Differential protection method and system for long-distance lead on high-voltage side of transformer

Abstract

The invention relates to a differential protection method and system for a transformer high-voltage side long-distance lead, and belongs to the technical field of power system relay protection. The method comprises the following steps: when a power grid system is disturbed, judging whether differential current starting elements on two sides of a line are connected with a voltage transformer or not; when the two sides are connected, the differential current starting element on one side with obvious voltage fault characteristics is automatically started, and the differential current starting element on one side with unobvious voltage fault characteristics is controlled to be started; when only one side is accessed and the voltage fault characteristic of the accessed side is obvious, the differential current starting element of the accessed side is automatically started, and the differential current starting element of the non-accessed side is controlled to be started; if the voltage fault characteristic of the accessed side is not obvious, the differential current starting elements at the two sides adopt the differential current criterion; and when the two sides are not connected, the differential current starting elements on the two sides adopt the differential current criterion. According to the invention, the differential current starting element can be started quickly and reliably.

Description

Technical Field

[0001] The invention relates to a differential protection method and system for long-distance leads at a high-voltage side of a transformer, belonging to the technical field of relay protection of power systems. Background Art

[0002] The relay protection device of the power system is required to have speed, sensitivity, reliability and selectivity. The step-up substation and the transformer body are connected by leads, and the distance of the leads is determined according to the actual situation. In order to ensure that the fault point can be quickly and reliably isolated when a lead fails, the lead needs to be included in the protection range of the relevant relay protection.

[0003] When the lead distance is short, the high-voltage side of the transformer can be directly connected to the current transformer (CT) installed on the substation system side. Therefore, the protection range of the transformer differential protection device can cover the lead part. When a lead segment fails, the fault can be isolated by relying on the rapid action of the transformer differential protection device. A short lead protection device can also be configured and connected to the CT at both ends of the lead. When a lead segment fails, the fault can be quickly isolated by relying on the short lead differential protection action.

[0004] When the lead distance is long (in the power generation system, the lead length may exceed thousands of meters), the high-voltage side of the transformer cannot be connected to the CT on the substation system side, and the short-lead protection device cannot be connected to the CTs at both ends of the lead at the same time. At this time, the transformer differential protection or the short-lead differential protection cannot cover the lead part. When a fault occurs on the lead, the fault can only be removed by relying on the transformer backup protection action outlet. Since a long delay is required to ensure the accuracy of the protection action, the speed requirement cannot be met.

[0005] In order to solve the above problems, in engineering applications, a simple cable protection device is generally configured on the lead, and the overcurrent protection function is used to quickly cut off the fault on the lead, but at this time, the problem of overcurrent setting needs to be considered. If the overcurrent setting value is too small, it may not be able to cooperate with related protection when an out-of-zone fault occurs, resulting in malfunction; if the overcurrent setting value is too small, it may refuse to operate when a minor fault occurs in the lead. Therefore, the requirement for reliable action of the lead fault cannot be achieved. Summary of the invention

[0006] The object of the present invention is to provide a differential protection method and system for long-distance leads on the high-voltage side of a transformer, so as to solve the problem in the prior art that the differential protection device cannot be started quickly and reliably when a fault occurs in the long-distance leads on the high-voltage side of the transformer.

[0007] To achieve the above object, the solution of the present invention includes: A differential protection method for long-distance leads on the high-voltage side of a transformer of the present invention comprises the following steps: When a disturbance occurs in the power grid system, determine whether the differential current starting elements on the local side and the opposite side of the line are connected to voltage transformers; When voltage transformers are connected on both the local side and the opposite side, the differential current starting element on the side with obvious voltage fault characteristics starts automatically, and controls the differential current starting element on the side with less obvious voltage fault characteristics to start; When only the voltage transformer is connected on this side and the voltage fault characteristics on this side are obvious, the differential current starting element on this side starts automatically and controls the differential current starting element on the opposite side to start; if the voltage fault characteristics on this side are not obvious, the differential current starting elements on this side and the opposite side both use the differential current criterion; When only the voltage transformer is connected on the opposite side and the voltage fault characteristics on the opposite side are obvious, the differential current starting element on the opposite side starts automatically and controls the differential current starting element on this side to start; if the voltage fault characteristics on the opposite side are not obvious, the differential current starting elements on both the opposite and local sides adopt the differential current criterion; When there is no voltage transformer on both the local side and the opposite side, the differential current starting elements on both the local side and the opposite side adopt the differential current criterion; Among them, the differential current criterion is: when the differential current is greater than the action threshold value, the differential current starting element starts; obvious voltage fault characteristics refer to the voltage fault characteristics meeting the preset conditions; unclear voltage fault characteristics refer to the voltage fault characteristics not meeting the preset conditions.

[0008] Furthermore, a first flag bit and a second flag bit are configured inside the differential current starting element on the local side and the opposite side; When the first flag bit is 1, it indicates that a voltage transformer is connected to this side; when the first flag bit is 0, it indicates that no voltage transformer is connected to this side; When the second flag bit is 1, it indicates that a voltage transformer is connected to the opposite side; when the second flag bit is 0, it indicates that no voltage transformer is connected to the opposite side.

