WO2020224537A1 - Transformer digital adaptive protection apparatus and method based on pressure characteristics - Google Patents

Abstract

A transformer digital adaptive protection apparatus and method based on pressure characteristics, comprising: a transient oil pressure characteristic quantity measurement module, a switch quantity input module, a signal conditioning and acquisition module, and a digital core module; the transient oil pressure characteristic quantity measurement module is connected to the signal conditioning and acquisition module, and the signal conditioning and acquisition module and the switch quantity input module are both connected to the digital core module. The present invention acquires in real time digital information of the transient oil pressure at a plurality of measuring points in an oil tank, calculates the operating pressure value that characterises the oil pressure magnitude, and uses the significant differences between said characteristic quantity of the transformer under different operating conditions in order to construct a protection criterion and threshold value setting method to implement reliable, rapid, and sensitive identification and removal of internal faults of the tank of the transformer without being affected by an excitation surge current. In addition, the present invention designs a protection solution with fault state adaption and threshold value adaption in order to increase the operating speed of protection.

Description

Transformer digital self-adaptive protection device and method based on pressure characteristics Technical field

The invention belongs to the field of electric power systems, and relates to a digital self-adaptive protection device and method for transformers based on pressure characteristics, which are used to reliably, quickly and sensitively identify internal faults in oil tanks of oil-immersed power transformers.

Background technique

As an important component of power transmission, power transformers will have a serious impact on power supply reliability and operational stability in the event of a failure. Especially the large power transformers installed in the system hub, because of their high voltage level, large capacity, complex structure, and high cost, damage due to failure will inevitably cause huge economic losses. Therefore, a relay protection device with good performance and reliable operation must be installed according to the capacity and importance of the transformer.

The development of relay protection technology depends on the understanding of fault characteristics. It is generally believed that there are three main characteristics of transformer internal faults, one is the increase of phase current, the other is the increase of differential current, and the third is the formation of fault gas. Corresponding to the first two electrical characteristics, widely used protection measures include overcurrent protection and current differential protection, and the latter is currently one of the main protection methods for internal short-circuit faults in transformers. However, there are two main defects in the principle of transformer current differential protection: First, the magnetizing inrush current in the excitation circuit when the transformer is closed at no load may cause the differential protection to malfunction; second, in the face of single-turn or In the case of weak faults such as short circuits with small turns, the differential protection may refuse to operate due to insufficient sensitivity. In view of this, as early as the 1920s, scholars invented transformer gas protection to make up for the lack of electrical protection. Compared with the electrical quantity protection, the non-electric quantity protection generated by the fault gas is more comprehensive, directly reflects the operating status of the protected object, and has unique advantages in terms of sensitivity. Although traditional mechanical non-electrical protection has successfully protected tens of thousands of oil-immersed transformers in the course of nearly a hundred years of use, it has difficulties in theoretical modeling, theoretical defects, threshold values based on experience, and insufficient mechanical structure action performance. It is increasingly difficult to meet the higher requirements of current large-capacity, high-voltage power transformers. System power outages and transformer explosion accidents caused by protection refusal and misoperation accidents often occur, which seriously affect the safe and reliable operation of the power system, and seriously threaten the life and property safety of substation operators and the surrounding people.

When a serious overheating or arc fault occurs inside an oil-immersed power transformer, the liquid insulating oil will be vaporized and decomposed instantaneously to form high internal energy bubbles with a certain volume. With the continuous injection of faulty electrical energy, the internal pressure of the faulty bubble is also increasing. At the same time, due to the expansion inertness of the liquid insulating oil near the fault point, the gas-liquid interface between the faulty bubble and the surrounding liquid insulating oil will inevitably produce a significant pressure increase , And propagate inside the transformer tank in the form of pressure waves, resulting in an overall surge of oil pressure inside the tank. In addition, since the transformer oil tank is not a pressure vessel, the tank body is often deformed and cracked under the impact of the internal pressure wave. On the other hand, when an external short-circuit fault occurs in the transformer, the fault point is located at the outlet of the transformer, and the impact on the internal pressure of the tank is only reflected in the winding vibration caused by the short-circuit ride-through current. At the same time, because the mechanical strain of the winding will consume a lot of energy, the oil pressure change caused by this process is limited. Similar to external faults, the normal operation of the transformer and the inrush current are caused by the vibration of the current flowing through the winding, which causes the oil pressure to change. Therefore, the difference in the oil pressure characteristics of the transformer under different operating conditions can be used to effectively identify the internal fault status of the transformer.

Summary of the invention

The purpose of the present invention is to provide a digital adaptive protection device and method for transformers based on pressure characteristics. The application of the method can reliably, sensitively and quickly identify internal faults of oil-immersed power transformers without being affected by the inrush current.

