A distribution network differential protection method for high-proportion renewable energy generation

Abstract

The present application discloses a distribution network amplitude differential protection method for high-proportion renewable energy power generation, which specifically relates to the field of relay protection technology. The steps are: obtaining the capacity ratio information of the traditional synchronous motor power supply and the inverter power supply on the A and B sides of the distribution network line in the protection installation; collecting the measured short-circuit current information; according to the ratio of the traditional synchronous motor power supply and the inverter power supply, converting the measured short-circuit current information into the corresponding equivalent fault current value and the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides, constructing an equivalent power model, and then converting the virtual equivalent short-circuit current and the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides; the present application can adaptively change the braking coefficient according to the parameters of the equivalent power model on both sides and the amplitude relationship of the virtual short-circuit current of the fault inside and outside the area to meet the selectivity requirements.

Description

Technical Field

[0001] The present application relates to the field of relay protection technology, and more specifically, to a distribution network amplitude differential protection method for high-proportion renewable energy power generation. Background Art

[0002] The wide access of new energy sources to the distribution network has changed the topological structure of the distribution network, and the power flow of the distribution network has changed from the original one-way flow to a two-way flow. For the upstream line of the power electronic power supply grid connection point, the rotating motor power supply and the power electronic power supply exist on both sides of the line, which changes the line structure from the original single-end power supply structure to a double-end power supply structure. If the current protection method without directionality is still used, it may cause the protection device to malfunction or refuse to operate.

[0003] The principle of current differential protection is based on Kirchhoff's Current Law (KCL). The phasor difference of the current at both ends of the line is used as the action criterion to determine whether the fault occurs inside or outside the area. This protection method has excellent selectivity and can ensure that the fault in the area is quickly and sensitively removed. At the same time, the differential protection based on current phasors has high requirements for the communication conditions and communication synchronization of the information exchange of the protection devices before and after the line and at both ends. However, most of the current communication conditions of the distribution network cannot meet the high requirements. Especially after the widespread access of new energy to the distribution network, it is very difficult to achieve large-scale and accurate synchronization of the current phasor information at both ends of the line. If it is only necessary to compare the relationship between the current phasor amplitudes, it will be relatively simple, and the synchronization requirements for the protection device will be greatly reduced.

[0004] Therefore, in order to solve the above problems, a distribution network amplitude differential protection method for high proportion of renewable energy generation is proposed. Summary of the invention

[0005] In order to overcome the above-mentioned defects of the prior art, the present application provides a distribution network amplitude differential protection method for high-proportion renewable energy power generation to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above purpose, the present application provides the following technical solutions: a distribution network differential protection method for high-proportion renewable energy power generation, the steps of the distribution network differential protection method for high-proportion renewable energy power generation are:

[0007] The protection device measures the capacity ratio of the traditional synchronous motor power supply and the inverter power supply on both sides A and B of the distribution network line, and obtains the power supply ratio of the distribution network through online identification;

[0008] The distribution network at least includes a conventional synchronous motor power supply and an inverter power supply;

[0009] Collect measured short-circuit current information;

[0010] According to the proportion of the traditional synchronous motor power supply and the inverter power supply to which it belongs, the measured short-circuit current information is converted into the corresponding equivalent fault current value and the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides, an equivalent power supply model is constructed, and then the virtual equivalent short-circuit current and the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides are converted;

[0011] According to the functional relationship f(μ) between the braking coefficient k and the current amplitude ratio μ, the setting value of the braking coefficient k is calculated. According to the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides, the location of the fault is determined, the setting value of the braking coefficient k is calculated, and the braking current is calculated. and differential current

[0012] Compare brake items and the differential term f(μ) If the differential term is smaller than the braking term, the action equation does not hold, which means it is an out-of-zone fault and the current differential protection does not operate. If the differential term and the action equation hold, it means it is an in-zone fault and the current differential protection operates to isolate the faulty line and reduce the scope of the fault.

[0013] Furthermore, the amplitude of the equivalent simulated short-circuit current flowing through line A is:

[0014]

[0015] in, is the virtual equivalent short-circuit current output by the equivalent power supply on side A flowing through the short-circuit point on the line, is the equivalent phase electromotive force of the power supply on side A, is the equivalent phase electromotive force of the fault additional power supply, is the equivalent internal impedance of the power supply on side A; x is the distance from bus A to short-circuit point K in The ratio of the line length to the total length of line AB, where 0 <x<1, is the line impedance on the left side of the short-circuit point;

[0016] Furthermore, the amplitude of the equivalent virtual short-circuit current flowing through line B is calculated as:

[0017]

[0018] In the formula, is the virtual equivalent short-circuit current output by the equivalent power supply on the B side flowing through the short-circuit point on the line, is the equivalent phase electromotive force of the power supply on side B; The equivalent phase electromotive force of the fault additional power supply; is the equivalent internal impedance of the power supply on the B side; x is the ratio of the line length from bus A to the short-circuit point KIn to the total length of line AB, where 0<x<1; is the line impedance on the right side of the short-circuit point.