[0009] Furthermore, it also includes: when a disturbance occurs in the power grid system, after entering the open fault processing logic, according to the voltage sampling value of the local side and the first voltage threshold value, correcting the state of the voltage transformer on the opposite side according to the voltage sampling value of the opposite side and the second voltage threshold value; Among them, the open fault handling logic refers to the fact that after the differential current starting element detects a disturbance in the power grid system, it quickly and reliably automatically enters the strategy logic processing for various types of disturbances and puts the relevant relays in the pre-action state; the status of the voltage transformer includes the exit state and the connection state.

[0010] Further, when the voltage sampling value on this side is greater than the first voltage threshold value, if the voltage transformer on this side is in the exit state, the voltage transformer on this side is corrected to be in the entry state; when the voltage sampling value on this side is less than the first voltage threshold value, if the voltage transformer on this side is in the entry state, the voltage transformer on this side is corrected to be in the exit state; When the voltage sampling value on the opposite side is greater than the second voltage threshold value, if the voltage transformer on the opposite side is in the exit state, the voltage transformer on the opposite side is corrected to the connection state; when the voltage sampling value on the opposite side is less than the second voltage threshold value, if the voltage transformer on the opposite side is in the connection state, the voltage transformer on the opposite side is corrected to the exit state.

[0011] Furthermore, when using the differential current criterion, the action threshold is raised so that when the current transformer is disconnected, the differential current starting element will not malfunction, and when a fault occurs in the line area, the differential current starting element will not refuse to operate.

[0012] A differential protection system for long-distance leads on the high-voltage side of a transformer of the present invention comprises a processor, and the processor is used to execute a computer program to implement the following steps: When a disturbance occurs in the power grid system, determine whether the differential current starting elements on the local side and the opposite side of the line are connected to voltage transformers; When voltage transformers are connected on both the local side and the opposite side, the differential current starting element on the side with obvious voltage fault characteristics starts automatically, and controls the differential current starting element on the side with less obvious voltage fault characteristics to start; When only the voltage transformer is connected on this side and the voltage fault characteristics on this side are obvious, the differential current starting element on this side starts automatically and controls the differential current starting element on the opposite side to start; if the voltage fault characteristics on this side are not obvious, the differential current starting elements on this side and the opposite side both use the differential current criterion; When only the voltage transformer is connected on the opposite side and the voltage fault characteristics on the opposite side are obvious, the differential current starting element on the opposite side starts automatically and controls the differential current starting element on this side to start; if the voltage fault characteristics on the opposite side are not obvious, the differential current starting elements on both the opposite and local sides adopt the differential current criterion; When there is no voltage transformer on both the local side and the opposite side, the differential current starting elements on both the local side and the opposite side adopt the differential current criterion; Among them, the differential current criterion is: when the differential current is greater than the action threshold value, the differential current starting element starts; obvious voltage fault characteristics refer to the voltage fault characteristics meeting the preset conditions; unclear voltage fault characteristics refer to the voltage fault characteristics not meeting the preset conditions.

[0013] Furthermore, a first flag bit and a second flag bit are configured inside the differential current starting element on the local side and the opposite side; When the first flag bit is 1, it indicates that a voltage transformer is connected to this side; when the first flag bit is 0, it indicates that no voltage transformer is connected to this side; When the second flag bit is 1, it indicates that a voltage transformer is connected to the opposite side; when the second flag bit is 0, it indicates that no voltage transformer is connected to the opposite side.

[0014] Furthermore, it also includes: when a disturbance occurs in the power grid system, after entering the open fault processing logic, correcting the state of the voltage transformer on the local side according to the voltage sampling value on the local side and the first voltage threshold value; correcting the state of the voltage transformer on the opposite side according to the voltage sampling value on the opposite side and the second voltage threshold value; Among them, the open fault handling logic refers to the fact that after the differential current starting element detects a disturbance in the power grid system, it quickly and reliably automatically enters the strategy logic processing for various types of disturbances and puts the relevant relay circuit in a pre-action state; the status of the voltage transformer includes the exit state and the connection state.

[0015] Further, when the voltage sampling value on this side is greater than the first voltage threshold value, if the voltage transformer on this side is in the exit state, the voltage transformer on this side is corrected to be in the entry state; when the voltage sampling value on this side is less than the first voltage threshold value, if the voltage transformer on this side is in the entry state, the voltage transformer on this side is corrected to be in the exit state; When the voltage sampling value on the opposite side is greater than the second voltage threshold value, if the voltage transformer on the opposite side is in the exit state, the voltage transformer on the opposite side is corrected to the connection state; when the voltage sampling value on the opposite side is less than the second voltage threshold value, if the voltage transformer on the opposite side is in the connection state, the voltage transformer on the opposite side is corrected to the exit state.

[0016] Furthermore, when using the differential current criterion, the action threshold is raised so that when the current transformer is disconnected, the differential current starting element will not malfunction, and when a fault occurs in the line area, the differential current starting element will not refuse to operate.

