Arc suppression coil grounding system single-phase disconnection fault protection method and system

Abstract

The invention discloses a single-phase broken line fault protection method for an arc suppression coil grounding system, and the method comprises the following steps: determining the amplitude threshold value and phase threshold value of the zero-sequence voltage of a line when different types of single-phase broken line fault line protection devices act according to the parameters of the arc suppression coil grounding system; zero-sequence voltage at two ends of the line is monitored and extracted, and whether the zero-sequence voltage at the head end of the line is out-of-limit or not or whether the amplitude difference of the zero-sequence voltage at two ends of the line is larger than a protection starting threshold is judged; if the zero-sequence voltage at the head end of the line is out-of-limit or the amplitude difference of the zero-sequence voltages at the two ends of the line is larger than a protection starting threshold value, starting a protection device, and calculating the amplitude ratio and phase difference of the zero-sequence voltages at the two ends of the line by taking the zero-sequence voltage at the head end of the line as reference; and judging whether the amplitude ratio and the phase difference of the zero-sequence voltages at the two ends of the line are greater than an amplitude threshold or a phase threshold or not, if the conditions are met, determining that the line has a single-phase broken line fault and a protection device acts to cut off the faulty line, otherwise, determining that the fault is an external fault, thereby realizing various single-phase broken line fault protection.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection, and in particular to a single-phase line break fault protection method and system for an arc suppression coil grounding system based on zero-sequence voltage amplitude and phase characteristics. Background Art

[0002] Relay protection is one of the most effective measures to improve the power supply stability of the distribution network. In the arc suppression coil grounding system, factors such as severe climate and external mechanical forces can easily damage weak insulation parts, resulting in single-phase line break faults. Single-phase line break faults are often accompanied by conductors falling to the ground, forming a single-phase line break and grounding composite fault, which includes three types: single-phase line break plus power side grounding fault, single-phase line break plus load side grounding fault, and single-phase line break plus two-side grounding fault. Single-phase line break faults in the arc suppression coil grounding system will cause the system to operate in a phase-loss state, and the step voltage threat generated by the line break and grounding may cause damage to electrical equipment, forest fires, and electric shock accidents.

[0003] For many years, ground fault protection has received considerable attention, while research on line break faults has been relatively insufficient. Given the different characteristics of ground faults and line break faults, protection methods cannot replace each other. At the same time, distribution networks lack protection equipment specifically designed for line break faults. In arc suppression coil-grounded distribution networks, the compensating effect of the arc suppression coil significantly reduces the line break fault current. Combined with the complex and diverse types of single-phase line break faults, these factors exacerbate the difficulty of implementing line break protection. Existing single-phase line break fault protection methods are primarily based on phase voltage information. They can implement single-phase line break without grounding or single-phase line break with single-side grounding protection. However, they can only handle specific or partial types of single-phase line break faults, resulting in low protection reliability. Furthermore, this method carries the risk of refusal to operate when the transition resistance fluctuates over a wide range, and its applicability to distributed power generation access scenarios requires further verification. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that the existing technology cannot be applied to various types of single-phase line break faults and is prone to failure under extreme working conditions. A single-phase line break fault protection method and system are provided for an arc suppression coil grounding system. By combining the zero-sequence voltage amplitude and phase characteristics upstream and downstream of the fault point, a longitudinal protection criterion is constructed to form a protection scheme suitable for various types of single-phase line break faults in the arc suppression coil grounding system. It can still remain reliable under working conditions such as fault location changes, load fluctuations, arc suppression coil compensation adjustment and transition resistance changes, and can be effectively applied to distribution networks with a high proportion of distributed power sources.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A single-phase line break fault protection method for an arc suppression coil grounding system includes the following steps:

[0007] S1: Determine the amplitude threshold and phase threshold of the line zero-sequence voltage when the line protection device operates for different types of single-phase disconnection faults based on the arc suppression coil grounding system parameters;

[0008] S2: Monitor and extract the zero-sequence voltage at both ends of the line to determine whether the zero-sequence voltage at the line head end exceeds the limit, or whether the zero-sequence voltage amplitude difference at both ends of the line is greater than the protection start threshold;

[0009] S3: If the zero-sequence voltage at the line head end exceeds the limit, or the zero-sequence voltage amplitude difference at both ends of the line is greater than the protection start threshold, the protection device is activated and the amplitude ratio and phase difference of the zero-sequence voltage at both ends of the line are calculated with the zero-sequence voltage at the line head end as a reference;

[0010] S4: Determine whether the amplitude ratio and phase difference of the zero-sequence voltage at both ends of the line are greater than the amplitude threshold or phase threshold. If the conditions are met, it is determined that a single-phase disconnection fault has occurred in the line, and the protection device is activated to cut off the faulty line. Otherwise, it is determined to be an external fault.