In order to achieve the above objectives, the present invention adopts the following technical solutions:

A digital adaptive protection device for transformers based on pressure characteristics, including: transient oil pressure characteristic quantity measurement module, switch input module, signal conditioning and acquisition module, and digital core module; among them, transient oil pressure characteristic quantity measurement module It is connected to the signal conditioning and acquisition module, and the signal conditioning and acquisition module and the digital input module are both connected to the digital core module;

The transient oil pressure characteristic measurement module is used to measure the oil pressure change characteristics at different positions inside the transformer, and output the corresponding analog voltage/current signal;

The signal conditioning and acquisition module is used to receive the analog voltage/current signal output by the transient oil pressure characteristic measurement module, and convert it into a standard digital signal that the digital core module can recognize, and then output the standard digital signal;

The switch input module is used to collect the relevant switch signals that need to be known, and output them as high level 1 or low level 0 as the input digital signal of the digital core module;

The digital core module is used to perform protection operations on the received standard digital signal and the input digital signal, complete standard digital signal processing tasks, and then realize the relay protection function.

A further improvement of the present invention is that the transient oil pressure characteristic quantity measurement module is composed of several high frequency dynamic oil pressure sensors and their communication cables; the high frequency dynamic oil pressure sensor is installed on the transformer body, and the high frequency dynamic oil pressure sensor end The probe is in contact with the insulating oil of the transformer to measure the characteristics of oil pressure changes at different positions inside the transformer.

The further improvement of the present invention is that the measurement frequency of the high-frequency dynamic oil pressure sensor is 20kHz, the measurement error is less than 1%, the working temperature is -45～120 DEG C, and the range is -0.1～6MPa.

A further improvement of the present invention is that the signal conditioning and acquisition module is composed of wiring terminals, a signal conditioning circuit, a low-pass filter, a signal sampling circuit, and an analog-to-digital A/D conversion circuit; the wiring terminals are connected to the signal conditioning circuit, and the signal conditioning circuit is connected to the signal conditioning circuit. The low-pass filter is connected, the low-pass filter is connected to the signal sampling circuit, the signal sampling circuit is connected to the analog-to-digital A/D conversion circuit; the terminal block is also connected to the transient oil pressure characteristic measurement module, the analog-to-digital A/D conversion circuit It is also connected to the digital core module.

A further improvement of the present invention is that the digital core module is composed of a bus, a central processing unit, a timer/counter, a random access memory, and a control circuit; the bus includes a data bus, an address bus and a control bus to realize data exchange and operation control; the central processing unit Use single-chip microprocessor, general-purpose microprocessor or digital signal processor to realize digital signal processing in real time; timer/counter is used to provide timing sampling trigger signal, form interruption, protection delay action timing; random access memory is used to temporarily store temporary Data includes the data information input by the signal conditioning and acquisition module, and the intermediate results of the calculation process; the control circuit realizes the connection and coordination of the entire digital circuit through a complex programmable logic device or a field programmable gate array.

A further improvement of the present invention lies in that it also includes an external communication interface module, a man-machine dialogue module and a switch output module connected to the digital core module;

The external communication interface module is used to provide the information channel with the computer communication network and the remote communication network;

The man-machine dialogue module is used to establish the information connection between the digital protection device and the user;

The switch output module controls the on or off of the tripping circuit through the output state of 0 or 1.

A further improvement of the present invention is that the switch output module is composed of a photoelectric isolation device and an outlet relay, one end of the photoelectric isolation device is connected to the digital core module, and the other end is connected to the outlet relay;

The man-machine dialogue module includes a compact keyboard, display screen, indicator light, buttons, printer interface and debugging communication interface.

A protection method for a transformer digital adaptive protection device based on the above pressure characteristics includes the following steps:

(1) The transient oil pressure characteristic measurement module measures the characteristics of oil pressure changes at different positions inside the transformer, and outputs analog voltage/current signals. The signal conditioning and acquisition module receives the analog voltage/output from the transient oil pressure characteristic measurement module. The current signal is converted into a standard digital signal that can be recognized by the digital core module, and then the standard digital signal is output; the switch input module is used to collect the relevant switch signal that needs to be known, and output it as a high level 1 or Low level 0, as the input digital signal of the digital core module; after the digital core module receives the input digital signal and the standard digital signal, compare whether the transient oil pressure value p _ms.i (t) of each measuring point at the current time t reaches the preset value. Set the protection start threshold p _st to determine whether the transformer adaptive protection based on the pressure characteristic is started. If the formula ① is established, the start flag is set, and the step (2) is entered;

