Protection method for preventing override trip of substation

Abstract

The invention relates to the technical field of power systems, and provides a protection method for preventing override trip of a substation, which comprises the following steps of: sampling voltage and current of circuit breakers in the substation, automatically identifying power supply circuit breakers and load circuit breakers in the substation based on the phase difference of the circuit breakers, and for each identified load circuit breaker, when protection is started, automatically identifying the power supply circuit breakers and the load circuit breakers in the substation. Detecting a protection starting value of the ith sampling point of the load circuit breaker, and generating a corresponding blocking signal according to the protection starting value of the load circuit breaker; according to the blocking signal, determining whether the power supply circuit breaker override blocking signal is subjected to override blocking; when the override locking signal of the power supply circuit breaker does not perform override locking and the protection of the power supply circuit breaker is started, if the starting condition of the protection is always met within the set protection action time, an action instruction is sent at the end of the protection action time; if the starting condition is not continuously met within the protection action time, protection is returned, and the action instruction is not sent out.

Description

Technical Field

[0001] This invention relates to the technical field of power systems, and in particular to a protection method for substations to prevent cascading trips. Background Technology

[0002] As the core node for power distribution and transmission in a power system, substations contain a complex array of equipment and diverse protection types (covering protection devices for incoming and outgoing lines, busbars, transformers, and other equipment). However, existing substation protection technologies have significant shortcomings and are ill-suited to complex operating scenarios:

[0003] On the one hand, under the traditional single-power supply architecture, incoming and outgoing line protection often operates independently without coordination. If the protection settings (such as the current threshold of overcurrent and instantaneous overcurrent protection) or the operating time limit are not set reasonably, when a fault occurs, the protection devices that should isolate the fault locally cannot cooperate accurately. This can lead to unnecessary expansion of the power outage area, or even trigger over-level protection actions of the superior substation, resulting in a wider power outage and even inducing a serious power grid accident.

[0004] On the other hand, with the large-scale integration of green energy sources such as photovoltaics and wind power, more and more substations are adopting multi-source power supply modes. This makes the power flow direction of the power system no longer fixed, breaking the traditional clear hierarchical relationship between the "supply side and load side," and making the coordination logic between protection devices extremely complex. The original protection strategies that rely on fixed topology and a single power flow direction are difficult to adapt to the new scenario, further increasing the risk of expanding the power outage area during faults and posing a severe challenge to the safe and stable operation of substations.

[0005] In summary, traditional substation protection technologies, due to their lack of flexible and collaborative protection mechanisms in complex equipment environments and multi-power supply scenarios, can no longer meet the needs of accurately isolating faults and reducing the scope of power outages. There is an urgent need to propose a better anti-cascading protection scheme. Summary of the Invention

[0006] To solve the above-mentioned technical problems, the present invention provides a protection method for substations to prevent cascading tripping, comprising:

[0007] (1) Sample the voltage and current of the circuit breakers in the substation, and automatically identify the power supply circuit breaker and load circuit breaker in the substation based on the phase difference of the circuit breaker, wherein the phase difference is the absolute value of the voltage and current phase angle difference and the preset phase angle difference of the circuit breaker voltage and current.

[0008] (2) For each identified load circuit breaker, when the protection is started, the protection start value Act(i) of the i-th sampling point of the load circuit breaker is detected, and the corresponding blocking signal Sbk is generated according to the protection start value Act(i) of the load circuit breaker. This can effectively distinguish between real faults and instantaneous disturbances, avoid the false blocking signal due to accidental fluctuations, and ensure the reliability of the blocking logic.

[0009] (3) Confirm whether the power supply circuit breaker over-level blocking signal Sin is over-level blocked based on the blocking signal Sbk.

[0010] (4) When the circuit breaker over-level blocking signal Sin is not over-level blocked, after the circuit breaker protection is started, if the start conditions of the protection are always met within the set protection action time, an action command is issued at the end of the protection action time; if the start conditions are not met continuously within the protection action time, the protection returns and no action command is issued.

