WO2021174631A1 - Power transmission line distance protection current transformer saturation identification method and system - Google Patents

Abstract

Disclosed are a power transmission line distance protection current transformer saturation identification method and system. According to the present invention, a distance protection locking criterion and a distance protection opening criterion are constructed on the basis of an incomplete differential locking criterion, an incomplete differential opening criterion, a working voltage locking criterion, a working voltage opening criterion, and a current harmonic unlocking criterion, thereby ensuring that, in case of a reverse direction fault and current transformer saturation in a half-switch wiring or annular wiring mode, distance protection is still reliable and free of maloperation, and ensuring that, in case of a forward direction fault and various reverse direction to forward direction faults, distance protection can still operate reliably.

Description

Method and system for identifying saturation of current transformer for distance protection of transmission line Technical field

The invention relates to a method and system for identifying the saturation of a current transformer for distance protection of a transmission line, and belongs to the technical field of power system relay protection.

Background technique

The operating range and sensitivity of distance protection are less affected by the operation mode of the system, which can meet the needs of complex systems for rapid fault removal, and is widely used in high-voltage transmission lines. The basic working principle of distance protection is to measure the distance from the fault point to the protection installation location, and determine the action time according to the distance. The transfer characteristic of the current transformer (TA) is one of the important factors affecting the distance protection. The distortion of the secondary current when the current transformer is saturated will affect the action behavior of the distance protection.

The IEEE Std C37.110 standard points out that in the loop wiring or one and a half switch wiring mode, the current used for line protection is the sum of the currents of the two current transformers. When the bus fails, the current transformer will flow a large through current. If the current transformer is saturated, and the current may show a large reverse current, the distance protection may malfunction.

In order to solve the problem of the fault current transformer saturation distance protection misoperation in a half-switch connection (ie 3/2 connection mode) or ring connection mode, scholars at home and abroad have conducted a lot of research. The existing methods cannot meet the requirements of various working conditions, and the distance protection may still malfunction when the fault current transformer in the reverse direction is saturated.

Summary of the invention

The present invention provides a method and system for identifying the saturation of a current transformer for distance protection of a transmission line, which solves the problems disclosed in the background art.

In order to solve the above technical problems, the technical solutions adopted by the present invention are:

A transmission line distance protection current transformer saturation recognition method, including:

According to the current change of the current transformer involved in the distance protection, construct an incomplete differential lockout criterion and an incomplete differential open criterion;

According to the voltage variation and the working voltage variation of the protection installation, construct the working voltage blocking criterion and the working voltage opening criterion;

According to the incomplete differential lockout criterion, the incomplete differential open criterion, the working voltage lockout criterion and the working voltage open criterion, construct the lock distance protection criterion and the open distance protection criterion;

Based on the blocking distance protection criterion and the open distance protection criterion, the saturation recognition of the distance protection current transformer is performed.

The criterion of incomplete differential lockout is,

The criterion of incomplete differential opening is,

in,

Is the incomplete differential current,

For incomplete braking current,

It is the current variation of the two sub-current transformers involved in distance protection in a half-wire or ring-wire mode, I _{SET_ZD} is the incomplete braking current threshold, and k _res is the differential ratio braking coefficient.

The working voltage lockout criterion is,

The operating voltage opening criterion is,

in,

Is the change in operating voltage,

To protect the voltage variation at the installation location, U _{SET_DIF} is the voltage threshold, and k is the coefficient.

The incomplete differential blocking criterion and the working voltage blocking criterion are combined to construct the blocking distance protection criterion, and the incomplete differential opening criterion and the working voltage opening criterion are to be ORed to construct the open distance protection criterion.

After meeting the blocking distance protection criterion and performing blocking distance protection, if the current transformer current involved in the distance protection and their sum current meet the current harmonic release blocking criterion, the distance protection will be opened.