[0019] Furthermore, the current amplitude ratio μIn on both sides of A and B is calculated by the equivalent simulated short-circuit current amplitude flowing through the line A side and the equivalent virtual short-circuit current amplitude flowing through the line B side:

[0020]

[0021] Furthermore, the protection criterion of the distribution network current amplitude difference protection method is:

[0022]

[0023] In the formula, is the differential current; is the braking current; k is the braking coefficient. The braking coefficient k changes with the change of μ value and is positively correlated with the μ value. When the μ value reaches the maximum value of 1, the k value also reaches the maximum value of 1.

[0024] Furthermore, when μ<1, and the braking current Ir is much smaller than the differential current Id, the fault must have occurred in the zone;

[0025] When μ=1 and the differential current Id is much smaller than the braking current Ir, the fault occurs outside the zone.

[0026] Technical effects and advantages of this application:

[0027] 1. Compared with the prior art, this distribution network amplitude differential protection method for high-proportion renewable energy generation collects measured short-circuit current information, constructs an equivalent power model, and then converts the virtual equivalent short-circuit current and the amplitude ratio μ of the virtual equivalent short-circuit current on both sides. Then, the amplitude relationship of the virtual short-circuit current on both sides when the fault occurs inside and outside the protection zone is derived. The braking coefficient can be adaptively changed according to the parameters of the equivalent power model on both sides and the amplitude relationship of the virtual short-circuit current of the fault inside and outside the zone to meet the selectivity requirements;

[0028] 2. This application makes up for the defect that the existing power grid current differential protection is difficult to adapt to the high proportion of new energy power generation on the power supply side, so that the improved power grid differential protection method fully considers the sensitivity requirements. The protection braking coefficient of this application can adaptively change with the capacity ratio composition information of the two types of power sources on both sides of the line and the location of the fault point, greatly improving the protection action sensitivity of the current differential protection and meeting the sensitivity requirements.

[0029] 3. The present application proposes a distribution network amplitude differential protection method for high-proportion renewable energy power generation, which can utilize the original power grid protection device without changing the circuit structure, and has a certain degree of adaptability and high engineering practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of current amplitude difference protection;

[0031] Figure 2 This is a schematic diagram of the fault in the area;

[0032] Figure 3 is the fault equivalent circuit diagram of the fault in the zone;

[0033] Figure 4 This is a schematic diagram of an out-of-area fault;

[0034] Figure 5 It is the fault equivalent circuit diagram of the out-of-zone fault;

[0035] Figure 6 This is a simplified action flow chart of the current amplitude difference protection method. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] Example 1

[0038] As attached Figures 1 to 6 A distribution network amplitude differential protection method for high-proportion renewable energy power generation is shown, and the steps of the distribution network amplitude differential protection method for high-proportion renewable energy power generation are as follows:

[0039] The protection device measures the capacity ratio of the traditional synchronous motor power supply and the inverter power supply on both sides A and B of the distribution network line, and obtains the power supply ratio of the distribution network through online identification;

[0040] The distribution network at least includes a conventional synchronous motor power supply and an inverter power supply;

[0041] Collect measured short-circuit current information;

[0042] According to the proportion of the traditional synchronous motor power supply and the inverter power supply to which it belongs, the measured short-circuit current information is converted into the corresponding equivalent fault current value and the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides, an equivalent power supply model is constructed, and then the virtual equivalent short-circuit current and the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides are converted;

[0043] According to the functional relationship f(μ) between the braking coefficient k and the current amplitude ratio μ, the setting value of the braking coefficient k is calculated. According to the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides, the location of the fault is determined, the setting value of the braking coefficient k is calculated, and the braking current is calculated. and differential current

[0044] Compare brake items and the differential term f(μ) If the differential term is smaller than the braking term, the action equation does not hold, which means it is an out-of-zone fault and the current differential protection does not operate. If the differential term and the action equation hold, it means it is an in-zone fault and the current differential protection operates to isolate the faulty line and reduce the scope of the fault.

