Backup protection method and system based on reactive power direction and medium

Abstract

The invention discloses a backup protection method and system based on a reactive power direction and a medium. Relates to the technical field of power system relay protection. According to the scheme, on the basis of new energy fault characteristic analysis and traditional protection adaptability analysis, after the type of a power supply providing fault current is judged, targeted criteria are adopted according to the characteristics of the power supply, so that protection can flexibly adapt to various operation modes of a power distribution network containing high-proportion new energy; the condition that protection is carried out on the system side and the fault current is large is considered; the problem of insufficient sensitivity of protection on the new energy side under the condition that the fault current amplitude is limited is also considered, the problems caused by the access influence of high-proportion new energy can be effectively solved, and the phenomena of protection operation refusal, even maloperation and the like are avoided; the problem that traditional directional current protection is insufficient in sensitivity and reliability under the condition of high-proportion new energy grid connection is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection of electric power systems, and in particular to a backup protection method, system and medium based on reactive power direction. Background Art

[0002] In recent years, more and more new energy distributed generation has been connected to the distribution network due to its advantages of cleanness, environmental protection, and flexible power generation. After a large number of distributed new energy sources are connected to the distribution network, the short-circuit current shows characteristics such as limited amplitude and frequency deviation. Traditional protection based on power frequency phasors has the risk of incorrect operation.

[0003] Given the intermittent and unstable nature of renewable energy generation, it is significantly sensitive to system disturbances, and its fault current performance is significantly different from that of synchronous generators due to the control strategy. When distributed renewable energy is widely integrated into the distribution network, short-circuit current exhibits characteristics such as amplitude limitation and frequency deviation. These characteristics make the traditional three-stage overcurrent protection strategy no longer suitable for distribution network protection with a high proportion of renewable energy access. Summary of the invention

[0004] The technical problem to be solved by the present invention is: when distributed renewable energy sources are widely integrated into the distribution network, the characteristics of short-circuit current limitation, frequency deviation, etc. make the traditional three-stage overcurrent protection strategy no longer suitable for the protection of distribution networks with a high proportion of renewable energy access; the purpose of the present invention is to provide a backup protection method, system and medium based on reactive power direction, which, on the basis of the analysis of new energy fault characteristics and the analysis of traditional protection adaptability, after judging the type of power supply providing the fault current, adopts targeted criteria according to the power supply characteristics, so that the protection can flexibly adapt to various operating modes of the distribution network containing a high proportion of renewable energy; and solves the problem of insufficient sensitivity and reliability of traditional directional current protection under the condition of high proportion of renewable energy grid connection.

[0005] The present invention is achieved through the following technical solutions:

[0006] This solution provides a backup protection method based on reactive power direction, including:

[0007] S1, collect electrical data;

[0008] S2, obtaining the voltage drop amplitude, and determining whether the voltage drop amplitude satisfies the low voltage action criterion. If so, proceeding to step S3, otherwise, the backup protection process ends;

[0009] S3, judging whether the current fault current is mainly provided by the power grid system or the new energy system. If the current fault current is mainly provided by the new energy system, proceeding to step S4; if the current fault current is mainly provided by the power grid system, proceeding to step S8;

[0010] S4, determine whether the current voltage of each phase is under voltage; if there is no voltage in the three phases, proceed to step S5, otherwise, proceed to step S6;

[0011] S5, based on the memory voltage direction criterion, using the memory voltage as a reference for the phase, determine the direction of the current fault current. If the direction is positive, proceed to step S7; otherwise, return to step S2;

[0012] S6, judging the direction of the current fault current based on the reactive direction criterion, if the fault direction is positive, proceed to step S7; otherwise, return to step S2;

[0013] S7, judging whether the fault is removed based on the voltage maintenance criterion, if so, proceeding to step S9; otherwise, returning to step S2;

[0014] S8, judging whether the fault is in the positive direction based on the traditional directional current criterion, if so, proceeding to step S9; otherwise, returning to step S2;

[0015] S9. Configure the delay time of the backup protection based on the time of the previous level protection, and when the delay time is reached, the backup protection is activated. A further optimization scheme is that the low voltage action criterion in step S2 includes:

[0016] min(U Arms (t),U Brms (t),U Crms (t))<0.7U N

[0017] Where U Arms (t), U Brms (t), U Crms (t) represent the effective value of the three-phase voltage at the protection position, U N Indicates the rated phase voltage of the protection line.