[0011] Furthermore, the conditions for automatic identification as a power supply circuit breaker in step (1) are:

[0012] Condition 1: The circuit breaker is in the closed state, and the voltage of the circuit breaker meets the following requirements:

[0013]

[0014] In the formula, UA(i), UB(i), and UC(i) are the voltage values ​​of the i-th sampling point of phases A, B, and C of the circuit breaker, respectively; Ub is the rated voltage value of the circuit breaker; K is the voltage coefficient, usually 0.7; n is the number of sampling points, which is calculated as n = T1 × f × Dot points; T1 is a time parameter used to determine the sampling time length, typically 10 seconds; f is the frequency, typically 50 Hz or 60 Hz; Dot is the number of sampling points per cycle, typically ranging from [24, 128]; and t is the current calculation point. 1-n ,t 2-n These are the first 1-n and 2-n calculation points;

[0015] Condition 2: The phase difference of the circuit breaker is less than 90°, and the circuit breaker belongs to the power supply line in the preset power supply mode;

[0016] Condition 3: The phase difference of the circuit breaker is greater than or equal to 90°, and the circuit breaker belongs to the load line in the preset power supply mode.

[0017] Furthermore, the conditions for automatically identifying a circuit breaker as a load circuit breaker in step (1) are:

[0018] Condition 1: The circuit breaker is in the closed state, and the voltage of the circuit breaker meets the following requirements:

[0019]

[0020] In the formula, UA(i), UB(i), and UC(i) are the voltage values ​​of the i-th sampling point of phases A, B, and C of the circuit breaker, respectively; Ub is the rated voltage value of the circuit breaker; K is the voltage coefficient, usually 0.7; n is the number of sampling points, which is calculated as n = T1 × f × Dot points; T1 is a time parameter used to determine the sampling time length, typically 10 seconds; f is the frequency, typically 50 Hz or 60 Hz; Dot is the number of sampling points per cycle, typically ranging from [24, 128]; and t is the current calculation point. 1-n ,t 2-n These are the first 1-n and 2-n calculation points;

[0021] Condition 2: The phase difference of the circuit breaker is greater than or equal to 90°, and the circuit breaker belongs to the power supply line in the preset power supply mode;

[0022] Condition 3: The phase difference of the circuit breaker is less than 90°, and the circuit breaker belongs to the load line in the preset power supply mode.

[0023] Furthermore, the preset power supply mode is the power supply mode under typical operating conditions of the substation, wherein the power factor of the total system load is [value missing]. The typical value is 0.8. This method specifies whether the circuit breaker belongs to a load line, power supply line, or tie line. If it belongs to a power supply line or a load line, the voltage and current angle of the circuit breaker is recorded.

[0024] Furthermore, in step (2), a corresponding blocking signal Sbk is generated based on the load circuit breaker protection start value Act(i), the specific content of which is as follows:

[0025] When all i satisfy At this time, the interlocking signal Sbk is set to 1;

[0026] When any i satisfies At that time, the interlocking signal Sbk is set to 0;

[0027] Where t1, t2, t m To start the calculation of the 1st, 2nd, and mth points, m is the number of blocking points, m = T × f × Dot / 1000, T is the blocking time in ms with a value range of [0, 10000], f is the frequency with a typical value of 50 Hz or 60 Hz, and Dot is the number of sampling points per cycle with a typical value range of [24, 128].

[0028] Furthermore, the specific content of step (3) is as follows:

[0029] If there exists a blocking signal Sbk==1 for any load circuit breaker, then the power supply circuit breaker over-level blocking signal Sin=1, and the power supply circuit breaker is over-level blocked; otherwise, the power supply circuit breaker over-level blocking signal Sin=0, and the power supply circuit breaker is not over-level blocked.

[0030] Furthermore, the calculation formula for the set protection action is as follows:

[0031]

[0032] In the formula, Ta is the initial protection action time value set by the power supply circuit breaker, and T is the blocking time of the load circuit breaker. Usually, T > Ta.

[0033] Furthermore, in step (4), the protection types of the power supply circuit breaker include overcurrent, overvoltage, undervoltage, low frequency, and high frequency, and the activation conditions of the protection are the logical judgment expressions corresponding to each protection type.

[0034] The present invention has the following beneficial effects:

[0035] (1) This invention automatically identifies the power supply circuit breaker and the load circuit breaker in the substation by using the voltage value of the i-th sampling point of phase A, B, and C of the circuit breaker and the absolute value of the voltage-current phase angle difference of the circuit breaker with the preset voltage-current phase angle difference. This ensures that the power supply / load circuit breaker can still be accurately distinguished under conditions such as load fluctuation and voltage transient, avoiding protection logic disorder caused by misjudgment, avoiding type confusion caused by traditional identification methods (such as manual labeling and fixed topology dependence), and ensuring that the subsequent blocking logic only acts on the corresponding power supply circuit breaker, thereby improving the accuracy of protection control from the source.