[0045] The amplitude of the equivalent simulated short-circuit current flowing through line A is:

[0046]

[0047] in, is the virtual equivalent short-circuit current output by the equivalent power supply on side A flowing through the short-circuit point on the line, is the equivalent phase electromotive force of the power supply on side A, is the equivalent phase electromotive force of the fault additional power supply, is the equivalent internal impedance of the power supply on side A; x is the distance from bus A to short-circuit point K in The ratio of the line length to the total length of line AB, where 0 <x<1, is the line impedance on the left side of the short-circuit point;

[0048] The calculated equivalent virtual short-circuit current amplitude flowing through line B is:

[0049]

[0050] In the formula, is the virtual equivalent short-circuit current output by the equivalent power supply on the B side flowing through the short-circuit point on the line, is the equivalent phase electromotive force of the power supply on side B; The equivalent phase electromotive force of the fault additional power supply; is the equivalent internal impedance of the power supply on the B side; x is the ratio of the line length from bus A to the short-circuit point KIn to the total length of line AB, where 0<x<1; is the line impedance on the right side of the short-circuit point.

[0051] The current amplitude ratio μ between the A and B sides is calculated by the equivalent simulated short-circuit current amplitude flowing through the A side of the line and the equivalent virtual short-circuit current amplitude flowing through the B side of the line. in for:

[0052]

[0053] The protection criterion of the current amplitude difference protection method of the distribution network is:

[0054]

[0055] In the formula, is the differential current; is the braking current; k is the braking coefficient. The braking coefficient k changes with the change of μ value and is positively correlated with the μ value. When the μ value reaches the maximum value of 1, the k value also reaches the maximum value of 1.

[0056] When μ<1, and the braking current Ir is much smaller than the differential current Id, the fault must occur within the zone;

[0057] When μ=1 and the differential current Id is much smaller than the braking current Ir, the fault occurs outside the zone.

[0058] Example 2

[0059] The present embodiment provides a distribution network amplitude differential protection method for high-proportion renewable energy power generation. The specific method is to replace the inverter power supply with a traditional rotating power supply of the same capacity according to the proportion of different types of power supplies measured before the short-circuit fault occurs, so as to construct a "virtual power supply end", that is, from the protection installation point, its power supply side only includes a rotating motor, which is then used for steady-state analysis and calculation. After the short circuit occurs, the measured short-circuit current information is collected and modified to a virtual short-circuit current corresponding to the above-mentioned "virtual power supply end", that is, the inverter power supply on the power supply side is replaced in imagination. The replacement principle is to keep the total power supply capacity unchanged, and at the same time completely convert the power supply components into traditional rotating motors, and then the corresponding amplitude ratio μ of the virtual equivalent short-circuit current on both sides, the setting value of the braking coefficient k, and the braking current are converted. and differential current Then, determine the location where the fault occurred.

[0060] The present application will be further described below in conjunction with the accompanying drawings.

[0061] Assuming that a metallic short circuit fault occurs in the AB section of the distribution network, its equivalent power supply model is as follows: Figure 2 As shown, its fault equivalent circuit is as follows Figure 3 shown.

[0062] The amplitude of the equivalent simulated short-circuit current flowing through line A is:

[0063]

[0064] in, is the virtual equivalent short-circuit current output by the equivalent power supply on side A flowing through the short-circuit point on the line, is the equivalent phase electromotive force of the power supply on side A, is the equivalent phase electromotive force of the fault additional power supply, is the equivalent internal impedance of the power supply on side A; x is the distance from bus A to short-circuit point K in The ratio of the line length to the total length of line AB, where 0 <x<1, is the line impedance on the left side of the short-circuit point;

[0065] The calculated equivalent virtual short-circuit current amplitude flowing through line B is:

[0066]

[0067] In the formula, is the virtual equivalent short-circuit current output by the equivalent power supply on the B side flowing through the short-circuit point on the line, is the equivalent phase electromotive force of the power supply on side B; The equivalent phase electromotive force of the fault additional power supply; is the equivalent internal impedance of the power supply on the B side; x is the ratio of the line length from bus A to the short-circuit point KIn to the total length of line AB, where 0<x<1; is the line impedance on the right side of the short-circuit point.

[0068] The current amplitude ratio μ between the A and B sides is calculated by the equivalent simulated short-circuit current amplitude flowing through the A side of the line and the equivalent virtual short-circuit current amplitude flowing through the B side of the line. in for:

[0069]

[0070] According to the equivalent principle of virtual power supply, it can be considered that and Same line impedance With the same impedance angle, μ in The relationship between μ and x is positively correlated, that is, μ in The value of increases monotonically with the increase of x, that is, the closer the fault location is to the B side, the greater the current amplitude ratio μ on both sides of A and B. in The larger the value of , the greater the current amplitude ratio on both sides of A and B reaches its maximum value when x=1.

