Online Monitoring Method for PT Short Circuit Fault in 4PT Connection of Low Current Grounding System

Abstract

The present invention discloses an online monitoring method for PT short-circuit faults in a 4PT connection in a low-current grounding system. The method comprises: the 4PT connection includes a phase A PT, a phase B PT, a phase C PT, and a harmonic elimination PT; under normal system operation, calculating the primary voltage value supported by the harmonic elimination PT and determining the primary voltage value to monitor for PT short-circuit faults; and when a single-phase grounding fault occurs in the system, calculating the primary voltage value supported by the harmonic elimination PT and again determining the primary voltage value to monitor for PT short-circuit faults. The present invention enables real-time and accurate monitoring of PT short-circuit faults without shutting down or disassembling the PT, thereby improving monitoring efficiency.

Description

Technical Field

[0001] The present invention relates to the field of short-circuit fault monitoring, and in particular to an online monitoring method for PT short-circuit faults in a 4PT connection of a small current grounding system. Background Art

[0002] When a ground fault occurs on a phase, the ground fault current is often much smaller than the load current because no short-circuit loop is formed. This is why this system is called a "low-current grounding system." A low-current grounding system is a three-phase system in which the neutral point is ungrounded or grounded via an arc suppression coil and high impedance. This is also known as an indirect neutral grounding system.

[0003] PT short-circuit faults sometimes occur in low-current grounding systems. Currently, the monitoring of PT short-circuit faults mainly adopts the method of shutting down the PT and then disassembling and inspecting the PT. This not only interrupts the normal operation of the PT and affects production efficiency, but also greatly reduces the efficiency of PT short-circuit fault monitoring because it mainly relies on manual disassembly and inspection. At the same time, the existence of human errors will also reduce the accuracy of PT short-circuit fault monitoring.

[0004] Therefore, a method for online monitoring of PT short-circuit faults in a 4PT connection of a low-current grounding system is needed to solve the above problems. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to overcome the defects in the prior art and provide an online monitoring method for PT short-circuit faults in a 4PT connection of a small current grounding system, which can accurately monitor PT short-circuit faults in real time without stopping the PT from operation or disassembling, thereby improving the monitoring efficiency.

[0006] The present invention provides an online monitoring method for PT short-circuit faults in a 4PT connection of a low-current grounding system, comprising: the 4PT connection includes an A-phase PT, a B-phase PT, a C-phase PT, and a detuning PT;

[0007] Under normal system operation, calculate the primary voltage value that the detuning PT bears And judge the short circuit fault as follows:

[0008] If Z A Z B =Z C , Then the A-phase PT has a short circuit fault;

[0009] If Z B Z A =Z C , Then the B phase PT has a short circuit fault;

[0010] If ZC Z A =Z B , Then the C phase PT has a short circuit fault; A is the PT impedance of phase A, Z B is the B-phase PT impedance, Z C is the C-phase PT impedance;

[0011] When a single-phase ground fault occurs in the system, calculate the primary voltage value that the detuning PT bears And judge the short circuit fault as follows:

[0012] If Z0Z A =Z B =Z C , Then a short circuit fault occurs in the detuning PT; where Z0 is the detuning PT impedance.

[0013] Furthermore, under normal system operation, calculate the primary voltage value that the detuning PT bears

[0014] Among them, Z A is the impedance of phase A, Z B is the impedance of phase B, Z C is the C-phase impedance, is the voltage of phase A relative to ground; is the voltage of B relative to ground; is the voltage between phase C and ground; Z0 is the detuning PT impedance.

[0015] Furthermore, when a single-phase ground fault occurs in the system, the primary voltage value that the detuning PT bears is calculated.

[0016] Among them, Z B is the impedance of phase B, Z C is the impedance of phase C, Z A' is the impedance of A relative to the neutral point; is the voltage of phase A relative to ground; is the voltage of B relative to ground; is the voltage of phase C relative to ground.

[0017] Furthermore, it also includes: adding a secondary winding for PT short-circuit fault online monitoring:

[0018] Calculate the output voltage u of the secondary winding n' ;

[0019] When the system is operating normally, if the voltage u n'If it is greater than the set value, there is a short circuit fault in the A-phase PT, B-phase PT, and C-phase PT;

[0020] When a single-phase grounding occurs in the system, if the voltage u n' If it is less than the set value, the detuning PT will have a short circuit fault.

[0021] Furthermore, the output voltage u of the secondary winding is calculated according to the following formula: n' :

[0022]

[0023] Among them, U N' is the 4PT neutral point to ground voltage, and k is the new winding ratio.