The criterion of the current harmonic release blocking is,

Among them, I _m is the sum current, I _{m_h2} is the second harmonic content of the sum current, I _m1 and I _m2 are the current transformer currents involved in the distance protection, and I _{m1_h2} and I _{m2_h2} are the current transformer currents involved in the distance protection. Second harmonic content, k _H is the threshold of harmonic content ratio.

A transmission line distance protection current transformer saturation recognition system, including:

Incomplete differential criterion module: According to the collected current changes of the current transformer involved in the distance protection, construct an incomplete differential lockout criterion and an incomplete differential open criterion;

Working voltage criterion module: According to the voltage variation and the working voltage variation of the protection installation, construct the working voltage blocking criterion and the working voltage opening criterion;

Distance protection criterion module: According to the incomplete differential blocking criterion, incomplete differential opening criterion, working voltage blocking criterion and working voltage opening criterion, construct the blocking distance protection criterion and the open distance protection criterion;

Distance protection module: distance protection based on the blocking distance protection criterion and the open distance protection criterion.

The distance protection criterion module includes and module and or module;

And module: The incomplete differential lockout criterion and the working voltage lockout criterion are ANDed to construct the lockout distance protection criterion;

Or module: The incomplete differential open criterion and the working voltage open criterion are ORed to construct an open distance protection criterion.

A computer-readable storage medium storing one or more programs, the one or more programs including instructions that, when executed by a computing device, cause the computing device to perform transmission line distance protection current transformer saturation recognition method.

A computing device includes one or more processors, a memory, and one or more programs, where one or more programs are stored in the memory and configured to be executed by the one or more processors, the One or more programs include instructions for executing the method for identifying saturation of current transformers for distance protection of transmission lines

The beneficial effects achieved by the present invention: the present invention constructs the blocking distance protection criterion and the open distance protection criterion based on the incomplete differential lockout criterion, the incomplete differential open criterion, the working voltage lockout criterion and the working voltage open criterion According to data, it is ensured that the distance protection is reliable and does not malfunction when the reverse direction fault current transformer is saturated in a half-switch connection or ring connection mode, and the distance protection is reliable in the case of forward direction faults and various reverse direction to forward direction faults.

Description of the drawings

Figure 1 is a system diagram of a half-wiring mode;

Figure 2 is the current distribution diagram when a short-circuit fault occurs in the forward direction;

Figure 3 is a diagram of the current distribution when a short-circuit fault occurs in the opposite direction;

Figure 4 is the system diagram when the BRK3 double-circuit line on the same tower is disconnected;

Figure 5 shows the fault voltage distribution in the opposite direction;

Figure 6 shows the fault voltage distribution in the positive direction;

Figure 7 is the system diagram when the BRK4 double-circuit line on the same tower is disconnected;

Figure 8 is a logical diagram of the method of the present invention;

Figure 9 shows the RTDS simulation system;

Figure 10 shows the characteristics of the criterion in the case of a positive fault;

Figure 11 shows the criterion characteristic when the fault occurs in the reverse direction;

Figure 12 shows the criterion characteristics when the fault occurs in the reverse direction and the current transformer is saturated.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and cannot be used to limit the protection scope of the present invention.

A transmission line distance protection current transformer saturation recognition method includes the following steps:

Step 1. Construct an incomplete differential lockout criterion and an incomplete differential open criterion based on the current change of the two-way sub-current transformer involved in distance protection in a half-wiring mode or ring wiring mode; The blocking criterion and the incomplete differential opening criterion are collectively referred to as the incomplete differential criterion.

For UHV line protection that is applied to loop wiring or one and a half switch wiring, the two currents involved in line protection are connected to the protection by two-way current transformers, and the sampling calculations are performed separately, which is different from the traditional two-way current transformer. Circuit current transformer current is physically synthesized externally and the current is reconnected to the protection method. Take a half-switch wiring mode as an example, as shown in Figure 1. In the traditional mode, the current obtained by the protection of line L1 is externally physically synthesized

(

Is a physically synthesized sum current,

They are the side switch and middle switch current transformer output current). In the present invention, the protection of line L1 collects the current transformer current involved in distance protection respectively, that is, the current transformer currents I _m1 and I _{m2 in the} figure, and use short The data window algorithm (half-wave Fourier algorithm) calculates the respective current changes.

