A transformer zero-sequence differential protection self-checking system and method

Abstract

The present invention is a transformer zero-sequence differential protection self-checking system and method, including a first current transformer module, a zero-sequence current transformer module, a second current transformer module, a signal conditioning module, a signal processing module, a power supply module, a display and input module, the secondary current signal output ends of the first current transformer module, the zero-sequence current transformer module and the second current transformer module are respectively connected to the input end of the signal conditioning module, the output end of the signal conditioning module is connected to the analog sampling input port of the signal processing module, the communication port of the signal processing module is connected to the communication end of the display and input module, and the power supply module supplies power to the signal conditioning module, the signal processing module and the display and input module respectively. The present invention improves the zero-sequence differential polarity check efficiency, improves the operational reliability of the zero-sequence differential protection, prevents the occurrence of malfunction accidents after the transformer zero-sequence differential is put into operation, and reduces the operating cost. The method of the present invention is simple to operate, convenient and practical.

Description

Technical Field

[0001] The invention belongs to the technical field of zero-sequence differential protection, and in particular relates to a transformer zero-sequence differential protection self-checking system and method. Background Art

[0002] As an important part of the field of AC power transmission technology, the transformer converts AC into different voltage and current levels through the principle of electromagnetic induction, completing the energy transmission from the power supply side to the load side. When a short circuit or other fault occurs in the transformer and its line, the insulating oil in the transformer is subjected to high temperature and arc, producing a large amount of flammable mixed gas, causing the pressure in the oil chamber to increase sharply. In severe cases, the transformer may explode, posing a great threat to personnel and equipment, and having a great negative impact on the social economy. Therefore, how to ensure the safe and stable service of transformers has always been the research focus of experts and scholars in the field of power systems.

[0003] Transformer zero-sequence differential protection is highly sensitive to transformer winding grounding faults and is not affected by magnetizing inrush current. Transformer zero-sequence differential protection is essential for the power supply side and is an effective supplement to transformer longitudinal differential protection. The key factors affecting transformer zero-sequence differential protection are usually the polarity of the transformer neutral point current transformer and the correctness of the adopted channel. According to the years of operation experience of the power system, there have been many incidents of transformer zero-sequence differential protection misoperation. For example, a certain power grid has a prominent problem of protection misoperation due to the secondary circuit of the current transformer of the transformer zero-sequence differential protection. Since 2011, the causes of protection misoperation such as reverse polarity of the current transformer circuit and improper safety measures for the current transformer circuit maintenance accounted for 74%, as shown in the following table, of which 3 were caused by the reverse polarity of the secondary circuit of the neutral point current transformer of the transformer zero-sequence differential protection.

[0004]

[0005] In 2015, a power plant had a single-phase grounding fault in the line, which caused the A set of transformer protection to trip erroneously. After accident analysis, the plant connected the secondary circuit of the current transformer in reverse during the modification of the transformer neutral point current transformer to the fault recorder, that is, the current transformer terminal box 1S1 was connected to the cable TH01-S2, and 1S2 was connected to the cable TH01-S1. As a result, the zero-sequence differential current generated during the out-of-zone fault caused the A set of protection to trip erroneously. Later, the wiring was modified to connect the current transformer terminal box 1S1 to the cable TH01-S1, and 1S2 to the cable TH01-S2. No more zero-sequence differential protection erroneous events occurred in the power plant.

[0006] The main transformers of a certain power grid with a voltage of 220 kV or above have an average of 20 to 30 failures per year. The fundamental reason for these accidents is that when the transformer is operating normally, the three-phase current balance will not produce zero-sequence current. After the zero-sequence differential protection is put into operation, the staff cannot observe the braking current as intuitively as the longitudinal differential protection. Even if the zero-sequence differential protection neutral point current transformer circuit is reversed or the sampling channel fails, the protection device will not alarm. It is difficult to determine the correctness of the polarity of the zero-sequence differential protection current transformer under non-accident conditions, which leads to accidents that should not have occurred. Circuit problems may occur in the zero-sequence differential protection of the transformer during commissioning and operation. Due to the difficulty in verifying the zero-sequence differential protection of the transformer and the high risk of false protection, many power plants have withdrawn from the zero-sequence differential protection of the main transformer, which is not conducive to protecting the transformer. How to verify the polarity of the current transformer of the zero-sequence differential protection of the transformer and whether the channel is correct is an indispensable part of the safe commissioning of the transformer.