[0071] According to the requirements of State Grid Corporation of China Q / GDW 480-2012 "Technical Regulations for Distributed Power Sources Connected to the Grid", the total capacity of distributed power sources connected to the grid shall not exceed 25% of the total capacity of the regional load supplied by the upper transformer. It can be considered that the proportion of the aggregated power electronic power supply capacity on the B side will not exceed 25% of the total capacity of the two aggregated power supplies on the A side. Considering the extreme case that the aggregated power electronic power supply capacity on the B side accounts for 20% of the total power supply capacity, at this time P B =0.25P A , can be obtained In this case, if the metallic short circuit fault occurs at point B, the current amplitudes on both sides of A and B are greater than μ in.max for:

[0072]

[0073] From the above analysis, we can see that when When in.max =1, that is, the current amplitudes on both sides of A and B are equal. However, in actual situations, the internal impedance of the main transformer of the 10kV distribution network is about 2 to 3 times the unit impedance of the line. Therefore, the length of a single-circuit line must reach 9 to 10 km to meet the above impedance relationship. The single-circuit line of a conventional 10kV distribution network does not meet this length specification. Therefore, it can be considered that when a short-circuit fault occurs in the area, the current amplitude output by the power supply on both sides of A and B is greater than μ in Less than 1.

[0074] Assuming that a metallic short circuit fault occurs outside the AB section of the distribution network, its equivalent power supply model is as follows: Figure 4 As shown, its fault equivalent circuit is as follows Figure 5 shown.

[0075] The amplitude of the equivalent virtual short-circuit current flowing through line A is:

[0076]

[0077] Using Millman's theorem, it can be calculated that the amplitude of the equivalent virtual short-circuit current flowing through line B is:

[0078]

[0079] Then the current amplitude flowing through A and B is μ out for:

[0080]

[0081] From the above formula, it can be seen that when a metallic short-circuit fault occurs outside the AB section of the distribution network line, ignoring the measurement error and transmission error of the current transformer, it can be considered that the amplitude of the equivalent virtual short-circuit current flowing through the A and B sides of the line is equal, that is, the current amplitude ratio of A and B is μ outAlways equal to 1.

[0082] According to the above analysis, under the ideal condition of ignoring the current transformer error, according to the different values ​​of the amplitude ratio μ of the equivalent virtual short-circuit current flowing through the lines A and B after the short-circuit fault occurs, it can be roughly divided into the following two cases:

[0083] (1) When μ<1, μ out It is always equal to 1, so we can preliminarily divide the faults inside the area and outside the area. It is considered that the fault inside the area of ​​AB section occurs at this time.

[0084] (2) When μ = 1, it is not possible to simply use the amplitude ratio of the virtual short-circuit current to determine whether the fault occurs inside or outside the zone. It is necessary to further analyze the braking current I r and the differential current I d If the fault occurs outside the zone, ideally, the phase and amplitude of the virtual short-circuit current calculated by the protection devices on both sides of the line are almost the same. At this time, the differential current I d is approximately equal to 0, and the braking current I r Approximately equal to the short-circuit ride-through current, that is, the braking current I r Much larger than the differential current I d ; If the fault occurs in the zone, the virtual short-circuit current calculated by the protection devices on both sides of the line has opposite phases. At this time, the braking current I r is approximately equal to 0, the differential current I d Much larger than the braking current I r .

[0085] Therefore, we can draw the following conclusions:

[0086] (1) When μ<1, and the braking current I r Much smaller than the differential current I d When , the fault must occur in the area;

[0087] (2) When μ = 1, and the differential current I d Much smaller than the braking current I r , the fault occurred outside the zone.

[0088] According to the analysis in the previous article, the protection criterion of the distribution network current amplitude difference protection method based on the power supply model proposed in this chapter is:

[0089]

[0090] In the formula, is the differential current; is the braking current; k is the braking coefficient. The braking coefficient k changes with the change of μ value and is positively correlated with μ value. When μ value reaches the maximum value of 1, k value also reaches the maximum value of 1.

[0091] The current amplitude difference protection method proposed in this application simplifies the action process as follows: Figure 6 shown.