[0011] Furthermore, in step S1, the amplitude threshold and phase threshold of the line zero-sequence voltage when the line protection device for different types of single-phase disconnection faults is actuated are determined according to the arc suppression coil grounding system parameters, specifically:

[0012] According to the circuit topology of the arc suppression coil grounding system, the symmetrical component method is used to construct a composite sequence network diagram for single-phase line break without grounding, single-phase line break plus power side grounding, single-phase line break plus load side grounding, and single-phase line break plus two-side grounding faults. The amplitude and phase of the zero-sequence voltage ratio downstream and upstream of the fault point for different types of single-phase line break faults are solved, and the minimum values of the amplitude and phase of the zero-sequence voltage ratio downstream and upstream of the fault point for different types of single-phase line break faults are obtained. The amplitude threshold and phase threshold of the line zero-sequence voltage that meet the action of the line protection device for different types of single-phase line break faults under extreme conditions are determined.

[0013] Furthermore, the zero-sequence voltage ratio between the downstream and upstream of the fault point is solved for the single-phase disconnected line and ungrounded fault. The formula is:

[0014]

[0015] Where, is the zero-sequence voltage upstream of the fault point; is the zero-sequence voltage downstream of the fault point; ω is the system angular frequency; C j0Σ is the total zero-sequence capacitance of the non-fault line; C u(0) is the zero-sequence capacitance of the fault line upstream of the fault point; C d(0) is the zero-sequence capacitance of the fault line downstream of the fault point; L p is the arc suppression coil inductance;

[0016] Arc suppression coil inductance L pThe expression is:

[0017] L p =1 / 3ω 2 C 0Σ (1-v)

[0018] Where, v is the detuning degree of the arc suppression coil; C 0Σ is the total zero-sequence capacitance of all lines;

[0019] The amplitude K sg and phase θ sg for:

[0020]

[0021] To solve the zero-sequence voltage amplitude ratio downstream and upstream of the fault point when a single-phase line is broken and a ground fault occurs on the power supply side, the formula is:

[0022]

[0023] Where R f1 is the transition resistance at the grounding point on the power supply side;

[0024] The amplitude K sg and phase θ sg for

[0025]

[0026] Furthermore, the zero-sequence voltage amplitude ratio downstream and upstream of the fault point when a single-phase line is broken and a load-side ground fault occurs is solved. The formula is:

[0027]

[0028] Where R f2 is the transition resistance at the load side grounding point; Z Dn(2) is the load impedance;

[0029] The amplitude K lg and phase θ lg for:

[0030]

[0031] Where α is the load power factor angle.

[0032] Furthermore, the zero-sequence voltage amplitude ratio of the downstream and upstream of the fault point is calculated when a single-phase line is broken and a ground fault occurs on both sides. The formula is:

[0033]

[0034] The amplitude K tg and phase θ tg for:

[0035]

[0036] where θ t The expression is:

[0037]

[0038] Furthermore, according to the amplitude and phase of the zero-sequence voltage ratio downstream and upstream of the fault point during different types of single-phase line break faults, the amplitude threshold and phase threshold of the line zero-sequence voltage when the line protection device is activated are determined according to:

[0039] Amplitude threshold K set Through single-phase disconnection without grounding, single-phase disconnection plus power supply side grounding and R f1 ≤2R f2 +3|Z Dn(2) The minimum value of the zero-sequence voltage amplitude ratio downstream and upstream of the fault point in the single-phase disconnection plus the grounding fault on both sides at |cosα is determined. When the fault occurs at the head end of the line, the transition resistance R f1 In the extreme case where the zero-sequence voltage is zero and there is only one non-fault line, the amplitude ratio of the zero-sequence voltage reaches the minimum, and this value is determined as the amplitude threshold;

[0040] Phase threshold θ set According to the single-phase disconnection load side grounding and R f1 >2R f2 +3|Z Dn(2) The minimum phase difference between the zero-sequence voltages downstream and upstream of the fault point in a single-phase line break plus a ground fault on both sides at |cosα is determined. When the fault occurs at the head end of the line, R f1 When the maximum value is taken, the zero-sequence voltage phase difference is the smallest, and this value is used as the standard for determining the zero-sequence voltage phase threshold.

[0041] Furthermore, in step S2, the zero-sequence voltage at both ends of the line is monitored and extracted to determine whether the zero-sequence voltage at the line head end exceeds the limit, or whether the zero-sequence voltage amplitude difference at both ends of the line is greater than the protection start threshold. The process is as follows:

[0042] The protection devices at both ends of the line extract the zero-sequence voltage, calculate the absolute value of the zero-sequence voltage amplitude difference at both ends of the line, and determine whether the protection startup criterion is met, that is, whether the zero-sequence voltage at the head end of the line exceeds the limit, or whether the zero-sequence voltage amplitude difference at both ends of the line is greater than the protection startup threshold. The protection startup criterion is:

[0043] U M(0) >U 0,set or|U M(0) -UN(0) |>ΔU 0,set

[0044] Where U M(0) It is the zero sequence voltage extracted by the line head end protection device; U N(0) It is the zero sequence voltage extracted by the line end protection device; U 0,set is the threshold for voltage over-limit startup; ΔU 0,set is the starting threshold of the zero-sequence voltage amplitude difference.

[0045] Furthermore, in step S3, after the protection device is activated, the amplitude ratio and phase difference of the zero-sequence voltages at both ends of the line are calculated with the zero-sequence voltage at the line head end as a reference, and the expression is:

[0046]

[0047] Where K MN is the zero-sequence voltage amplitude ratio at both ends of the line; θ MN is the zero-sequence voltage amplitude difference at both ends of the line.