[0007] The common transformer zero-sequence differential protection polarity verification methods are as follows:

[0008] 1) When there is an external ground fault in the transformer area, the zero-sequence current verification circuit flows through the current transformer on the high-voltage side and the neutral point side of the transformer. Usually, the zero-sequence differential protection is not put into operation when the transformer is put into operation. After the substation outgoing line fails, the main transformer protection device recording is extracted, and the protection is put into operation after verifying that the zero-sequence differential protection circuit is correct.

[0009] 2) When the transformer is closed under no-load condition, a magnetizing inrush current will be generated. That is, due to different initial angles, transformer residual magnetism and other conditions when closing, the three-phase magnetizing inrush current is asymmetric and has different harmonic contents. Zero-sequence current is generated in the three phases, and the second and third harmonics in the zero-sequence current account for a large proportion, showing typical inrush current characteristics. At this time, if there is no internal fault when the transformer is closed under no-load condition, the magnetizing inrush current is a penetrating current. The polarity of the zero-sequence differential protection current transformer is checked according to the size and phase of the zero-sequence magnetizing inrush current on the high-voltage side of the transformer and the zero-sequence magnetizing inrush current on the neutral point side.

[0010] The existing technology for transformer zero-sequence differential protection verification has the following defects and deficiencies:

[0011] 1) The method of verifying the zero-sequence differential protection circuit through an out-of-zone grounding fault is effective. However, its disadvantage is that the zero-sequence differential protection cannot be put into operation at the same time as the transformer. It is necessary to passively wait for out-of-zone faults. The zero-sequence differential protection may be withdrawn for a long time and cannot play the role of zero-sequence differential protection in time.

[0012] 2) The verification method of closing the main transformer without load solves the problem that the zero-sequence differential protection of the main transformer cannot be put into operation at the same time as the main transformer. However, it still does not solve the problem of circuit verification of the zero-sequence differential protection during operation. This verification method requires protection professionals to have a good theoretical foundation and practical experience to make correct analysis, and the actual operation is difficult. Summary of the invention

[0013] The purpose of the present invention is to provide a transformer zero-sequence differential protection self-verification system in view of the shortcomings of the existing transformer zero-sequence differential protection verification. The system of the present invention not only improves the zero-sequence differential polarity verification efficiency, but also can timely, accurately and automatically verify the zero-sequence differential protection circuit, improve the operational reliability of the zero-sequence differential protection, and prevent the occurrence of false operation accidents after the transformer zero-sequence differential is put into operation, but also can reduce the workload of professionals and further reduce the labor operation cost.

[0014] Another object of the present invention is to provide a transformer zero-sequence differential protection self-checking method, which is simple to operate, convenient and practical.

[0015] In order to achieve the above object, the present invention adopts the following technical solutions:

[0016] A transformer zero-sequence differential protection self-checking system of the present invention comprises a first current transformer module, a zero-sequence current transformer module, a second current transformer module, a signal conditioning module, a signal processing module, a power supply module, and a display and input module. The secondary current signal output ends of the first current transformer module, the zero-sequence current transformer module, and the second current transformer module are respectively connected to the input end of the signal conditioning module, the output end of the signal conditioning module is connected to the analog quantity sampling input port of the signal processing module, the communication port of the signal processing module is connected to the communication end of the display and input module, and the power supply module supplies power to the signal conditioning module, the signal processing module, and the display and input module respectively.

[0017] The transformer zero-sequence differential protection self-checking method of the present invention comprises the following steps:

[0018] 1) The first current transformer module collects the three-phase current on the line side of the transformer, the zero-sequence current transformer module collects the neutral point current of the transformer, and the second current transformer module collects the three-phase current on the neutral point side of the transformer;

[0019] 2) The signal conditioning module converts the secondary current signals output by the first current transformer module, the zero-sequence current transformer module and the second current transformer module into analog voltage signals compatible with the signal processing module;