[0092] The implementation principle of the embodiment of the present application is as follows: first, the protection device measures the capacity ratio information of the traditional synchronous motor power supply and the inverter power supply on both sides A and B of the distribution network line, and online identifies and obtains the power supply composition ratio of the distribution network; the distribution network at least includes the traditional synchronous motor power supply and the inverter power supply; collects the measured short-circuit current information; according to the composition ratio of the traditional synchronous motor power supply and the inverter power supply to which it belongs, converts the measured short-circuit current information into the corresponding equivalent fault current value and the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides, constructs an equivalent power model, and then converts the virtual equivalent short-circuit current and the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides; according to the functional relationship f(μ) between the braking coefficient k and the current amplitude ratio μ, calculates the setting value of the braking coefficient k, judges the location of the fault according to the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides, calculates the setting value of the braking coefficient k, and calculates the braking current and differential current Compare brake items and the differential term f(μ) If the differential term is smaller than the braking term, the action equation does not hold, which means it is an out-of-zone fault and the current differential protection does not operate. If the differential term and the action equation hold, it means it is an in-zone fault and the current differential protection operates to isolate the faulty line and reduce the scope of the fault. The above is the working principle of the differential protection method for distribution network with a high proportion of renewable energy power generation.

Claims

1. A distribution network amplitude differential protection method for high-proportion renewable energy generation, characterized by: The steps of the distribution network amplitude protection method for high-proportion renewable energy generation are as follows: The protection device measures the capacity ratio of the traditional synchronous motor power supply and the inverter power supply on both sides A and B of the distribution network line, and obtains the power supply ratio of the distribution network through online identification; The distribution network at least includes a conventional synchronous motor power supply and an inverter power supply; Collect measured short-circuit current information; According to the proportion of the traditional synchronous motor power supply and the inverter power supply to which it belongs, the measured short-circuit current information is converted into the corresponding equivalent fault current value and the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides, an equivalent power supply model is constructed, and then the virtual equivalent short-circuit current and the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides are converted; According to the functional relationship f(μ) between the braking coefficient k and the current amplitude ratio μ, the setting value of the braking coefficient k is calculated. According to the value of the amplitude ratio μ of the virtual equivalent short-circuit current on both sides, the location of the fault is determined, the setting value of the braking coefficient k is calculated, and the braking current is calculated. and differential current Compare brake items and the differential term f(μ) If the differential term is smaller than the braking term, the action equation does not hold, which means it is an out-of-zone fault and the current differential protection does not operate. If the differential term and the action equation hold, it means it is an in-zone fault and the current differential protection operates to isolate the faulty line and reduce the scope of the fault.

2. According to claim 1, a distribution network amplitude differential protection method for high-proportion renewable energy power generation is characterized in that: The equivalent simulated short-circuit current amplitude flowing through line A is: in, is the virtual equivalent short-circuit current output by the equivalent power supply on side A flowing through the short-circuit point on the line, is the equivalent phase electromotive force of the power supply on side A, is the equivalent phase electromotive force of the fault additional power supply, is the equivalent internal impedance of the power supply on side A; x is the distance from bus A to short-circuit point K in The ratio of the line length to the total length of line AB, where 0 <x<1, is the line impedance on the left side of the short-circuit point.

3. The method for distribution network amplitude differential protection for high-proportion renewable energy generation according to claim 2 is characterized in that: The calculated equivalent virtual short-circuit current amplitude flowing through line B is: In the formula, is the virtual equivalent short-circuit current output by the equivalent power supply on the B side flowing through the short-circuit point on the line, is the equivalent phase electromotive force of the power supply on side B; The equivalent phase electromotive force of the fault additional power supply; is the equivalent internal impedance of the power supply on the B side; x is the ratio of the line length from bus A to the short-circuit point KIn to the total length of line AB, where 0<x<1; is the line impedance on the right side of the short-circuit point.

4. The method for distribution network amplitude differential protection for high-proportion renewable energy generation according to claim 3 is characterized in that: The current amplitude ratio μIn on both sides of A and B is calculated by the equivalent simulated short-circuit current amplitude flowing through the line A side and the equivalent virtual short-circuit current amplitude flowing through the line B side:

5. A distribution network amplitude differential protection method for high-proportion renewable energy power generation according to claim 4, characterized in that: The protection criterion of the distribution network current amplitude difference protection method is: In the formula, is the differential current; is the braking current; k is the braking coefficient. The braking coefficient k changes with the change of μ value and is positively correlated with the μ value. When the μ value reaches the maximum value of 1, the k value also reaches the maximum value of 1.

6. A distribution network amplitude differential protection method for high-proportion renewable energy generation according to claim 5, characterized in that: When μ<1, and the braking current Ir is much smaller than the differential current Id, the fault must occur in the zone; When μ=1 and the differential current Id is much smaller than the braking current Ir, the fault occurs outside the zone.

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