In formula ①, p _ms.i (t) represents the transient oil pressure value of the i-th measuring point inside the transformer at time t, where i is 1, 2, ..., N; p _st represents the protection start threshold;

(2) Determine whether the transformer is currently in no-load closing state, if yes, proceed to step (3), otherwise, proceed to step (5);

(3) Use formula ② to calculate the no-load closing action pressure p _op.k ;

In formula ②, T _k is the length of the no-load closing data window;

(4) If the calculated no-load closing action pressure p _{op.k is} greater than or equal to the preset no-load closing protection action threshold p _th.k , that is, the formula ③ is established, the protection action, tripping and removing the fault, the entire device Reset, waiting for manual reset;

p _{op.k ≥p th.k} ③

Under the condition of transformer magnetizing inrush current, the operating pressure p _op.k is an unbalanced quantity p _ub.k that is not 0, which is less than the protection threshold p _th.k ; once the airdrop is in the internal short-circuit fault, the fault gas generation and pressure wave propagation will be Cause the pressure inside the fuel tank to rise _sharply , at this time p _op.k will be greater than the threshold value p _th.k; therefore, by judging whether the formula ③ holds, determine the action of the protection;

(5) Use formula ④ to calculate the operating pressure p _op.i at the current time t:

In formula ④, T is the length of the data window;

(6) Compare the calculated operating pressure p _op.i with the preset pressure protection operating threshold p _th . If the calculated operating pressure p _{op.i is} greater than or equal to the preset pressure protection operating threshold p _th , That is, if the formula ⑤ is established, the protection will be activated, the fault will be tripped and the whole set will be reset, waiting for manual reset;

p _{op.i ≥p th} ⑤.

A further improvement of the present invention is that in step (1), the protection start threshold p _{st is} defined as:

p _st ＝k _rel p _nm·max ⑥

In formula ⑥, k _rel is the reliability coefficient, and the reliability coefficient k _rel is 1.2; p _nm.max is the maximum value of the transient oil pressure under the normal operating conditions of the transformer;

In step (3), the no-load closing data window length T _k is the same as the data window length selected during the preset no-load closing action threshold setting; the no-load closing data window length T _{k is} set to 5ms, 10ms or 20ms.

A further improvement of the present invention is that in step (4), the no-load closing action threshold p _th.k is set as:

p _th.k = k _rel p _ub.kmax ⑦

In formula ⑦: p _ub.kmax is the unbalanced amount of the operating pressure inside the oil tank under the condition of the maximum pressure fluctuation caused by the magnetizing inrush current, and the transient oil pressure value measured at the internal measuring point of the transformer during the magnetizing inrush current is brought into formula ②. The value of p _th.k is the imbalance p _{ub.kmax of the} operating pressure inside the fuel tank under the maximum pressure fluctuation caused by the magnetizing inrush current;

In step (5), the data window length T is set to 5ms, 10ms or 20ms;

In step (6), define the pressure protection action threshold p _th as:

p _th ＝k _rel p _ub.max ⑧

In formula ⑧: p _ub.max is the maximum imbalance of the internal operating pressure of the oil tank under the most severe external short-circuit fault, and the transient oil pressure value measured at the internal measuring point of the transformer during the most severe external short-circuit fault is brought into equation ④. The calculated value of p _op.i is the maximum imbalance p _{ub.max of the} internal operating pressure of the fuel tank in the case of the most severe external short circuit fault.

Compared with the prior art, the present invention has the following beneficial effects:

The invention uses digital oil pressure information to form protection to identify transformer internal faults. Compared with the previous mechanical non-electrical protection, the present invention has the following advantages: First, the internal pressure characteristics of the oil tank generate pressure when the power transformer is normal, abnormal, and internal faults. The mechanism of change is completely different. Once the transformer has an internal fault, the rapid release of the faulty electrical energy will produce a faulty bubble with a certain volume and internal energy. The continuous heating and pressure increase of the bubble will cause the internal pressure of the fuel tank to rise sharply. When an external short circuit occurs, the fault point is located outside the transformer, and the impact on the internal pressure of the tank is only reflected in the winding vibration caused by the short-circuit ride-through current. At this time, the pressure characteristic presents the characteristics of limited amplitude and positive and negative oscillation. Second, the propagation speed of pressure waves in the insulating oil is as high as 1.26m/ms. For large power transformers with geometric dimensions of 10m, no matter what causes the pressure characteristic changes, the protection measurement device only needs a few to capture the pressure changes. millisecond. Therefore, the selection of pressure characteristics to construct protection has sufficient speed. Third, compared to electrical energy protection that exhibits insufficient sensitivity when facing single-turn or small-turn short circuits and other low-energy faults, the common advantage of non-electricity protection is that it is more sensitive to weak faults. From the perspective of energy conversion, electrical network failures will accompany the conversion of faulty electrical energy, while non-electrical physical quantities are often direct representations of different forms of energy, and at the same time have cumulative effects in nature. The device of the invention can realize real-time digital measurement, collection and calculation of the oil pressure characteristic information inside the oil tank without damaging the existing structural integrity of the transformer.