[0020] 3) The signal processing module collects the analog voltage signal output by the signal conditioning module, and restores the voltage signal into an actual current signal. The polarity of the transformer zero-sequence differential protection module is checked according to the restored current signal. The signal processing module 5 determines whether a ground fault occurs in the transformer through the transformer zero-sequence differential protection logic and constant value.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] 1) The present invention collects the three-phase current of the transformer line side in real time, obtains the self-generated zero-sequence current of the line side by calculating the vector sum of the three-phase current, and at the same time collects the three-phase and zero-sequence actual currents of the transformer neutral point side, and also obtains the self-generated zero-sequence current of the neutral point side by the vector sum of the three-phase current. When the transformer is no-loaded and the turns are closed, the differential current of the self-generated zero-sequence current of the line side or the self-generated zero-sequence current of the neutral point side and the actual measured current of the neutral point is calculated. When the secondary circuit of the current transformer is correctly connected, the differential current fluctuates around the zero line, and the polarity of the transformer zero-sequence differential protection current transformer is judged according to the physical characteristics of the transformer zero-sequence differential current; further, the three-phase current and self-generated zero-sequence current of the line side, the three-phase current and self-generated zero-sequence current of the neutral point side, and the actual measured zero-sequence current of the neutral point are displayed in time on the system display and input module, and when the polarity of the transformer zero-sequence differential is wrong, an alarm message is issued in time to remind the staff to take relevant measures to avoid the malfunction of the transformer zero-sequence differential protection after commissioning. The improvement of the present invention over the traditional transformer zero-sequence differential protection verification method is that, currently, secondary maintenance work is usually carried out in conjunction with primary equipment power outages, so changes in the zero-sequence differential protection circuit usually occur during the main transformer power outage. When the main transformer is restored to power and closed at no load, the transformer zero-sequence differential protection self-verification system can verify the correctness of the circuit, thereby ensuring that hidden dangers are discovered in a timely manner.

[0023] 2) The present invention is powerful and can not only verify the polarity of the transformer zero-sequence differential protection, but also use the first current transformer module and the second current transformer module to form a transformer line-side longitudinal differential protection that is sensitive to phase-to-phase and grounding faults. By using the differential currents of phases A, B and C on the line side and the neutral point side, the longitudinal differential protection constant is set according to the display and input module, and the transformer is judged in real time on the winding operation status of the transformer and the grounding side, thereby ensuring the safe and stable operation of the transformer.

[0024] 3) The present invention improves the verification efficiency of transformer zero-sequence differential protection, saves the investment time of transformer zero-sequence differential protection, replaces the traditional manual out-of-zone fault, i.e., the excitation inrush current verification method of zero-sequence differential polarity, reduces the workload of protection personnel, and further reduces labor operation costs.

[0025] 4) The cross-check method of the present invention improves the reliability of the transformer zero-sequence differential protection verification. The self-generated zero-sequence current on the line side and the self-generated zero-sequence current on the neutral point side are compared with the measured zero-sequence current on the neutral point, respectively, to further confirm the correctness of the polarity of the current transformer of the transformer zero-sequence differential protection. At the same time, during operation, the two modes are output in a logical or mode, which improves the flexibility and accuracy of the transformer zero-sequence differential protection.

[0026] 5) The present invention utilizes the internal analog sampling circuit of the signal processor module to avoid the additional investment in analog sampling modules, thereby indirectly reducing the cost of the entire calibration system. At the same time, the internal analog sampling circuit is utilized to make the system analog sampling and data processing more compatible, and data processing more convenient and faster.

[0027] 6) The present invention improves the transformer zero-sequence differential protection verification method, adopts the transformer zero-sequence differential protection with self-verification technology, realizes timely, accurate and automatic verification of the zero-sequence differential protection circuit, and improves the operational reliability of the zero-sequence differential protection.

[0028] 7) The display and input module of the present invention has a high degree of integration. It can not only display and record the collected current information, but also set the transformer zero-sequence differential protection and longitudinal differential protection settings and output modes by touch. When the transformer zero-sequence differential polarity is wrong, it will display and issue error alarm information in time.

[0029] 8) The signal processing module of the present invention adopts the STM32F103 embedded intelligent processor with rich peripheral resources, which minimizes the power consumption of the system operation and reasonably allocates each input and output port of the processor. At the same time, the STM32F103 embedded intelligent processor has high integration and only requires simple peripheral circuits to complete various functions.

[0030] 9) The present invention adopts modular hardware design, and each module is connected through terminals, which is easy to assemble and has strong expansibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a principle block diagram of the system of the present invention;

[0032] Figure 2 It is a schematic diagram of a three-phase current conditioning circuit on the line side of a signal conditioning module of the present invention;

[0033] Figure 3 It is a schematic diagram of a three-phase current conditioning circuit on the neutral point side of a signal conditioning module of the present invention;

[0034] Figure 4 It is a schematic diagram of a neutral point single-phase current conditioning circuit of a signal conditioning module of the present invention;

[0035] Figure 5 It is a schematic diagram of the signal processing module circuit of the present invention.