[0048] Furthermore, in step S4, it is determined whether the amplitude ratio and phase difference of the zero-sequence voltage at both ends of the line are greater than the amplitude threshold or the phase threshold. The protection action criterion is:

[0049] K MN >K set orθ MN >θ set

[0050] Where K set is the determined amplitude threshold; θ set is the determined phase threshold;

[0051] When the protection action criteria are met, the line section is determined as the section where a single-phase line break fault occurs within the zone, and the protection device operates to isolate the faulty line. Otherwise, it is determined to be an out-of-zone fault, and the line protection device does not operate.

[0052] A single-phase line break fault protection system for an arc suppression coil grounding system, applied to any of the above-mentioned single-phase line break fault protection methods for an arc suppression coil grounding system, comprising:

[0053] A protection threshold determination module is used to determine the amplitude threshold and phase threshold of the line zero-sequence voltage when the line protection device is activated for different types of single-phase disconnection faults based on the arc suppression coil grounding system parameters;

[0054] The data monitoring and extraction module is used to monitor the three-phase voltage at both ends of the line and calculate the zero-sequence voltage at both ends of the line based on the three-phase voltage waveform data at both ends of the line;

[0055] The protection start module is used to determine whether the zero-sequence voltage at the head end of the line exceeds the limit or whether the difference in the zero-sequence voltage amplitude at the two ends of the line is greater than the protection start threshold based on the zero-sequence voltage at both ends of the line. If the conditions are met, the protection device is started;

[0056] The fault judgment module is used to calculate the amplitude ratio and phase difference of the zero-sequence voltage at both ends of the line based on the zero-sequence voltage at the line head end, determine whether a single-phase disconnection fault has occurred in the line, and choose whether to send a protection trip signal;

[0057] The protection trip module is used to receive the protection trip signal, control the circuit breaker to trip, cut off the fault line, and realize all types of single-phase line break fault protection under various extreme conditions.

[0058] Compared with the existing technology, the longitudinal protection method proposed in the present invention can solve the protection problems of all types of single-phase line break faults, and analyzes the operating conditions of various fault types under extreme conditions. It can achieve rapid protection for single-phase line break ungrounded and line break grounded composite faults, while the existing methods can only target some of these fault types and are not reliable enough.

[0059] The present invention adopts a protection scheme that combines the zero-sequence voltage amplitude and phase to construct a protection scheme. It will not fail when the fault location, load, arc suppression coil compensation degree and transition resistance change widely. It is even applicable in scenarios where the line is broken and arc grounding occurs. It has high reliability and a wide range of application scenarios.

[0060] This invention uses a zero-sequence voltage ratio as its criterion, ensuring accurate protection regardless of the location and capacity of distributed power sources. It is suitable for modern distribution networks with a high proportion of distributed power sources. Requiring only zero-sequence voltage, this method requires minimal signal processing complexity and sampling frequency, resulting in a simple principle and easy implementation. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 The figure is a flow chart of the single-phase line break fault protection method for arc suppression coil grounding system.

[0062] Figure 2 This is a schematic diagram of a single-phase line break fault in the arc suppression coil grounding system.

[0063] Figure 3 Based on Figure 2 The obtained composite sequence network diagram of single-phase line break fault in arc suppression coil grounding system.

[0064] Figure 4 Schematic diagram of a 10kV arc suppression coil grounding system model with T-connected branches and loads based on RTDS.

[0065] Figure 5 This is a schematic diagram of the zero-sequence voltage action waveform when a single-phase line break and no grounding fault occurs at the fault point f2.

[0066] Figure 6 This is a schematic diagram of the zero-sequence voltage action waveform when a single-phase line break and no grounding fault occurs at the fault point f3.

[0067] Figure 7 The figure is a schematic diagram of the zero-sequence voltage waveform when a single-phase line is disconnected and a power-side ground fault occurs with a transition resistance of 500Ω at the power-side grounding point.

[0068] Figure 8 This is a schematic diagram of the zero-sequence voltage waveform when a single-phase line is broken and a power-side ground fault occurs when the transition resistance at the power-side grounding is 800Ω.

[0069] Figure 9 This is a schematic diagram of the zero-sequence voltage waveform when a single-phase line is disconnected and a load-side grounding fault occurs with a transition resistance of 500Ω at the load-side grounding point.

[0070] Figure 10 The figure is a schematic diagram of the zero-sequence voltage waveform when a single-phase line is broken and a load-side grounding fault occurs with a transition resistance of 800Ω at the load-side grounding point.

[0071] Figure 11 This is a schematic diagram of the zero-sequence voltage waveform when a single-phase line break plus a two-side ground fault occurs with a transition resistance of 500Ω at the power side grounding point and the load side grounding point.

[0072] Figure 12 This is a schematic diagram of the zero-sequence voltage waveform when a single-phase line break plus a two-side ground fault occurs with a transition resistance of 800Ω at the power side grounding point and the load side grounding point.

[0073] Figure 13 This is a schematic diagram of the zero-sequence voltage action waveform when a single-phase line break and no grounding occurs during an out-of-zone fault.