[0018] A further optimization scheme is that the current fault current is mainly provided by the power grid system or by the new energy system, including the method:

[0019] If the current fault current meets the operation mode criterion, it is determined that the current fault current is mainly provided by the new energy system; otherwise, it is determined that the current fault current is provided by the power grid system;

[0020] The operation mode criterion includes: maximum phase current < current limit threshold, and reactive power > reactive power threshold.

[0021] A further optimization scheme is that the current voltage determination includes the following method:

[0022] Determine whether the current voltage meets the voltage criterion:

[0023] max9U Arms (t),U Brms (t),U Crms (t))>0.1U N

[0024] Where U Arms (t), U Brms (t), U Crms (t) represent the effective value of the three-phase voltage at the protection position, U N Indicates the rated phase voltage of the protection line;

[0025] If so, it is determined that there is no voltage in the three phases; otherwise, it is determined that there is voltage in at least one phase.

[0026] A further optimization scheme is that the memory voltage direction criterion includes:

[0027]

[0028] In the formula, Indicates the positive sequence memory voltage, It represents the positive sequence sensitivity angle of the directional element, I1 represents the current positive sequence current; arg() represents the angle; j represents a complex number.

[0029] A further optimization scheme is that the reactive direction criterion includes:

[0030] Q(t)>Q set

[0031] In the formula, Q set It indicates the reactive power direction determination setting value; Q(t) indicates the currently measured reactive power.

[0032] A further optimization scheme is that the voltage maintenance criterion includes:

[0033] min(U Arms (t),U Brms (t),U Crms (t))<0.7U N

[0034] Where U Arms (t), U Brms (t), U Crms (t) represent the effective value of the three-phase voltage at the protection position, U N Indicates the rated phase voltage of the protection line.

[0035] A further optimization scheme is that the traditional directional current criterion includes:

[0036] max(I Arms (t),I Brms (t),ICrms (t)0 set

[0037]

[0038] In the formula,

[0039] I Arms (t) represents the current A phase current; I Brms (t) represents the current B phase current; I Crms (t) represents the current C phase current; I set represents the current threshold, U1 represents the current positive sequence voltage phasor, It represents the sensitivity angle of the directional element, and I1 represents the current positive sequence current phasor.

[0040] The present solution also provides a distribution network backup protection system based on reactive power direction, which is used to implement the above-mentioned distribution network backup protection method based on reactive power direction; the system comprises:

[0041] An acquisition module for collecting electrical data;

[0042] The judgment module is used to perform the following steps:

[0043] S2, obtaining the voltage drop amplitude, and determining whether the voltage drop amplitude satisfies the low voltage action criterion. If so, proceeding to step S3, otherwise, the backup protection process ends;

[0044] S3, judging whether the current fault current is mainly provided by the power grid system or the new energy system. If the current fault current is mainly provided by the new energy system, proceeding to step S4; if the current fault current is mainly provided by the power grid system, proceeding to step S8;

[0045] S4, determine whether the current voltage is present; if there is no voltage in the three phases, proceed to step S5, otherwise, proceed to step S6;

[0046] S5, based on the memory voltage direction criterion, using the memory voltage as a reference for the phase, determine the direction of the current fault current. If the fault direction is positive, proceed to step S7; otherwise, return to step S2;

[0047] S6, judging the fault direction based on the reactive direction criterion, if the fault direction is the positive direction, proceed to step S7; otherwise, return to step S2;

[0048] S7, judging whether the fault is removed based on the voltage maintenance criterion, if so, proceeding to step S9; otherwise, returning to step S2;

[0049] ​S8, judging whether the fault is in the positive direction based on the traditional directional current criterion, if so, proceeding to step S9; otherwise, returning to step S2;

[0050] S9. Configure the delay time of the backup protection based on the time of the previous level protection. When the delay time is reached, the backup protection will be activated.