[0036] In the figure: a first current transformer module 1, a zero-sequence current transformer module 2, a second current transformer module 3, a signal conditioning module 4, a signal processing module 5, a power supply module 6, a display and input module 7, and a digital signal input and output module 8. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0038] like Figure 1 As shown, a transformer zero-sequence differential protection self-checking system of the present invention includes a first current transformer module 1, a zero-sequence current transformer module 2, a second current transformer module 3, a signal conditioning module 4, a signal processing module 5, a power supply module 6, and a display and input module 7. The secondary current signal output ends of the first current transformer module 1, the zero-sequence current transformer module 2, and the second current transformer module 3 are respectively connected to the input end of the signal conditioning module 4, the output end of the signal conditioning module 4 is connected to the analog sampling input port of the signal processing module 5, the communication port of the signal processing module 5 is connected to the communication end of the display and input module 7, and the power supply module 6 supplies power to the signal conditioning module 4, the signal processing module 5, and the display and input module 7, respectively.

[0039] The transformer zero-sequence differential protection self-checking system of the present invention further includes a digital signal input and output module 8 , which is connected to the digital input and output ports of the signal processing module 5 .

[0040] In this embodiment, the output voltage level of the power module 6 is ±3.3V, ±5V, ±12V, ±24V; the power module 6 is used to provide power energy for the signal conditioning module 4, the signal processing module 5 and the display and input module 7; the digital signal input and output module 8 is used to receive the action information of the transformer electrical quantity and non-electrical quantity protection and to issue the transformer zero-sequence differential protection alarm and tripping signal.

[0041] In this embodiment, the first current transformer module 1 includes three single-phase current transformers, which respectively collect the A, B, and C phase currents on the line side of the transformer; the zero-sequence current transformer module 2 includes a single-phase current transformer, which collects the single-phase current of the neutral point on the grounding side of the transformer; the second current transformer module 3 includes three single-phase current transformers, which respectively collect the A, B, and C phase currents on the neutral point side of the transformer.

[0042] In this embodiment, the first current transformer module 1 or the second current transformer module 3 and the zero-sequence current transformer module 2 constitute a transformer zero-sequence differential protection system that is sensitive to transformer winding grounding faults; the signal processing module 5 obtains the self-produced zero-sequence current on the line side of the transformer by calculating the three-phase current vector sum of the first current transformer module 1, and further uses the neutral point current collected by the zero-sequence current transformer module 2 to verify the polarity of the transformer zero-sequence differential protection current transformer; the signal processing module 5 obtains the self-produced zero-sequence current on the neutral point side of the transformer by calculating the three-phase current vector sum of the second current transformer module 3, and uses the zero-sequence current transformer Module 2 collects the neutral point current to check the polarity of the current transformer of the zero-sequence differential protection of the transformer; the first current transformer module 1 and the second current transformer module 3 constitute a differential protection system that is sensitive to phase-to-phase and grounding faults within the protection range of the transformer line side; the signal processing module 5 calculates the A-phase current vector sum, the B-phase current vector sum and the C-phase current vector sum of the first current transformer module 1 and the second current transformer module 3, respectively, and further obtains the A-phase differential current, the B-phase differential current and the C-phase differential current. The signal processing module 5 determines whether grounding and phase-to-phase faults occur within the differential protection range of the transformer through the A-phase differential current, the B-phase differential current and the C-phase differential current.

[0043] like Figure 2 , Figure 3 , Figure 4 As shown, the signal conditioning module 4 includes a plurality of identical single-phase current signal conditioning circuits, and the single-phase current signal conditioning circuit includes a signal input port P2, a current transformer CT1, an operational amplifier OP1, an operational amplifier OP2, a signal output port P1, a variable resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R8 and a capacitor C1, a capacitor C2;

