An on-line identification method for operating conditions of grounding transformer based on equivalent resistance

Abstract

The application discloses a grounding transformer operation condition online identification method based on equivalent resistance and belongs to the technical field of transformer safe operation. The method comprises the following steps: a, acquiring high-voltage side and low-voltage side voltage and current signals of the grounding transformer; b, calculating effective values of each phase voltage and current and a power factor angle; c, calculating equivalent resistances of each phase winding; d, f and h, judging whether the equivalent resistances of each phase are less than 0; e, system A-phase single-phase grounding fault; g, system B-phase single-phase grounding fault; i, system C-phase single-phase grounding fault; j, determining that the grounding transformer only carries a low-voltage side load to operate; and k, determining that a low-voltage side load and an arc suppression coil simultaneously operate. The method realizes online identification of the operation condition of the grounding transformer through the equivalent resistance, and lays a foundation for researching an online detection method of the operation state under different operation conditions.

Description

Technical Field

[0001] This invention belongs to the field of transformer safe operation technology, and more specifically relates to an online identification method for the operating conditions of grounding transformers based on equivalent resistance. Background Technology

[0002] Medium-voltage systems primarily employ an ungrounded neutral point operation mode. However, with the increasingly widespread use of cable lines, the capacitive current to ground increases during single-phase ground faults, preventing the grounding arc from self-extinguishing and easily leading to overvoltage that endangers system operational safety. This operating mode no longer meets the requirements for safe and stable operation of power systems. To address these issues, a ZNyn11 type grounding transformer is connected to the low-voltage busbar of the main transformer, forming a neutral point and then connected to an arc suppression coil or grounding resistor. Simultaneously, it serves as a station service transformer, providing power to substation internal lighting, measurement, relay protection, and other equipment.

[0003] Therefore, the operating conditions of grounding transformers can be divided into two types: low-voltage side load operation only and low-voltage side load plus arc suppression coil operation. The winding connection method is complex, and the change law of electrical parameters when a short circuit fault occurs under different operating conditions is different.

[0004] Currently, there is no dedicated method for detecting the operating status of grounding transformers. The existing methods mainly rely on offline detection methods for ordinary distribution transformers, which suffer from drawbacks such as long maintenance times and large measurement errors. Grounding transformers are equipped with protection systems including instantaneous overcurrent protection and overcurrent protection. However, during normal system operation, the operating current on the high-voltage side of the grounding transformer is much lower than the rated current. Even if a short-circuit fault occurs in the winding, the protection setting is difficult to reach in the early stages of the fault, rendering the protection ineffective. Therefore, researching online detection methods for the operating status of grounding transformers under different operating conditions is of great significance, and the ability to accurately determine its operating condition in real time is a prerequisite for such research.

[0005] Existing technologies can determine whether a single-phase ground fault has occurred in a system by detecting the presence of zero-sequence current. However, after compensation by the inductive current of the arc suppression coil, the zero-sequence current is small and the sensitivity is low. At the same time, it is easily affected by the three-phase imbalance of the system. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the existing defects and propose an online identification method for the operating conditions of grounding transformers based on equivalent resistance. This method can accurately determine the operating conditions of grounding transformers in real time, laying the foundation for the research of online detection methods for the operating status of grounding transformers under different operating conditions.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] An online identification method for the operating conditions of a grounding transformer based on equivalent resistance, which acquires the high-voltage and low-voltage side voltage and current signals of the grounding transformer through a voltage and current monitoring system, includes the following steps:

[0009] Step a: Obtain the voltage values ​​u on the high and low voltage sides of the grounding transformer through a voltage and current monitoring system. A (t), u B (t), u C (t), u a (t), u b (t), u c (t) and the current values ​​i on the high and low voltage sides A (t), i B (t), i C (t), i a (t), i b (t), i c (t);

[0010] Step b: Calculate the effective values ​​of voltage and current on the high and low voltage sides of the grounding transformer, as well as the power factor angle of each phase, using the voltage and current monitoring system.

