Construction method and device of high-sensitivity differential protection criterion based on high voltage and low cosine value

Abstract

The application discloses a kind of based on high-voltage low cosine value's high sensitivity differential protection criterion construction method and device, comprising: obtaining the voltage phasor of line two sides and;With the included angle of the voltage phasor and and the differential current phasor, calculate cosine value;According to the voltage phasor and and cosine value, construct the identification criterion of non-fault phase;According to differential current amplitude and low brake phase differential protection setting value, construct low brake phase differential protection criterion;According to zero sequence differential current amplitude and zero difference protection braking current setting value, construct zero sequence differential protection criterion;From the identification criterion of non-fault phase, low brake phase differential protection criterion and zero sequence differential protection criterion, construct high sensitivity differential protection criterion.Solve the problem of low sensitivity of prior art differential protection discrimination.

Description

Technical Field

[0001] This invention relates to the field of automated relay protection technology, specifically to a method and apparatus for constructing a highly sensitive differential protection criterion based on high voltage and low cosine value. Background Technology

[0002] In existing AC systems, current differential protection is widely used as the main protection for line protection. Based on Kirchhoff's current law, the differential current is zero when there is no fault or a fault outside the protection zone, and becomes the fault current when there is a fault within the protection zone, thus exhibiting good sensitivity and reliability.

[0003] Due to the influence of the transmission line's ground capacitance, the differential current is the capacitive current during normal operation. In order to improve the sensitivity of the current differential protection, it is necessary to compensate for the capacitive current so that the differential current is zero when the line is fault-free. However, capacitive current compensation requires high accuracy of line parameters. Therefore, the key issue restricting the performance of the current differential protection is that the high transition resistance makes it difficult to distinguish between the reduced fault current and the magnitude of the line capacitive current. This problem is more obvious in weak feeder systems and may even lead to incorrect protection operation and expand the scope of the accident. Summary of the Invention

[0004] To address the above problems, this invention provides a method for constructing a high-sensitivity differential protection criterion based on high voltage and low cosine value, comprising:

[0005] Obtain the sum of voltage phasors on both sides of the line; calculate the cosine value using the angle between the sum of voltage phasors and the differential current phasor;

[0006] Based on the voltage phasor sum and cosine value, a criterion for identifying non-faulty phases is constructed;

[0007] Based on the differential current amplitude and the differential protection setting of the low braking phase, a criterion for low braking phase differential protection is constructed.

[0008] Based on the zero-sequence differential current amplitude and the zero-sequence differential protection braking current setting, a zero-sequence differential protection criterion is constructed.

[0009] A highly sensitive differential protection criterion is constructed based on the identification criteria for the non-faulty phase, the differential protection criterion for the low braking phase, and the differential protection criterion for the zero sequence.

[0010] Furthermore, the sum of voltage phasors on both sides of the line is obtained, including:

[0011]

[0012] In the formula: For the M side of the line Phase voltage phasors For the N side of the line Phase voltage phasors

[0013]

[0014] Furthermore, using the angle between the voltage phasor and the differential current phasor, the cosine value is calculated, including:

[0015]

[0016] In the formula: This represents the phasor value of the line differential current. For the M side of the line Phase current phasor For the N side of the line Phase current phasor.

[0017] Furthermore, based on the voltage phasor sum and cosine value, a criterion for identifying non-faulty phases is constructed, including:

[0018]

[0019] In the formula: U e This is the line's rated voltage.

[0020] Furthermore, based on the differential current amplitude and the low braking phase differential protection setting, a low braking phase differential protection criterion is constructed, including:

[0021] The criterion for low braking phase differential protection is:

[0022] In the formula: I is the differential current amplitude. setL This is the setting for the low braking phase differential protection.

[0023] Furthermore, based on the zero-sequence differential current amplitude and the zero-sequence differential protection braking current setting, a zero-sequence differential protection criterion is constructed, including:

[0024] The criterion for zero-sequence differential protection is: I Σ0 >I set0 ,

[0025] In the formula: I is the amplitude of the zero-sequence differential current. set0 Set the braking current value for zero-differential protection.

