Active power distribution network fault detection method based on positive sequence impedance

Abstract

The application relates to the technical field of active power distribution network fault detection, in particular to an active power distribution network fault detection method based on positive sequence impedance, which comprises the following steps: (S1) calculating differential superimposed positive sequence impedance; (S2) defining an energy operator and calculating an energy value based on the differential superimposed positive sequence impedance; (S3) defining a fault classification index as FCI and a fault monitoring index as FDI; and (S4) judging based on the fault classification index and the fault monitoring index. The active power distribution network fault detection method based on the positive sequence impedance can effectively monitor low-impedance faults and high-impedance faults and has strong anti-interference performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of active distribution network fault detection, and particularly relates to an active distribution network fault detection method based on positive sequence impedance. BACKGROUND

[0002] With the increasing demand for energy with the development of society, integrating distributed power in the distribution system and forming an active distribution network has gradually attracted attention. The active distribution network is generally composed of multiple microgrids or multi-microgrids constructed in remote areas and connected in a similar geographical location, and is one of the effective solutions to realize rural electrification. Compared with extending the national power grid to remote areas, the active distribution network is more economical. At the same time, the active distribution network has many advantages, such as lower transmission loss, lower transmission cost, and higher reliability.

[0003] Such integrated distribution network changes the radial characteristics of the existing distribution system and the fault characteristics caused by the distributed power, and also increases the complexity of dealing with this problem. In the multi-microgrid, the independent microgrid will exchange power with the main grid, so there are different characteristics between the microgrid and the multi-microgrid when a fault occurs. The traditional protection method often ignores the interconnection and interaction between the microgrids, and has unreliability in dealing with the above problems, so a new protection method is needed to solve the above problems to protect the active distribution network. Commonly used methods for multi-microgrid protection include using fault current limiters, inverse time limit characteristics based on relays and feeder admittance, and protection methods based on line parameters. However, it is difficult to distinguish and classify high-impedance faults and low-impedance faults in the existing methods for protecting microgrids or multi-microgrids, and if there is a communication delay problem, it is difficult to ensure its effectiveness. SUMMARY

[0004] Technical purpose: In order to overcome the deficiencies in the prior art, the present application provides an active distribution network fault detection method based on positive sequence impedance.

[0005] Technical scheme: In order to achieve the above purpose, the present application discloses an active distribution network fault detection method based on positive sequence impedance, comprising the following steps:

[0006] (S1) Obtain current data and voltage data through intelligent electronic devices at both ends of the feeder, and calculate positive sequence current and positive sequence voltage. Calculate the positive sequence impedance under the conditions of before fault and fault, and the superimposed positive sequence impedance of the two connected buses based on the positive sequence current and the positive sequence voltage, and calculate the differential superimposed positive sequence impedance based on this;

[0007] (S2) Define an energy operator to calculate the energy value based on the differential superimposed positive sequence impedance;

[0008]

[0009] In formula (1) and formula (2), E is an energy value of a signal, n is a number of samples, and represents an energy operator used to calculate an energy related to is a difference superimposed positive sequence impedance, V 11error is a voltage after bus 1 fault, I 11error is a current after bus 1 fault, V 11pre is a voltage before bus 1 fault, I 11pre is a current before bus 1 fault, V 12pre is a voltage before bus 2 fault, V 12error is a voltage after bus 2 fault, I 12pre is a current before bus 2 fault, I 12error is a current after bus 2 fault;

[0010] (S3) defining a fault classification index as FCI and a fault monitoring index as FDI, the FCI and FDI indexes are as follows:

[0011]

[0012] In the above formula, d represents a length of a signal;

[0013] (S4) judging based on the fault classification index and the fault monitoring index.

[0014] Further, a specific judging step of step (S4) is as follows:

[0015] (A1) judging a relationship between the FCI and 0, if the FCI < 0, then jumping to step (A2), if the FCI > 0, then jumping to step (A3);

[0016] (A2) judging a relationship between the FDI and ε1, if the FDI > ε1, then judging a high impedance fault, and generating a trip signal, if the FDI < ε1, then judging a switch fault or an external fault, and no trip signal is generated;

[0017] (A3) judging a relationship between the FDI and ε2, if the FDI > ε2, then judging a low impedance fault, and generating a trip signal, if the FDI < ε1, then judging a switch fault or an external fault.