[0074] Figure 14 This is a schematic diagram of the zero-sequence voltage action waveform when a single-phase line is broken and a ground fault occurs on the power supply side during an out-of-zone fault.

[0075] Figure 15 This is a schematic diagram of the zero-sequence voltage action waveform when a single-phase line is broken and a load-side grounding fault occurs during an out-of-zone fault.

[0076] Figure 16 This is a schematic diagram of the zero-sequence voltage action waveform when a single-phase line is broken and grounding faults occur on both sides during an out-of-zone fault. DETAILED DESCRIPTION

[0077] The single-phase line break fault protection method of the arc suppression coil grounding system of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0078] See also Figure 1The present invention discloses a single-phase line break fault protection method for an arc suppression coil grounding system, comprising the following steps:

[0079] S1: Determine the amplitude threshold and phase threshold of the line zero-sequence voltage when the line protection device operates for different types of single-phase disconnection faults based on the arc suppression coil grounding system parameters;

[0080] S2: Monitor and extract the zero-sequence voltage at both ends of the line to determine whether the zero-sequence voltage at the line head end exceeds the limit, or whether the zero-sequence voltage amplitude difference at both ends of the line is greater than the protection start threshold;

[0081] S3: If the zero-sequence voltage at the line head exceeds the limit, or the zero-sequence voltage amplitude difference at both ends of the line is greater than the protection start threshold, the protection device is activated and the amplitude ratio and phase difference of the zero-sequence voltage at both ends of the line are calculated with the zero-sequence voltage at the line head as a reference;

[0082] S4: Determine whether the amplitude ratio and phase difference of the zero-sequence voltage at both ends of the line are greater than the amplitude threshold or phase threshold. If the conditions are met, it is determined that a single-phase disconnection fault has occurred in the line, and the protection device is activated to cut off the faulty line. Otherwise, it is determined to be an external fault.

[0083] In step S1, based on the arc suppression coil grounding system parameters, the amplitude threshold and phase threshold of the line zero-sequence voltage when the line protection device for different types of single-phase disconnection faults is actuated are determined, specifically:

[0084] According to the circuit topology of the arc suppression coil grounding system, the symmetrical component method is used to construct a composite sequence network diagram for single-phase line break without grounding, single-phase line break plus power side grounding, single-phase line break plus load side grounding, and single-phase line break plus two-side grounding faults. The amplitude and phase of the zero-sequence voltage ratio downstream and upstream of the fault point for different types of single-phase line break faults are solved, and the minimum values of the amplitude and phase of the zero-sequence voltage ratio downstream and upstream of the fault point for different types of single-phase line break faults are obtained. The amplitude threshold and phase threshold of the line zero-sequence voltage that meet the requirements for the action of the line protection device for different types of single-phase line break faults under extreme conditions are determined.

[0085] See also Figure 2 and Figure 3 , Figure 3 The middle switches K1 and K2 are both disconnected, which is the composite sequence network diagram of a single-phase disconnection fault in the arc suppression coil grounding system. The zero-sequence voltage ratio of the downstream and upstream of the fault point in the case of a single-phase disconnection fault is obtained by solving the formula:

[0086]

[0087] Where, is the zero-sequence voltage upstream of the fault point; is the zero-sequence voltage downstream of the fault point; ω is the system angular frequency; C j0Σ is the total zero-sequence capacitance of the non-fault line; Cu(0) is the zero-sequence capacitance of the fault line upstream of the fault point; C d(0) is the zero-sequence capacitance of the fault line downstream of the fault point; L p is the arc suppression coil inductance;

[0088] Arc suppression coil inductance L p The expression is:

[0089] L p =1 / 3ω 2 C 0Σ (1-v)

[0090] Where, v is the detuning degree of the arc suppression coil; C 0Σ is the total zero-sequence capacitance of all lines;

[0091] The amplitude K sg and phase θ sg for:

[0092]

[0093] See also Figure 2 and Figure 3 , Figure 3 When the middle switch K1 is closed and K2 is open, the composite sequence network diagram of the arc suppression coil grounding system with a single-phase line break plus a power supply side grounding fault is obtained. The zero-sequence voltage amplitude ratio downstream and upstream of the fault point when the single-phase line break plus the power supply side grounding fault occurs is obtained by solving the formula:

[0094]

[0095] Where R f1 is the transition resistance at the grounding point on the power supply side;

[0096] The amplitude K sg and phase θ sg for

[0097]

[0098] See also Figure 2 and Figure 3 , Figure 3 When the middle switch K1 is open and K2 is closed, the composite sequence network diagram of the single-phase disconnection and load-side grounding fault in the arc suppression coil grounding system is obtained. The zero-sequence voltage amplitude ratio of the downstream and upstream of the fault point in the case of a single-phase disconnection and load-side grounding fault is obtained by solving the formula:

[0099]

[0100] Where R f2 is the transition resistance at the load side grounding point; Z Dn(2)is the load impedance;

[0101] The amplitude K lg and phase θ lg for:

[0102]

[0103] Where α is the load power factor angle.