[0044] The first and second pins of the signal input port P2 are connected in parallel to the primary end of the current transformer CT1, the two ends of the resistor R6 are connected in parallel to the secondary end of the current transformer CT1, the non-polar end of the secondary end of the current transformer CT1 is connected to the power ground, the polar end of the secondary end of the current transformer CT1 is connected to the second pin of the operational amplifier OP1 via the capacitor C2 and the resistor R4 in sequence, the third pin of the operational amplifier OP1 is connected to the middle tap end of the variable resistor R1 via the resistor R2, one end of the variable resistor R1 is connected to the power ground, and the other end is connected to the 5V power supply, the second pin of the operational amplifier OP1 is connected to the sixth pin of the operational amplifier OP1 via the resistor R8, and the fourth pin of the operational amplifier OP1 is connected to the 5V The operational amplifier OP1 is connected to a -5V power supply, the 7th pin of the operational amplifier OP1 is connected to a -5V power supply, the 6th pin of the operational amplifier OP1 is connected to the 3rd pin of the operational amplifier OP2 via a resistor R3, one end of the capacitor C1 is connected to the 3rd pin of the operational amplifier OP2, and the other end is connected to a power ground, the 2nd pin of the operational amplifier OP2 is connected to the 6th pin, the 4th pin of the operational amplifier OP2 is connected to a 5V power supply, the 7th pin of the operational amplifier OP2 is connected to a -5V power supply, the 6th pin of the operational amplifier OP2 is connected to the 1st pin of the signal output port P1 via a resistor R5, the 2nd pin of the signal output port P1 is connected to the power ground and then connected to the 6th pin of the operational amplifier OP2 via a resistor R7.

[0045] like Figure 5 As shown, the signal processing module 5 includes an STM32F103 microprocessor U203, a capacitor C212, a capacitor C213, a capacitor C210, a capacitor C208, a capacitor C231, a capacitor C230, a capacitor C232, a capacitor C207, a capacitor C209, a capacitor C202, a capacitor C206, a capacitor C200, a capacitor C201, a capacitor C203, a resistor R214, a resistor R215, a resistor R202, a crystal oscillator Y200, a crystal oscillator Y201, a TPS73233 voltage regulator chip U210, a diode D201, a diode D200 and a battery BT200;

[0046] The 64th pin of the STM32F103 microprocessor U203 is connected to a 3.3V power supply, the two ends of the capacitor C212 are connected in parallel to the 64th pin and the 63rd pin of the STM32F103 microprocessor U203, and the 60th pin of the STM32F103 microprocessor U203 is connected to a power ground via a resistor R214. The two ends of the capacitor C213 are connected in parallel to the 48th and 47th pins of the STM32F103 microprocessor U203, the negative end of the battery BT200 is grounded and connected to one end of the capacitor C203, the other end of the capacitor C203 is connected to the 1st pin of the STM32F103 microprocessor U203, the positive end of the battery BT200 is connected to the 1st pin of the STM32F103 microprocessor U203 through the anode and cathode of the diode D200 respectively, the anode of the diode D201 is connected to the 3.3V power supply, and the cathode is connected to the cathode of the diode D200, the two ends of the crystal oscillator Y200 are connected in parallel to the ST The 3rd and 4th pins of the STM32F103 microprocessor U203 are connected to the 3rd and 4th pins of the STM32F103 microprocessor U203, one end of the crystal oscillator Y200 is connected to the power ground via capacitor C200, and the other end of the crystal oscillator Y200 is connected to the power ground via capacitor C201, and the resistor R202 is connected in parallel with the crystal oscillator Y201, and the two ends are respectively connected to the 5th and 6th pins of the STM32F103 microprocessor U203, one end of the capacitor C202 and one end of the capacitor C206 are grounded and then connected to the 12th pin of the STM32F103 microprocessor U203, the other end of the capacitor C202 is connected to the 1st pin of the crystal oscillator Y201, and the capacitor C206 is connected to the 12th pin of the STM32F103 microprocessor U203. The other end is connected to the second pin of the crystal oscillator Y201, the capacitor C207 and the capacitor C209 are connected in parallel, one end is connected to the power ground and the 12th pin of the STM32F103 microprocessor U203 respectively, and the other end is connected to the 13th pin of the STM32F103 microprocessor U203, the two ends of the capacitor C230 are connected in parallel to the 1st pin and the 2nd pin of the TPS73233 voltage regulator chip U210, the 1st pin of the TPS73233 voltage regulator chip U210 is connected to 3.3V, the 2nd pin of the TPS73233 voltage regulator chip U210 is connected to the power ground, and the TPS73233 voltage regulator chip U210 Pin 3 is connected to pin 1, pin 4 of the TPS73233 voltage regulator chip U210 is connected to the power ground via capacitor C231, pin 5 of the TPS73233 voltage regulator chip U210 is connected to pin 13 of the STM32F103 microprocessor U203, pin 28 of the STM32F103 microprocessor U203 is connected to the power ground via resistor R215, and both ends of the capacitor C210 are connected in parallel to pins 31 and 32 of the STM32F103 microprocessor U203; pin 20 of the STM32F103 microprocessor U203 is connected to pin 1 of the signal output port P1.

