Differential protection constant value adaptability evaluation method and system for new energy transmission line
By calculating the short-circuit ratio and short-circuit capacity of the new energy transmission and outlet line, and adjusting the differential value to ensure that the differential current meets the settings, the problem of differential protection refusal during the failure of the new energy transmission and outlet line is solved and the safe operation of the power grid is ensured.
Patent Information
- Application Number
- CN202510095041.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-21
- Publication Date
- 2025-05-30
AI Technical Summary
During the failure of the new energy supply line, the differential current may not meet the differential fixed value setting, resulting in the differential protection refusal. The system cannot control the circuit breaker and other switching equipment to cut off the faulty circuit, which in turn threatens the safe operation of the power grid.
By calculating the short-circuit ratio of the new energy and the short-circuit capacity of the receiving end system, comparing the minimum short-circuit ratio with the fixed value, adjusting the differential fixed value to ensure that the short-circuit capacity of the receiving end system is greater than the minimum short-circuit capacity, and ensuring that the differential current meets the differential fixed value setting.
It solves the problem that the differential current does not meet the differential fixed value during the failure of the new energy transmission line, avoids the refusal of differential protection, and ensures the safe operation of the power grid.
Smart Images
Figure CN120073596A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method and system for evaluating the adaptability of differential protection setting values of a new energy transmission line, belonging to the technical field of power systems. Background Art
[0002] With the rapid development of new energy such as photovoltaic and wind power in China, the installed capacity of new energy has been continuously improved. As the main protection of the high-voltage power grid, the setting of differential protection setting values directly affects the operation performance of differential protection, thus affecting the operation safety of the power grid.
[0003] The setting of differential protection setting values mainly considers avoiding unbalanced differential current outside the zone. Currently, the primary value of differential protection setting values in the high-voltage power grid is generally set between 600 and 800 A. In the lines of traditional power sources, due to the inertia support of synchronous generators, the current amplitudes on both sides of the transmission line are approximately constant during faults, and the currents on both sides are approximately in the same direction. Therefore, the obtained differential current is relatively large, and when the differential current is greater than the differential protection setting value, the differential protection can be normally started.
[0004] However, due to the different control strategies of the converters of new energy power sources and the control strategies of traditional synchronous machine power sources, during faults, the current at the new energy sending end shows the characteristics of limited amplitude and controlled phase angle, resulting in limited short-circuit current provided by new energy. Therefore, when a short-circuit fault occurs, the differential current may not meet the setting of the differential protection setting value, resulting in the refusal of the differential protection to operate, and the system cannot control switch devices such as circuit breakers to cut off the fault circuit, thereby threatening the safe operation of the power grid. Summary of the Invention
[0005] The purpose of the present invention is to provide a method and system for evaluating the adaptability of differential protection setting values of a new energy transmission line to solve the problem that during faults in the existing new energy transmission line, the differential current may not meet the setting of the differential protection setting value, resulting in the refusal of the differential protection to operate, and the system cannot control switch devices such as circuit breakers to cut off the fault circuit, thereby threatening the safe operation of the power grid.
[0006] To achieve the above purpose, the solution of the present invention includes:
[0007] A method for evaluating the adaptability of differential protection setting values of a new energy transmission line according to the present invention includes the following steps:
[0008] 1) Calculate the short-circuit ratio of the new energy transmission line according to the short-circuit capacity of the receiving-end system and the installed capacity of new energy.
[0009] 2) Compare the calculated short - circuit ratio with the minimum set short - circuit ratio. If the calculated short - circuit ratio is less than or equal to the minimum set short - circuit ratio, calculate the minimum short - circuit capacity at this time as the first minimum short - circuit capacity. If the short - circuit capacity of the receiving - end system at this time is greater than the first minimum short - circuit capacity, the differential setting value remains unchanged; otherwise, adjust the differential setting value so that the short - circuit capacity of the receiving - end system is greater than the first minimum short - circuit capacity.