[0104] See also Figure 2 and Figure 3 , Figure 3 When switches K1 and K2 are closed, the composite sequence network diagram of a single-phase line break plus a ground fault on both sides of the arc suppression coil grounding system is obtained. The zero-sequence voltage amplitude ratio of the downstream and upstream of the fault point when a single-phase line break plus a ground fault on both sides is obtained. The formula is:

[0105]

[0106] The amplitude K tg and phase θ tg for:

[0107]

[0108] where θ t The expression is:

[0109]

[0110] According to the amplitude and phase of the zero-sequence voltage ratio downstream and upstream of the fault point during different types of single-phase line break faults, the amplitude threshold and phase threshold of the line zero-sequence voltage when the line protection device is activated are determined according to the following:

[0111] Amplitude threshold K set Through single-phase disconnection without grounding, single-phase disconnection plus power supply side grounding and R f1 ≤2R f2 +3|Z Dn(2) The minimum value of the zero-sequence voltage amplitude ratio downstream and upstream of the fault point in the case of a single-phase line break plus a ground fault on both sides at |cosα is determined. In these cases, the zero-sequence voltage amplitude downstream of the fault point is always greater than the zero-sequence voltage amplitude upstream of the fault point, with a significant amplitude characteristic. When the fault occurs at the head end of the line, the transition resistance R f1 In the extreme case where the zero-sequence voltage amplitude ratio is zero and there is only one non-fault line, the amplitude ratio of the zero-sequence voltage under these three fault conditions reaches the minimum, and this value is determined as the amplitude threshold. In this embodiment, the minimum value of the zero-sequence voltage amplitude ratio is 1.45. Considering a certain error and margin, the amplitude threshold K can be taken as set =1.4.

[0112] Phase threshold θ set According to the single-phase disconnection load side grounding and R f1 >2R f2 +3|Z Dn(2) The minimum phase difference between the zero-sequence voltages downstream and upstream of the fault point in the case of a single-phase line break plus a ground fault on both sides at |cosα is determined. In these two cases, the single-phase line break fault has obvious phase characteristics. When the fault occurs at the head end of the line, R f1 When the maximum value is taken, the zero-sequence voltage phase difference is the smallest, and this value is used as the standard for determining the zero-sequence voltage phase threshold.

[0113] According to the above phase solution formula, the phase difference between the downstream and upstream zero-sequence voltages in a single-phase line break plus a load-side grounding fault is within the range of (70°, 90°+α), and the phase difference between the downstream and upstream zero-sequence voltages in a single-phase line break plus a two-side grounding fault is within the range of (90°, 270°+α). Considering the influence of line impedance and measurement error, the phase threshold θ set Can be set to 50°.

[0114] Note that in the case of an out-of-zone fault, the zero-sequence voltage amplitudes upstream and downstream of the fault point are equal, and the phase difference is 0°.

[0115] In step S2, the zero-sequence voltage at both ends of the line is monitored and extracted to determine whether the zero-sequence voltage at the line head end exceeds the limit, or whether the zero-sequence voltage amplitude difference at both ends of the line is greater than the protection start threshold. The process is as follows:

[0116] The protection devices at both ends of the line extract the zero-sequence voltage, calculate the absolute value of the zero-sequence voltage amplitude difference at both ends of the line, and determine whether the protection startup criterion is met, that is, whether the zero-sequence voltage at the head end of the line exceeds the limit, or whether the zero-sequence voltage amplitude difference at both ends of the line is greater than the protection startup threshold. The protection startup criterion is:

[0117] U M(0) >U 0,set or|U M(0) -U N(0) |>ΔU 0,set

[0118] Where U M(0) It is the zero sequence voltage extracted by the line head end protection device; U N(0) The zero-sequence voltage extracted by the line end protection device can be set according to the maximum unbalanced voltage under normal conditions, which can be taken as 0.1U N , U N is the rated phase voltage; U 0,set is the threshold for voltage over-limit startup; ΔU 0,set It is the starting threshold of the zero-sequence voltage amplitude difference, which must be greater than the maximum zero-sequence voltage that appears on the line impedance when the three phases are unbalanced. It can be taken as 0.01UN .

[0119] In step S3, after the protection device is activated, the amplitude ratio and phase difference of the zero-sequence voltages at both ends of the line are calculated with the zero-sequence voltage at the line head end as a reference, and the phase difference is taken as the absolute value, and the expression is:

[0120]

[0121] Where K MN is the zero-sequence voltage amplitude ratio at both ends of the line; θ MN is the zero-sequence voltage amplitude difference at both ends of the line.

[0122] In step S4, it is determined whether the amplitude ratio and phase difference of the zero-sequence voltage at both ends of the line are greater than the amplitude threshold or the phase threshold. The protection action criterion is:

[0123] K MN >K set orθ MN >θ set

[0124] Where K set is the determined amplitude threshold; θ set is the determined phase threshold;

[0125] When the zero-sequence voltage amplitude and phase characteristics of a single-phase line break fault meet the protection action criteria, the line section is determined to be the section where the single-phase line break fault occurs within the zone, and the protection device operates to isolate the faulty line. When both the amplitude and phase characteristics do not meet the protection action criteria, it is determined to be an out-of-zone fault, and the line protection device does not operate.