[0026] Furthermore, it also includes:

[0027] Based on the aforementioned high-sensitivity differential protection criteria, determine whether a line fault has occurred;

[0028] Once a line fault is identified, the faulty phase is determined.

[0029] Furthermore, based on the aforementioned high-sensitivity differential protection criterion, determining whether a line fault has occurred includes:

[0030] A line fault is determined when both the low braking phase differential protection criterion and the zero sequence differential protection criterion are met simultaneously.

[0031] Furthermore, once a line fault is confirmed, the faulty phase is identified, including:

[0032] When a line fault occurs, the faulty phase is determined based on the identification criteria of the non-faulty phases.

[0033] This invention also provides a device for constructing a high-sensitivity differential protection criterion based on high voltage and low cosine value, comprising:

[0034] The cosine value calculation unit is used to obtain the sum of voltage phasors on both sides of the line; and to calculate the cosine value using the angle between the sum of voltage phasors and the differential current phasor.

[0035] A non-faulty phase identification criterion construction unit is used to construct the non-faulty phase identification criterion based on the voltage phasor sum and cosine value.

[0036] The low braking phase differential protection criterion construction unit is used to construct the low braking phase differential protection criterion based on the differential current amplitude and the low braking phase differential protection setting.

[0037] The zero-sequence differential protection criterion construction unit is used to construct the zero-sequence differential protection criterion based on the zero-sequence differential current amplitude and the zero-sequence differential protection braking current setting.

[0038] The high-sensitivity differential protection criterion construction unit is used to construct a high-sensitivity differential protection criterion from the identification criterion of the non-faulty phase, the differential protection criterion of the low braking phase, and the zero-sequence differential protection criterion.

[0039] This invention provides a method and apparatus for constructing a highly sensitive differential protection criterion based on high voltage and low cosine value. It can reliably identify non-faulty phases during high transition resistance faults, correctly identify faults inside and outside the fault zone without being affected by weak feeder systems, and reliably operate during fault and non-full-phase oscillation processes. It balances the sensitivity and reliability of differential protection and improves the safe and stable operation level of the system. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating a method for constructing a high-sensitivity differential protection criterion based on high voltage and low cosine value, as provided in an embodiment of the present invention.

[0041] Figure 2 This is a logic diagram of the high-sensitivity differential protection criterion involved in an embodiment of the present invention;

[0042] Figure 3 This is a system diagram of a conventional power access scenario involved in an embodiment of the present invention;

[0043] Figure 4 This is the differential protection action result of the longitudinal and transverse hybrid braking of the fault zone involved in the embodiments of the present invention;

[0044] Figure 5 This is the differential protection action result of the cross-sectional and longitudinal hybrid braking for external faults involved in the embodiments of the present invention;

[0045] Figure 6 This is a system diagram of a conventional power access scenario involved in an embodiment of the present invention;

[0046] Figure 7 This is the differential protection action result of the longitudinal and transverse hybrid braking of the fault zone involved in the embodiments of the present invention;

[0047] Figure 8 This is the differential protection action result of the cross-sectional and longitudinal hybrid braking for external faults involved in the embodiments of the present invention.

[0048] Figure 9 This is a schematic diagram of a device for constructing a high-sensitivity differential protection criterion based on high voltage and low cosine value, provided in an embodiment of the present invention. Detailed Implementation

[0049] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0050] Figure 1 This is a flowchart illustrating a method for constructing a high-sensitivity differential protection criterion based on high voltage and low cosine value, as provided in an embodiment of the present invention. The following is a detailed explanation in conjunction with... Figure 1 The method provided by this invention will be described in detail.

[0051] Step S101: Obtain the sum of voltage phasors on both sides of the line; calculate the cosine value using the angle between the sum of voltage phasors and the differential current phasor.

[0052] Calculate the voltage phasor sum using the voltages on both sides of the line.