The incomplete differential lockout criterion and the incomplete differential open criterion constructed according to the current change are as follows:

Incomplete differential lockout criterion:

Incomplete differential opening criterion:

in,

Is the incomplete differential current,

For incomplete braking current,

Is the current change of the sub-current transformer involved in distance protection, I _{SET_ZD} is the incomplete braking current threshold, k _res is the differential ratio braking coefficient, and the value is 1.1.

FIG 2 is a positive direction of the additional status line short-circuit fault point F1 proximal end, a predetermined current to point to the positive direction of the line, i.e., before applying the opposite direction with the same amplitude of the voltage ΔU _f at the fault point F1, flowing through the voltage caused by the edge Current change of switch and middle switch current transformer

They are all in the opposite direction, and their relationship satisfies the incomplete differential opening criterion expressed by equation (1).

Figure 3 shows the additional state when a short-circuit fault occurs at point F2 at the near end of the line in the opposite direction, that is, the current change caused by the voltage _{at point F2 that is the same as the voltage amplitude before the fault and the opposite ΔU f is applied.}

Is the positive direction,

In the opposite direction, the two directions are opposite, and the relationship satisfies the incomplete differential lockout criterion expressed by equation (2).

In formulas (1) and (2),

All calculations adopt the short data window algorithm (half-wave Fourier algorithm). In the event of a failure of the near-end metallicity in the forward and reverse directions, the incomplete differential opening criterion and the blocking criterion can act quickly. However, for near-end via high-impedance faults or far-end faults, the criterion is not sensitive enough and will cause misjudgment. For example, under the special working conditions shown in Figure 4, two outgoing wires of a half switch are erected on the same tower, BRK3 When disconnected (defined as working condition A), a short-circuit fault occurs at the end of the line or the N-side bus,

Will be very small, at this time ΔI _cd ≈ _{ΔI zd} , the incomplete differential lockout criterion will act, causing the distance protection to refuse to move.

Therefore, the above-mentioned incomplete differential criterion alone cannot perform comprehensive current transformer saturation recognition, and needs to be combined with other criteria, that is, the subsequent working voltage criterion.

Step 2: According to the voltage variation and the working voltage variation of the protection installation, construct the working voltage blocking criterion and the working voltage opening criterion; the working voltage blocking criterion and the working voltage opening criterion are collectively referred to as the working voltage criterion.

Working voltage lockout criterion:

Criterion of working voltage opening:

In formulas (3) and (4):

in,

Is the change in operating voltage,

In order to protect the voltage variation at the installation place,

In order to protect the current variation at the installation location, Z _L is the total line impedance, U _{SET_DIF} is the voltage threshold, k is the coefficient, and the value is 1.1.

For faults in the reverse direction, there are:

Among them, Z _R is the equivalent positive sequence impedance in the positive direction of the protection;

Substituting formula (6) into formula (5), we can get:

The amount of voltage change at the fault point is:

in,

Is the voltage change at the fault point, and Z _F is the positive sequence impedance from the short-circuit point to the protection installation.

According to the above relationship, the potential diagram of the voltage change in the reverse direction short circuit can be obtained. As shown in Figure 5, it can be seen that there must be a short circuit in the reverse direction.

For faults in the positive direction, there are:

Among them, Z _S is the equivalent positive sequence impedance of the power supply behind the protection;

Substituting formula (9) into formula (5), we can get:

The amount of voltage change at the fault point is:

Among them, Z _F is the positive sequence impedance from the short-circuit point to the protection installation.