[0126] In order to verify the proposed method for single-phase line-break fault longitudinal protection of arc suppression coil grounding system based on zero-sequence voltage amplitude and phase characteristics, a closed-loop dynamic simulation test experimental environment was established based on RTDS and the developed protection device. A 10kV arc suppression coil grounding system model considering T-connected branches and loads was constructed on the RTDS platform. Figure 4 As shown, the line is divided into three sections: BM, MN, and NQ. PD1, PD2, PD3, and PD4 serve as protection devices. The arc suppression coils are overcompensated by 8%. Table 1 lists the system and overhead line parameters set in the model. Fault point f1 is located 1 km from busbar B, and fault point f4 is located 1 km from busbar Q. Fault points f2 and f3 in the MN feeder section are located 1 km and 3 km from busbar M, respectively. The focus is on the operation of the protection at both ends of the MN section. Inverter-type distributed generation units IIDG1 and IIDG2 will be connected to the grid to verify the reliability of line break protection in a distribution network containing distributed generation units.

[0127] Table 1 Line and system parameters

[0128] parameter Value parameter Value Line positive sequence impedance per unit length 0.17+j0.35Ω / km Length of BM, MN, NQ 3km, 4km, 3km Line positive sequence capacitance per unit length 11.5μF Line branch 1 length 2km Line zero-sequence impedance per unit length 0.32+j1.12Ω / km Load1~Load3 capacity 6+j1.97 MVA Zero-sequence capacitance per unit length of line 0.0062μF

[0129] Figures 5 to 12 The zero-sequence voltage waveforms at MN under four different types of single-phase line failure are given in various situations. Figure 6 The rest of the figures show that the faults occurred in Figure 4 The result at f2. Figure 5 This is the result of a single-phase disconnection and ungrounded fault at f2. Figure 6 This is the result of a single-phase disconnection and ungrounded fault at f3. Figure 7 For single-phase disconnection and ground fault on the power supply side, f1 Result when =500Ω. Figure 8 For single-phase disconnection and ground fault on the power supply side, f1 Result when =800Ω.

[0130] Figure 9 For single-phase disconnection and load side ground fault, f2 Result when =500Ω. Figure 10 For single-phase disconnection and load side ground fault, f2 Result when =800Ω. Figure 11 For single-phase disconnection plus ground fault on both sides, f1 =R f2 =500Ω, Figure 12 For single-phase disconnection plus ground fault on both sides, f1 =R f2 The results show that under the influence of different fault locations, transition resistance and other factors, the four types of single-phase line-break fault protection can accurately identify internal faults and operate quickly.

[0131] Figure 13 F4 fault and R f1 =R f2 =500Ω when the single-phase disconnection and ungrounded fault occurs. Figure 14 F4 fault and R f1 =R f2 =500Ω when a single-phase line break plus a ground fault on the power supply side occurs. Figure 15 F4 fault and R f1 =R f2 =500Ω when a single-phase line break and a load-side ground fault occur. Figure 16 F4 fault and R f1 =R f2 =500Ω, a single-phase line break plus a ground fault on both sides. It can be seen that the protection devices on both sides of MN do not malfunction, and the circuit breaker remains closed during the external fault.

[0132] In addition, multiple different tests were conducted at fault points f1 to f4 and at different transition resistances, and arc grounding was also tested. Table 2 lists the action results of the protection at MN under four different single-phase line break faults. All the results in Table 2 show that K MN >1.4 or θ MN >50°, and K in case of external fault MN and θ MN They are close to 1° and 0° respectively. The protection action is accurate.

[0133] Table 2 Protection action results under different fault locations and transition resistances

[0134]

[0135]

[0136] In order to reveal the impact of T-connected IIDG on the conservation protection method, Figure 5 In this example, IIDG1 and IIDG2 are connected at distances M and N, 1 km apart, with rated capacities of 3 MW and 4.5 MW, respectively. The fault occurs at point f2. The experimental results of the protection scheme under the influence of the IIDGs are shown in Table 3. The results in Table 3 show that the IIDGs do not affect the zero-sequence voltage ratio. Even when the zero-sequence voltages at both ends of segment MN differ significantly in amplitude or phase, the protection still trips accurately.

[0137] Table 3 Protection action when IIDG is connected

[0138]

[0139] Based on the same inventive concept, the present invention also proposes a single-phase line break fault protection system for an arc suppression coil grounding system, which is applied to any of the above-mentioned single-phase line break fault protection methods for an arc suppression coil grounding system, comprising:

[0140] A protection threshold determination module is used to determine the amplitude threshold and phase threshold of the line zero-sequence voltage when the line protection device is activated for different types of single-phase disconnection faults based on the arc suppression coil grounding system parameters;

[0141] The data monitoring and extraction module is used to monitor the three-phase voltage at both ends of the line and calculate the zero-sequence voltage at both ends of the line based on the three-phase voltage waveform data at both ends of the line;

[0142] The protection start module is used to determine whether the zero-sequence voltage at the head end of the line exceeds the limit or whether the difference in the zero-sequence voltage amplitude at the two ends of the line is greater than the protection start threshold based on the zero-sequence voltage at both ends of the line. If the conditions are met, the protection device is started;

[0143] The fault judgment module is used to calculate the amplitude ratio and phase difference of the zero-sequence voltage at both ends of the line based on the zero-sequence voltage at the line head end, determine whether a single-phase disconnection fault has occurred in the line, and choose whether to send a protection trip signal;

[0144] The protection trip module is used to receive the protection trip signal, control the circuit breaker to trip, cut off the fault line, and realize all types of single-phase line break fault protection under various extreme conditions.