[0011] Step c: Calculate the equivalent resistance value of each phase using the voltage and current monitoring system;

[0012] Step d: Determine if the equivalent resistance of phase A of the grounding transformer is <0; if the equivalent resistance of phase A is <0, proceed to step e; if the equivalent resistance of phase A is >0, proceed to step f.

[0013] Step e: A single-phase ground fault occurs in phase A of the system; proceed to step k.

[0014] Step f: Determine if the equivalent resistance of phase B of the grounding transformer is <0; if the equivalent resistance of phase B is <0, proceed to step g; if the equivalent resistance of phase B is >0, proceed to step h.

[0015] Step g: A single-phase ground fault occurs in phase B of the system; proceed to step k.

[0016] Step h: Determine if the equivalent resistance of phase C of the grounding transformer is <0; if the equivalent resistance of phase C is <0, proceed to step i; if the equivalent resistance of phase C is >0, proceed to step j.

[0017] Step i: A single-phase ground fault occurs in phase C of the system; proceed to step k.

[0018] Step j: The grounding transformer operates with only the low-voltage side load;

[0019] In step k, the low-voltage load of the grounding transformer and the arc suppression coil are put into operation simultaneously.

[0020] Furthermore, the obtained electrical parameters are substituted into formula (1) to calculate the equivalent resistance of each phase:

[0021]

[0022] Among them, U G U d These are the high and low side voltages, I. G I d These are the high-voltage and low-voltage side currents, respectively. P1 and P2 are the power factor angles of a certain high-voltage and low-voltage side, respectively, and P0 is the no-load loss.

[0023] Furthermore, when a single-phase ground fault occurs in phase A, the equivalent resistance of phase A calculated by formula (1) will be negative. However, when the system is running normally, the input power is greater than the output power, and the equivalent resistance is positive. If the equivalent resistance is less than 0, a single-phase ground fault occurs in the system, and the low-voltage side load and the arc suppression coil of the grounding transformer are put into operation. If the equivalent resistance is greater than 0, the grounding transformer only operates with the low-voltage side load.

[0024] Furthermore, the voltage and current monitoring system includes a high-voltage side voltage transformer, a low-voltage side voltage transformer, a high-voltage side current transformer, a low-voltage side current transformer, a signal acquisition unit, a logic calculation unit, a communication unit, and a human-machine interface. The low-voltage side voltage transformer is installed at the low-voltage outgoing terminal. The high-voltage side current transformer and the low-voltage side current transformer are respectively installed at the high-voltage side incoming terminal and the low-voltage side outgoing terminal of the grounding transformer. The output terminals of the high-voltage side voltage transformer, the low-voltage side voltage transformer, the high-voltage side current transformer, and the low-voltage side current transformer are all connected to the input terminal of the signal acquisition unit. The output terminal of the signal acquisition unit is connected to the input terminal of the logic calculation unit. The output terminal of the logic calculation unit is connected to the human-machine interface through the communication unit.

[0025] The beneficial effects of this invention are as follows:

[0026] This invention presents an online identification method for the operating conditions of grounding transformers based on equivalent resistance. It is highly sensitive, unaffected by the unbalanced operation of the three-phase system, and can accurately determine the operating conditions of the grounding transformer in real time, as well as identify the grounded phase. This lays the foundation for research on the detection technology of the operating status of grounding transformers under different operating conditions. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present utility model. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0028] Figure 1 This is a flowchart of the method of the present invention;

[0029] Figure 2 This is a block diagram of the voltage and current monitoring system.

[0030] Figure 3 This is the wiring diagram of the grounding transformer in actual operation. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] This invention discloses an online identification method for the operating conditions of a grounding transformer based on equivalent resistance. The method acquires the high-voltage and low-voltage side voltage and current signals of the grounding transformer through a voltage and current monitoring system, and includes the following steps:

[0033] Step a: Obtain the voltage values ​​u on the high and low voltage sides of the grounding transformer through a voltage and current monitoring system. A (t), u B (t), u C (t), u a (t), u b (t), u c (t) and the current values ​​i on the high and low voltage sides A (t), i B (t), i C (t), i a (t), i b (t), i c (t);

[0034] Step b: Calculate the effective values ​​of voltage and current on the high and low voltage sides of the grounding transformer, as well as the power factor angle of each phase, using the voltage and current monitoring system.

