Calculation method of overcurrent protection delay time in urban rail transit power supply system

Abstract

The present invention provides a method for calculating the overcurrent protection delay time of an urban rail transit power supply system, comprising the following steps: S1: determining the upper and lower level coordination relationship between multiple protection devices; S2: determining the delay time t of the overcurrent protection of the lower level protection device; n ; S3: Calculate the time difference Δt between the delay time of the upper protection device and the lower protection device; S4: Calculate the delay time t of the overcurrent protection of the upper protection device n+1 =t n +Δt. This invention addresses the entire protection process, from startup to exit, and ultimately to circuit breaker tripping, by proposing a minimum time interval for overcurrent protection delays that can reliably distinguish between two switching sequences. This significantly alleviates the problem of limited overcurrent protection levels when the maximum delay time is limited, while also providing a theoretical basis for effective selective implementation.

Description

Technical Field

[0001] The present invention belongs to the field of urban rail transit power supply system protection, and in particular relates to a method for calculating an overcurrent protection delay time of an urban rail transit power supply system. Background Art

[0002] System-configured protection should technically meet four basic requirements: reliability, sensitivity, selectivity, and speed—the four characteristics of protection. These four characteristics are both interrelated and contradictory. Whether these four characteristics are met and the degree of their realization serve as the basis for judging the rationality of relay protection design, configuration, and maintenance, and are also the foundation for analyzing and evaluating relay protection. In urban rail transit power supply systems, because substations are only approximately 1-3 kilometers apart, the length of the ring network cables is relatively short, and the short-circuit current at the beginning and end of the line is not significantly different. For overcurrent protection whose current setting is based on avoiding the system's maximum load current, selectivity cannot be achieved by relying on the current setting value. Relying on individual delay times and creating the necessary time differences between overcurrent protections becomes the only means of achieving selectivity.

[0003] Existing urban rail transit power supply systems generally use a fixed time step, Δt, to achieve overcurrent protection selectivity. This time step has been reduced from 0.3s to 0.25s and even 0.15s. This gradual decrease in time step introduces certain risks to the implementation of protection selectivity and reduces system reliability to a certain extent.

[0004] With the gradual expansion of large-ring power supply systems in urban rail transit, the number of levels of overcurrent protection selectivity required has increased. However, the overcurrent protection delay time of the external power supply provided by the power system has not increased accordingly, and even tends to decrease. As a result, the time difference of overcurrent protection is no longer likely to increase.

[0005] Therefore, in order to address the above contradictions, a method for calculating the overcurrent protection delay time of urban rail transit power supply systems is urgently needed, which can ensure the accurate implementation of overcurrent protection selectivity without "wasting" the limited delay time. Summary of the Invention

[0006] This invention addresses the technical problems existing in the prior art by providing a method for calculating the overcurrent protection delay time for urban rail transit power supply systems. This method proposes a minimum time interval for overcurrent protection delays that can reliably distinguish between two sequential switch actions, covering the entire protection process from initiation to termination and ultimately circuit breaker tripping. This method significantly alleviates the problem of limited number of overcurrent protection stages when the maximum delay time is limited, and provides a theoretical basis for selective and effective implementation.

[0007] The technical solution adopted by the present invention is: a method for calculating the overcurrent protection delay time of an urban rail transit power supply system, comprising the following steps:

[0008] S1: Determine the hierarchical coordination relationship between multiple protection devices based on the structure of the power supply system and the location of the protection devices in the power supply system;

[0009] S2: Determine the delay time t of the overcurrent protection of the lower protection device n (s);

[0010] S3: Calculate the time difference Δt between the delay time of the upper protection device and the lower protection device;

[0011] Δt=2×E t ×t n +t r +t b +t s

[0012] Among them, E t Indicates the timing error of the protection device timer (%), t r Indicates the action time of the protection output relay (s), t b Indicates the circuit breaker full breaking time (s), t s Indicates safety factor (s); E t , t r , t b These are device parameters provided by the device manufacturer.

[0013] S4: Calculate the delay time t of the overcurrent protection of the upper protection device n+1 =t n +Δt.