[0036] (2) Based on the real-time protection information of the load circuit breaker, the present invention generates a blocking signal by combining the set blocking time. The blocking signal directly acts on the protection of the power supply circuit breaker without the need for complex intermediate transmission links, reducing signal delay and ensuring that the power supply circuit breaker can respond to changes in the load side status in a timely manner.

[0037] (3) The present invention generates a blocking signal Sbk based on the protection start value Act(i) of the load circuit breaker. When any load circuit breaker triggers Sbk=1 due to a real fault, the power supply circuit breaker is immediately blocked by Sin=1, giving priority to the protection action of the load circuit breaker to clear the fault; the power supply circuit breaker is only allowed to operate when all load circuit breakers are not blocked (Sbk is all 0), thus avoiding cascading tripping.

[0038] (4) In this invention, after the power supply circuit breaker protection is started, when the blocking signal Sbk = 1, the power supply circuit breaker will extend the operation time based on the signal, specifically the blocking time of the load circuit breaker, to reserve sufficient fault isolation window for the load-side circuit breaker; if the blocking signal Sbk = 0, the power supply circuit breaker will operate according to the original set time. This dynamic delay design based on the load status avoids the cascading trip caused by the simultaneous operation of the load circuit breaker and the power supply circuit breaker. It is the core technical support for reducing the fault range and power outage time. By automatically extending the operation time, the cascading fault caused by the simultaneous operation of the load and the power supply circuit breaker is reduced, which can reduce the fault range, shorten the power outage time, and reduce the probability of cascading tripping of the upper-level substation switch. Attached Figure Description

[0039] Figure 1 This is a flowchart of the protection method of the present invention. Detailed Implementation

[0040] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. However, these embodiments are not intended to limit the present invention. Any similar structures and similar variations of the present invention should be included in the protection scope of the present invention. The commas in the present invention all indicate the relationship between and. The English letters in the present invention are case-sensitive.

[0041] like Figure 1 As shown, the present invention provides a protection method for preventing substation tripping, comprising:

[0042] S1, sample the voltage and current of the circuit breakers in the substation, and automatically identify the power supply circuit breaker and load circuit breaker in the substation based on the phase difference of the circuit breaker. The phase difference is the absolute value of the voltage and current phase angle difference and the preset phase angle difference of the circuit breaker voltage and current.

[0043] The conditions for automatic identification as a power supply circuit breaker are:

[0044] Condition 1: The circuit breaker is in the closed state, and the voltage of the circuit breaker meets the following requirements:

[0045]

[0046] In the formula, UA(i), UB(i), and UC(i) are the voltage values ​​of the i-th sampling point of phases A, B, and C of the circuit breaker, respectively; Ub is the rated voltage value of the circuit breaker; K is the voltage coefficient, usually 0.7; n is the number of sampling points, which is calculated as n = T1 × f × Dot points; T1 is a time parameter used to determine the sampling time length, typically 10 seconds; f is the frequency, typically 50 Hz or 60 Hz; Dot is the number of sampling points per cycle, typically ranging from [24, 128]; and t is the current calculation point. 1-n ,t2-n These are the first 1-n and 2-n calculation points;

[0047] Condition 2: The phase difference of the circuit breaker is less than 90°, and the circuit breaker belongs to the power supply line in the preset power supply mode;

[0048] Condition 3: The phase difference of the circuit breaker is greater than or equal to 90°, and the circuit breaker belongs to the load line in the preset power supply mode.

[0049] The conditions for automatic identification as a load circuit breaker are:

[0050] Condition 1: The circuit breaker is in the closed state, and the voltage of the circuit breaker meets the following requirements:

[0051]

[0052] In the formula, UA(i), UB(i), and UC(i) are the voltage values ​​of the i-th sampling point of phases A, B, and C of the circuit breaker, respectively; Ub is the rated voltage value of the circuit breaker; K is the voltage coefficient, usually 0.7; n is the number of sampling points, which is calculated as n = T1 × f × Dot points; T1 is a time parameter used to determine the sampling time length, typically 10 seconds; f is the frequency, typically 50 Hz or 60 Hz; Dot is the number of sampling points per cycle, typically ranging from [24, 128]; and t is the current calculation point. 1-n ,t 2-n These are the first 1-n and 2-n calculation points;

[0053] Condition 2: The phase difference of the circuit breaker is greater than or equal to 90°, and the circuit breaker belongs to the power supply line in the preset power supply mode;

[0054] Condition 3: The phase difference of the circuit breaker is less than 90°, and the circuit breaker belongs to the load line in the preset power supply mode.