[0035] Step c: Calculate the equivalent resistance value of each phase using the voltage and current monitoring system;

[0036] Step d: Determine if the equivalent resistance of phase A of the grounding transformer is <0; if the equivalent resistance of phase A is <0, proceed to step e; if the equivalent resistance of phase A is >0, proceed to step f.

[0037] Step e: A single-phase ground fault occurs in phase A of the system; proceed to step k.

[0038] Step f: Determine if the equivalent resistance of phase B of the grounding transformer is <0; if the equivalent resistance of phase B is <0, proceed to step g; if the equivalent resistance of phase B is >0, proceed to step h.

[0039] Step g: A single-phase ground fault occurs in phase B of the system; proceed to step k.

[0040] Step h: Determine if the equivalent resistance of phase C of the grounding transformer is <0; if the equivalent resistance of phase C is <0, proceed to step i; if the equivalent resistance of phase C is >0, proceed to step j.

[0041] Step i: A single-phase ground fault occurs in phase C of the system; proceed to step k.

[0042] Step j: The grounding transformer operates with only the low-voltage side load;

[0043] In step k, the low-voltage load of the grounding transformer and the arc suppression coil are put into operation simultaneously.

[0044] Substitute the obtained electrical parameters into formula (1) to calculate the equivalent resistance of each phase:

[0045]

[0046] Among them, U G U d These are the high and low side voltages, I. G I d These are the high-voltage and low-voltage side currents, respectively. P1 and P2 are the power factor angles of a certain high-voltage and low-voltage side, respectively, and P0 is the no-load loss.

[0047] Since the voltage of phase a on the low-voltage side of the grounding transformer is generated by the induction of phase A main winding and phase B shift winding, if phase A of the system is grounded, the voltage is close to 0, the input power of this phase decreases, while the voltage and current of phase B shift winding both increase, increasing the input power to meet the power demand of the low-voltage phase a load. Therefore, when phase A is grounded, the equivalent resistance of phase A calculated by formula (1) will be negative. When the system is running normally, the input power is greater than the output power, and the equivalent resistance is positive. If the equivalent resistance is less than 0, a single-phase grounding fault occurs in the system, and both the low-voltage side load and the arc suppression coil of the grounding transformer are put into operation. If the equivalent resistance is greater than 0, the grounding transformer only operates with the low-voltage side load.

[0048] The voltage and current monitoring system includes a high-voltage side voltage transformer, a low-voltage side voltage transformer, a high-voltage side current transformer, a low-voltage side current transformer, a signal acquisition unit, a logic calculation unit, a communication unit, and a human-machine interface. The high-voltage side voltage transformer of the grounding transformer adopts a bus voltage transformer, which does not require reinstallation. The low-voltage side voltage transformer is installed at the low-voltage outgoing terminal. The high-voltage side current transformer and the low-voltage side current transformer are installed at the high-voltage side incoming terminal and the low-voltage side outgoing terminal of the grounding transformer, respectively. The output terminals of the high-voltage side voltage transformer, the low-voltage side voltage transformer, the high-voltage side current transformer, and the low-voltage side current transformer are all connected to the input terminal of the signal acquisition unit. The output terminal of the signal acquisition unit is connected to the input terminal of the logic calculation unit. The output terminal of the logic calculation unit is connected to the human-machine interface through the communication unit.

[0049] This invention presents an online identification method for the operating conditions of grounding transformers based on equivalent resistance. It is highly sensitive, unaffected by the unbalanced operation of the three-phase system, and can accurately determine the operating conditions of the grounding transformer in real time, as well as identify the grounded phase. This lays the foundation for research on the detection technology of the operating status of grounding transformers under different operating conditions.

[0050] Example

[0051] like Figure 1 As shown, an online identification method for the operating conditions of a grounding transformer based on equivalent resistance includes the following steps:

[0052] Step 1001: Obtain the voltage and current signals of the high and low voltage sides of the grounding transformer;

[0053] like Figure 3 As shown, the ZNyn11 type grounding transformer is connected to the low-voltage side busbar of the main transformer, and the neutral point is grounded through the arc suppression coil. The low-voltage side supplies power to the substation.