[0014] Furthermore, when the upper protection device corresponds to a lower protection device, t n The delay time of the overcurrent protection of the lower protection device;

[0015] When the upper protection device corresponds to multiple lower protection devices that are activated simultaneously, t n The delay time of the overcurrent protection of the lower level protection device with the longest delay time;

[0016] When the upper protection device corresponds to multiple lower protection devices that are activated in sequence, t n It is the sum of the delay times of overcurrent protection of all lower level protection devices.

[0017] Furthermore, in step S3, t s It is 0.05s-0.1s.

[0018] Working principle: When a short-circuit fault occurs, the upper and lower protection devices will start simultaneously if the short-circuit current exceeds the overcurrent setting value. At startup, the protection device timer starts timing. After reaching the respective delay time, the protection device outputs, starts the output relay, and then the output relay drives the circuit breaker to trip. After the circuit breaker is fully disconnected, the fault is cleared. In order to achieve selectivity, it should be ensured that the fault is cleared by the lower-level protection device tripping after the fault occurs, and during this period, the upper-level protection device can be started, but should not be output. Therefore, the delay time of the upper-level protection device should be greater than the time from the startup to the complete removal of the fault of the lower-level protection device. In addition to the delay time of the lower-level protection device, this time also includes the action time of the lower-level protection device output relay and the full disconnection time of the circuit breaker. The positive and negative errors of the protection device timer during the timing process should also be considered, and the margin should be appropriately increased.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention can accurately calculate the time difference of the overcurrent protection delay time between the upper and lower level protection devices, and then calculate the delay time of the overcurrent protection of the upper level protection device, thereby reducing the blindness of directly borrowing from other projects in the project.

[0021] 2. The present invention can effectively compress the overcurrent protection delay without losing protection selectivity, solving the bottleneck problem of coordination with the main overcurrent protection interface.

[0022] 3. The present invention lays a theoretical foundation for the selectivity of overcurrent protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of a flow chart of an embodiment of the present invention;

[0024] Figure 2 Schematic diagram of a dual-power chain power supply solution according to an embodiment of the present invention;

[0025] Figure 3 A schematic diagram of a dual-power parallel ring power supply solution according to an embodiment of the present invention;

[0026] Figure 4 A schematic diagram of the coordination of overcurrent time between the ring-type power supply partition incoming line and the simultaneously activated lower-level protection device according to an embodiment of the present invention;

[0027] Figure 5 This is a schematic diagram of the coordination of overcurrent time between the ring-type power supply partition incoming line and the sequentially started lower-level protection device in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] The embodiment of the present invention provides a method for calculating the overcurrent protection delay time of an urban rail transit power supply system. Figure 1 As shown, it includes the following steps:

[0031] S1: The power supply system adopts independent dual-circuit power supply outside the access system, ring network power supply, open loop operation, and the power supply partition topology is chain type, that is, dual power supply chain power supply scheme, as shown in the schematic diagram Figure 2 The upper and lower levels of the ring network switches are arranged from upper to lower levels according to the direction of current.

[0032] The upper and lower level coordination relationship of each protection device corresponding to the power supply of independent power supply 1 is: A1→A2→B1→B2→C1;

[0033] The upper and lower level coordination relationship of each protection device corresponding to the power supply of independent power supply 2 is: F1→F2→E1→E2→D1→D2.

[0034] S2: Determine the delay time t of the overcurrent protection of the lower protection device n (s). Taking independent power supply 1 as an example, among the corresponding protection devices, protection device C1 is at the lowest level, and its overcurrent protection delay time is t c1 =0.3s.

[0035] S3: Calculate the time difference Δt of the delay time between the upper protection device and the lower protection device.

[0036] The equipment parameters corresponding to the current mainstream manufacturers are E t =5%, t r =0.03s, t b =0.07s, t s Take 0.05s, then

[0037] Δt=t n+1 -t n =2×E t ×t n +t r +t b +t s =2×5%×t n +0.03+0.07+0.05=0.1×t n +0.15(s).

[0038] E t Indicates the timing error of the protection device timer (%), tr Indicates the action time of the protection output relay (s), t b Indicates the circuit breaker full breaking time (s), t s Indicates the safety factor (s).

[0039] In this embodiment, the models of relays and circuit breakers corresponding to the various protection devices are the same.

[0040] S4: Calculate the delay time t of the overcurrent protection of the upper protection device n+1 =t n +Δt.