Furthermore, in the present invention, a high-frequency dynamic pressure sensor with a measuring frequency of 20kHz, a measuring error of less than 1%, a working temperature of -45～120℃, and a range of -0.1～6MPa is used, which can meet the requirements of power High temperature, oil pollution, and strong electromagnetic environment inside the transformer; high frequency dynamic pressure sensor is independent of the power network, the measurement and transmission of pressure characteristics suffer from less interference, and no harmonics are injected into the power system; data acquisition and processing components can fully meet the requirements of fast , Real-time processing of multi-channel, high-frequency data requirements.

Furthermore, traditional Buchholz relays can only sense the flow rate of the oil flow through a mechanical spring device and can only output switch information. A single flow rate amplitude often cannot correctly distinguish the internal and external faults of the transformer, resulting in protection malfunction or refusal to operate. The device of the invention is composed of a transient oil pressure characteristic quantity measurement module, a switch input module, a signal conditioning and acquisition module, a digital core module, an external communication interface module, a man-machine dialogue module, and a switch output module. Taking advantage of the increase in the amplitude of the oil pressure in the oil tank when the transformer is internally faulty, the oil pressure presents the characteristics of limited amplitude and periodic oscillation under normal operation, external short circuit or magnetizing inrush current conditions. The calculation is based on the transient oil pressure values of multiple measuring points. The operating pressure is compared with the protection operating threshold to determine the operating state of the transformer. When it is judged as an internal fault, a trip signal is issued, the faulty transformer is removed, and the entire protection device is reset.

According to the protection principle and functional requirements, the present invention monitors the protection device, fault handling, man-machine dialogue, communication, self-checking, accident recording and analysis report, and debugging functions, and utilizes the transient oil pressure information inside the fuel tank and the information that appears under different operating conditions. The pressure difference realizes the fast, sensitive and reliable identification of the internal faults of the transformer tank, and is not affected by the magnetizing inrush current. In addition, considering that the oil pressure amplitude under the excitation inrush current condition is significantly smaller than the external short-circuit fault, and the inherent time window will affect the action speed of the protection under the airdrop fault condition, the present invention designs a protection scheme with adaptive fault status and adaptive threshold value. Improve the action speed of the protection in the face of an airdrop failure. The principle of the invention is simple, and the device is easy to implement, and the mechanical non-electricity protection based on experience and feeling in the past is improved to a new stage of quantitative analysis, high reliability judgment, and digital realization, so as to adapt to current and future large-capacity, high-voltage power The transformer's requirements for the "four characteristics" of non-electricity protection.

Description of the drawings

Figure 1 is a schematic diagram of the device structure of the present invention.

Figure 2 is a flowchart of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the drawings.

Referring to Figure 1, the pressure characteristic-based transformer adaptive protection device used in the present invention includes: a transient oil pressure characteristic quantity measurement module, a switch input module, a signal conditioning and acquisition module, a digital core module, an external communication interface module, Man-machine dialogue module and switch output module; among them, the transient oil pressure characteristic quantity measurement module is connected to the signal conditioning and acquisition module, the signal conditioning and acquisition module, the switch input module, the external communication interface module, the man-machine dialogue module and the switch The quantity output modules are all connected with the digital core module.

The transient oil pressure characteristic measurement module is composed of several high-frequency dynamic oil pressure sensors and their communication cables. It is used to measure the internal oil pressure variation characteristics at different positions of the transformer and output the corresponding analog voltage/current signals. The high-frequency dynamic oil pressure sensor is installed on the transformer body, and the sensor end probe is directly in contact with the transformer insulating oil to measure the characteristics of the internal oil pressure change at different positions of the transformer. The measurement frequency of the high frequency dynamic oil pressure sensor is 20kHz, the measurement error is less than 1%, the working temperature is -45～120℃, and the range is -0.1～6MPa.

