Photovoltaic station sending line interphase short circuit fault identification method

Abstract

The invention relates to a photovoltaic station sending line interphase short-circuit fault identification method, which comprises the following steps of: measuring and calculating three-phase power frequency short-circuit current by using a voltage transformer and a current transformer which are arranged at a station side protection M position and a power grid side protection N position when a short-circuit fault occurs in a line, and performing compensation calculation to obtain a full-phase current differential protection function expression; according to a protection action criterion constructed according to line fault characteristics and protection function result differences, three-phase protection is returned without action when an external fault occurs, a fault type and a fault phase are correctly identified through full-phase current differential protection when an internal fault occurs, and the action is correspondingly performed on tripping of a circuit breaker. According to the method, a protection theory which is not influenced by factors such as fault types, fault positions and station capacity is constructed from the principle level, the interphase short circuit fault can be correctly identified, and safe and stable operation of the new energy station and a sending-out line thereof is facilitated.

Description

Technical Field

[0001] The present invention relates to a technology in the field of power grid protection, and specifically to a method for identifying phase-to-phase short-circuit faults in the outgoing lines of photovoltaic power stations. Background Art

[0002] Currently, traditional phase-separated current differential protection is generally adopted as the main protection for the outgoing lines of photovoltaic power stations. The traditional phase-separated current differential protection relies on constructing a ratio criterion with differential current and restraint current, and its essence is affected by the amplitude ratio and phase angle difference of the short-circuit currents of the faulty phases on both sides of the line. However, affected by factors such as converter control strategies, fault types, fault locations, and station capacities, the amplitude ratio and phase angle difference of the short-circuit currents of the faulty phases on both sides will show large distortions in different fault scenarios, resulting in a decrease in the sensitivity of the traditional phase-separated current differential protection and even facing the risk of refusal to operate. Summary of the Invention

[0003] Aiming at the problem of reduced sensitivity of traditional phase-differential protection for the outgoing lines of new energy power stations, the present invention proposes a method for identifying phase-to-phase short-circuit faults in the outgoing lines of photovoltaic power stations, constructs a protection theory that is not affected by factors such as fault types, fault locations, and station capacities at the principle level, can correctly identify phase-to-phase short-circuit faults, and is conducive to the safe and stable operation of new energy power stations and their outgoing lines.

[0004] The present invention is realized through the following technical solutions:

[0005] The present invention relates to a method for identifying phase-to-phase short-circuit faults in the outgoing lines of photovoltaic power stations. When a short-circuit fault occurs in the line, the voltage transformers and current transformers set at the protection M on the station side and the protection N on the grid side are used to measure and calculate the three-phase power-frequency short-circuit currents, and the full-phase current differential protection function expression is obtained through compensation calculation. According to the protection action criterion constructed based on the line fault characteristics and the difference in the protection function results, when a fault occurs outside the zone, the three-phase protection returns and does not operate, and when a fault occurs inside the zone, the full-phase current differential protection correctly identifies the fault type and the faulty phase and correspondingly operates to trip the circuit breaker.

[0006] The short-circuit fault mentioned above refers to: during normal operation, the magnitude of any phase voltage measured at the protection M on the station side and the protection N on the grid side is within 0.9 p.u. to 1.1 p.u.; when the measured voltage of any phase is lower than 0.9 p.u., that is, |U φ | < 0.9 p.u., it is determined that a short-circuit fault has occurred resulting in a voltage drop, and the protection is started.

[0007] The protection action criterion constructed based on the line fault characteristics and the difference in the protection function results refers to: according to the line fault characteristics, a calculation function for the full-phase current differential protection action criterion is proposed: when a short-circuit fault occurs at point f of the outgoing line, the three-phase power-frequency short-circuit currents at the protection M on the station side are extracted And the three-phase power frequency short-circuit current at the grid-side protection point N Then calculate the criterion expression of the all-phase current differential protection: Where α, β, and γ represent phases A, B, and C, And Are the positive-sequence components of the short-circuit current on both sides of the line, which can be obtained from the three-phase short-circuit current on both sides of the line by the symmetrical component method. By calculating f MA 、f NA 、f MB 、f NB 、f MC 、f NC And comparing their differences, the protection action criterion is constructed, specifically including:

[0008] Under normal operating conditions, the result of the criterion expression is f MA =f NA =f MB =f NB =f MC =f NC =1.