[0041] The overcurrent protection delay time of B2 is t B2 =t C1 +Δt1=0.3+0.1×0.3+0.15=0.48s;

[0042] The overcurrent protection delay time of B1 is t B1 =t B2 +Δt2=0.48+0.1×0.48+0.15=0.68s;

[0043] The overcurrent protection delay time of A2 is t A2 =t B1 +Δt3=0.68+0.1×0.68+0.15=0.90s;

[0044] The overcurrent protection delay time of A1 is t A1 =t A2 +Δt4=0.90+0.1×0.90+0.15=1.14s.

[0045] The delay time of the overcurrent protection of each protection device corresponding to the independent power supply 2 is calculated using the above method, and the results are shown in the following table:

[0046]

[0047] Example 2

[0048] The embodiment of the present invention provides a method for calculating the overcurrent protection delay time of an urban rail transit power supply system. Figure 1 As shown, it includes the following steps:

[0049] S1: The power supply system is connected to the dual power supply running in parallel outside the system, with ring network power supply and closed ring operation. The power supply partition topology is ring type, that is, dual power supply parallel ring type power supply scheme, as shown in the schematic diagram Figure 3 The current must be in the positive direction, and the upper and lower levels are connected from the upper level to the lower level when the current direction is consistent with the protection positive direction.

[0050] The upper and lower level coordination relationship of each protection device corresponding to the clockwise power supply in the ring power supply zone is: M1→A1→B1→C1→D1→E1→F1

[0051] The upper and lower level coordination relationship of each protection device corresponding to the counterclockwise power supply in the ring power supply zone is: M2→F2→E2→D2→C2→B2→A2.

[0052] The upper and lower level coordination relationship between the protection device of the ring power supply partition and the incoming line switch protection device is:

[0053] The protection device MN is the upper level, and the protection devices M1 and A2 are both the lower levels.

[0054] The protection device MN is the upper level, and the protection devices M2 and F1 are both the lower levels.

[0055] S2-S4: Determine the delay time of overcurrent protection of each lower-level protection device.

[0056] The equipment parameters corresponding to the current mainstream manufacturers are E t =5%, t r =0.03s, t b =0.07s, t s Taking 0.05s, the delay time of the overcurrent protection of the protection devices M1, A1, B1, C1, D1, E1, F1, M2, F2, E2, D2, C2, B2 and A2 can be calculated using the same method as in Example 1. The calculation results are shown in the following table.

[0057]

[0058]

[0059] The loop impedances between the two lower-level protection devices in a ring-shaped power supply and the power source vary depending on the power supply direction (clockwise or counterclockwise). This causes the short-circuit currents flowing through the upper-level protection device MN to also differ when flowing through the lower-level protection devices M1 and A2 (or M2 and F1) in parallel. These different short-circuit currents flowing through the lower-level protection devices M1 and A2 (or M2 and F1) result in different activation sequences, meaning that protection devices M1 and A2 (or M2 and F1) activate simultaneously or sequentially.

[0060] Protection devices M1 and A2 are activated simultaneously: Assume that a fault occurs between protection devices M1 and A2, and the overcurrent protection setting value of the protection devices is 1000A. When a short-circuit fault occurs, the short-circuit current flowing through protection device M1 is 6000A, the short-circuit current flowing through protection device A2 is 2000A, and the short-circuit current flowing through protection device MN is 6000+2000=8000A. In this case, the overcurrent protection of protection devices M1 and A2 are both activated. Protection device A2 is activated after the delay time t A2 =0.3s; after the protection device A2 trips, the total short-circuit current of the loop will decrease from 8000A to 7500A due to the increase in loop impedance. The short-circuit current flowing through the protection devices M1 and MN is 7500A. Then the protection device M1 will trip when the delay time t M1 =1.69s. Then for the protection device MN, the time to clear the lower fault is the time of the protection device M1, 1.69s. Therefore, the overcurrent protection extension time of the protection device MN should meet

[0061] t MN =t M1 +Δt=1.69+0.1×1.69+0.15=2.01s.