[0051] The present solution also provides a computer-readable medium on which a computer program is stored. The computer program is executed by a processor to implement a backup protection method based on reactive power direction as described above.

[0052] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0053] 1. The present invention provides a backup protection method, system and medium based on reactive power direction; using low voltage criterion as the starting criterion to increase the sensitivity of the starting element under the condition of new energy grid connection; and adding an operation mode discrimination element; for the fault current of new energy, after voltage judgment, the reactive power direction criterion is used to judge the fault direction, and then the voltage holding element and the delay element are combined to complete the protection action; compared with the traditional backup protection scheme, the scheme has higher sensitivity and good reliability for the condition of high proportion of new energy grid connection;

[0054] 2. The present invention provides a backup protection method, system and medium based on reactive power direction; it not only takes into account the situation that the fault current is large when the protection is on the system side, but also takes into account the problem that the fault current amplitude is limited when the protection is on the new energy side and the sensitivity is insufficient, which can effectively deal with the problems caused by the high proportion of new energy access, and avoid the phenomenon of protection refusal or even malfunction;

[0055] 3. The present invention provides a backup protection method, system and medium based on reactive power direction; the dead zone problem of faults at the protection outlet is also considered; when a symmetrical fault occurs at the protection point, the three-phase voltages all drop to zero; the reliability of the voltage measurement value cannot be guaranteed and can no longer be used as a reference for the phase; under this condition, the memory voltage is selected as the phase reference to ensure accurate judgment of the protection for faults inside and outside the zone. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0057] Figure 1It is a flowchart of a backup protection method based on reactive power direction;

[0058] Figure 2 It is a schematic diagram of the principle of the backup protection method based on reactive power direction;

[0059] Figure 3 This is a schematic diagram of the distribution network topology of Example 3. DETAILED DESCRIPTION

[0060] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0061] When distributed renewable energy is widely integrated into the distribution network, the characteristics of short-circuit current limitation, frequency deviation, etc. make the traditional three-stage overcurrent protection strategy no longer suitable for the protection of distribution networks with a high proportion of renewable energy access. In view of this, this solution provides the following embodiments to solve the above technical problems:

[0062] Example 1

[0063] This embodiment provides a backup protection method based on reactive power direction, such as Figure 1 and Figure 2 As shown, including:

[0064] S1, collect current and voltage data;

[0065] The voltage and current at the protection position are sampled in real time, and the voltage and current sampling values ​​obtained are calculated according to the discrete cosine transform formula to obtain the effective values ​​of voltage, current and reactive power. The transformation formula is as follows:

[0066]

[0067] Q(t)=∑U Krms (t)I Krms (t)sin(θ K (t)),K=A,B,C.

[0068] Where U Krms (t) represents the effective value of voltage; I Krms (t) represents the effective value of current; θ K (t) represents the effective value of reactive power; t represents time; θ K (t) represents the power factor angle; Q(t) represents the calculated reactive power; t represents time; u K (n) represents the voltage sampling value at point n; i K(n) represents the current sampling value at point n; N represents the number of sampling points in one cycle; S2, obtain the voltage drop amplitude, and determine whether the voltage drop amplitude meets the low voltage action criterion. If so, enter step S3, otherwise, the backup protection process ends; the low voltage action criterion in this step includes:

[0069] min(U Arms (t),U Brms (t),U Crms (t))<0.7U N

[0070] Where U Arms (t), U Brms (t), U Crms (t) represent the effective value of the three-phase voltage at the protection position, U N Indicates the rated phase voltage of the protection line.

[0071] S3, judging whether the current fault current is mainly provided by the power grid system or the new energy system. If the current fault current is mainly provided by the new energy system, proceeding to step S4; if the current fault current is mainly provided by the power grid system, proceeding to step S8;

[0072] In this step, the current fault current is mainly provided by the power grid system or the new energy system, including the method:

[0073] If the current fault current meets the operation mode criterion, it is determined that the current fault current is provided by the new energy system; otherwise, it is determined that the current fault current is provided by the power grid system;

[0074] The operation mode criterion includes: maximum phase current < current limit threshold, and reactive power > reactive power threshold. The operation mode criterion formula in this scheme is expressed as:

[0075]

[0076] In the formula, I Arms (t), I Brms (t), I Crms (t) is the three-phase current at the protection location, Q(t) is the reactive power at the protection location, Q lset is the reactive power threshold.