[0017] The beneficial effects of the present invention are as follows: as a pioneering invention, the present invention provides a differential protection method and system for long-distance leads on the high-voltage side of a transformer. When a disturbance occurs in the power grid system, by judging whether the differential current starting elements on the local side and the opposite side of the line are connected with voltage transformers, the connection status of the voltage transformers on both sides can be understood; when voltage transformers are connected on both the local side and the opposite side, the differential current starting element on the side with obvious voltage fault characteristics starts automatically, and controls the differential current starting element on the side with unclear voltage fault characteristics to start; when only one side has voltage transformers connected and the voltage fault characteristics on the side with voltage transformers are obvious, the differential current starting element on the side with voltage transformers starts automatically, and controls the differential current starting element on the side without voltage transformers to start; if the voltage fault characteristics on the side with voltage transformers are not obvious, the differential current starting elements on the local side and the opposite side both adopt differential current criterion; when there are no voltage transformers on both the local side and the opposite side, the differential current starting elements on the local side and the opposite side both adopt differential current criterion. On the one hand, when a voltage transformer is connected and the voltage fault characteristics are obvious, the differential current starting element on the side with obvious voltage fault characteristics can be used to control the start of the differential current starting element on the side with unclear voltage fault characteristics, which can accurately determine the occurrence of the fault, and can ensure that the differential current starting element on the side with obvious voltage fault characteristics can be quickly and reliably self-started, and the differential current starting element on the side with unclear voltage characteristics can be quickly and reliably started; when a voltage transformer is connected but the voltage fault characteristics are not obvious, or when no voltage transformer is connected, the differential current criterion is used to ensure that the differential current starting elements on both sides are quickly and reliably opened. On the other hand, the differential protection logic can be adjusted according to the actual situation of configuring voltage transformers on both sides of the lead, which can improve the protection of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a flow chart of a differential protection method for long-distance leads on the high-voltage side of a transformer provided by an embodiment of the present invention; Figure 2 is a schematic diagram of a situation of correcting a voltage transformer on the local side provided by an embodiment of the present invention; Figure 3 It is a schematic diagram of a situation of correcting a voltage transformer on the opposite side provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0020] The idea of ​​the present invention is to select a corresponding differential protection method according to a combination of whether the voltage transformers on the local side and the opposite side of the line are respectively connected to corresponding differential current starting elements.

[0021] Specifically, when a disturbance occurs in the power grid system, it is determined whether the differential current starting elements on the local side and the opposite side of the line are connected to a voltage transformer; when voltage transformers are connected to both the local side and the opposite side, the differential current starting element on the side with obvious voltage fault characteristics starts automatically, and controls the differential current starting element on the side with unclear voltage fault characteristics to start; when only one side has a voltage transformer connected and the voltage fault characteristics on the side with the voltage transformer are obvious, the differential current starting element on the side with the voltage transformer starts automatically, and controls the differential current starting element on the side without the voltage transformer to start; if the voltage fault characteristics on the side with the voltage transformer are not obvious, the differential current starting elements on both the local side and the opposite side adopt a differential current criterion; when there are no voltage transformers on both the local side and the opposite side, the differential current starting elements on both the local side and the opposite side adopt a differential current criterion; wherein, the differential current criterion is: when the differential current is greater than the action threshold value, the differential current starting element starts.

[0022] By judging whether the differential current starting elements on the local side and the opposite side of the line are connected with voltage transformers when a disturbance occurs in the power grid system, the connection status of the voltage transformers on both sides can be understood; when the voltage transformers are connected and the voltage fault characteristics are obvious, the differential current starting elements on the side with obvious voltage fault characteristics can be used to control the start-up of the differential current starting elements on the side with unclear voltage fault characteristics, so as to accurately judge the occurrence of the fault, and ensure both the rapid and reliable self-starting of the differential current starting elements on the side with obvious voltage fault characteristics and the rapid and reliable start-up of the differential current starting elements on the side with unclear voltage characteristics; when the voltage transformers are connected but the voltage fault characteristics are not obvious, or when no voltage transformers are connected, the differential current criterion is used to ensure the rapid and reliable opening of the differential current starting elements on both sides.

[0023] An embodiment of a differential protection method for long-distance leads on the high-voltage side of a transformer: The step-up substation and the transformer body are connected by a lead wire. When the lead wire is a long distance, current transformers are configured on both the local and opposite sides of the lead wire (also called the line) and differential current starting elements can be connected.

[0024] Among them, the line has the conditions for laying an optical fiber channel; the differential current starting element can be an ordinary differential current protection device, or an optical fiber current differential protection device, etc. The present invention does not specifically limit this. In order to increase the information transmission rate and meet the speed requirement, this embodiment will be exemplified by taking the case where the differential current starting element is an optical fiber current differential protection device.

[0025] Among them, this side and the opposite side are relative, and are used to indicate the two ends of the transformer high-voltage side lead. In order to more clearly illustrate the differential protection method provided in this embodiment, it is assumed that one end of a high-voltage direct current transmission line is marked as M and the other end is marked as N. If the M end is taken as the reference object, the M end is the this side and the N end is the opposite side; if the N end is taken as the reference object, the N end is the this side and the M end is the opposite side. In order to facilitate the description of the principle of the differential protection method provided in this embodiment, the M end is taken as the reference object as an example for exemplary description.

[0026] Figure 1 is a flow chart of a differential protection method for long-distance leads on the high-voltage side of a transformer provided by an embodiment of the present invention, such as Figure 1 As shown, the method includes the following steps: S101, when a disturbance occurs in the power grid system, determine whether the differential current starting elements on the local side and the opposite side of the line are connected with voltage transformers.

[0027] In engineering applications, when a disturbance occurs in the power grid system, if both the M and N ends of the line are connected to a large power source, the differential current starting elements at both ends can be reliably started according to the differential current criterion to perform differential protection; if one of the M and N ends of the line is not connected to a power source or is connected to a small power source, the differential current starting element at the end that is not connected to the power source or is connected to the small power source cannot be reliably started according to the differential current criterion. In order to ensure that the differential current starting element can be reliably started and differential protection is performed, a differential current starting element based on the differential current composite voltage criterion is generally used to ensure the reliable operation of the differential protection.