[0009] When a two-phase interphase short-circuit fault occurs in the zone, taking the BC two-phase interphase short-circuit fault as an example, the result of the criterion expression is Where: f MA 、f NA Are the criterion values of phase A based on the positive-sequence current on the substation side and the grid side respectively; f MB 、f NB Are the criterion values of phase B based on the positive-sequence current on the substation side and the grid side respectively; f MC 、f NC Are the criterion values of phase C based on the positive-sequence current on the substation side and the grid side respectively.

[0010] When a three-phase short-circuit fault occurs in the zone, taking the ABC three-phase short-circuit fault as an example, the result of the criterion expression is

[0011] When an external fault occurs, the result of the criterion expression is f MA =f NA =f MB =f NB =f MC =f NC =1, and the protection does not operate.

[0012] When f Mα Or f Nα Is in the interval [0.995, 1.005], it is considered that f Mα =1 or f Nα =1.

[0013] When |fMα -f Mβ | < 0.05 or |f Nα -f Nβ | < 0.05, it is considered that f Mα = f Mβ or f Nα = f Nβ 。 Technical effects

[0014] The present invention uses the three-phase short-circuit currents on the substation side and the power grid side to construct the full-phase current differential protection function expression for compensation calculation, and forms a new protection criterion by comparing the differences in the function results. Compared with the prior art, the full-phase current differential protection expression constructed by the present invention using the three-phase short-circuit currents on the substation side and the power grid side for compensation calculation avoids the influence of the phase angle relationship of the same-phase currents on both sides of the line on the protection performance. The full-phase current differential protection criterion constructed by the present invention can identify the fault location, fault type and fault phase according to the differences in the results of the protection criterion expressions under different interphase short-circuit fault scenarios. Brief description of the drawings

[0015] Figure 1 It is a schematic diagram of the outgoing line model of the new energy substation;

[0016] Figure 2 It is the flow chart of the present invention;

[0017] Figure 3 It is a schematic diagram of the identification result of the two-phase interphase short-circuit fault in the outgoing line area;

[0018] Figure 4 It is a schematic diagram of the identification result of the three-phase short-circuit fault in the outgoing line area;

[0019] Figure 5 It is a schematic diagram of the identification result of the fault outside the outgoing line area. Detailed implementation manners

[0020] As Figure 2 shown, this embodiment relates to a method for identifying interphase short-circuit faults in the outgoing line of a photovoltaic substation. In the scenario as Figure 1 shown, when a short-circuit fault occurs on the line, the three-phase power frequency short-circuit currents are measured and calculated by using the voltage transformers and current transformers installed at the protection M on the substation side and the protection N on the power grid side. After compensation calculation, the full-phase current differential protection function expression is obtained. According to the line fault characteristics and the differences in the protection function results, a protection criterion is constructed to realize that when a fault occurs outside the area, the three-phase protection returns and does not operate, and when a fault occurs inside the area, the full-phase current differential protection correctly identifies the fault type and fault phase, and correspondingly operates to trip the circuit breaker. Specifically, it includes:

[0021] Step 1: Sample and measure the voltage and current at the flexible DC side protection point M in real time, with a sampling frequency of 1.2 kHz.

[0022] Step 2: If the measured value of the phase voltage meets the starting criterion, the protection starts and proceeds to Step 3; otherwise, return to Step 1.

[0023] Step 3: Extract the three-phase power frequency short-circuit currents on both sides and calculate the zero-sequence current on the grid side. If then proceed to Step 4; otherwise, return to Step 1.

[0024] Step 4: Calculate the results f of the three-phase criterion expressions Mα and f Nα . If there is one phase criterion result that satisfies f Nα = 1, proceed to Step 5; otherwise, proceed to Step 6.

[0025] Step 5: Determine whether the phase corresponding to f Nα = 1 satisfies f Mα = 1. If it is satisfied, proceed to Step 7; otherwise, proceed to Step 8.

[0026] Step 6: Determine whether the three-phase criterion satisfies f MA = f MB = f MC and f NA = f NB = f NC . If it is satisfied, proceed to Step 9; otherwise, return to Step 1.

[0027] Step 7: Determine whether the criterion results of the remaining two phases satisfy f Mα = 1 and f Nα = 1. If it is satisfied, proceed to Step 10; otherwise, return to Step 1.