[0077] S4, judging whether the current voltage is under voltage; if there is no voltage in the three phases at present, proceed to step S5, otherwise, proceed to step S6; the judgment of whether there is voltage in this step includes the following method:

[0078] Determine whether the current voltage criterion is met:

[0079] max(U Arms (t),U Brms(t),U Crms (t))>0.1U N

[0080] Where U Arms (t), U Brms (t), U Crms (t) represent the effective value of the three-phase voltage at the protection position, U N Indicates the rated phase voltage of the protection line;

[0081] If so, it is determined that there is no voltage on the three phases; otherwise, it is determined that there is voltage on at least one phase.

[0082] S5, based on the memory voltage direction criterion, using the memory voltage as a reference for the phase, determine the direction of the current fault current. If the direction is positive, proceed to step S7; otherwise, return to step S2;

[0083] The memory voltage direction criterion includes:

[0084]

[0085] In the formula, Indicates the positive sequence memory voltage, It represents the positive sequence sensitivity angle of the directional element, I1 represents the positive sequence component of the current; arg() represents the angle; j represents a complex number.

[0086] S6, judging the direction of the current fault current based on the reactive direction criterion, if the direction is positive, proceeding to step S7; otherwise, returning to step S2;

[0087] The reactive direction criterion includes:

[0088] Q(t)>Q set

[0089] In the formula, Q set It indicates the reactive power direction determination setting value; Q(t) indicates the currently measured reactive power.

[0090] S7, judging whether the fault is removed based on the voltage maintenance criterion, if so, proceeding to step S9; otherwise, returning to step S2; the voltage maintenance criterion in this step includes:

[0091] min(U Arms (t),U Brms (t),U Crms (t))<0.7U N

[0092] Where U Arms (t), U Brms (t), U Crms(t) represent the effective value of the three-phase voltage at the protection position, U N Indicates the rated phase voltage of the protection line.

[0093] S8, judging whether the fault is in the positive direction based on the traditional directional current criterion, if so, proceeding to step S9; otherwise, returning to step S2; the traditional directional current criterion in this step includes:

[0094] max(I Arms (t),I Brms (t),I Crms (t)) set

[0095]

[0096] In the formula,

[0097] I Arms (t) represents the current A phase current; I Brms (t) represents the current B phase current; I Crms (t) represents the current C phase current; I set represents the current threshold, U1 represents the positive sequence component of the current voltage, It represents the sensitivity angle of the directional element, and I1 represents the positive sequence component of the current.

[0098] S9. Configure the delay time of the backup protection based on the time of the previous level protection. When the delay time is reached, the backup protection will be activated.

[0099] This embodiment proposes that in the intra-area fault scenario, the backup protection based on the reactive power direction element set on the new energy side can correctly determine the type of power supply providing the fault current, select the reactive power direction criterion to determine the fault direction, and the protection has high sensitivity to ensure the reliability of the protection.

[0100] Example 2

[0101] This embodiment provides a backup protection system based on reactive power direction, which is used to implement the backup protection method based on reactive power direction described in Embodiment 1; the system includes:

[0102] An acquisition module, used for collecting current and voltage data;

[0103] The judgment module is used to perform the following steps:

[0104] S2, obtaining the voltage drop amplitude, and determining whether the voltage drop amplitude satisfies the low voltage action criterion. If so, proceeding to step S3, otherwise, the backup protection process ends;

[0105] ​S3, judging whether the current fault current is mainly provided by the power grid system or the new energy system. If the current fault current is mainly provided by the new energy system, proceeding to step S4; if the current fault current is mainly provided by the power grid system, proceeding to step S8;

[0106] S4, determine whether the current voltage is present; if there is no voltage in the three phases, proceed to step S5, otherwise, proceed to step S6;

[0107] S5, based on the memory voltage direction criterion, using the memory voltage as a reference for the phase, determine the direction of the current fault current. If the fault direction is positive, proceed to step S7; otherwise, return to step S2;