[0053]

[0054] In the formula: For the M side of the line Phase voltage phasors For the N side of the line Phase voltage phasors

[0055] The cosine value is calculated using the angle between the voltage phasors and the differential current phasors on both sides of the line.

[0056]

[0057] In the formula: This represents the phasor value of the line differential current. For the M side of the line Phase current phasor For the N side of the line Phase current phasor.

[0058] Step S102: Based on the sum and cosine of the voltage phasors, construct the identification criteria for the non-faulty phase.

[0059] Specifically,

[0060]

[0061] In the formula: U e This is the line's rated voltage.

[0062] Step S103: Based on the differential current amplitude and the low braking phase differential protection setting, construct the low braking phase differential protection criterion.

[0063] The criterion for low braking phase differential protection is:

[0064] In the formula: I is the differential current amplitude. setL This is the setting for the low braking phase differential protection.

[0065] Step S104: Construct zero-sequence differential protection criteria based on the zero-sequence differential current amplitude and the zero-sequence differential protection braking current setting.

[0066] The criterion for zero-sequence differential protection is: I Σ0 >I set0 ,

[0067] In the formula: I is the amplitude of the zero-sequence differential current. set0 Set the braking current value for zero-differential protection.

[0068] Step S105: Construct a highly sensitive differential protection criterion based on the identification criterion of the non-faulty phase, the differential protection criterion of the low braking phase, and the differential protection criterion of the zero sequence.

[0069] Based on the aforementioned high-sensitivity differential protection criterion, it is determined whether a line fault has occurred. Specifically, when the low-resistance phase differential protection criterion is simultaneously met... Zero-sequence differential protection criteria At that time, it was determined that a line fault had occurred;

[0070] Once a line fault is confirmed, the faulty phase is identified. Specifically, this is done based on the identification criteria for non-faulty phases, meaning that the phase that meets the criteria... If this phase is a non-faulty phase, then if it does not meet the condition of being grounded, this phase will be identified as a faulty phase.

[0071] For example, the line includes three phases A, B, and C, according to Figure 2 The high-sensitivity differential protection criterion logic diagram shown distinguishes whether phases A, B, and C are faulty phases. First, it determines if a line fault has occurred, then it identifies the faulty phase. Specifically, when the low-resistance phase differential protection criterion is simultaneously met... Zero-sequence differential protection criteria At this point, a line fault is confirmed, but it cannot be determined which phase (A, B, or C) is faulty. Taking phase A as an example, when phase A meets the identification criteria for a non-faulty phase... Then phase A is a non-faulty phase; conversely, if phase A does not meet the identification criteria for a non-faulty phase, then... Then phase A is the faulty phase. Similarly, determine whether phases B and C are faulty phases.

[0072] The specific implementations selected the following scenarios:

[0073] (1) Conventional power supply access scenario

[0074] In a scenario where conventional power supply is used, both ends of the line are powered by conventional power sources, as shown in the system diagram below. Figure 3 As shown, the cases of single-phase grounding faults via high resistance (800Ω) within the line zone and faults outside the zone are discussed respectively.

[0075] 1) Fault within the area

[0076] A single-phase ground fault occurred in the line area via an 800Ω transition resistor. The protection operation was as follows: Figure 4 As shown, the phase differential protection and zero-sequence differential protection for phase A with low braking entered the operating zone at 10.83ms, and the high voltage low power factor non-fault phase identification criterion was released from blocking at 1.67ms, so the phase A protection operated reliably. The phase differential protection and zero-sequence differential protection for phases B and C with low braking did not operate, and the high voltage low power factor non-fault phase identification criterion remained blocked, so the protection did not operate reliably.

