and Id is the current flowing through the equivalent transition resistor; S3, use the Hall sensor to detect the current size of the two balancing resistors R1 and R2. If the difference current of the two balancing resistors |I R1 -I R2 |≤Ⅰ yzR , then it is determined that the positive and negative busbars are grounded at the same time; if |I R1 -I R2 |>Ⅰ yzR , then it is determined that one of the positive bus and the negative bus is grounded. If I R1 -I R2 >Ⅰ yzR , then it is determined that the negative bus is grounded. If I R2 -I R1 >Ⅰ yzR , then the positive busbar is determined to be grounded; among them, I yzR is the threshold of the differential current flowing through the two balancing resistors, I R1 ,I R2 are the currents on the two balancing resistors R1 and R2 respectively; The two balancing resistors have a differential current |I R1 -I R2 The calculation method of | is as follows: When the positive bus is grounded, due to the shunt effect of R+, I R1 R2 , we get:​ When the negative bus is grounded, due to R - The shunting effect makes I R1 >I R2 , we get: When the positive and negative busbars are grounded at the same time, the insulation between the positive and negative poles and the ground is the same, that is, R + =R - , we get: I R1 =I R2 Among them, R+ and R- are the equivalent resistance to ground when the positive bus and negative bus are grounded, respectively. R+ ,I R- They are the currents flowing through the equivalent resistance to ground when the positive bus and negative bus are grounded, R=R1=R2.

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