The signal conditioning and acquisition module is composed of terminal blocks, signal conditioning circuits, low-pass filters, signal sampling circuits, and analog-to-digital A/D conversion circuits; the terminal blocks are connected to the signal conditioning circuit, and the signal conditioning circuit is connected to the low-pass filter. The pass filter is connected with the signal sampling circuit, and the signal sampling circuit is connected with the analog-to-digital A/D conversion circuit; the connection terminal is also connected with the communication cable. The signal conditioning and acquisition module is used to receive the analog voltage/current signal output by the transient oil pressure characteristic measurement module, and convert it into a standard digital signal that the digital core module can recognize, and then output the standard digital signal;

The switch input module is used to collect relevant switch signals that need to be ascertained, and output them as high level 1 or low level 0 as the input digital signal of the digital core module.

The digital core module is composed of a bus, a central processing unit, a timer/counter, a random access memory, and a control circuit; the bus includes a data bus, an address bus, and a control bus to realize data exchange and operation control; the central processing unit uses a single-chip microprocessor, General-purpose microprocessor or digital signal processor realizes digital signal processing quickly in real time; timer/counter is used to provide timing sampling trigger signal, form interruption, protection delay action precise timing; random access memory is used to temporarily store a large amount of temporary that needs fast exchange Data, including the data information input by the signal conditioning and acquisition module, and the intermediate results of the calculation process; the control circuit realizes the effective connection and coordination of the entire digital circuit through complex programmable logic devices or field programmable gate arrays.

The digital core module is used to perform protection operations on the received standard digital signals and input digital signals, complete digital signal processing tasks, direct the normal operation of the connected modules, realize data exchange and operation control, and realize the relay protection function.

The external communication interface module is used to provide an information channel with a computer communication network and a remote communication network to realize information interaction, data sharing, remote operation and remote maintenance.

The man-machine dialogue module includes a compact keyboard, display screen, indicator light, buttons, printer interface and debugging communication interface, etc., used to establish the information connection between the digital protection device and the user, so that the operator can manually operate the protection device, Debug and get information feedback.

The switch output module is composed of a photoelectric isolation device and an outlet relay. The photoelectric isolation device is connected to the outlet relay and is used to control the on or off of the trip circuit through the output state of 0 or 1, so as to realize the reliable action of the protection.

Refer to Figure 2. Based on the protection method of the above protection device, the protection device is controlled in accordance with the protection principle and functional requirements, and various operations such as data collection, external communication, digital calculation, logic judgment and action instruction execution are completed in an orderly manner. Specific steps as follows:

(1) After the protection device is powered on or hardware reset (referred to as reset), first perform system initialization to make the entire protection device in a normal working state;

(2) Perform a comprehensive self-inspection after power-on, check the correctness and integrity of its own working status, and send an alarm signal and lock the entire device if a device defect is found, and wait for the technician to eliminate the fault and reset it manually;

(3) If the self-check is passed, the data acquisition initialization will be performed, and the timing sampling interrupt will be started to allocate the address of the loop saving sample data buffer, set the dynamic address pointer that marks the current latest data, and then control the loop according to the specified sampling period Assign and start the sampling interrupt timer to open the sampling interrupt;

(4) The transient oil pressure characteristic quantity measurement module measures the characteristics of oil pressure changes at different positions inside the transformer, and outputs corresponding analog voltage/current signals; the signal conditioning and acquisition module receives the transient oil pressure characteristic quantity measurement module output The analog voltage/current signal is converted into a standard digital signal that can be recognized by the digital core module, and then the standard digital signal is output; the switch input module collects the relevant switch signal that needs to be known and outputs it as a high level 1 or low level 0, as the input digital signal of the digital core module; after the digital core module receives the standard digital signal and the input digital signal, the protection function is temporarily blocked, waiting for enough data in the sampling data buffer (one to two Data of several cycles), and then open the protection function;

(5) The whole group is initialized, and the operation self-check is performed in the running state. If a device defect is found, an alarm signal will be issued and the entire device will be locked, waiting for the technician to troubleshoot and reset manually;

(6) If there is no failure, perform communication task processing to prepare data for information transmission and reception; including: collecting relevant data according to data transmission requests of other parts of the protection method, organizing and packaging communication information according to the communication protocol, and matching Sort and interpret the data in the data receiving buffer;

(7) Perform human-machine dialogue processing, perform tasks such as scanning the keyboard, control buttons, and displaying data on the display screen, and explain and classify various operating commands, and deliver corresponding task processing according to task categories;

(8) Judge whether the protection device is in working operation mode; if it is not in working operation mode, perform debugging task processing, and return to step (5) after the debugging task is completed; if it is in working operation mode, proceed to step (9);

(9) Determine whether the start flag is set. If it is set, it means that the protection device has detected a possible accident disturbance before, go to step (11); otherwise, go to step (10);

(10) Compare whether the transient oil pressure value p _ms.i (t) of each measuring point at the current time t reaches the preset protection start threshold p _st to determine whether the transformer adaptive protection based on pressure characteristics is activated, if the formula ① is not established , Return to step (5); if formula ① is established, the start flag is set, and go to step (11);

p _ms.i (t) _{≥p st} ①

In formula ①, p _ms.i (t) represents the transient oil pressure value of the i-th measuring point inside the transformer at time t, where i is 1, 2, ..., N; p _st represents the protection start threshold.