[0028] Step 8: Determine whether the f Mα and f Nα calculated from two adjacent sampling points satisfy f Mα (i) - f Mα (i - 1) < 0.01 p.u. and f Nα (i) - f Nα (i - 1) < 0.01 p.u., and the number of consecutive sampling points that meet the above conditions is not less than 5. If it is satisfied, determine it as an in-zone two-phase interphase short-circuit fault and send a tripping signal to the circuit breaker; otherwise, return to Step 1.

[0029] Step 9: Determine whether the f Mα and f Nα calculated from two adjacent sampling points satisfy f Mα (i) - f Mα (i - 1) < 0.01 p.u. and fNα (i)-f Nα (i - 1) < 0.01 p.u., and the number of consecutive sampling points satisfying the above conditions is not less than 5. If satisfied, it is determined as a three-phase short-circuit fault within the zone, and a tripping signal is sent to the circuit breaker; otherwise, return to step 1.

[0030] Step 10: Determine whether f Mα and f Nα calculated from two adjacent sampling points satisfy f Mα (i)-f Mα (i - 1) < 0.01 p.u. and f Nα (i)-f Nα (i - 1) < 0.01 p.u., and the number of consecutive sampling points satisfying the above conditions is not less than 5. If satisfied, it is determined as an external fault, and the protection is blocked; otherwise, return to step 1.

[0031] Take a transmission line from a certain PV power station in Shanghai Chongming power grid as a verification example, and the topology diagram is as Figure 1 . The PV generator units are connected to the 110 kV step-up transformer (transformer on the substation side) through the 35 kV in-field collection system, and then connected to the receiving power grid through the 110 kV overhead transmission line. According to the above method, the recognition results of BC two-phase interphase short-circuit faults at the fault location of the transmission line are as Figure 3 shown. The present invention can detect internal faults in a timely manner and operate reliably. The recognition results of three-phase short-circuit faults at the fault location of the transmission line are as Figure 4 shown. The present invention can detect internal faults in a timely manner and operate reliably. The recognition results of external faults on the transmission line are as Figure 5 shown. The present invention can detect external faults in a timely manner and not operate reliably.

[0032] In summary, the present invention effectively improves the recognition ability of the transmission line of the new energy substation for interphase short-circuit faults and enhances its safe and stable operation ability.

[0033] The above specific implementation can be locally adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention is subject to the claims and is not limited by the above specific implementation, and all implementation schemes within its scope are restricted by the present invention.

Claims

1. A method for identifying interphase short - circuit faults in the outgoing line of a photovoltaic power station, characterized in that, When a short - circuit fault occurs in the line, the voltage transformers and current transformers set at the substation - side protection M and the grid - side protection N are used to measure and calculate the three - phase power - frequency short - circuit current. After compensation calculation, the full - phase current differential protection function expression is obtained. According to the line fault characteristics and the differences in the protection function results, the protection action criterion is constructed to achieve that the three - phase protection returns and does not act during external faults, and the full - phase current differential protection correctly identifies the fault type and fault phase during internal faults and accordingly acts on the circuit breaker tripping.

2. The method for identifying interphase short - circuit faults in the outgoing line of a photovoltaic power station according to claim 1, characterized in that, The short-circuit fault mentioned above means that during normal operation, the magnitude of any phase voltage measured at the substation-side protection M and the grid-side protection N is within 0.9 p.u. to 1.1 p.u.; when the magnitude of any phase voltage measured is lower than 0.9 p.u., i.e., |U φ | < 0.9 p.u., it is determined that a short-circuit fault has occurred, resulting in a voltage drop, and the protection is activated.

3. The method for identifying interphase short - circuit faults in the outgoing line of a photovoltaic power station according to claim 1, characterized in that, The protection action criterion constructed based on the differences between the line fault characteristics and the protection function results means: According to the line fault characteristics, a calculation function for the full-phase current differential protection action criterion is proposed. When a short-circuit fault occurs at point f on the outgoing line, the three-phase power-frequency short-circuit currents at the protection M on the substation side are extracted and the three-phase power-frequency short-circuit currents at the protection N on the grid side Then, the expression of the full-phase current differential protection criterion is calculated: where: α, β, and γ represent phases A, B, and C, and are the positive-sequence components of the short-circuit currents on both sides of the line, which can be obtained from the three-phase short-circuit currents on both sides of the line by the symmetrical component method. By calculating f MA , f NA , f MB , f NB , f MC , f NC and comparing their differences, the protection action criterion is constructed accordingly.