[0108] S6, judging the direction of the current fault current based on the reactive direction criterion, if the direction is positive, proceeding to step S7; otherwise, returning to step S2;

[0109] S7, judging whether the fault is removed based on the voltage maintenance criterion, if so, proceeding to step S9; otherwise, returning to step S2;

[0110] S8, judging whether the fault is in the positive direction based on the traditional directional current criterion, if so, proceeding to step S9; otherwise, returning to step S2;

[0111] S9. Configure the delay time of the backup protection based on the time of the previous level protection. When the delay time is reached, the backup protection will be activated.

[0112] Example 3

[0113] This embodiment provides a computer-readable medium on which a computer program is stored. The computer program is executed by a processor to implement a backup protection method based on reactive power direction as described in Embodiment 1. Specifically, the following steps are performed:

[0114] S1, collect electrical data;

[0115] S2, obtaining the voltage drop amplitude, and determining whether the voltage drop amplitude satisfies the low voltage action criterion. If so, proceeding to step S3, otherwise, the backup protection process ends;

[0116] S3, judging whether the current fault current is mainly provided by the power grid system or the new energy system. If the current fault current is mainly provided by the new energy system, proceeding to step S4; if the current fault current is mainly provided by the power grid system, proceeding to step S8;

[0117] S4, determine whether the current voltage is present; if there is no voltage in the three phases, proceed to step S5, otherwise, proceed to step S6;

[0118] S5, based on the memory voltage direction criterion, using the memory voltage as a reference for the phase, determine the direction of the current fault current. If the direction is positive, proceed to step S7; otherwise, return to step S2;

[0119] S6, judging the direction of the current fault current based on the reactive direction criterion, if the direction is positive, proceeding to step S7; otherwise, returning to step S2;

[0120] S7, judging whether the fault is removed based on the voltage maintenance criterion, if so, proceeding to step S9; otherwise, returning to step S2;

[0121] S8, judging whether the fault is in the positive direction based on the traditional directional current criterion, if so, proceeding to step S9; otherwise, returning to step S2;

[0122] S9. Configure the delay time of the distribution network backup protection based on the time of the previous level protection. When the delay time is reached, the backup protection will be activated.

[0123] This embodiment uses Figure 3 Taking the distribution network topology shown as an example, the fault occurs at F1, and CT1 is backed up according to S1-S9; this solution proposes that in the fault scenario within the area, the protection set on the system side can correctly determine the type of power supply providing the fault current and flexibly select the judgment criterion type, thereby improving the sensitivity of the protection and ensuring the reliability of the protection.

[0124] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A backup protection method based on reactive power direction, characterized in that: include: S1, collects the current and voltage data of the protected line; S2, obtaining the voltage drop amplitude, and determining whether the voltage drop amplitude satisfies the low voltage action criterion. If so, proceeding to step S3, otherwise, the backup protection process ends; S3, judging whether the current fault current is provided by the power grid system or the new energy system. If the current fault current is provided by the new energy system, proceeding to step S4; if the current fault current is provided by the power grid system, proceeding to step S8; S4, determine whether the current voltage of each phase is under voltage; if there is no voltage in the three phases, proceed to step S5, otherwise, proceed to step S6; S5, based on the memory voltage direction criterion, using the memory voltage as a reference for the phase, determine the direction of the current fault current. If the fault direction is positive, proceed to step S7; Otherwise, return to step S2; S6, judging the current fault current direction based on the reactive direction criterion, if the fault direction is positive, proceeding to step S7; Otherwise, return to step S2; S7, judging whether the fault is removed based on the voltage maintenance criterion, if so, proceeding to step S9; Otherwise, return to step S2; S8, judging whether the fault is in the positive direction based on the traditional directional current criterion, if so, proceeding to step S9; otherwise, returning to step S2; S9. Configure the delay time of the backup protection based on the time of the previous level protection. When the delay time is reached, the backup protection will be activated.