In order to ensure that the pressure protection can start to work under fault and abnormal disturbance conditions, the protection start threshold p _{st is} defined as:

p _st ＝k _rel p _nm·max ②

In the formula ②, k _rel is the reliability coefficient, and the value is 1.2; p _nm.max is the maximum value of the transient oil pressure under the normal operating conditions of the transformer.

(11) Determine whether the transformer is currently in no-load closing state, if yes, proceed to step (12), otherwise, proceed to step (14);

(12) Use formula ③ to calculate the no-load closing action pressure p _op.k

In formula ③, T _k is the length of the no-load closing data window, which is the same as the length of the data window selected during the preset no-load closing action threshold setting. 5ms, 10ms or 20ms can be selected as needed.

(13) If the calculated no-load closing action pressure p _{op.k is} greater than or equal to the preset no-load closing protection action threshold p _th.k , that is, the formula ④ is established, the protection action, tripping and removing the fault, the entire device Reset, wait for manual reset; otherwise, return to step (5);

p _{op.k ≥p th.k} ④

Under the condition of transformer magnetizing inrush current, the operating pressure p _op.k is an unbalanced quantity p _ub.k that is not 0, which is less than the protection threshold p _th.k ; once the airdrop is in the internal short-circuit fault, the fault gas generation and pressure wave propagation will be As a result, the pressure inside the fuel tank rises _sharply . At this time, p _op.k will be greater than the threshold p _th.k. Therefore, the protection action can be determined by judging whether formula ④ holds.

In order to ensure that the transformer adaptive protection based on pressure characteristics does not malfunction under the most severe pressure fluctuations caused by the magnetizing inrush current, the no-load closing action threshold p _th.k is set as:

p _th.k = k _rel p _ub.kmax ⑤

In the formula ⑤: p _ub.kmax is the unbalanced amount of the operating pressure inside the oil tank under the condition of the maximum pressure fluctuation caused by the magnetizing inrush current, and the transient oil pressure value measured at the internal measuring point of the transformer during the magnetizing inrush current is taken into the formula ③, and then calculated The value of p _th.k is the imbalance p _{ub.kmax of the} operating pressure inside the fuel tank under the condition of the maximum pressure fluctuation caused by the magnetizing inrush current.

(14) Use formula ⑥ to calculate the operating pressure p _op.i at the current time t:

In formula ⑥, T is the length of the data window, which is the same as the length of the data window selected during the preset protection action threshold setting. 5ms, 10ms or 20ms can be selected as needed

(15) Compare the calculated action pressure p _op.i with the preset pressure protection action threshold p _th . If the calculated action pressure p _{op.i is} greater than or equal to the preset pressure protection action threshold p _th , That is, if formula ⑦ is established, the protection will act, trip and remove the fault, and the whole set of equipment will reset, waiting for manual reset; otherwise, return to step (5);

p _{op.i ≥p th} ⑦

In order to ensure that the transformer adaptive protection based on pressure characteristics does not malfunction under the most severe pressure fluctuation conditions caused by the most severe external short-circuit fault, the pressure protection action threshold p _th is defined as:

p _th ＝k _rel p _ub.max ⑧

In formula ⑧: p _ub.max is the maximum imbalance of the internal operating pressure of the oil tank in the case of the most severe external short-circuit fault, and the transient oil pressure value measured at the internal measuring point of the transformer during the most severe external short-circuit fault is brought into formula ⑥. The calculated value of p _op.i is the maximum imbalance p _{ub.max of the} internal operating pressure of the fuel tank in the case of the most severe external short circuit fault.

The following takes the SFSZ8-40000/110 three-phase three-winding transformer as an example to illustrate the effect of the present invention. The main geometric structure and nameplate parameters of this type of transformer are shown in Table 1.

Table 1 The main geometric structure and nameplate parameters of SFSZ8-40000/110 transformer

In view of the normal operation of the transformer, the external short circuit and the excitation inrush current conditions, the internal pressure oscillation frequency of the fuel tank is mainly concentrated at 100Hz and 50Hz. In order to take into account the protection reliability and calculation time, a time window of 20ms is selected in the pressure protection element, and the no-load closing element The selected time window is 20ms long. Therefore, the calculated protection start threshold is 0.226kPa, the pressure protection element action threshold is 11.974kPa, and the no-load closing element action threshold is 1.832kPa.