[0018] Further, in step (S2), since the energy of the constant signal is 0, the energy value observed completely depends on the fault value, and therefore for the constant signal, the energy equation is as follows:

[0019]

[0020] Further, in step (S1), the positive sequence impedance before fault is as shown in the following formula (6), and the positive sequence impedance after fault is as shown in the following formula (7):​

[0021]

[0022] In formula (6), |Z 11pre | is the positive sequence impedance before the fault of bus 1, |Z 12pre | is the positive sequence impedance before the fault of bus 2, |Z 11error | is the positive sequence impedance after the fault of bus 1, |Z 12error | is the positive sequence impedance after the fault of bus 2.

[0023] Further,

[0024]

[0025] The positive sequence superposition impedance of bus 1 is shown in formula (8), the positive sequence superposition impedance of bus 2 is shown in formula (9), and the differential superposition positive sequence impedance is shown in formula (10).

[0026] The present application has the following technical effects:

[0027] (1) The present method can effectively monitor and classify low impedance faults and high impedance faults occurring in an active power distribution network composed of a single distributed power source or multiple microgrids.

[0028] (2) The present method has high accuracy in identifying faults of microgrid feeders, and can classify faults as internal faults and external faults.

[0029] (3) The present method can effectively distinguish switching events such as load switching and capacitor switching from fault events, effectively ensuring that no false judgments or misoperations occur.

[0030] (4) The present application can effectively handle noise in data and has certain anti-interference performance. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 A flowchart of the detection and classification index method disclosed in the present application. DETAILED DESCRIPTION

[0032] The following will be described in conjunction with the accompanying Figure 1 The principles and features of the present application are described, and the examples are only used to explain the present application, and are not used to limit the scope of the present application.

[0033] An active power distribution network fault detection method based on positive sequence impedance, comprising the following steps:

[0034] (S1) Obtain current data and voltage data through the intelligent electronic device (line end current and voltage collector) at both ends of the feeder, and calculate the positive sequence current and the positive sequence voltage, calculate the positive sequence impedance before and after the fault and the superimposed positive sequence impedance of the two connected buses based on the positive sequence current and the positive sequence voltage, and calculate the differential superimposed positive sequence impedance based on this.

[0035] The positive sequence impedance of the fault cavity calculated based on the positive sequence current and the positive sequence voltage is shown in the following formula (6), and the positive sequence impedance after the fault is shown in the following formula (7):

[0036]

[0037] In formula (6), |Z 11pre is the positive sequence impedance of bus 1 before the fault, |Z 12pre is the positive sequence impedance of bus 2 before the fault, |Z 11error is the positive sequence impedance of bus 1 after the fault, |Z 12error is the positive sequence impedance of bus 2 after the fault.

[0038] The positive sequence superimposed impedance of bus 1 is shown in formula (8), and the positive sequence superimposed impedance of bus 2 is shown in formula (9):

[0039]

[0040] In formula (8) and formula (9), is the superimposed impedance of bus 1, is the superimposed impedance of bus 2.

[0041] The differential superimposed positive sequence impedance is shown in formula (10).

[0042]

[0043] Since |I 11pre |≈|I 12pre |, and V 11pre and V 12pre are fixed, the second part of the calculation formula of in the above formula is a constant value.

[0044] (S2) Define an energy operator to calculate the energy value based on the differential superimposed positive sequence impedance;

[0045]

[0046] In formula (1) and formula (2), E is the energy value of the signal, n is the number of samples, and Φ represents the energy operator used to calculate the energy related to , is the differential superimposed positive sequence impedance, V 11errorVbus1 is the voltage before bus 1 fault, V 11eror Ibus1 is the current after bus 1 fault, V 11pre Vbus1 is the voltage before bus 1 fault, V 11pre Ibus1 is the current after bus 1 fault, V 12pre Vbus2 is the voltage before bus 2 fault, V 12error Ibus2 is the current after bus 2 fault, V 12pre Ibus2 is the current before bus 2 fault, V 12eror Ibus2 is the current after bus 2 fault, V

[0047] Since the energy of constant signal is 0, the energy value observed completely depends on the fault value, thus for constant signal, the energy equation after correction is:

[0048]

[0049] (S3) Define fault classification index as FCI, define fault monitoring index as FDI, FCI and FDI index are as follows:

[0050]

[0051] In the above formula, d represents the length of the signal.