[0010] 3) If the calculated short - circuit ratio is greater than the minimum set short - circuit ratio, calculate the minimum short - circuit capacity at this time as the second minimum short - circuit capacity. If the short - circuit capacity of the receiving - end system at this time is greater than the second minimum short - circuit capacity, the differential setting value remains unchanged; otherwise, adjust the differential setting value so that the short - circuit capacity is greater than the second minimum short - circuit capacity.
[0011] Further, the first minimum short - circuit capacity S min1 is obtained through the following formula:
[0012]
[0013] where k lmd is the sensitivity coefficient; U n is the rated voltage of the system; I set is the differential setting value; is the angular difference between the currents on both sides of the transmission line between the sending - end and the receiving - end.
[0014] Further, the second minimum short - circuit capacity S min2 is obtained through the following formula:
[0015]
[0016] where U n is the rated voltage of the system; k lmd is the sensitivity coefficient; I set is the differential setting value; k is the short - circuit current providing ability of the new - energy power source; k scr is the short - circuit ratio of the new - energy; is the angular difference between the currents on both sides of the transmission line between the sending - end and the receiving - end.
[0017] Further, the short - circuit capacity S of the receiving - end system ac is obtained through the following formula:
[0018]
[0019] where U n is the rated voltage of the system; I sf is the short - circuit current of the receiving - end system.
[0020] Further, the minimum set short - circuit ratio k scr_min is obtained through the following formula:
[0021]
[0022] Among them, k is the short-circuit current supply capacity of the new energy power source; is the angular difference between the currents on both sides of the transmission line at the sending and receiving ends.
[0023] Furthermore, when adjusting the differential setting value to make the short-circuit capacity greater than the first minimum short-circuit capacity, the adjusted differential setting value I set shall satisfy the following formula:
[0024]
[0025] Among them, is the angular difference between the currents on both sides of the transmission line at the sending and receiving ends; S ac is the short-circuit capacity of the receiving-end system; k lmd is the sensitivity coefficient; U n is the rated voltage of the system.
[0026] Furthermore, when adjusting the differential setting value to make the short-circuit capacity greater than the second minimum short-circuit capacity, the adjusted differential setting value I set shall satisfy the following formula:
[0027]
[0028] Among them, S ac is the short-circuit capacity of the receiving-end system; k is the short-circuit current supply capacity of the new energy power source; k scr is the new energy short-circuit ratio; is the angular difference between the currents on both sides of the transmission line at the sending and receiving ends; U n is the rated voltage of the system; k lmd is the sensitivity coefficient.
[0029] The present invention also provides a differential protection setting value adaptability evaluation system for a new energy transmission line, including a processor, and the processor is used to execute a computer program to implement the steps of a differential protection setting value adaptability evaluation method for a new energy transmission line as described in any one of the above.
[0030] The beneficial effects of the present invention are as follows: As an improved invention, when a fault occurs in the new energy transmission line, the new energy short-circuit ratio and the short-circuit capacity of the receiving-end system are first calculated; then, the calculated short-circuit ratio is compared with the fixed minimum short-circuit ratio. If the calculated short-circuit ratio is less than or equal to the fixed minimum short-circuit ratio, the minimum short-circuit capacity at this time is calculated as the first minimum short-circuit capacity. If the short-circuit capacity of the receiving-end system is greater than the first minimum short-circuit capacity at this time, it means that the differential current at this time meets the situation of the differential setting value, and the differential setting value remains unchanged; otherwise, the differential current may not meet the situation of the differential setting value, and the differential setting value needs to be adjusted so that the short-circuit capacity of the receiving-end system is greater than the first minimum short-circuit capacity. Similarly, if the calculated short-circuit ratio is greater than the fixed minimum short-circuit ratio, the minimum short-circuit capacity at this time is calculated as the second minimum short-circuit capacity; if the short-circuit capacity of the receiving-end system is greater than the second minimum short-circuit capacity at this time, the differential setting value remains unchanged; otherwise, the differential setting value needs to be adjusted so that the short-circuit capacity is greater than the second minimum short-circuit capacity. In summary, the present invention solves the problem that the differential current during the fault of the new energy transmission line may not meet the situation of the differential setting value, resulting in the refusal of differential protection to operate, and the system cannot control switch equipment such as circuit breakers to cut off the fault circuit, thereby threatening the safe operation of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Figure 1 is the model diagram of the new energy transmission line adopted by the present invention;
[0032] Figure 2 is the schematic diagram of the relationship between the currents on both sides of the line and the corresponding differential current in the present invention. DETAILED DESCRIPTION OF THE INVENTION
[0033] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be described in detail clearly and completely below with reference to the drawings and embodiments.