[0077] 2) External faults

[0078] When a phase-A ground fault occurs outside the designated area on the line, the protection operation is as follows: Figure 5As shown, neither the phase differential protection nor the zero-sequence differential protection for phase A under low braking operates. The high voltage, low power factor, and non-faulty phase identification criterion is released after 5.83ms. Based on the overall judgment, the phase A protection is reliable and does not operate. Similarly, neither the phase differential protection nor the zero-sequence differential protection for phases B and C under low braking operates, and the high voltage, low power factor, and non-faulty phase identification criterion remains blocked. Therefore, the phase B and C protections are reliable and do not operate.

[0079] (2) Scenario where the switch on one side of the line is disconnected

[0080] The scenario of a weak feeder system being simulated by disconnecting a switch on one side of the line is shown in the system diagram below. Figure 6 As shown, the N-side circuit breaker tripped, and the faults at fault points F1 within the zone and F2 outside the zone were analyzed. The protection operation is as follows.

[0081] 1) Fault within the area

[0082] A single-phase ground fault occurred at point F1 within the line area, with phase AN connected to an 800Ω transition resistor. The protection operation is as follows: Figure 7 As shown, the phase differential protection and zero-sequence differential protection for phase A with low braking enter the operating zone in 12.5ms. The high voltage low power factor non-fault phase identification criterion is released from blocking in 13.33ms, and the phase A protection operates reliably. The phase differential protection for phases B and C with low braking does not operate, while the zero-sequence differential protection operates, but the high voltage low power factor non-fault phase identification criterion remains blocked, and the protection does not operate reliably.

[0083] (2) External fault

[0084] When a phase-A ground fault occurs outside the designated area on the line, the protection operation is as follows: Figure 8 As shown, neither the phase differential protection nor the zero-sequence differential protection for phase A under low braking operates. The high voltage, low power factor, and non-faulty phase identification criterion is released after 5ms. Based on the overall judgment, the phase A protection is reliable and does not operate. Similarly, neither the phase differential protection nor the zero-sequence differential protection for phases B and C under low braking operates, and the high voltage, low power factor, and non-faulty phase identification criterion remains blocked. Therefore, the phase B and C protections are reliable and do not operate.

[0085] Based on the same inventive concept, this invention also provides a device 900 for constructing a highly sensitive differential protection criterion based on high voltage and low cosine value, such as... Figure 9 As shown, it includes:

[0086] The cosine value calculation unit 910 is used to obtain the sum of voltage phasors on both sides of the line; and to calculate the cosine value using the angle between the sum of voltage phasors and the differential current phasor.

[0087] The non-faulty phase identification criterion construction unit 920 is used to construct the non-faulty phase identification criterion based on the voltage phasor sum and cosine value.

[0088] The low braking phase differential protection criterion construction unit 930 is used to construct the low braking phase differential protection criterion based on the differential current amplitude and the low braking phase differential protection setting.

[0089] Zero-sequence differential protection criterion construction unit 940 is used to construct zero-sequence differential protection criterion based on the zero-sequence differential current amplitude and the zero-sequence differential protection braking current setting.

[0090] The high-sensitivity differential protection criterion construction unit 950 is used to construct a high-sensitivity differential protection criterion from the identification criterion of the non-faulty phase, the low braking phase differential protection criterion, and the zero-sequence differential protection criterion.