According to the above relationship, the potential diagram of the voltage change during a short-circuit in the positive direction can be obtained, as shown in Figure 6. It can be seen from the figure that there must be a short circuit within the full length of the line in the positive direction

In formulas (3) and (4),

Both use short data window algorithm (half-wave Fourier algorithm) to calculate. Under normal working conditions, when a fault occurs in the forward direction, the operating voltage opening criterion acts; when a fault occurs in the reverse direction, the working voltage blocking criterion acts. However, for some special working conditions, as shown in Figure 7, when the BRK4 is disconnected and running, when the reverse direction bus fault occurs, the sum current obtained by the protection is zero.

Cause the criterion to become invalid.

Thus, in

Multiply the front by a coefficient k slightly greater than 1, to ensure that the blocking criterion can operate reliably in this case, and when the positive direction fails

Is much larger than

Yes, so the coefficient k does not affect the judgment of the open criterion. Under this working condition, the incomplete differential lockout criterion can operate correctly and has high sensitivity.

Step 3: Construct a blocking distance protection criterion and an open distance protection criterion according to the incomplete differential lockout criterion, the incomplete differential open criterion, the working voltage lockout criterion and the working voltage open criterion.

The actions of the incomplete differential criterion and the working voltage criterion at each fault point under different system conditions are shown in Table 1, where F1, F2, and F3 are the near-end, far-end, and reverse bus fault points of the line, respectively. The following conclusions can be drawn from Table 1:

1) Working condition 1, no matter what kind of failure, the working voltage blocking criterion is always active, and the working voltage opening criterion is always inactive; the incomplete differential criterion works normally;

2) Working condition 2: When a fault occurs at point F3, the incomplete differential lockout criterion will act, the incomplete differential open criterion will not act, and the operating voltage criterion will act normally;

3) Under normal working conditions, both the incomplete differential criterion and the working voltage criterion operate normally.

Therefore, the incomplete differential lockout criterion and the working voltage lockout criterion are ANDed to construct the blocking distance protection criterion, and the incomplete differential open criterion and the working voltage open criterion are ORed to construct the open distance protection criterion. According to; Realize that the criterion has strict directionality under all working conditions.

Since the criterion is obtained based on the characteristics of the linear transmission region before saturation of the current transformer, in order to avoid the influence of the current distortion on the criterion after saturation, the blocking criterion and the open criterion are mutually blocked (as shown in Figure 8) to ensure that the saturation period is judged. The continuity of the data.

Table 1 Actions of incomplete differential criterion and working voltage criterion

Step 4: Perform distance protection based on the blocking distance protection criterion and the open distance protection criterion; after the blocking distance protection criterion is met, if the distance protection involves two sub-current transformer currents and their sum currents The current harmonic releases the blocking criterion, and the distance protection is opened.

Criteria for unlocking current harmonics:

Among them, I _m is the sum current, I _{m_h2} is the second harmonic content of the sum current, I _m1 and I _m2 are the current transformer currents involved in the distance protection, and I _{m1_h2} and I _{m2_h2} are the current transformer currents involved in the distance protection. Second harmonic content, k _H is the threshold of harmonic content ratio, generally 0.15.

When the reverse fault distance protection enters the blocking period, the harmonic content in the current is calculated. When the harmonic content is lower than a certain threshold and the distance protection meets the operating conditions, the distance protection blocking is released. This criterion can realize that the distance protection can operate again when the current transformer saturation disappears when the fault in the reverse direction turns into the fault in the forward direction.

The above method is based on the incomplete differential lockout criterion, the incomplete differential open criterion, the working voltage lockout criterion, and the working voltage open criterion to construct the lockup distance protection criterion and the open distance protection criterion to ensure a half-switch wiring or In the ring wiring mode, the distance protection is reliable and does not malfunction when the reverse direction fault current transformer is saturated, and at the same time, the distance protection is guaranteed to operate reliably in the case of forward direction faults and various reverse direction to forward direction faults.