[0034] The concept of the present invention is that when a short-circuit fault occurs in the new energy transmission line, the new energy short-circuit ratio and the short-circuit capacity of the receiving-end system are first calculated; when the new energy short-circuit ratio is less than or equal to the fixed minimum short-circuit ratio, the minimum short-circuit capacity at this time is calculated as the first minimum short-circuit capacity. If the short-circuit capacity of the receiving-end system is greater than the calculated first minimum short-circuit capacity at this time, the differential setting value does not need to be adjusted; otherwise, the differential setting value is adjusted so that the short-circuit capacity of the receiving-end system is greater than the first minimum short-circuit capacity; when the new energy short-circuit ratio is greater than the fixed minimum short-circuit ratio, the minimum short-circuit capacity at this time is calculated as the second minimum short-circuit capacity. If the short-circuit capacity of the receiving-end system is greater than the second minimum short-circuit capacity at this time, the differential setting value does not need to be adjusted; otherwise, the differential setting value is adjusted so that the short-circuit capacity of the receiving-end system is greater than the second minimum short-circuit capacity.
[0035] Method Embodiment:
[0036] AsFigure 1 As shown is a model diagram of a new - energy power transmission line, which mainly includes a receiving - end power grid, an S - side bus, current transformers, sending - and - receiving - end circuit breakers, a W - side bus, a sending - end connection transformer, and a new - energy AC network side, etc. The AC side of the receiving - end power grid is connected to the AC side of the receiving - end circuit breaker through the S - side bus. The DC side of the receiving - end circuit breaker is connected to the sending - end current transformer through the receiving - end current transformer, and the currents on both the sending and receiving sides are detected through the current transformers. and The DC side of the sending - end current transformer is connected to the DC side of the sending - end circuit breaker. The AC side of the sending - end circuit breaker is connected to the new - energy AC network side through the W - side bus and the sending - end connection transformer. When a fault occurs, the system starts differential protection to control switch devices such as circuit breakers to cut off the fault circuit and maintain the safe operation of the power grid.
[0037] When Figure 1 a short - circuit fault occurs at point K, the high - voltage power grid starts differential protection, and its differential equation is:
[0038]
[0039] Among them, and are the currents on both sides of the transmission line, is the differential current synthesized from the currents on both sides, and I set is the differential setting value.
[0040] In the new - energy power transmission line, during a fault, shows fault characteristics of limited amplitude and controlled phase angle. When the angle changes to a certain extent, it may lead to the situation that the differential current I d during the fault does not satisfy the I set setting value, resulting in the problem that the differential protection refuses to operate and the system cannot control switch devices such as circuit breakers to cut off the fault circuit.
[0041] Therefore, in this embodiment, according to the new - energy short - circuit ratio, the minimum setting short - circuit ratio, the short - circuit capacity of the receiving - end system, and the required minimum short - circuit capacity, it is timely determined whether the setting of the differential setting value I set is appropriate to avoid the risk of the safe and stable operation of the power grid caused by the refusal of differential protection to operate.
[0042] Specifically,
[0043] 1) Define the new - energy short - circuit ratio k scr as follows:
[0044]
[0045] Among them, S ac is the system short - circuit capacity of the S - side AC power grid, P w is the installed capacity of the new - energy power station, and Un is the rated voltage of the system, I sf is the short-circuit current of the S-side system, I wn is the rated current of the new energy power station on the W side.