[0091] This invention provides a method and apparatus for constructing a highly sensitive differential protection criterion based on high voltage and low cosine value. It can reliably identify non-faulty phases during high transition resistance faults, correctly identify faults inside and outside the fault zone without being affected by weak feeder systems, and reliably operate during fault and non-full-phase oscillation processes. It balances the sensitivity and reliability of differential protection and improves the safe and stable operation level of the system.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for constructing a high-sensitivity differential protection criterion based on a high-voltage low-cosine value, characterized in that, include: Obtain the sum of voltage phasors on both sides of the line; calculate the cosine value using the angle between the sum of voltage phasors and the differential current phasor; Based on the voltage phasor sum and cosine value, a criterion for identifying non-faulty phases is constructed; Based on the differential current amplitude and the differential protection setting of the low braking phase, a criterion for low braking phase differential protection is constructed. Based on the zero-sequence differential current amplitude and the zero-sequence differential protection braking current setting, a zero-sequence differential protection criterion is constructed. A highly sensitive differential protection criterion is constructed based on the identification criteria for the non-faulty phase, the differential protection criterion for the low braking phase, and the differential protection criterion for the zero sequence. Obtain the sum of voltage phasors on both sides of the line, including: wherein: is the line M side phase voltage phasor, is the line N side phase voltage phasor, ; Using the angle between the voltage phasor and the differential current phasor, the cosine value is calculated, including: In the formula: This represents the phasor value of the line differential current. , For the M side of the line Phase current phasor For the N side of the line Phase current phasor; Based on the voltage phasor sum and cosine value, a criterion for identifying non-faulty phases is constructed, including: In the formula: This is the rated voltage of the line; Based on the differential current amplitude and the low braking phase differential protection setting, a low braking phase differential protection criterion is constructed, including: The criterion for low braking phase differential protection is: , In the formula: This is the amplitude of the differential current. The setting is for low braking phase differential protection; Based on the zero-sequence differential current amplitude and the zero-sequence differential protection braking current setting, a zero-sequence differential protection criterion is constructed, including: The criterion for zero-sequence differential protection is: , In the formula: This represents the amplitude of the zero-sequence differential current. Set the braking current value for zero-differential protection.

2. The method according to claim 1, characterized in that, Also includes: Based on the aforementioned high-sensitivity differential protection criteria, determine whether a line fault has occurred; Once a line fault is identified, the faulty phase is determined.

3. The method according to claim 2, characterized in that, Based on the aforementioned high-sensitivity differential protection criteria, determine whether a line fault has occurred, including: A line fault is determined when both the low braking phase differential protection criterion and the zero sequence differential protection criterion are met simultaneously.

4. The method according to claim 2, characterized in that, Once a line fault is confirmed, the faulty phase is identified, including: When a line fault occurs, the faulty phase is determined based on the identification criteria of the non-faulty phases.

5. A device for constructing a high-sensitivity differential protection criterion based on high voltage and low cosine value, characterized in that, include: The cosine value calculation unit is used to obtain the sum of voltage phasors on both sides of the line; and to calculate the cosine value using the angle between the sum of voltage phasors and the differential current phasor. The non-faulty phase identification criterion construction unit is used to construct the non-faulty phase identification criterion based on the voltage phasor sum and cosine value. The low braking phase differential protection criterion construction unit is used to construct the low braking phase differential protection criterion based on the differential current amplitude and the low braking phase differential protection setting. The zero-sequence differential protection criterion construction unit is used to construct the zero-sequence differential protection criterion based on the zero-sequence differential current amplitude and the zero-sequence differential protection braking current setting. A high-sensitivity differential protection criterion construction unit is used to construct a high-sensitivity differential protection criterion from the identification criterion of the non-faulty phase, the low braking phase differential protection criterion, and the zero-sequence differential protection criterion. Obtain the sum of voltage phasors on both sides of the line, including: In the formula: For the M side of the line Phase voltage phasors For the N side of the line Phase voltage phasors ; Using the angle between the voltage phasor and the differential current phasor, the cosine value is calculated, including: In the formula: This represents the phasor value of the line differential current. , For the M side of the line Phase current phasor For the N side of the line Phase current phasor; Based on the voltage phasor sum and cosine value, a criterion for identifying non-faulty phases is constructed, including: In the formula: This is the rated voltage of the line; Based on the differential current amplitude and the low braking phase differential protection setting, a low braking phase differential protection criterion is constructed, including: The criterion for low braking phase differential protection is: , In the formula: This is the amplitude of the differential current. The setting is for low braking phase differential protection; Based on the zero-sequence differential current amplitude and the zero-sequence differential protection braking current setting, a zero-sequence differential protection criterion is constructed, including: The criterion for zero-sequence differential protection is: , In the formula: This represents the amplitude of the zero-sequence differential current. Set the braking current value for zero-differential protection.

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