Combining the content of the above method, the following simulation embodiment is provided for a certain AC power transmission system model:

As shown in Figure 9, the 500kV voltage level is built on the RTDS platform, one side is a half-switch connection, and the other side is a double-bus connection on the same tower double-circuit line simulation model. In the model, F1-F3 are set in the area. Fault points, F4 and F5 fault points outside the area, each fault point can simulate various types of faults respectively. The system impedance and line parameters on both sides of the simulation system are shown in Table 2. The equivalent systems on both sides can be changed according to the test needs.

Table 2 System impedance and line parameters

project	parameter	unit
Positive sequence resistance	0.028	ohm/km
Positive sequence inductive resistance	0.275	ohm/km
Positive sequence parallel capacitive reactance	0.225	Mohm*km
Zero sequence resistance	0.094	ohm/km
Zero sequence inductive reactance	0.674	ohm/km
Zero sequence parallel capacitive reactance	0.313	Mohm*km
Line length	100	km
M system equivalent impedance	10∠85°	ohm
N system equivalent impedance	20∠85°	ohm

Connect the device (device A) and the ordinary protection device (device B) developed according to the above method to the M side of the line L1, respectively. Among them, the device A is connected to the output current of the current transformer 1 and the current transformer 2 (that is, the current transformer involved in line protection), and the device B is connected to the sum current. The fixed value of distance Ⅰ is set according to 0.8 of the impedance of the full length of the line; the fixed value of distance Ⅱ is set according to 1.2 times of the full length of the line, and the fixed value of time is 0.5s.

Under different operating modes, the analog line has metallic faults in the forward and reverse directions. The simulation results are shown in Table 3.

Table 3 Action behaviors of protection devices in different operating modes

To	Point of failure	Device A	Device B
Strong on both sides	F1	12ms from section Ⅰ	12ms from section Ⅰ
Strong on both sides	F2	21ms from section I	21ms from section I
Strong on both sides	F4	No action	No action
Strong on M side and weak on N side	F1	10ms from section Ⅰ	10ms from section Ⅰ
Strong on M side and weak on N side	F3	521ms from section II	521ms from section II
Strong on M side and weak on N side	F5	No action	No action

Comparing device A and device B, it can be seen that under normal operating conditions, when the forward and reverse directions fail, the distance protection action characteristics of the two are the same, indicating that the above method does not affect the original action characteristics of the distance protection.

When the F1 point fault is simulated, the device A record is shown in Figure 10. After the fault, the incomplete differential opening criterion and the working voltage open criterion are quickly satisfied, and the distance protection is opened; when the F5 point fault is simulated, the device record is shown in Figure 11. As shown, the incomplete differential blocking criterion and the working voltage blocking criterion are quickly satisfied after the fault, and the distance protection is blocked.

The simulation result is shown in Table 4 with a conversion failure in the forward and reverse directions. It can be seen from the simulation results that for transitional faults, the actions of the two sets of protection devices are the same. When the fault occurs in the reverse direction to the forward direction, the distance protection can accurately open and then operate, which verifies the feasibility of the current harmonic content unlocking criterion.

Table 4 Action behavior of protection device under transitional fault

The single-phase grounding fault at point F4 in the opposite direction is simulated, and one and a half switch wiring sides are simulated respectively. The two current transformers are saturated to different degrees. The action behavior of the protection device is shown in Table 5. When the fault current transformer in the reverse direction is saturated and the linear transmission area is greater than or equal to 2ms, the device A can be reliably blocked, and the device B will malfunction.