[0024] The beneficial effects of the present invention are as follows: the present invention discloses an online monitoring method for PT short-circuit faults in a 4PT connection of a small current grounding system, which adds a group of windings in addition to the existing voltage acquisition requirements by detuning the PT, and the windings are selected to be consistent with the transformation ratio of the existing measurement windings; the output voltage of the newly added secondary winding is used as the voltage input of an electronic device with a voltage value discrimination function, the voltage discrimination result of the electronic device is used as a telesignaling signal, and the voltage value of the newly added winding is used as a telemetry signal, which are transmitted to the monitoring main station by using the existing automation system of the substation, and it is judged whether the PT has a short-circuit fault based on the obtained telesignaling and telemetry signals; the present invention can accurately monitor the operating status of the PT without exiting operation or disassembling the PT, effectively avoiding grid shocks and various losses caused by accidents such as PT explosions due to the failure of the PT to be discovered in time and continued operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0026] Figure 1 This is a schematic diagram of a PT short-circuit fault scenario of the present invention;

[0027] Figure 2 This is the equivalent schematic diagram of the 4PT wiring impedance circuit under normal system operation;

[0028] Figure 3 This is the equivalent schematic diagram of the 4PT wiring impedance circuit when metallic grounding occurs on phase A of the system;

[0029] Figure 4 This is a schematic diagram of the newly added secondary winding online monitoring of the present invention. DETAILED DESCRIPTION

[0030] The present invention is further described below with reference to the accompanying drawings, as shown in the drawings:

[0031] The present invention provides an online monitoring method for PT short-circuit faults in a 4PT connection of a low-current grounding system, comprising: the 4PT connection includes an A-phase PT, a B-phase PT, a C-phase PT, and a detuning PT; wherein the 4PT connection is mainly used for voltage measurement in ungrounded systems of voltage levels such as 35kV and 10kV;

[0032] Under normal system operation, calculate the primary voltage value that the detuning PT bears And judge the short circuit fault as follows:

[0033] If Z A Z B =Z C , Then the A-phase PT has a short circuit fault;

[0034] If Z B Z A =Z C , Then the B phase PT has a short circuit fault;

[0035] If Z C Z A =Z B , Then the C phase PT has a short circuit fault; A is the PT impedance of phase A, Z B is the B-phase PT impedance, Z C is the C-phase PT impedance;

[0036] When a single-phase ground fault occurs in the system, calculate the primary voltage value that the detuning PT bears And judge the short circuit fault as follows:

[0037] If Z0Z A =Z B =Z C , Then a short circuit fault occurs in the detuning PT, and Z0 is the detuning PT impedance.

[0038] In this embodiment, the PT is a voltage transformer that proportionally changes high voltage into low voltage. The PT has a high-voltage side winding and a low-voltage side winding. The high-voltage side winding is connected to the power system under test. The low-voltage side proportional output voltage is used for measurement, monitoring, etc. The number of low-voltage side windings is determined according to actual needs.

[0039] The PT short circuit fault refers to any short circuit fault occurring in any of the 4PTs. The probability of multiple short circuit faults occurring at the same time is extremely low and will not be discussed. Figure 1 As shown, the PT short circuit fault refers to a short circuit between poles, layers or turns of the primary winding, or a short circuit between poles, layers or turns of the secondary winding.

[0040] In the 4PT connection mode, the primary voltage borne by the harmonic elimination PT is related to the primary side impedance values ​​of the A, B, and C phase PTs and the harmonic elimination PT.

[0041] In this embodiment, under normal system operation, the three-phase voltage to ground is balanced, and the system neutral point potential N coincides with the ground potential G. Therefore, the 4PT wiring impedance circuit diagram is equivalent to the following: Figure 2 shown.

[0042] according to Figure 2 The equivalent circuit diagram of the detuning PT can be calculated as follows:

[0043]

[0044] Among them, Z A is the impedance of phase A, Z B is the impedance of phase B, Z C is the C-phase impedance, is the voltage of phase A relative to ground; is the voltage of B relative to ground; is the voltage between phase C and ground; Z0 is the detuning PT impedance.

[0045] When PT is normal, Z A =Z B =Z C , according to formula (1) we can calculate

[0046] When a short circuit occurs on the A-phase PT, the A-phase impedance Z A Z B =Z C , according to formula (1) we can calculate

[0047] When a short circuit occurs on the B-phase PT, the B-phase impedance Z B Z A =Z C , according to formula (1) we can calculate

[0048] When a short circuit occurs on the C phase PT, the C phase impedance Z C Z A =Z B , according to formula (1) we can calculate

[0049] In this embodiment, when a single-phase grounding fault occurs in the system, when metallic grounding occurs in phase A of the system, the 4PT wiring impedance circuit diagram is equivalent to the following: Figure 3 shown.

[0050] At this time, the impedance value Z of A relative to the neutral point N' A' As shown in the following formula:

[0051]

[0052] Therefore, according to Figure 3 The equivalent circuit diagram of the detuning PT can be calculated as follows:

[0053]

[0054] Among them, Z B is the impedance of phase B, Z C is the C-phase impedance, is the voltage of phase A relative to ground; is the voltage of B relative to ground; is the voltage of phase C relative to ground.