Table 2 shows the action of adaptive protection under different operating conditions of the transformer. It can be seen that: 1) The adaptive protection strategy with no-load closing protection components also has high reliability and sensitivity, and can correctly identify single-turns. Many fault states, including short-circuit faults, are not affected by the inrush current. 2) Since the time window of protection calculation is actively shortened under the condition of excitation inrush current, and the protection threshold value is calculated according to the maximum unbalanced pressure generated by excitation inrush current, the adaptive protection strategy is effective when faced with the failure type of airdrop. Movement speed is significantly improved. In summary, the transformer adaptive protection scheme based on pressure characteristics has the characteristics of simple principle and easy implementation, and it also satisfies the "four characteristics" requirements of relay protection.

Table 2 Actions of adaptive protection under different operating conditions of transformers

The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be considered that the specific embodiments of the present invention are limited to this. For those of ordinary skill in the art to which the present invention belongs, without departing from the concept of the present invention Below, several simple deductions or substitutions can be made, all of which should be regarded as belonging to the invention and the scope of patent protection determined by the submitted claims.

Claims (10)

1. A digital self-adaptive protection device for transformers based on pressure characteristics, which is characterized by comprising: transient oil pressure characteristic quantity measurement module, switch input module, signal conditioning and acquisition module, and digital core module; wherein, transient oil pressure The characteristic quantity measurement module is connected to the signal conditioning and acquisition module, and the signal conditioning and acquisition module and the switch input module are both connected to the digital core module;

   The transient oil pressure characteristic measurement module is used to measure the oil pressure change characteristics at different positions inside the transformer, and output the corresponding analog voltage/current signal;

   The signal conditioning and acquisition module is used to receive the analog voltage/current signal output by the transient oil pressure characteristic measurement module, and convert it into a standard digital signal that the digital core module can recognize, and then output the standard digital signal;

   The switch input module is used to collect the relevant switch signals that need to be known, and output them as high level 1 or low level 0 as the input digital signal of the digital core module;

   The digital core module is used to perform protection operations on the received standard digital signal and the input digital signal, complete standard digital signal processing tasks, and then realize the relay protection function.
2. A digital adaptive protection device for transformers based on pressure characteristics according to claim 1, wherein the transient oil pressure characteristic quantity measurement module is composed of several high-frequency dynamic oil pressure sensors and their communication cables; The high-frequency dynamic oil pressure sensor is installed on the transformer body, and the end probe of the high-frequency dynamic oil pressure sensor is in contact with the transformer insulating oil to measure the characteristics of oil pressure changes at different positions inside the transformer.
3. The digital adaptive protection device for transformers based on pressure characteristics according to claim 2, wherein the high-frequency dynamic oil pressure sensor has a measurement frequency of 20kHz, a measurement error of less than 1%, and an operating temperature of -45～120 ℃, the range is -0.1～6MPa.
4. The digital adaptive protection device for transformers based on pressure characteristics according to claim 1, wherein the signal conditioning and acquisition module is composed of terminal blocks, signal conditioning circuits, low-pass filters, signal sampling circuits, and analog-to-digital A /D conversion circuit composition; the terminal block is connected with the signal conditioning circuit, the signal conditioning circuit is connected with the low-pass filter, the low-pass filter is connected with the signal sampling circuit, and the signal sampling circuit is connected with the analog-to-digital A/D conversion circuit; It is connected to the transient oil pressure characteristic quantity measurement module, and the analog-to-digital A/D conversion circuit is also connected to the digital core module.
5. A digital adaptive protection device for transformers based on pressure characteristics according to claim 1, wherein the digital core module is composed of a bus, a central processing unit, a timer/counter, a random access memory, a read-only memory, and a control circuit. ; The bus includes a data bus, an address bus and a control bus to realize data exchange and operation control; the central processing unit uses a single-chip microprocessor, general-purpose microprocessor or digital signal processor to realize digital signal processing in real time; timer/counter is used Provide timing sampling trigger signal, form interruption, protection delay action timing; random access memory is used to temporarily store temporary data, including data information input by signal conditioning and acquisition modules, and intermediate results of calculation processing; read-only memory is used to save data; The control circuit realizes the connection and coordination of the entire digital circuit through a complex programmable logic device or a field programmable gate array.
6. A digital adaptive protection device for transformers based on pressure characteristics according to claim 1, characterized in that it further comprises an external communication interface module, a man-machine dialogue module and a switch output module connected to the digital core module;

   The external communication interface module is used to provide the information channel with the computer communication network and the remote communication network;

   The man-machine dialogue module is used to establish the information connection between the digital protection device and the user;