4. The method for identifying interphase short - circuit faults in the outgoing line of a photovoltaic power station according to claim 1 or 3, characterized in that, The protection action criterion described above specifically includes: Under normal operating conditions, the result of the criterion expression is f MA = f NA = f MB = f NB = f MC = f NC = 1; When a two-phase short-circuit fault occurs in the fault area, taking the BC two-phase short-circuit fault as an example, the result of the criterion expression is where: f MA , f NA are the criterion values of phase A based on the positive-sequence current on the substation side and the grid side respectively; f MB , f NB are the criterion values of phase B based on the positive-sequence current on the substation side and the grid side respectively; f MC , f NC are the criterion values of phase C based on the positive-sequence current on the substation side and the grid side respectively; When a three-phase short-circuit fault occurs in the fault area, taking the ABC three-phase short-circuit fault as an example, the result of the criterion expression is When a fault occurs outside the occurrence area, the result of the criterion expression is f MA = f NA = f MB = f NB = f MC = f NC = 1, and the protection does not operate.

5. The method for identifying interphase short - circuit faults in the outgoing line of a photovoltaic power station according to claim 4, characterized in that, When f Mα or f Nα is in the interval [0.995, 1.005], it is considered that f Mα = 1 or f Nα = 1; when |f Mα - f Mβ | < 0.05 or |f Nα - f Nβ | S 0.05, it is considered that f Mα = f Mβ or f Nα = f Nβ .

6. The method for identifying interphase short - circuit faults in the outgoing line of a photovoltaic power station according to any one of claims 1 - 5, characterized in that, specifically It includes: Step 1: Real - time sample and measure the voltage and current at the flexible - DC - side protection M, and the sampling frequency is 1.2 kHz; Step 2: If the measured value of the phase voltage meets the starting criterion, the protection starts and proceeds to Step 3; otherwise, return to Step 1. Step 3: Extract the three-phase power-frequency short-circuit currents on both sides and calculate the zero-sequence current on the grid side If then go to Step 4; otherwise, return to Step 1 Step 4: Calculate the result f of the three-phase criterion expression Mα and f Nα , if the criterion result of one phase satisfies f Nα = 1, go to Step 5; otherwise go to Step 6; Step 5: Determine whether the corresponding phase where f Nα = 1 meets the condition that f Mα = 1. If it meets the condition, go to Step 7; otherwise, go to Step 8. Step 6: Determine whether the three-phase criterion satisfies f MA = f MB = f MC and f NA = f NB = f NC , if satisfied, go to Step 9, otherwise return to Step 1; Step 7: Determine whether the remaining two-phase criteria satisfy f Mα = 1 and f Nα = 1. If satisfied, go to Step 10; otherwise, return to Step 1. Step 8: Determine whether the f calculated from two adjacent sampling points Mα and f Nα meet the conditions of f Mα (i) - f Mα (i - 1) < 0.01 p.u. and f Nα (i) - f Nα (i - 1) < 0.01 p.u., and the number of consecutive sampling points that meet the above conditions is not less than 5. If so, determine it as an in-zone two-phase interphase short-circuit fault and send a trip signal to the circuit breaker; otherwise, return to Step 1. Step 9: Determine whether the f calculated from two adjacent sampling points Mα and f Nα meet the conditions of f Mα (i) - f Mα (i - 1) < 0.01 p.u. and f Nα (i) - f Nα (i - 1) < 0.01 p.u., and the number of consecutive sampling points satisfying the above conditions is not less than 5. If satisfied, it is determined as a three-phase short-circuit fault in the zone, and a trip signal is sent to the circuit breaker; otherwise, return to Step 1. Step 10: Determine whether f calculated from two adjacent sampling points Mα and f Nα meet the conditions of f Mα (i) - f Mα (i - 1) < 0.01 p.u. and f Nα (i) - f Nα (i - 1) < 0.01 p.u., and the number of consecutive sampling points satisfying the above conditions is not less than 5. If satisfied, it is determined as an external fault and the protection is blocked; otherwise, return to Step 1.

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