[0054] Figure 2 This is a voltage and current monitoring system consisting of high-voltage side voltage transformers, low-voltage side voltage transformers, high-voltage side current transformers, low-voltage side current transformers, a signal acquisition unit, a logic calculation unit, a communication unit, and a human-machine interface on the busbar connected to the high-voltage side of the grounding transformer. The high and low voltage sides of the grounding transformer are acquired by voltage transformers TV1 and TV2, respectively, and the high and low voltage sides are acquired by current transformers TA1 and TA2, respectively. The output terminals of the high-voltage side voltage transformers, low-voltage side voltage transformers, and the current transformers on both sides are connected to the input terminals of the signal acquisition unit. The output terminals of the signal acquisition unit are connected to the input terminals of the logic calculation unit. The output terminals of the logic calculation unit are connected to the human-machine interface through the communication unit.

[0055] Step 1002: Calculate the effective values ​​of voltage and current on the high and low voltage sides of the grounding transformer, as well as the power factor angle;

[0056] The logic calculation unit uses the data provided by the signal acquisition unit to calculate the effective values ​​of the high-voltage and low-voltage sides of the grounding transformer, respectively. The calculation formula is as follows:

[0057]

[0058] Where u(t) and i(t) are the instantaneous values ​​of voltage and current, respectively, and T is time.

[0059] The logic calculation unit simultaneously calculates the power factor angle of each phase on both the high and low voltage sides of the grounding transformer. This is based on the voltage u of phase A of the grounding transformer. A (t), current i A Taking (t) as an example, the calculation process is as follows:

[0060] Voltage and current are obtained by Fourier decomposition

[0061]

[0062] In the formula: f is the frequency; a u0 a i0 These are the DC components of the voltage and current in phase A, respectively; A uk A ik These are the kth harmonic amplitudes of the voltage and current of phase A, respectively. These are the phases of the kth harmonics of the voltage and current of phase A, respectively.

[0063] Taking the fundamental components of voltage and current, i.e., k=1, the expression is:

[0064]

[0065] Voltage and current phase angles are

[0066]

[0067] The power factor angle is

[0068]

[0069] Step 1003: Calculate the equivalent resistance of each phase of the grounding transformer. The calculation formula is as follows:

[0070]

[0071] In the formula: U G U d These are the high and low side voltages, I. G I d These are the high-voltage and low-voltage side currents, respectively. P1 and P2 are the power factor angles of a certain high-voltage and low-voltage side, respectively, and P0 is the no-load loss.

[0072] Step 1004: Determine whether the equivalent resistance of phase A of the grounding transformer is <0;

[0073] The logic calculation unit determines whether the equivalent resistance of phase A of the grounding transformer is <0; if the equivalent resistance of phase A is <0, proceed to step 1005; if the equivalent resistance of phase A is >0, proceed to step 1006.

[0074] Step 1005: A single-phase ground fault occurs in phase A of the system;

[0075] The logic calculation unit determines that a single-phase ground fault has occurred in phase A of the system and executes step 1011.

[0076] Step 1006: Determine whether the equivalent resistance of phase B of the grounding transformer is <0;

[0077] The logic calculation unit determines whether the equivalent resistance of phase B of the grounding transformer is <0; if the equivalent resistance of phase B is <0, proceed to step 1007; if the equivalent resistance of phase B is >0, proceed to step 1008.

[0078] Step 1007: A single-phase ground fault occurs in phase B of the system;

[0079] The logic calculation unit determines that a single-phase ground fault has occurred in phase B of the system and executes step 1011.

[0080] Step 1008: Determine whether the equivalent resistance of phase C of the grounding transformer is <0;

[0081] The logic calculation unit determines whether the equivalent resistance of phase C of the grounding transformer is <0; if the equivalent resistance of phase C is <0, execute step 1009; if the equivalent resistance of phase C is >0, execute step 1010.