Table 5 F4 point fault protection action behavior in the reverse direction

Saturation current transformer	Linear transfer time	Device A	Device B
Current transformer 1	2ms	No action	action
Current transformer 1	2.5ms	No action	action
Current transformer 1	5ms	No action	action
Current transformer 2	2ms	No action	No action
Current transformer 2	5ms	No action	No action

When the F4 point fault is simulated and the current transformer 1 is saturated, the device recording is shown in Figure 12. In the linear transmission area of the current transformer after the fault, the incomplete differential lockout criterion and the working voltage lockout criterion are quickly satisfied. The distance protection blocking criterion action. After entering the saturation region of the current transformer, the operating voltage opening criterion and the incomplete differential opening criterion are satisfied successively, but because the distance protection blocking criterion is satisfied first and the opening criterion is blocked, the blocking state of the distance protection is maintained.

Under simulated operating conditions 1, single-phase grounding fault occurs at point F3 again under various operating modes, and the action behavior of the distance protection device of the protection device is shown in Table 6.

Table 6 F3 point fault protection action in the positive direction

Simulation condition two, single-phase ground fault at point F5 in the opposite direction, respectively simulate one and a half switch wiring sides, the two current transformers are saturated to varying degrees, and the action behavior of the protection device is shown in Table 7.

Action behavior of fault protection at point F5 outside of Table 7

Saturation current transformer	Linear transfer time	Device A	Device B
Current transformer 1	2ms	No action	No action
Current transformer 1	5ms	No action	No action
Current transformer 2	2ms	No action	action
Current transformer 2	5ms	No action	action

From the simulation results of the two special working conditions, it can be seen that device A does not refuse to move when a fault occurs in the forward direction, and does not malfunction when a fault occurs in the reverse direction and the current transformer is saturated, while device B has a malfunction. It is verified that the combination of the incomplete differential criterion and the working voltage criterion solves the problem of the misoperation of a single criterion under special working conditions and ensures the correct operation of the criterion under all working conditions.

A transmission line distance protection current transformer saturation recognition system, including:

Incomplete differential criterion module: According to the collected current changes of the current transformer involved in the distance protection, an incomplete differential lockout criterion and an incomplete differential open criterion are constructed.

Working voltage criterion module: According to the voltage change amount and the working voltage change amount of the protection installation, the working voltage blocking criterion and the working voltage opening criterion are constructed.

Distance protection criterion module: According to the incomplete differential lockout criterion, the incomplete differential open criterion, the working voltage lockout criterion and the working voltage open criterion, the blocking distance protection criterion and the open distance protection criterion are constructed.

The distance protection criterion module includes and module and or module;

AND module: the incomplete differential lockout criterion and the working voltage lockout criterion are ANDed to construct the locking distance protection criterion; or the module: the incomplete differential open criterion and the working voltage open criterion are ORed to construct Open distance protection criterion.

Distance protection module: distance protection based on the blocking distance protection criterion and the open distance protection criterion.

A computer-readable storage medium storing one or more programs, the one or more programs including instructions that, when executed by a computing device, cause the computing device to execute a method for protecting a distance from a transmission line.

A computing device includes one or more processors, a memory, and one or more programs, where one or more programs are stored in the memory and configured to be executed by the one or more processors, the One or more programs include instructions for implementing the distance protection method of the transmission line.

Those skilled in the art should understand that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, this application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, this application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

This application is described with reference to flowcharts and/or block diagrams of methods, devices (systems), and computer program products according to embodiments of this application. It should be understood that each process and/or block in the flowchart and/or block diagram, and the combination of processes and/or blocks in the flowchart and/or block diagram can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing equipment to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing equipment are generated It is a device that realizes the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.

These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing equipment to work in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including the instruction device. The device implements the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.

These computer program instructions can also be loaded on a computer or other programmable data processing equipment, so that a series of operation steps are executed on the computer or other programmable equipment to produce computer-implemented processing, so as to execute on the computer or other programmable equipment. The instructions provide steps for implementing the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.

The above are only the embodiments of the present invention and are not used to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the pending application of the present invention. Within the scope of the claims.