[0062] That is, when a short circuit fault occurs, the overcurrent protection of protection devices M1 and A2 is activated at the same time. The overcurrent protection time of protection device M1 is 1.69s, and the overcurrent protection time of protection device A2 is 0.3s. The overcurrent protection time of protection device M1 is greater than that of protection device A2. The time difference Δt is only related to the lower-level protection device M1 with the longest delay time. Therefore, the overcurrent protection time t of protection device MN is MN Should be at least 2.01s, such as Figure 4 shown.

[0063] Protective devices M1 and A2 start sequentially: Assuming a fault occurs between protective devices M1 and A2, the overcurrent protection setting value of the protective devices is 1000A. When a short-circuit fault occurs, the short-circuit current flowing through protective device M1 is 7200A, the short-circuit current flowing through protective device A2 is 800A, and the short-circuit current flowing through protective device MN is 7200+800=8000A. Then the overcurrent protection of protective device M1 is started while the overcurrent protection of protective device A2 is not started. Protective device M1 starts after the delay time t M1 =1.69s; after the protection device M1 trips, the total short-circuit current of the loop will decrease from 8000A to 6000A due to the increase in loop impedance. The short-circuit current flowing through the protection devices A2 and MN is 6000A. Then the protection device A2 will trip when the delay time t A2=0.3s. Then for the protection device MN, the time to clear the lower fault is the sum of the delay time of the protection devices M1 and A2, 1.69 + 0.3 = 1.99s. Therefore, the overcurrent protection extension time of the protection device MN should meet

[0064] t MN =t M1 +t A2 +Δt=1.69+0.3+0.1×(1.69+0.3)+0.25=2.44s.

[0065] The two lower-level protection devices are started sequentially, so when calculating the time difference Δt, it is necessary to use the operating time of the two output relays and the full disconnection time of the circuit breaker.

[0066] That is, when a short circuit occurs, the overcurrent protection of protection devices M1 and A2 starts in sequence. The overcurrent protection of protection device M1 starts first, and the overcurrent protection delay time is 1.69s. The overcurrent protection of protection device A2 starts after the protection device M1 trips, and the overcurrent protection delay time is 0.3s. The time difference Δt is related to the lower-level protection devices M1 and A2. The overcurrent protection time t of protection device MN is t. MN Should be at least 2.44s, such as Figure 5 shown.

[0067] When the fault occurs between M2 and F1, the calculation formula is the same as above, that is, the overcurrent protection time t' of the protection device MN MN It should be 2.01s (lower level protection devices start simultaneously) or 2.44s (lower level protection devices start sequentially). Therefore, the overcurrent protection time of protection device MN should be MAX (t MN， t' MN ).

[0068] The present invention has been described in detail above through the embodiments, but the contents described are only exemplary embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. The scope of protection of the present invention is defined by the claims. Any use of the technical solution described in the present invention, or any person skilled in the art who, inspired by the technical solution of the present invention, designs a similar technical solution within the essence and scope of protection of the present invention to achieve the above-mentioned technical effects, or any equivalent changes and improvements made to the scope of application, shall still fall within the scope of protection covered by the patent of the present invention.

Claims

1. A method for calculating the overcurrent protection delay time of an urban rail transit power supply system, characterized in that: The following steps are involved: S1: Determine the superior-subordinate coordination relationship between multiple protection devices; S2: Determine the delay time t of the overcurrent protection of the lower protection device n ; S3: Calculate the time difference Δt between the delay time of the upper protection device and the lower protection device; Δt=2×E t ×t n +t r +t b +t s Among them, E t Indicates the timing error of the protection device timer, t r Indicates the action time of the protection output relay, t b Indicates the circuit breaker full breaking time, t s represents the safety factor; S4: Calculate the delay time t of the overcurrent protection of the upper protection device n+1 =t n +Δt.

2. The method for calculating the overcurrent protection delay time of the urban rail transit power supply system according to claim 1, wherein: When the upper protection device corresponds to a lower protection device, t n The delay time of the overcurrent protection of the lower protection device; When the upper protection device corresponds to multiple lower protection devices that are activated simultaneously, t n The delay time of the overcurrent protection of the lower level protection device with the longest delay time; When the upper protection device corresponds to multiple lower protection devices that are activated in sequence, t n It is the sum of the delay times of overcurrent protection of all lower level protection devices.

3. The method for calculating the overcurrent protection delay time of the urban rail transit power supply system according to claim 1, wherein: ts is 0.05s-0.1s.

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