[0028] The differential current composite voltage criterion refers to the use of both the differential current criterion and the voltage fault criterion. Under the action of the two criteria, the differential current element is started together to ensure reliable opening of the differential current starting element.

[0029] The differential current criterion is: when the differential current is greater than the action threshold value, the differential current starting element starts; when the differential current is less than or equal to the action threshold value, the differential current starting element does not start.

[0030] The voltage fault criterion may be any voltage fault feature known to those skilled in the art. For example, it may be the phase voltage on either side, or the sudden change of the phase voltage on either side, or the zero-sequence voltage, or the sudden change of the zero-sequence voltage, etc., and the present invention does not specifically limit this.

[0031] When the voltage fault characteristic is the phase voltage on either side, the voltage fault criterion is: when the phase voltage on either side is less than the preset phase voltage, the differential current starting element starts; when the phase voltage on either side is greater than or equal to the preset phase voltage, the differential current starting element does not start.

[0032] When the voltage fault characteristic is the sudden change of the phase voltage on either side, the voltage fault judgment criterion is: when the sudden change of the phase voltage on either side is greater than the preset phase voltage sudden change, the differential current starting element starts; when the sudden change of the phase voltage on either side is less than or equal to the preset sudden change, the differential current starting element does not start.

[0033] When the voltage fault characteristic is zero-sequence voltage, the voltage fault judgment criterion is: when the zero-sequence voltage is greater than the preset zero-sequence voltage, the differential current starting element starts; when the zero-sequence voltage is less than or equal to the preset zero-sequence voltage, the differential current starting element does not start.

[0034] When the voltage fault characteristic is the sudden change of zero-sequence voltage, the voltage fault judgment criterion is: when the sudden change of zero-sequence voltage is greater than the preset zero-sequence voltage sudden change, the differential current starting element starts; when the sudden change of zero-sequence voltage is less than or equal to the preset zero-sequence voltage sudden change, the differential current starting element does not start.

[0035] The embodiments of the present invention are described hereinafter by taking the case where the voltage fault characteristic is the sudden change of the phase voltage on either side as an example.

[0036] When the voltage fault characteristic is the sudden change of phase voltage on either side, the differential current composite voltage judgment criterion is: when the differential current is greater than the action threshold value, determine whether the sudden change of phase voltage on either side is greater than the preset phase voltage sudden change; if it is, start the differential current starting element; if it is less than or equal to, do not start the differential current starting element.

[0037] It is understandable that for those skilled in the art, after knowing the differential current composite voltage criterion when the voltage fault characteristic is the sudden change of the phase voltage on either side, the differential current composite voltage criterion when the voltage fault characteristic is other characteristics can be easily thought of, and the embodiments of the present application will not be repeated.

[0038] However, the voltage fault judgment criteria rely on the potential transformer (PT). When there is a potential transformer, the voltage fault characteristics are collected. If there is no voltage transformer, the voltage fault characteristics cannot be known. In real life, it is unknown whether PTs are configured on both sides of the lead to access the differential current starting element. It may be configured on one side, on both sides, or not on both sides. When one of the two sides is not connected to the power supply or is connected to a small power supply, whether the side that is not connected to the power supply or connected to a small power supply is configured with PT will affect the sensitivity of the differential current starting element on that side. When PTs are not configured on both sides or when PTs are not configured on the side connected to the large power supply, the differential current starting element may refuse to operate. Therefore, when a disturbance occurs in the power grid system, it is necessary to first determine the access status of the PT.

[0039] Among them, whether there is access to the voltage transformer can be judged by whether there is access voltage, and whether there is access to the voltage transformer can also be judged by judging the flag bit, etc. The present invention does not make any special limitation to this. In order to improve the accuracy of the judgment, the following will take judging whether there is access to the voltage transformer by judging the flag bit as an example for exemplary explanation.

[0040] Specifically, a first flag bit and a second flag bit are added to the interior of the optical fiber current differential protection device (i.e., differential current starting element) on both the local side and the opposite side of the lead-in, the first flag bit is used to indicate the connected state or the disconnected state of the voltage transformer on this side, and the second flag bit is used to indicate the connected state or the disconnected state of the voltage transformer on the opposite side.

[0041] When the M side is taken as the reference object, the M side is the current side and the L side is the opposite side: when the fiber optic current differential protection device on the M side detects that the first flag bit is 1, it indicates that a voltage transformer is connected to the M side (i.e., the voltage transformer is put into operation); when the first flag bit is detected to be 0, it indicates that no voltage transformer is connected to the M side (i.e., the voltage transformer is withdrawn); when the fiber optic current differential protection device on the M side detects that the second flag bit is 1, it indicates that a voltage transformer is connected to the L side; when the second flag bit is detected to be 0, it indicates that no voltage transformer is connected to the L side.

[0042] As an optional implementation, when the fiber optic current differential protection device on the M side detects that the first flag bit is 1, it indicates that there is no voltage transformer connected to the M side, and when the first flag bit is 0, it indicates that there is a voltage transformer connected to the M side (that is, the voltage transformer exits); when the fiber optic current differential protection device on the M side detects that the second flag bit is 1, it indicates that there is no voltage transformer connected to the L side, and when the second flag bit is 0, it indicates that there is a voltage transformer connected to the L side.