   The switch output module controls the on or off of the tripping circuit through the output state of 0 or 1.
7. A digital adaptive protection device for transformers based on pressure characteristics according to claim 6, wherein the switch output module is composed of an optoelectronic isolation device and an outlet relay, one end of the optoelectronic isolation device is connected to the digital core module, and the other end Connect with the outlet relay;

   The man-machine dialogue module includes a compact keyboard, display screen, indicator light, buttons, printer interface and debugging communication interface.
8. A protection method for a transformer digital adaptive protection device based on pressure characteristics according to any one of claims 1-7, characterized in that it comprises the following steps:

   (1) The transient oil pressure characteristic measurement module measures the characteristics of oil pressure changes at different positions inside the transformer, and outputs analog voltage/current signals. The signal conditioning and acquisition module receives the analog voltage/output from the transient oil pressure characteristic measurement module. The current signal is converted into a standard digital signal that can be recognized by the digital core module, and then the standard digital signal is output; the switch input module is used to collect the relevant switch signal that needs to be known, and output it as a high level 1 or Low level 0, as the input digital signal of the digital core module; after the digital core module receives the input digital signal and the standard digital signal, compare whether the transient oil pressure value p _ms.i (t) of each measuring point at the current time t reaches the preset value. Set the protection start threshold p _st to determine whether the transformer adaptive protection based on the pressure characteristic is started. If the formula ① is established, the start flag is set, and the step (2) is entered;

   p _ms.i (t) _{≥p st} ①

   In formula ①, p _ms.i (t) represents the transient oil pressure value of the i-th measuring point inside the transformer at time t, where i is 1, 2, ..., N; p _st represents the protection start threshold;

   (2) Determine whether the transformer is currently in no-load closing state, if yes, proceed to step (3), otherwise, proceed to step (5);

   (3) Use formula ② to calculate the no-load closing action pressure p _op.k ;

   

   In formula ②, T _k is the length of the no-load closing data window;

   (4) If the calculated no-load closing action pressure p _{op.k is} greater than or equal to the preset no-load closing protection action threshold p _th.k , that is, the formula ③ is established, the protection action, tripping and removing the fault, the entire device Reset, waiting for manual reset;

   p _{op.k ≥p th.k} ③

   (5) Use formula ④ to calculate the operating pressure p _op.i at the current time t:

   

   In formula ④, T is the length of the data window;

   (6) Compare the calculated operating pressure p _op.i with the preset pressure protection operating threshold p _th . If the calculated operating pressure p _{op.i is} greater than or equal to the preset pressure protection operating threshold p _th , That is, if the formula ⑤ is established, the protection will be activated, the fault will be tripped and the whole set will be reset, waiting for manual reset;

   p _{op.i ≥p th} ⑤.
9. A digital adaptive protection method for transformers based on pressure characteristics according to claim 8, characterized in that, in step (1), the protection start threshold p _{st is} defined as:

   p _st ＝k _rel p _nm·max ⑥

   In formula ⑥, k _rel is the reliability coefficient, and the reliability coefficient k _rel is 1.2; p _nm.max is the maximum value of the transient oil pressure under the normal operating conditions of the transformer;

   In step (3), the no-load closing data window length T _k is the same as the data window length selected during the preset no-load closing action threshold setting; the no-load closing data window length T _{k is} set to 5ms, 10ms or 20ms.
10. A digital adaptive protection method for transformers based on pressure characteristics according to claim 8, characterized in that, in step (4), the no-load closing action threshold p _th.k is set as:

    p _th.k = k _rel p _ub.kmax ⑦

    In formula ⑦: p _ub.kmax is the unbalanced amount of the operating pressure inside the oil tank under the condition of the maximum pressure fluctuation caused by the magnetizing inrush current, and the transient oil pressure value measured at the internal measuring point of the transformer during the magnetizing inrush current is brought into formula ②. The value of p _th.k is the imbalance p _{ub.kmax of the} operating pressure inside the fuel tank under the maximum pressure fluctuation caused by the magnetizing inrush current;

    In step (5), the data window length T is set to 5ms, 10ms or 20ms;

    In step (6), define the pressure protection action threshold p _th as:

    p _th ＝k _rel p _ub.max ⑧

    In formula ⑧: p _ub.max is the maximum imbalance of the internal operating pressure of the oil tank under the most severe external short-circuit fault, and the transient oil pressure value measured at the internal measuring point of the transformer during the most severe external short-circuit fault is brought into equation ④. The calculated value of p _op.i is the maximum imbalance p _{ub.max of the} internal operating pressure of the fuel tank in the case of the most severe external short circuit fault.

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