[0055] The preset power supply mode is the power supply mode under typical operating conditions of the substation, where the power factor of the total system load is [value missing]. The typical value is 0.8. This method specifies whether the circuit breaker belongs to a load line, power supply line, or tie line. If it belongs to a power supply line or a load line, the voltage and current angle of the circuit breaker is recorded.

[0056] S2, for each identified load circuit breaker, when the protection is activated, the protection activation value Act(i) at the i-th sampling point of the load circuit breaker is detected, and a corresponding blocking signal Sbk is generated based on the load circuit breaker protection activation value Act(i). This effectively distinguishes between real faults and transient disturbances, avoids false blocking signals due to accidental fluctuations, and ensures the reliability of the blocking logic; the specific content is as follows:

[0057] When all i satisfy At this time, the interlocking signal Sbk is set to 1;

[0058] When any i satisfies At that time, the interlocking signal Sbk is set to 0;

[0059] Where t1, t2, t m To initiate the calculation of the 1st, 2nd, and mth points, where m is the number of blocking points, m = T × f × Dot / 1000, T is the blocking time in milliseconds (ms), with a value range of [0, 10000], f is the frequency (typically 50 Hz or 60 Hz), and Dot is the number of sampling points per cycle (typically [24, 128]). This transforms the abstract blocking time into a concrete number of sampling points, allowing the generation conditions of the blocking signal Sbk to be flexibly adjusted according to load type (e.g., inductive, capacitive) and fault characteristics (e.g., short circuit, ground fault).

[0060] S3, based on the blocking signal Sbk, confirm whether the over-level blocking signal Sin of the power supply circuit breaker is over-level blocked. The specific content is as follows:

[0061] If any load circuit breaker has a blocking signal Sbk==1, then the power supply circuit breaker's over-level blocking signal Sin=1. This means the power supply circuit breaker is over-level blocked, indicating at least one load circuit is operating (energized). In this case, the power supply circuit breaker's over-level blocking signal Sin=1 (blocking is issued). If a fault occurs in a downstream circuit, the protection of the load circuit breaker at this level should be tripped first to prevent the power supply circuit breaker from tripping over-level and thus preventing the power outage from spreading. Otherwise, the power supply circuit breaker's over-level blocking signal Sin=0, meaning the power supply circuit breaker does not over-level block, indicating all load circuits are out of service (not energized). In this case, the power supply circuit breaker's over-level blocking signal Sin=0 (no blocking), because there is no operating downstream circuit. If a fault occurs, it is highly likely to be within the upstream circuit's own range, and the power supply circuit breaker's protection should be allowed to trip normally to ensure the fault is cleared in a timely manner.

[0062] S4, when the circuit breaker's over-level blocking signal Sin is not over-level blocked, after the circuit breaker protection is activated, if the activation condition of the protection is always met within the set protection action time, an action command is issued at the end of the protection action time; if the activation condition is not continuously met within the protection action time, the protection returns and no action command is issued. Specifically, if the activation value of the protection is always 1, an action command is issued at the end of the protection action time; if the activation value is not continuously 1 within the protection action time, the protection returns and no action command is issued. The protection types of the circuit breaker include overcurrent, overvoltage, undervoltage, low frequency, and high frequency, and the activation conditions of the protection are the logical judgment expressions corresponding to their respective protection types.

[0063] The formula for calculating the action time Tact is:

[0064]

[0065] In the formula, Ta is the initial protection action time value set by the power supply circuit breaker, and T is the blocking time of the load circuit breaker. Usually, T > Ta.

[0066] After the power supply circuit breaker protection is activated, when Sbk=1, the power supply circuit breaker will extend its operating time based on this signal, specifically the blocking time of the load circuit breaker, to reserve sufficient fault isolation window for the load-side circuit breaker; if Sbk=0, the power supply circuit breaker will operate according to the original set time. This dynamic delay design based on load status avoids cascading tripping caused by the simultaneous operation of the load circuit breaker and the power supply circuit breaker, and is the core technical support for reducing the scope of the fault and reducing the power outage time.