[0043] When the L side is taken as the reference object, the L side is the current side and the M side is the opposite side: when the fiber optic current differential protection device on the L side detects that the first flag bit is 1, it indicates that a voltage transformer is connected to the L side; when the first flag bit is 0, it indicates that no voltage transformer is connected to the L side; when the fiber optic current differential protection device on the L side detects that the second flag bit is 1, it indicates that a voltage transformer is connected to the M side; when the second flag bit is 0, it indicates that no voltage transformer is connected to the M side.

[0044] As an optional implementation, when the fiber optic current differential protection device on the L side detects that the first flag bit is 1, it indicates that there is no voltage transformer connected to the L side, and when the first flag bit is 0, it indicates that there is a voltage transformer connected to the L side (that is, the voltage transformer exits); when the fiber optic current differential protection device on the L side detects that the second flag bit is 1, it indicates that there is no voltage transformer connected to the M side, and when the second flag bit is 0, it indicates that there is a voltage transformer connected to the M side.

[0045] The present invention does not specifically limit the states indicated by "1" and "0" of the first flag bit and the second flag bit, and is subject to the actual situation. In the following, an example is taken where the first flag bit is 1, indicating that a voltage transformer is connected to this side, and the first flag bit is 0, indicating that no voltage transformer is connected to this side, for illustrative explanation; similarly, an example is taken where the second flag bit is 1, indicating that a voltage transformer is connected to the opposite side, and the second flag bit is 0, indicating that no voltage transformer is connected to the opposite side, for illustrative explanation.

[0046] S102. Select a corresponding differential protection method according to whether the voltage transformers on the local side and the opposite side of the line are respectively connected to corresponding differential current starting elements.

[0047] According to the judgment result of step S101, there are four combinations, namely: the first one, both the local side and the opposite side have voltage transformers connected; the second one, only the local side has voltage transformers connected; the third one, only the opposite side has voltage transformers connected; the fourth one, neither the local side nor the opposite side has voltage transformers connected. Among them, the second and third ones can be regarded as the case where only one side is connected to the voltage sensor.

[0048] According to different combinations, the corresponding differential protection method is selected. Specifically: for the first case, since voltage transformers are connected on both the local side and the opposite side, the differential current composite voltage criterion on either side of the local side or the opposite side can be used to start the differential current starting element.

[0049] When a disturbance occurs in the power grid system, the voltage fault characteristics of the side connected to the large power source are obvious, while the voltage fault characteristics of the side without power supply or connected to a small power source are not obvious. When voltage transformers are connected on both the local side and the opposite side, the differential current starting element on the side with obvious voltage fault characteristics starts automatically, and controls the differential current starting element on the side with inconspicuous voltage fault characteristics to start.

[0050] Among them, obvious voltage fault characteristics refer to the voltage fault characteristics meeting the preset conditions; unclear voltage fault characteristics refer to the voltage fault characteristics not meeting the preset conditions Taking the voltage fault characteristic being the sudden change of the phase voltage on either side as an example, an obvious voltage fault characteristic means that the sudden change of the phase voltage on either side is greater than the preset phase voltage sudden change; an unclear voltage fault characteristic means that the sudden change of the phase voltage on either side is less than or equal to the preset phase voltage sudden change.

[0051] It is understandable that for those skilled in the art, when knowing what the obvious voltage fault feature means when the voltage fault feature is the sudden change of the phase voltage on either side, and what the unclear voltage fault feature means, it is easy to think of the obvious voltage fault feature and the unclear voltage fault feature when the voltage fault feature is other features, and the embodiments of the present application will not be repeated here.

[0052] For the second case, when the voltage fault characteristics on this side are obvious, the differential current starting element on this side starts automatically and controls the differential current starting element on the opposite side to start; if the voltage fault characteristics on this side are not obvious, the differential current starting elements on this side and the opposite side both use the differential current criterion.

[0053] If the power supply is large, the voltage fault feature is obvious, which can ensure the self-start of the differential current starting element on this side. Since the differential current starting element on the opposite side is not connected to the voltage transformer, it is impossible to complete the self-start using the voltage fault criterion. In order to ensure that the differential current starting element on the opposite side can start quickly and reliably, the differential current starting element on this side controls the start of the differential current starting element on the opposite side.

[0054] If there is no power supply or a small power supply on this side, the voltage fault characteristics on this side are not obvious. The unclear voltage fault characteristics may not guarantee the self-starting of the differential current starting element on this side. The differential current starting element on the opposite side is not connected to the voltage transformer and cannot complete the self-starting using the voltage fault judgment criterion. In order to ensure that the differential current starting elements on this side and the opposite side can be started quickly and reliably, the differential current starting elements on this side and the opposite side both use the differential current judgment criterion.

[0055] For the third case, when the voltage fault characteristics on the opposite side are obvious, the differential current starting element on the opposite side starts automatically and controls the differential current starting element on this side to start; if the voltage fault characteristics on the opposite side are not obvious, the differential current starting elements on both the opposite side and this side adopt the differential current criterion.

[0056] If the opposite side is connected to a large power supply, the voltage fault characteristics on the opposite side are obvious, and the obvious voltage fault characteristics can ensure the self-starting of the differential current starting element on the opposite side. Since the differential current starting element on this side is not connected to the voltage transformer, it is impossible to complete the self-starting using the voltage fault judgment criteria. In order to ensure that the differential current starting element on this side can be started quickly and reliably, the differential current starting element on the opposite side controls the start of the differential current starting element on this side.