[0145] In summary, the longitudinal protection method proposed in the present invention can solve all types of single-phase line break fault protection problems, and analyzes the operating conditions of various fault types under extreme conditions. It can achieve rapid protection for single-phase line break ungrounded and line break grounded composite faults, while existing methods can only target some of these fault types and are not reliable enough.

[0146] The present invention adopts a protection scheme that combines the zero-sequence voltage amplitude and phase to construct a protection scheme. It will not fail when the fault location, load, arc suppression coil compensation degree and transition resistance change widely. It is even applicable in scenarios where the line is broken and arc grounding occurs. It has high reliability and a wide range of application scenarios.

[0147] This invention uses a zero-sequence voltage ratio as its criterion, ensuring accurate protection regardless of the location and capacity of distributed power sources. It is suitable for modern distribution networks with a high proportion of distributed power sources. Requiring only zero-sequence voltage, this method requires minimal signal processing complexity and sampling frequency, resulting in a simple principle and easy implementation.

[0148] The above description is a detailed description of the preferred embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. Any equivalent changes or modifications made under the technical spirit disclosed by the present invention should fall within the patent scope covered by the present invention.

Claims

1. A single-phase line break fault protection method for an arc suppression coil grounding system, characterized in that: The following steps are involved: S1: Determine the amplitude threshold and phase threshold of the line zero-sequence voltage when the line protection device operates for different types of single-phase disconnection faults based on the arc suppression coil grounding system parameters; S2: Monitor and extract the zero-sequence voltage at both ends of the line to determine whether the zero-sequence voltage at the line head end exceeds the limit, or whether the zero-sequence voltage amplitude difference at both ends of the line is greater than the protection start threshold; S3: If the zero-sequence voltage at the line head exceeds the limit, or the zero-sequence voltage amplitude difference at both ends of the line is greater than the protection start threshold, the protection device is activated and the amplitude ratio and phase difference of the zero-sequence voltage at both ends of the line are calculated with the zero-sequence voltage at the line head as a reference; S4: Determine whether the amplitude ratio and phase difference of the zero-sequence voltage at both ends of the line are greater than the amplitude threshold or phase threshold. If the conditions are met, it is determined that a single-phase disconnection fault has occurred in the line, and the protection device is activated to cut off the faulty line. Otherwise, it is determined to be an external fault.

2. The arc suppression coil grounding system single-phase disconnection fault protection method according to claim 1 is characterized in that: In step S1, based on the arc suppression coil grounding system parameters, the amplitude threshold and phase threshold of the line zero-sequence voltage when the line protection device for different types of single-phase disconnection faults is actuated are determined, specifically: According to the circuit topology of the arc suppression coil grounding system, the symmetrical component method is used to construct a composite sequence network diagram for single-phase line break without grounding, single-phase line break plus power side grounding, single-phase line break plus load side grounding, and single-phase line break plus two-side grounding faults. The amplitude and phase of the zero-sequence voltage ratio downstream and upstream of the fault point for different types of single-phase line break faults are solved, and the minimum values of the amplitude and phase of the zero-sequence voltage ratio downstream and upstream of the fault point for different types of single-phase line break faults are obtained. The amplitude threshold and phase threshold of the line zero-sequence voltage that meet the requirements for the action of the line protection device for different types of single-phase line break faults under extreme conditions are determined.

3. The arc suppression coil grounding system single-phase disconnection fault protection method according to claim 2, characterized in that: To solve the zero-sequence voltage ratio between the downstream and upstream of the fault point when a single-phase line is disconnected and not grounded, the formula is: Where, is the zero-sequence voltage upstream of the fault point; is the zero-sequence voltage downstream of the fault point; ω is the system angular frequency; C j0Σ is the total zero-sequence capacitance of the non-fault line; C u(0) is the zero-sequence capacitance of the fault line upstream of the fault point; C d(0) is the zero-sequence capacitance of the fault line downstream of the fault point; L p is the arc suppression coil inductance; Arc suppression coil inductance L p The expression is: L p =1 / 3ω 2 C 0Σ (1-in) Where, v is the detuning degree of the arc suppression coil; C 0Σ is the total zero-sequence capacitance of all lines; The amplitude K sg and phase θ sg for: To solve the zero-sequence voltage amplitude ratio downstream and upstream of the fault point when a single-phase line is broken and a ground fault occurs on the power supply side, the formula is: Where R f1 is the transition resistance at the grounding point on the power supply side; The amplitude K sg and phase θ sg for 4. The arc suppression coil grounding system single-phase line break fault protection method according to claim 3, characterized in that: To solve the zero-sequence voltage amplitude ratio downstream and upstream of the fault point when a single-phase line is broken and a load-side ground fault occurs, the formula is: Where R f2 is the transition resistance at the load side grounding point; Z Dn(2) is the load impedance; The amplitude K lg and phase θ lg for: Where α is the load power factor angle.