[0046] 2) Calculate the lowest short-circuit ratio corresponding to the minimum value of the differential current I d :
[0047] As Figure 2 shown in the schematic diagram of the relationship between the currents on both sides of the line and the corresponding differential current, remains unchanged, the amplitude of increases from small to large,
[0048]
[0049] If the differential protection is to operate reliably, it should satisfy:
[0050]
[0051] If a certain sensitivity is considered, it should satisfy:
[0052]
[0053] Among them, k lmd is the sensitivity coefficient, generally taken as 1.5; is the phase angle difference between the currents on both sides of the transmission line at the sending and receiving ends; I set is the set differential value.
[0054] During the fault, the short-circuit current provided by the S-side system Due to the influence of weather, the actual short-circuit current provided by the new energy power station on the W side shows volatility, and k is the short-circuit current supply capacity of the new energy power source, generally k = 1.2 - 1.5.
[0055] At this time, when the differential current I d takes the minimum value I d_min :
[0056]
[0057] 3) Calculate the short-circuit capacity of the receiving-end system on the S side and the first minimum short-circuit capacity S min1 required by the S-side AC power grid when the new energy short-circuit ratio is less than or equal to the lowest short-circuit ratio, and the second minimum short-circuit capacity S min2 required by the S-side AC power grid when the new energy short-circuit ratio is greater than the lowest short-circuit ratio, and determine the differential value adaptability evaluation equation of the new energy transmission line:
[0058] The short - circuit capacity of the receiving - end system on the S side is obtained according to the following formula:
[0059]
[0060] If the new - energy short - circuit ratio K obtained in step 1) scr ≤K scr_min When, the corresponding first minimum short - circuit capacity S min1 is obtained through the following formula:
[0061]
[0062] Under the condition of full output of new energy, I w is the rated current I wn of the new - energy power station on the W side. If the new - energy short - circuit ratio k obtained in step 1) at this time scr >k scr_min When (indicating that the amplitude of I wn is less than that of I w_min ), then when the new - energy output is insufficient (I w <I wn ), the amplitude of I w is even less than that of I w_min . Then, the minimum value of the differential current will not be reached, nor will the above - mentioned first minimum short - circuit capacity. The corresponding second minimum short - circuit capacity S min2 The calculation formula is as follows:
[0063]
[0064]
[0065] Thus, the evaluation formula for the adaptability of the differential setting value of the new - energy transmission line can be obtained:
[0066]
[0067] Among them, U n is the rated voltage of the system; k lmd is the sensitivity coefficient, generally taken as 1.5; I set is the differential setting value; k is the short - circuit current supply capacity of the new - energy power source, generally k = 1.2 - 1.5; is the angular difference between the currents on both sides of the sending - end and receiving - end transmission lines; k scr is the new - energy short - circuit ratio.
[0068] 4) Determine the value of the differential setting value I set :
[0069] When the new - energy short - circuit ratio K scr ≤K scr_min When:
[0070] If the short-circuit capacity of the receiving-end system satisfies S ac >S min1 at this time, then the differential setting value I set is reasonably set, the differential protection can operate reliably, and has a certain sensitivity; conversely, if the short-circuit capacity S ac ≤S min1 at this time, then it is necessary to modify the differential setting value I set to make it satisfy: S ac >S min1 , that is
[0071] When the short-circuit ratio K of the new energy scr >K scr_min at this time:
[0072] If the short-circuit capacity of the receiving-end system satisfies S ac >S min2 at this time, then set the differential setting value I set is reasonably set, the differential protection can operate reliably, and has a certain sensitivity; conversely, if the short-circuit capacity S ac ≤S min2 at this time, it is necessary to modify the differential setting value I set to make it satisfy S ac >S min2 , that is
[0073] System embodiment:
[0074] A differential protection setting value adaptability evaluation system for a new energy transmission line of the present invention, the system includes a processor, and the processor is used to execute computer program instructions to implement a differential protection setting value adaptability evaluation method for a new energy transmission line introduced in the method embodiment. This method has been introduced clearly enough in the method embodiment and will not be elaborated here.