[0057] If the opposite side is not connected to power or is connected to a small power supply, the voltage fault characteristics on the opposite side are not obvious. The unclear voltage fault characteristics may not necessarily ensure the self-starting of the differential current starting element on the opposite side. The differential current starting element on this side is not connected to the voltage transformer and cannot complete self-starting using the voltage fault judgment criterion. In order to ensure that the differential current starting elements on this side and the opposite side can be started quickly and reliably, the differential current starting elements on this side and the opposite side both use the differential current judgment criterion.

[0058] For the fourth case, the differential current starting elements on this side and the opposite side both adopt the differential current criterion.

[0059] Since the differential current starting elements on this side and the opposite side are not connected to the voltage transformer, the differential current starting elements cannot be self-started by using the differential current composite voltage criterion. Therefore, the differential current starting elements on both sides use the differential current criterion for judgment.

[0060] As an optional implementation, when using the differential current criterion, the action threshold is raised so that when the current transformer is disconnected, the differential current starting element will not malfunction, and when a fault occurs in the line area, the differential current starting element will not refuse to operate.

[0061] In order to reduce the occurrence of unreliable operation of the differential current starting element due to the voltage transformer being mistakenly switched on or off, as an optional implementation, the state of the voltage transformer may be corrected, that is, step S103 is executed.

[0062] S103: Correct the state of the voltage transformer.

[0063] Specifically, when a disturbance occurs in the power grid system, after entering the open fault processing logic, the state of the voltage transformer on this side is corrected according to the voltage sampling value on this side and the first voltage threshold value; the state of the voltage transformer on the opposite side is corrected according to the voltage sampling value on the opposite side and the second voltage threshold value; Among them, the open fault processing logic refers to the differential current starting element detecting a disturbance in the power grid system and quickly and reliably automatically entering the strategy logic processing for various disturbance types, and putting the circuit of the relevant relay in a pre-open state; the state of the voltage transformer includes an exit state and an entry state; wherein, the first voltage threshold value and the second voltage threshold value can be set according to actual conditions, and can be the same or different. The present invention does not make any special limitation on this. The following example of this embodiment takes the first voltage threshold value and the second voltage threshold value being different as an example for illustrative explanation.

[0064] Among them, when the circuit of the relevant relay is in the pre-opening state, the relevant relay is in the pre-action state; the relay in the pre-action state has not started to actually act, but is only in a preparatory state.

[0065] Specifically, when the voltage sampling value on this side is greater than the first voltage threshold value, if the voltage transformer on this side is in the exit state, the voltage transformer on this side is corrected to the connection state; when the voltage sampling value on this side is less than the first voltage threshold value, if the voltage transformer on this side is in the connection state, the voltage transformer on this side is corrected to the exit state.

[0066] When the voltage sampling value on the opposite side is greater than the second voltage threshold value, if the voltage transformer on the opposite side is in the exit state, the voltage transformer on the opposite side is corrected to the connection state; when the voltage sampling value on the opposite side is less than the second voltage threshold value, if the voltage transformer on the opposite side is in the connection state, the voltage transformer on the opposite side is corrected to the exit state.

[0067] Combine the following Figure 2 and Figure 3 Explain the corrections to the voltage transformer.

[0068] Figure 2 is a schematic diagram of a situation of correcting a voltage transformer on the local side provided by an embodiment of the present invention, such as Figure 2 As shown, in Figure 2 In the table shown, by observing the 3rd, 4th, 7th and 8th rows, it can be known that after a disturbance occurs in the power grid system, after the state of the voltage transformer on this side is determined according to the first flag bit, if the open fault handling logic is not entered, then no matter whether the state of the voltage transformer on this side is in the engaged state (i.e., connected state) or the exit state (i.e., not connected state), the initial state of the voltage transformer will not be corrected.

[0069] By observing the 1st and 5th rows, we can know that after the power grid system is disturbed, after judging the state of the voltage transformer on this side according to the first flag bit, the open fault handling logic is entered, and the voltage sampling value on this side collected by the differential current starting element is automatically identified in real time. When the voltage sampling value on this side is greater than the first voltage threshold value, if the voltage transformer on this side is in the on state, no correction is made. If the voltage transformer on this side is in the off state, the voltage transformer on this side is corrected to be in the on state.

[0070] By observing the 2nd and 6th rows, we can know that after the power grid system is disturbed, after judging the state of the voltage transformer on this side according to the first flag bit, the open fault handling logic is entered, and the voltage sampling value on this side collected by the differential current starting element is automatically identified in real time. When the voltage sampling value on this side is less than the first voltage threshold value, if the voltage transformer on this side is in the engaged state, the voltage transformer on this side is corrected to be in the exited state. If the voltage transformer on this side is in the exited state, it is not corrected.

[0071] Figure 3 is a schematic diagram of a situation of correcting a voltage transformer on the opposite side provided by an embodiment of the present invention, such as Figure 3 As shown, in Figure 3 In the table shown, by observing the 3rd, 4th, 7th and 8th rows, it can be known that after a disturbance occurs in the power grid system, after the state of the voltage transformer on the opposite side is determined according to the second flag bit, if the open fault handling logic is not entered, then no matter whether the state of the voltage transformer on the opposite side is in the engaged state (i.e., connected state) or the exit state (i.e., not connected state), the initial state of the voltage transformer will not be corrected.