[0082] Step 1009: A single-phase ground fault occurs in phase C of the system;

[0083] The logic calculation unit determines that a single-phase ground fault has occurred in phase C of the system and executes step 1011.

[0084] Step 1010: The grounding transformer operates with only the low-voltage side load;

[0085] The logic calculation unit determines that the grounding transformer is only operating with a low-voltage side load.

[0086] Step 1011: The low-voltage load of the grounding transformer and the arc suppression coil are put into operation simultaneously;

[0087] The logic calculation unit determines that the low-voltage load of the grounding transformer and the arc suppression coil are put into operation simultaneously.

[0088] After the logic calculation unit determines the operating condition of the grounding transformer, it transmits the result through the communication module and displays it on the human-machine interface, laying the foundation for the research on online detection technology of grounding transformer operating status under different operating conditions.

[0089] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0090] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for online identification of the operating conditions of a grounding transformer based on equivalent resistance, characterized in that, Obtaining the high-voltage and low-voltage side voltage and current signals of the grounding transformer through a voltage and current monitoring system includes the following steps: Step a: Obtain the voltage values ​​on the high and low voltage sides of the grounding transformer through a voltage and current monitoring system. , , , , , and the current values ​​on the high and low voltage sides , , , , , ; Step b: Calculate the effective values ​​of voltage and current on the high and low voltage sides of the grounding transformer, as well as the power factor angle of each phase, using the voltage and current monitoring system. Step c: Calculate the equivalent resistance value of each phase using the voltage and current monitoring system; Step d: Determine if the equivalent resistance of phase A of the grounding transformer is <0; if the equivalent resistance of phase A is <0, proceed to step e; if the equivalent resistance of phase A is >0, proceed to step f. Step e: A single-phase ground fault occurs in phase A of the system; proceed to step k. Step h: Determine if the equivalent resistance of phase C of the grounding transformer is <0; if the equivalent resistance of phase C is <0, proceed to step i; if the equivalent resistance of phase C is >0, proceed to step j. Step i: A single-phase ground fault occurs in phase C of the system; proceed to step k. Step j: The grounding transformer operates with only the low-voltage side load; Step k: The low-voltage load of the grounding transformer and the arc suppression coil are put into operation simultaneously; Substitute the obtained electrical parameters into formula (1) to calculate the equivalent resistance of each phase: （1） in, , These are the high-voltage and low-voltage side voltages, respectively. , These are the high-voltage and low-voltage side currents, respectively. , These are the power factor angles for the high and low voltage sides, respectively. This is the no-load loss.

2. The method for online identification of the operating conditions of a grounding transformer based on equivalent resistance according to claim 1, characterized in that, When a single-phase ground fault occurs in phase A, the equivalent resistance of phase A calculated using formula (1) will be negative. However, when the system is running normally, the input power is greater than the output power, and the equivalent resistance will be positive. If the equivalent resistance is less than 0, a single-phase ground fault occurs in the system, and both the low-voltage side load and the arc suppression coil of the grounding transformer are put into operation; if the equivalent resistance is greater than 0, the grounding transformer only operates with the low-voltage side load.

3. The method for online identification of the operating conditions of a grounding transformer based on equivalent resistance according to claim 1, characterized in that, The voltage and current monitoring system includes a high-voltage side voltage transformer, a low-voltage side voltage transformer, a high-voltage side current transformer, a low-voltage side current transformer, a signal acquisition unit, a logic calculation unit, a communication unit, and a human-machine interface. The low-voltage side voltage transformer is installed at the low-voltage outgoing terminal. The high-voltage side current transformer and the low-voltage side current transformer are respectively installed at the high-voltage side incoming terminal and the low-voltage side outgoing terminal of the grounding transformer. The output terminals of the high-voltage side voltage transformer, the low-voltage side voltage transformer, the high-voltage side current transformer, and the low-voltage side current transformer are all connected to the input terminal of the signal acquisition unit. The output terminal of the signal acquisition unit is connected to the input terminal of the logic calculation unit. The output terminal of the logic calculation unit is connected to the human-machine interface through the communication unit.

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