5. The arc suppression coil grounding system single-phase line break fault protection method according to claim 4, characterized in that: Calculate the zero-sequence voltage amplitude ratio downstream and upstream of the fault point when a single-phase line is broken and a ground fault occurs on both sides. The formula is: The amplitude K tg and phase θ tg for: where θ t The expression is:

6. The arc suppression coil grounding system single-phase disconnection fault protection method according to claim 5, characterized in that: According to the amplitude and phase of the zero-sequence voltage ratio downstream and upstream of the fault point during different types of single-phase line break faults, the amplitude threshold and phase threshold of the line zero-sequence voltage when the line protection device is activated are determined according to the following: Amplitude threshold K set Through single-phase disconnection without grounding, single-phase disconnection plus power supply side grounding and R f1 ≤2R f2 +3|Z Dn(2) The minimum value of the zero-sequence voltage amplitude ratio downstream and upstream of the fault point in the single-phase disconnection plus the grounding fault on both sides at |cosα is determined. When the fault occurs at the head end of the line, the transition resistance R f1 In the extreme case where the zero-sequence voltage is zero and there is only one non-fault line, the amplitude ratio of the zero-sequence voltage reaches the minimum, and this value is determined as the amplitude threshold; Phase threshold θ set According to the single-phase disconnection load side grounding and R f1 >2R f2 +3|Z Dn(2) The minimum phase difference between the zero-sequence voltages downstream and upstream of the fault point in a single-phase line break plus a ground fault on both sides at |cosα is determined. When the fault occurs at the head end of the line, R f1 When the maximum value is taken, the zero-sequence voltage phase difference is the smallest, and this value is used as the standard for determining the zero-sequence voltage phase threshold.

7. The arc suppression coil grounding system single-phase disconnection fault protection method according to claim 1, characterized in that: In step S2, the zero-sequence voltage at both ends of the line is monitored and extracted to determine whether the zero-sequence voltage at the line head end exceeds the limit, or whether the zero-sequence voltage amplitude difference at both ends of the line is greater than the protection start threshold. The process is as follows: The protection devices at both ends of the line extract the zero-sequence voltage, calculate the absolute value of the zero-sequence voltage amplitude difference at both ends of the line, and determine whether the protection startup criterion is met, that is, whether the zero-sequence voltage at the head end of the line exceeds the limit, or whether the zero-sequence voltage amplitude difference at both ends of the line is greater than the protection startup threshold. The protection startup criterion is: U M(0) >U 0,set or|U M(0) -U N(0) |>ΔU 0,set Where U M(0) It is the zero sequence voltage extracted by the line head end protection device; U N(0) It is the zero sequence voltage extracted by the line end protection device; U 0,set The threshold for voltage over-limit startup; ΔU 0,set is the starting threshold of the zero-sequence voltage amplitude difference.

8. The arc suppression coil grounding system single-phase line break fault protection method according to claim 7, characterized in that: In step S3, after the protection device is activated, the amplitude ratio and phase difference of the zero-sequence voltages at both ends of the line are calculated with the zero-sequence voltage at the line head end as a reference. The expression is: Where K MN is the zero-sequence voltage amplitude ratio at both ends of the line; θ MN is the zero-sequence voltage amplitude difference at both ends of the line.

9. The arc suppression coil grounding system single-phase disconnection fault protection method according to claim 8, characterized in that: In step S4, it is determined whether the amplitude ratio and phase difference of the zero-sequence voltage at both ends of the line are greater than the amplitude threshold or the phase threshold. The protection action criterion is: K MN >K set orth MN >θ set Where K set is the determined amplitude threshold; θ set is the determined phase threshold; When the protection action criteria are met, the line section is determined as the section where a single-phase line break fault occurs within the zone, and the protection device operates to isolate the faulty line. Otherwise, it is determined to be an out-of-zone fault, and the line protection device does not operate.

10. A single-phase line break fault protection system for arc suppression coil grounding system, characterized in that: The single-phase line break fault protection method for an arc suppression coil grounding system according to any one of claims 1 to 9 comprises: A protection threshold determination module is used to determine the amplitude threshold and phase threshold of the line zero-sequence voltage when the line protection device is activated for different types of single-phase disconnection faults based on the arc suppression coil grounding system parameters; The data monitoring and extraction module is used to monitor the three-phase voltage at both ends of the line and calculate the zero-sequence voltage at both ends of the line based on the three-phase voltage waveform data at both ends of the line; The protection start module is used to determine whether the zero-sequence voltage at the head end of the line exceeds the limit or whether the difference in the zero-sequence voltage amplitude at the two ends of the line is greater than the protection start threshold based on the zero-sequence voltage at both ends of the line. If the conditions are met, the protection device is started; The fault judgment module is used to calculate the amplitude ratio and phase difference of the zero-sequence voltage at both ends of the line based on the zero-sequence voltage at the line head end, determine whether a single-phase disconnection fault has occurred in the line, and choose whether to send a protection trip signal; The protection trip module is used to receive the protection trip signal, control the circuit breaker to trip, cut off the fault line, and realize all types of single-phase line break fault protection under various extreme conditions.

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