Claims
1. A method for evaluating the adaptability of differential protection settings of a renewable energy transmission line, characterized in that: The steps include: 1) Calculate the short-circuit ratio of the renewable energy transmission line based on the short-circuit capacity of the receiving system and the installed capacity of renewable energy; 2) Compare the calculated short-circuit ratio with the fixed minimum short-circuit ratio. If the calculated short-circuit ratio is less than or equal to the fixed minimum short-circuit ratio, calculate the minimum short-circuit capacity at this time as the first minimum short-circuit capacity; If the short-circuit capacity of the receiving end system is greater than the first minimum short-circuit capacity at this time, the differential constant value remains unchanged; Otherwise, the differential setting is adjusted so that the short-circuit capacity of the receiving-end system is greater than the first minimum short-circuit capacity; 3) If the calculated short-circuit ratio is greater than the fixed minimum short-circuit ratio, the minimum short-circuit capacity at this time is calculated as the second minimum short-circuit capacity; If the short-circuit capacity of the receiving system is greater than the second minimum short-circuit capacity at this time, the differential constant remains unchanged; Otherwise, adjust the differential setting so that the short-circuit capacity is greater than the second minimum short-circuit capacity.
2. The method for evaluating the adaptability of differential protection setting values of a new energy transmission line according to claim 1 is characterized in that: The first minimum short-circuit capacity S min1 Obtained by the following formula: Among them, k lmd is the sensitivity coefficient; U n is the rated voltage of the system; I set is the differential constant; It is the angular difference between the currents on both sides of the transmission line at the sending and receiving ends.
3. The method for evaluating the adaptability of differential protection setting values of a new energy transmission line according to claim 1 is characterized in that: The second minimum short-circuit capacity S min2 Obtained by the following formula: Among them, U n is the rated voltage of the system; k lmd is the sensitivity coefficient; I set is the differential setting; k is the short-circuit current providing capacity of the new energy power source; k scr is the short-circuit ratio of the new energy; It is the angular difference between the currents on both sides of the transmission line at the sending and receiving ends.
4. The method for evaluating the adaptability of differential protection setting values of a new energy transmission line according to claim 1 is characterized in that: Short-circuit capacity S of the receiving system ac Obtained by the following formula: Among them, U n is the rated voltage of the system; I sf It is the short-circuit current of the receiving system.
5. The method for evaluating the adaptability of differential protection setting values of a new energy transmission line according to claim 1 is characterized in that: Fixed minimum short circuit ratio k scr_min Obtained by the following formula: Among them, k is the short-circuit current providing capability of the new energy power source; It is the angular difference between the currents on both sides of the transmission line at the sending and receiving ends.
6. The method for evaluating the adaptability of differential protection settings of a new energy transmission line according to claim 1 or 2, characterized in that: When the differential constant is adjusted so that the short-circuit capacity is greater than the first minimum short-circuit capacity, the adjusted differential constant I set The following formula should be satisfied: in, is the angular difference of the current on both sides of the transmission line at the sending and receiving ends; S ac is the short-circuit capacity of the receiving system; k lmd is the sensitivity coefficient; U n is the rated voltage of the system.
7. The method for evaluating the adaptability of differential protection settings of a new energy transmission line according to claim 1 or 3, characterized in that: When the differential constant is adjusted so that the short-circuit capacity is greater than the second minimum short-circuit capacity, the adjusted differential constant I set The following formula should be satisfied: Among them, S ac is the short-circuit capacity of the receiving system; k is the short-circuit current providing capacity of the new energy power source; k scr is the short-circuit ratio of the new energy; It is the angular difference of the current on both sides of the transmission line at the sending and receiving ends; U n is the rated voltage of the system; k lmd is the sensitivity coefficient.
8. A differential protection setting adaptability evaluation system for a new energy transmission line, comprising a processor, characterized in that: The processor is used to execute a computer program to implement the steps of a method for evaluating the adaptability of differential protection settings of a new energy transmission line as described in any one of claims 1 to 7.