Claims (10)

1. A transmission line distance protection current transformer saturation recognition method, which is characterized in that it includes:

   According to the current change of the current transformer involved in the distance protection, construct an incomplete differential lockout criterion and an incomplete differential open criterion;

   According to the voltage variation and the working voltage variation of the protection installation, construct the working voltage blocking criterion and the working voltage opening criterion;

   According to the incomplete differential lockout criterion, the incomplete differential open criterion, the working voltage lockout criterion and the working voltage open criterion, construct the lock distance protection criterion and the open distance protection criterion;

   Based on the blocking distance protection criterion and the open distance protection criterion, the saturation recognition of the distance protection current transformer is performed.
2. The method for identifying the saturation of a current transformer for transmission line distance protection according to claim 1, wherein the incomplete differential lockout criterion is:

   

   The criterion of incomplete differential opening is,

   

   in,

   

   Is the incomplete differential current,

   

   For incomplete braking current,

   

   It is the current variation of the two sub-current transformers involved in distance protection in a half-wire or ring-wire mode, I _{SET_ZD} is the incomplete braking current threshold, and k _res is the differential ratio braking coefficient.
3. The method for identifying the saturation of a current transformer for distance protection of a transmission line according to claim 1, wherein the working voltage blocking criterion is:

   

   The operating voltage opening criterion is,

   

   in,

   

   Is the change in operating voltage,

   

   To protect the voltage variation at the installation location, U _{SET_DIF} is the voltage threshold, and k is the coefficient.
4. A method for identifying the saturation of a current transformer for transmission line distance protection according to claim 1, characterized in that: the incomplete differential blocking criterion and the working voltage blocking criterion are ANDed to construct the blocking distance protection criterion, and The incomplete differential opening criterion and the working voltage opening criterion are ORed to construct an open distance protection criterion.
5. The method for identifying the saturation of a current transformer for transmission line distance protection according to claim 1, characterized in that: after the criterion of blocking distance protection is met for blocking distance protection, if distance protection involves current transformer currents and their sum currents The distance protection will be opened when the criterion of current harmonic release blocking is met.
6. The method for identifying the saturation of a current transformer for distance protection of a transmission line according to claim 5, wherein the current harmonic release blocking criterion is:

   

   Among them, I _m is the sum current, I _{m_h2} is the second harmonic content of the sum current, I _m1 and I _m2 are the output currents of the side and middle switch current transformers, and I _{m1_h2} and I _{m2_h2} are the output of the side and middle switch current transformers The second harmonic content of the current, k _H is the harmonic content ratio threshold.
7. A transmission line distance protection current transformer saturation recognition system, which is characterized in that it includes:

   Incomplete differential criterion module: According to the collected current changes of the current transformer involved in the distance protection, construct an incomplete differential lockout criterion and an incomplete differential open criterion;

   Working voltage criterion module: According to the voltage variation and the working voltage variation of the protection installation, construct the working voltage blocking criterion and the working voltage opening criterion;

   Distance protection criterion module: According to the incomplete differential blocking criterion, incomplete differential opening criterion, working voltage blocking criterion and working voltage opening criterion, construct the blocking distance protection criterion and the open distance protection criterion;

   Distance protection module: distance protection based on the blocking distance protection criterion and the open distance protection criterion.
8. A transmission line distance protection current transformer saturation recognition system according to claim 7, wherein the distance protection criterion module includes an AND module and or a module;

   And module: The incomplete differential lockout criterion and the working voltage lockout criterion are ANDed to construct the lockout distance protection criterion;

   Or module: The incomplete differential open criterion and the working voltage open criterion are ORed to construct an open distance protection criterion.
9. A computer-readable storage medium storing one or more programs, wherein the one or more programs include instructions, which when executed by a computing device, cause the computing device to execute according to claims 1 to Any of the methods described in 6.
10. A computing device, characterized in that it includes,

    One or more processors, a memory, and one or more programs, where one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include Instructions for executing any one of the methods according to claims 1 to 6.

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