2. A backup protection method based on reactive power direction according to claim 1, characterized in that: The low voltage action criteria in step S2 include: min(U Arms (t),U Brms (t),U Crms (t))<0.7U N Where U Arms (t), U Brms (t), U Crms (t) represent the effective value of the three-phase voltage at the protection position, U N Indicates the rated phase voltage of the protection line.

3. A backup protection method based on reactive power direction according to claim 1, characterized in that: The current fault current is provided by a power grid system or a new energy system, including a method: If the current fault current meets the operation mode criterion, it is determined that the current fault current is provided by the new energy system; Otherwise, it is determined that the current fault current is provided by the power grid system; The operation mode criterion includes: maximum phase current < current limit threshold, and reactive power > reactive power threshold.

4. A backup protection method based on reactive power direction according to claim 1, characterized in that: The method of judging whether the current voltage is under pressure includes: Determine whether the current voltage meets the voltage criterion: max(U Arms (t),U Brms (t),U Crms (t))>0.1U N Where U Arms (t), U Brms (t), U Crms (t) represent the effective value of the three-phase voltage at the protection position, U N Indicates the rated phase voltage of the protection line; If so, it is determined that there is no voltage in the three phases; otherwise, it is determined that there is voltage in at least one phase.

5. The backup protection method based on reactive power direction according to claim 1, characterized in that: The memory voltage direction criterion includes: In the formula, Indicates the positive sequence memory voltage, It represents the positive sequence sensitivity angle of the directional element, I1 represents the positive sequence current corresponding to the current fault current; arg() represents the angle; j represents the imaginary unit.

6. A backup protection method based on reactive power direction according to claim 1, characterized in that: The reactive direction criterion includes: Q(t)>Q set In the formula, Q set It indicates the reactive power direction determination setting value; Q(t) indicates the currently measured reactive power.

7. A backup protection method based on reactive power direction according to claim 1, characterized in that: The voltage maintenance criteria include: min(U Arms (t),U Brms (t),U Crms (t))<0.7U N Where U Arms (t), U Brms (t), U Crms (t) represent the effective value of the three-phase voltage at the protection position, U N Indicates the rated phase voltage of the protection line.

8. The backup protection method based on reactive power direction according to claim 1, characterized in that: The conventional directional current criteria include: max(I Arms (t),I Brms (t),I Crms (t)0<I set In the formula, I Arms (t) represents the current A phase fault current; I Brms (t) represents the current B phase fault current; I Crms (t) represents the current C phase fault current; I set represents the current threshold, U1 represents the current positive sequence voltage phasor, It represents the sensitivity angle of the directional element, and I1 represents the current fault current phasor.

9. A backup protection system based on reactive power direction, characterized in that: A method for implementing a backup protection method based on reactive power direction as described in any one of claims 1 to 8; the system comprises: An acquisition module, used for collecting current and voltage data; The judgment module is used to perform the following steps: S2, obtaining the voltage drop amplitude, and determining whether the voltage drop amplitude satisfies the low voltage action criterion. If so, proceeding to step S3, otherwise, the backup protection process ends; S3, judging whether the current fault current is provided by the power grid system or the new energy system. If the current fault current is provided by the new energy system, proceeding to step S4; if the current fault current is provided by the power grid system, proceeding to step S8; S4, determine whether the current voltage is present; if there is no voltage in the three phases, proceed to step S5, otherwise, proceed to step S6; S5, based on the memory voltage direction criterion, using the memory voltage as a reference for the phase, determine the fault direction of the current fault current. If the fault direction is positive, proceed to step S7; otherwise, return to step S2; S6, judging the direction of the current fault current based on the reactive direction criterion, if the fault direction is positive, proceed to step S7; otherwise, return to step S2; S7, judging whether the fault is removed based on the voltage maintenance criterion, if so, proceeding to step S9; otherwise, returning to step S2; S8, judging whether the fault is in the positive direction based on the traditional directional current criterion, if so, proceeding to step S9; otherwise, returning to step S2; S9. Configure the delay time of the backup protection based on the time of the previous level protection. When the delay time is reached, the backup protection will be activated.

10. A computer readable medium having a computer program stored thereon, characterized in that: The computer program is executed by a processor to implement a backup protection method based on reactive power direction as described in any one of claims 1 to 8.

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