[0072] By observing the 1st and 5th rows, we can know that after the power grid system is disturbed, after judging the state of the voltage transformer on the opposite side according to the second flag bit, the open fault handling logic is entered, and the voltage sampling value on the opposite side collected by the differential current starting element from the optical fiber channel is automatically identified in real time. When the voltage sampling value on the opposite side is greater than the second voltage threshold value, if the voltage transformer on the opposite side is in the on state, no correction is made. If the voltage transformer on the opposite side is in the off state, the voltage transformer on the opposite side is corrected to be in the on state.

[0073] By observing the 2nd and 6th rows, we can know that after a disturbance occurs in the power grid system, after determining the state of the voltage transformer on the opposite side according to the second flag bit, the open fault handling logic is entered, and the voltage sampling value on the opposite side collected by the differential current starting element from the optical fiber channel is automatically identified in real time. When the voltage sampling value on the opposite side is less than the second voltage threshold value, if the voltage transformer on the opposite side is in the engaged state, the voltage transformer on the opposite side is corrected to be in the exited state. If the voltage transformer on the opposite side is in the exited state, no correction is made.

[0074] Those skilled in the art will appreciate that the above embodiments are exemplary and are not intended to limit the present application. Where possible, the execution order of one or more of the above steps may be adjusted, or may be selectively combined to obtain one or more other embodiments. Those skilled in the art may select and combine any of the above steps as needed, and all those that do not depart from the essence of the present application fall within the scope of protection of the present application.

[0075] A differential protection method for long-distance leads on the high-voltage side of a transformer provided by an embodiment of the present invention can understand the access status of the voltage transformers on both sides by judging whether the differential current starting elements on the local side and the opposite side of the line are connected with voltage transformers when a disturbance occurs in the power grid system; when voltage transformers are connected on both the local side and the opposite side, the differential current starting element on the side with obvious voltage fault characteristics starts automatically, and controls the differential current starting element on the side with unclear voltage fault characteristics to start; when only one side has voltage transformers connected and the voltage fault characteristics on the side with voltage transformers are obvious, the differential current starting element on the side with voltage transformers starts automatically, and controls the differential current starting element on the side without voltage transformers to start; if the voltage fault characteristics on the side with voltage transformers are unclear, the differential current starting elements on both the local side and the opposite side adopt differential current criterion; when there are no voltage transformers on both the local side and the opposite side, the differential current starting elements on both the local side and the opposite side adopt differential current criterion. On the one hand, when a voltage transformer is connected and the voltage fault characteristics are obvious, the differential current starting element on the side with obvious voltage fault characteristics can be used to control the start of the differential current starting element on the side with unclear voltage fault characteristics, which can accurately determine the occurrence of the fault, and can ensure that the differential current starting element on the side with obvious voltage fault characteristics can be quickly and reliably self-started, and the differential current starting element on the side with unclear voltage characteristics can be quickly and reliably started; when a voltage transformer is connected but the voltage fault characteristics are not obvious, or when no voltage transformer is connected, the differential current criterion is used to ensure that the differential current starting elements on both sides are quickly and reliably opened. On the other hand, the differential protection logic can be adjusted according to the actual situation of configuring voltage transformers on both sides of the lead, which can improve the protection of the power grid.

[0076] An embodiment of a differential protection system for long-distance leads on the high-voltage side of a transformer: A differential protection system for long-distance leads on the high-voltage side of a transformer provided in an embodiment of the present invention includes a processor, which is used to execute a computer program to implement the method steps of the aforementioned "a differential protection method for long-distance leads on the high-voltage side of a transformer".

[0077] Regarding the method steps of a differential protection method for long-distance leads on the high-voltage side of a transformer, please refer to the above-mentioned related statements and will not be repeated here.

[0078] A differential protection system for long-distance leads on the high-voltage side of a transformer provided in an embodiment of the present invention can achieve the same beneficial effects as the aforementioned differential protection method for long-distance leads on the high-voltage side of a transformer, which will not be described in detail here.

Claims

1. A differential protection method for long-distance leads on the high-voltage side of a transformer, characterized in that: The steps include: When a disturbance occurs in the power grid system, determine whether the differential current starting elements on the local side and the opposite side of the line are connected to voltage transformers; When voltage transformers are connected on both the local side and the opposite side, the differential current starting element on the side with obvious voltage fault characteristics starts automatically, and controls the differential current starting element on the side with less obvious voltage fault characteristics to start; When only one side has a voltage transformer connected and the voltage fault characteristics on the side with the voltage transformer are obvious, the differential current starting element on the side with the voltage transformer starts automatically and controls the differential current starting element on the side without the voltage transformer to start; if the voltage fault characteristics on the side with the voltage transformer are not obvious, the differential current starting elements on this side and the opposite side both use the differential current judgment criteria; When there is no voltage transformer on both the local side and the opposite side, the differential current starting elements on both the local side and the opposite side adopt the differential current criterion; Among them, the differential current criterion is: when the differential current is greater than the action threshold value, the differential current starting element is started; the obvious voltage fault feature means that the voltage fault feature meets the preset conditions; the unclear voltage fault feature means that the voltage fault feature does not meet the preset conditions.

2. The differential protection method for long-distance leads on the high-voltage side of a transformer according to claim 1, characterized in that: A first flag bit and a second flag bit are configured inside the differential current starting element on the local side and the opposite side; When the first flag bit is 1, it indicates that a voltage transformer is connected to this side; when the first flag bit is 0, it indicates that no voltage transformer is connected to this side; When the second flag bit is 1, it indicates that a voltage transformer is connected to the opposite side; when the second flag bit is 0, it indicates that no voltage transformer is connected to the opposite side.