[0067] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

Claims

1. A protection method for preventing a step-over trip of a substation, characterized by, The method comprises the following steps: (1) sampling voltage and current of circuit breakers in a substation, and automatically identifying power supply circuit breakers and load circuit breakers in the substation based on phase difference of the circuit breakers; wherein the phase difference is an absolute value of a voltage and current phase angle difference of the circuit breakers and a preset voltage and current phase angle difference of the circuit breakers; (2) for each identified load circuit breaker, detecting a protection starting value Act(i) of an i-th sampling point of the load circuit breaker when the protection is started, and generating a corresponding blocking signal Sbk according to the protection starting value Act(i) of the load circuit breaker; (3) confirming whether the power supply circuit breaker overstep blocking signal Sin is overstep blocked according to the blocking signal Sbk; (4) when the power supply circuit breaker overstep blocking signal Sin is not overstep blocked, if the starting condition of the protection is always met within a set protection action time after the power supply circuit breaker protection is started, an action instruction is sent at the end of the protection action time; if the starting condition cannot be continuously met within the protection action time, the protection returns and no action instruction is sent.

2. The protection method against misoperation of substation according to claim 1, characterized in that, The condition for automatically identifying the power supply circuit breaker in step (1) is as follows: Condition 1: the circuit breaker is in a closed state, and the voltage of the circuit breaker meets the following condition: In the formula, UA(i), UB(i), and UC(i) are voltage values of the i th sampling point of the circuit breakers A, B, and C respectively, Ub is the rated voltage value of the circuit breaker, K is the voltage coefficient, n is the number of sampling points, t is the current calculation point, t 1-n ,t 2-n is the previous 1-n, 2-n calculation points. Condition 2: the phase difference of the circuit breaker is less than 90°, and the circuit breaker belongs to a power supply line in a preset power supply mode; Condition 3: the phase difference of the circuit breaker is greater than or equal to 90°, and the circuit breaker belongs to a load line in the preset power supply mode.

3. The protection method against misoperation of substation according to claim 1, characterized in that, The condition for automatically identifying the load circuit breaker in step (1) is as follows: Condition 1: the circuit breaker is in a closed state, and the voltage of the circuit breaker meets the following condition: In the formula, UA(i), UB(i), and UC(i) are voltage values of the i th sampling point of the circuit breakers A, B, and C respectively, Ub is the rated voltage value of the circuit breaker, K is the voltage coefficient, n is the number of sampling points, t is the current calculation point, t 1-n ,t 2-n is the previous 1-n, 2-n calculation points. Condition 2: the phase difference of the circuit breaker is greater than or equal to 90°, and the circuit breaker belongs to a power supply line in a preset power supply mode; Condition 3: the phase difference of the circuit breaker is less than 90°, and the circuit breaker belongs to a load line in the preset power supply mode.

4. The protection method against misoperation of substation according to claim 3, characterized in that, The preset power supply mode is a power supply mode under typical operation conditions of a substation, wherein a power factor of total system load is The mode specifies that the circuit breaker belongs to a load line, a power supply line or a tie line, and if the belonging is the power supply line or the load line, the angle between the voltage and the current of the circuit breaker is recorded.

5. The protection method against misoperation of substation according to claim 1, characterized in that, The specific content of generating the corresponding blocking signal Sbk according to the protection starting value Act(i) of the load circuit breaker in step (2) is as follows: When all i satisfy the blocking signal Sbk is set to 1; When any one of i satisfies the lock signal Sbk is set to 0; Wherein, t1, t2, t m To start the first, second, m calculation points, m is the number of locking points.

6. The protection method against misoperation of substation according to claim 1, characterized in that, The specific content of step (3) is as follows: If the blocking signal Sbk of any one load circuit breaker is equal to 1, the power supply circuit breaker overstep blocking signal Sin is equal to 1, and the power supply circuit breaker is overstep blocked; otherwise, the power supply circuit breaker overstep blocking signal Sin is equal to 0, and the power supply circuit breaker is not overstep blocked.

7. The protection method against misoperation of substation according to claim 6, characterized in that, The calculation formula of the set protection action time is as follows: In the formula, Tact is the set protection action time, Ta is an initial set protection action time value of the power supply circuit breaker, and T is a blocking time of the load circuit breaker.

8. The protection method against misoperation of substation according to claim 1, characterized in that, The protection type of the power supply circuit breaker in step (4) includes overcurrent, overvoltage, loss of voltage, low frequency, and high frequency, and the starting condition of the protection is a corresponding logical judgment formula of each protection type.

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