[0055] When the detuning PT has a short circuit fault, Z0Z A =Z B =Z C , where Z0 is the detuning PT impedance; Substituting into equations (2) and (3), we can calculate Because phase A is metallically grounded, the voltage between phase A and ground is 0V, so the primary voltage borne by the detuning PT is the voltage between the neutral point N' and ground, that is,

[0056] Similarly, when metallic grounding occurs in phase B or phase C of the system, if a short circuit fault occurs in the detuning PT, the primary voltage value borne by the detuning PT is approximately 0V.

[0057] However, when the PT operates normally and a single-phase metallic grounding occurs in the system, the primary voltage value borne by the harmonic elimination PT is as shown in formula (3). Its magnitude is related to the impedance values ​​of the three-phase PTs A, B, and C and the harmonic elimination PT, and this value is greater than 0V.

[0058] In this embodiment, the following also includes: adding a secondary winding for online monitoring of PT short-circuit faults:

[0059] Calculate the output voltage u of the secondary winding n' ; Among them, the secondary winding output voltage value u is newly added for online monitoring of PT short circuit fault n' As shown below, k is the new winding ratio; U N' It is the voltage between the neutral point of 4PT and the ground.

[0060]

[0061] like Figure 4 As shown, the voltage collected by the electronic device is the secondary winding output voltage u newly added for PT short circuit fault online monitoringn' . When u n' When it is greater than the set value, the electronic device output state is pressure; when u n' When the voltage is less than a set value, the electronic device outputs a no-voltage state. The electronic device has voltage acquisition and set-value functions. The set value can be adjusted based on actual needs. The electronic device can output different states reflecting the magnitude of the acquired voltage. When the acquired voltage is greater than the set value, the electronic device outputs one state; when the acquired voltage is less than the set value, the electronic device outputs another state. For example, the connection and disconnection of a passive open contact can be used to respectively indicate whether the acquired voltage is greater than or less than the set value.

[0062] The corresponding relationship between the health status of the PT and the output status of the electronic device is shown in Table 1 below.

[0063] Table 1

[0064] Phase PT normal Phase PT short circuit Normal PT Harmonic elimination PT short circuit System normal No pressure Pressure × × Single-phase grounding × × Pressure No pressure

[0065] That is, when the system is operating normally, if the voltage u n' If it is greater than the set value, there is a short circuit fault in the A-phase PT, B-phase PT, and C-phase PT;

[0066] When a single-phase grounding occurs in the system, if the voltage u n' If it is less than the set value, the detuning PT will have a short circuit fault.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. An online monitoring method for PT short-circuit faults in a 4PT connection of a low-current grounding system, characterized by: The 4PT connection includes A-phase PT, B-phase PT, C-phase PT and detuning PT; Under normal system operation, calculate the primary voltage value that the detuning PT bears And judge the short circuit fault as follows: If Z A < <Z B =Z C , Then the A-phase PT has a short circuit fault; If Z B < <Z A =Z C , Then the B phase PT has a short circuit fault; If Z C < <Z A =Z B , Then the C phase PT has a short circuit fault; A is the PT impedance of phase A, Z B is the B-phase PT impedance, Z C is the C-phase PT impedance; is the voltage of phase A relative to ground; is the voltage of B relative to ground; is the voltage of C relative to ground; When a single-phase ground fault occurs in the system, calculate the primary voltage value that the detuning PT bears And judge the short circuit fault as follows: If Z0< <Z A =Z B =Z C , Then a short circuit fault occurs in the detuning PT; where Z0 is the detuning PT impedance.

2. The method for online monitoring of PT short-circuit faults in a 4PT connection of a low-current grounding system according to claim 1, characterized in that: Under normal system operation, calculate the primary voltage value that the detuning PT bears Among them, Z A is the PT impedance of phase A, Z B is the B-phase PT impedance, Z C is the C-phase PT impedance, is the voltage of phase A relative to ground; is the voltage of B relative to ground; is the voltage between phase C and ground; Z0 is the detuning PT impedance.

3. The method for online monitoring of PT short-circuit faults in a 4PT connection of a low-current grounding system according to claim 1, characterized in that: When a single-phase ground fault occurs in the system, calculate the primary voltage value that the detuning PT bears Among them, Z B is the B-phase PT impedance, Z C is the C-phase PT impedance, Z A' is the impedance of A relative to the neutral point; is the voltage of phase A relative to ground; is the voltage of B relative to ground; is the voltage of phase C relative to ground.

4. The method for online monitoring of PT short-circuit faults in a 4PT connection of a low-current grounding system according to claim 1, characterized in that: Also includes: Added secondary winding for online monitoring of PT short-circuit faults: Calculate the output voltage u of the secondary winding n' ; When the system is operating normally, if the voltage u n' If it is greater than the set value, there is a short circuit fault in the A-phase PT, B-phase PT, and C-phase PT; When a single-phase grounding occurs in the system, if the voltage u n' If it is less than the set value, the detuning PT will have a short circuit fault.

5. The method for online monitoring of PT short-circuit faults in a 4PT connection of a low-current grounding system according to claim 4, characterized in that: The output voltage u of the secondary winding is calculated according to the following formula n' : Among them, U N' is the 4PT neutral point to ground voltage, and k is the new winding ratio.

Images