3. The differential protection method for long-distance leads on the high-voltage side of a transformer according to claim 1, characterized in that: Also includes: When a disturbance occurs in the power grid system, after entering the open fault processing logic, the state of the voltage transformer on this side is corrected according to the voltage sampling value on this side and the first voltage threshold value; the state of the voltage transformer on the opposite side is corrected according to the voltage sampling value on the opposite side and the second voltage threshold value; Among them, the open fault processing logic refers to the differential current starting element detecting a disturbance in the power grid system and quickly and reliably automatically entering the strategy logic processing for various disturbance types, and putting the relevant relays in a pre-action state; the state of the voltage transformer includes an exit state and an entry state.

4. The differential protection method for long-distance leads on the high-voltage side of a transformer according to claim 3 is characterized in that: When the voltage sampling value on this side is greater than the first voltage threshold value, if the voltage transformer on this side is in the exit state, the voltage transformer on this side is corrected to be in the entry state; when the voltage sampling value on this side is less than the first voltage threshold value, if the voltage transformer on this side is in the entry state, the voltage transformer on this side is corrected to be in the exit state; When the voltage sampling value on the opposite side is greater than the second voltage threshold value, if the voltage transformer on the opposite side is in the exit state, the voltage transformer on the opposite side is corrected to the connection state; when the voltage sampling value on the opposite side is less than the second voltage threshold value, if the voltage transformer on the opposite side is in the connection state, the voltage transformer on the opposite side is corrected to the exit state.

5. The differential protection method for long-distance leads on the high-voltage side of a transformer according to any one of claims 1 to 4, characterized in that: When the differential current criterion is used, the action threshold is raised so that the differential current starting element will not malfunction when the current transformer is disconnected, and the differential current starting element will not refuse to operate when a fault occurs in the line.

6. A differential protection system for long-distance leads on the high-voltage side of a transformer, comprising a processor, characterized in that: The processor is used to execute a computer program to implement the following steps: When a disturbance occurs in the power grid system, determine whether the differential current starting elements on the local side and the opposite side of the line are connected to voltage transformers; When voltage transformers are connected on both the local side and the opposite side, the differential current starting element on the side with obvious voltage fault characteristics starts automatically, and controls the differential current starting element on the side with less obvious voltage fault characteristics to start; When only one side has a voltage transformer connected and the voltage fault characteristics on the side with the voltage transformer are obvious, the differential current starting element on the side with the voltage transformer starts automatically and controls the differential current starting element on the side without the voltage transformer to start; if the voltage fault characteristics on the side with the voltage transformer are not obvious, the differential current starting elements on this side and the opposite side both use the differential current judgment criteria; When there is no voltage transformer on both the local side and the opposite side, the differential current starting elements on both the local side and the opposite side adopt the differential current criterion; Among them, the differential current criterion is: when the differential current is greater than the action threshold value, the differential current starting element is started; the obvious voltage fault feature means that the voltage fault feature meets the preset conditions; the unclear voltage fault feature means that the voltage fault feature does not meet the preset conditions.

7. The differential protection system for long-distance leads on the high-voltage side of a transformer according to claim 6, characterized in that: A first flag bit and a second flag bit are configured inside the differential current starting element on the local side and the opposite side; When the first flag bit is 1, it indicates that a voltage transformer is connected to this side; when the first flag bit is 0, it indicates that no voltage transformer is connected to this side; When the second flag bit is 1, it indicates that a voltage transformer is connected to the opposite side; when the second flag bit is 0, it indicates that no voltage transformer is connected to the opposite side.

8. The differential protection system for long-distance leads on the high-voltage side of a transformer according to claim 6, characterized in that: Also includes: When a disturbance occurs in the power grid system, after entering the open fault processing logic, the state of the voltage transformer on this side is corrected according to the voltage sampling value on this side and the first voltage threshold value; the state of the voltage transformer on the opposite side is corrected according to the voltage sampling value on the opposite side and the second voltage threshold value; Among them, the open fault processing logic refers to the differential current starting element detecting a disturbance in the power grid system and quickly and reliably automatically entering the strategy logic processing for various disturbance types, and putting the relevant relays in a pre-action state; the state of the voltage transformer includes an exit state and an entry state.

9. The differential protection system for long-distance leads on the high-voltage side of a transformer according to claim 6, characterized in that: When the voltage sampling value on this side is greater than the first voltage threshold value, if the voltage transformer on this side is in the exit state, the voltage transformer on this side is corrected to be in the entry state; when the voltage sampling value on this side is less than the first voltage threshold value, if the voltage transformer on this side is in the entry state, the voltage transformer on this side is corrected to be in the exit state; When the voltage sampling value on the opposite side is greater than the second voltage threshold value, if the voltage transformer on the opposite side is in the exit state, the voltage transformer on the opposite side is corrected to the connection state; when the voltage sampling value on the opposite side is less than the second voltage threshold value, if the voltage transformer on the opposite side is in the connection state, the voltage transformer on the opposite side is corrected to the exit state.

10. The differential protection system for long-distance leads on the high-voltage side of a transformer according to any one of claims 6 to 9, characterized in that: When the differential current criterion is used, the action threshold is raised so that the differential current starting element will not malfunction when the current transformer is disconnected, and the differential current starting element will not refuse to operate when a fault occurs in the line.

Images