[0052] (S4) Based on the fault classification index and the fault monitoring index, the specific judgment criteria are:

[0053] (A1) Determine the relationship between FCI and 0, if FCI < 0, jump to step (A2), if FCI > 0, jump to step (A3);

[0054] (A2) Determine the relationship between FDI and ε1, if FDI > ε1, determine high impedance fault, and generate trip signal, if FDI < ε1, determine switch fault or external fault, and no trip signal is generated;

[0055] (A3) Determine the relationship between FDI and ε2, if FDI > ε2, determine low impedance fault, and generate trip signal, if FDI < ε1, determine switch fault or external fault.

[0056] The values of threshold values ε1 and ε2 are calculated by the above two formulas under normal operation of power system topology and operating parameters, taking the Institute of Electrical and Electronics Engineers 13-node standard distribution system model as an example, for FCI, the judgment value is usually 0, and the judgment threshold values ε1 and ε2 corresponding to FDI are usually 0 and 260, respectively.

[0057] The above merely describes preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for active power distribution network fault detection based on positive sequence impedance, characterized in that, The method comprises the following steps: (S1) obtaining current data and voltage data through the intelligent electronic device at both ends of the feeder, and calculating positive sequence current and positive sequence voltage, calculating positive sequence impedance before and after the fault and the superimposed positive sequence impedance of two connected buses through the positive sequence current and the positive sequence voltage, and calculating the differential superimposed positive sequence impedance based thereon; the positive sequence impedance before the fault is shown in the following formula (6), and the positive sequence impedance after the fault is shown in the following formula (7): In formula (6), |Z 11pre | is the positive sequence impedance before the fault of bus 1, |Z 12pre | is the positive sequence impedance before the fault of bus 2, |Z 11error | is the positive sequence impedance after the fault of bus 1, |Z 12error | is the positive sequence impedance after the fault of bus 2; wherein the positive sequence superposition impedance of bus 1 is shown as formula (8), and the positive sequence superposition impedance of bus 2 is shown as formula (9); In formula (8) and formula (9), is the superimposed impedance of bus 1, is the superimposed impedance of bus 2, the differential superimposed positive sequence impedance is shown as formula (10); (S2) defining an energy operator, and calculating an energy value based on the differential superimposed positive sequence impedance; In formula (2), E is an energy value of a signal, Φ represents an energy operator used to calculate energy related to a differential superimposed positive sequence impedance, V 11error Vbus1 is a voltage after bus 1 fault, I 11error Ibus1 is a current after bus 1 fault, V 11pre Vbus1 is a voltage before bus 1 fault, I 11pre Ibus1 is a current before bus 1 fault, V 12pre Vbus2 is a voltage before bus 2 fault, V 12error Vbus2 is a voltage after bus 2 fault, I 12pre Ibus2 is a current before bus 2 fault, I 12error Ibus2 is a current after bus 2 fault; (S3) defining a fault classification index as FCI, and defining a fault monitoring index as FDI, and the FCI and FDI indexes are shown as follows: In the above formula, d represents the length of the signal; (S4) judging based on the fault classification index and the fault monitoring index.

2. The positive sequence impedance based active power distribution network fault detection method of claim 1, wherein, The specific judging steps of step (S4) are as follows: (A1) judging the relationship between FCI and 0, if FCI < 0, then jumping to step (A2), if FCI > 0, then jumping to step (A3); (A2) judging the relationship between FDI and ε1, if FDI > ε1, then judging a high-impedance fault, and generating a tripping signal, if FDI < ε1, then judging a switch fault or an external fault, and no tripping signal is generated; (A3) judging the relationship between FDI and ε2, if FDI > ε2, then judging a low-impedance fault, and generating a tripping signal, if FDI < ε1, then judging a switch fault or an external fault.

3. The positive sequence impedance based active power distribution network fault detection method of claim 1, wherein, In step (S2), since the energy of the constant signal is 0, the observable energy value completely depends on the fault value, and therefore for the constant signal, the energy equation is:

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