[0047] The display and input module 7 uses a touch screen, and the display and input module 7 is connected to the signal processing module 5. In this embodiment, the display and input module 7 uses an industrial-grade integrated touch screen, and the display and input module 7 shares information with the signal processing module 5 in a serial communication mode, and records and displays the current amplitude, phase, trend and zero-sequence differential protection current transformer polarity information collected by the signal processing module 5 in real time, sets the transformer zero-sequence differential protection setting value through manual touch input, and transmits the setting value to the signal processing module 5.

[0048] The transformer zero-sequence differential protection self-checking method of the present invention comprises the following steps:

[0049] 1) The first current transformer module 1 collects the three-phase current on the line side of the transformer, the zero-sequence current transformer module 2 collects the neutral point current of the transformer, and the second current transformer module 3 collects the three-phase current on the neutral point side of the transformer;

[0050] 2) The signal conditioning module 4 converts the secondary current signals output by the first current transformer module 1, the zero-sequence current transformer module 2 and the second current transformer module 3 into analog voltage signals compatible with the signal processing module 5;

[0051] 3) The signal processing module 5 collects the analog voltage signal output by the signal conditioning module 4, and restores the voltage signal into an actual current signal, and checks the polarity of the transformer zero-sequence differential protection module according to the restored current signal. The signal processing module 5 determines whether a ground fault occurs in the transformer through the transformer zero-sequence differential protection logic and constant value.

[0052] The signal processing module 5 further confirms the correctness of the polarity of the transformer zero-sequence differential protection current transformer by cross-comparing the self-generated zero-sequence current on the line side and the self-generated zero-sequence current on the neutral point side with the measured zero-sequence current of the neutral point.

[0053] The signal processing module 5 is connected to a display and input module 7, which is used to display the current signals of the first current transformer module 1, the zero-sequence current transformer module 2, the second current transformer module 3 and the polarity information of the transformer zero-sequence differential protection module. When a ground fault occurs in the transformer or the zero-sequence differential protection polarity is wrong, an alarm message is displayed in time to remind the staff to take corresponding measures; the display and input module 7 is also used to set the transformer zero-sequence differential protection constant.

[0054] The specific method of verifying the polarity of the transformer zero-sequence differential protection of the present invention is as follows:

[0055] 1) When the transformer is closed without load or has an out-of-zone fault, the signal processing module automatically calculates the self-generated zero-sequence current of the three-phase current on the line side of the transformer, obtains the self-generated zero-sequence current on the line side, calculates the self-generated zero-sequence current of the three-phase current on the neutral point side of the transformer, obtains the self-generated zero-sequence current measured at the neutral point, and collects the zero-sequence current measured at the neutral point of the transformer. All three are through currents. According to the principle of subtractive polarity, the self-generated zero-sequence current on the line side and the zero-sequence current measured at the neutral point should be of the same polarity, and the self-generated zero-sequence current measured at the neutral point and the zero-sequence current measured at the neutral point should also be of the same polarity, with an angle difference of 0 degrees. If configured as additive polarity, the angle difference is 180 degrees;

[0056] 2) Set the effective value threshold of the self-produced zero-sequence current and the measured zero-sequence current. When the threshold is exceeded, the calibration is started. The minimum threshold value can be set to 10mA (0.01In, In=1A);

[0057] 3) If the angle difference between the self-generated zero sequence and the measured neutral point current satisfies , and the duration exceeds 60ms, it is determined that the zero-sequence differential protection circuit is wrong, and the system will issue an alarm signal. Where 3I0.cal is the three-phase self-generated zero-sequence current on the line side or neutral point side of the transformer, and 3I0.neu is the measured zero-sequence current of the transformer neutral point.

[0058] 4) If the zero-sequence differential protection circuit is judged to be wrong, after modifying the wiring, the transformer needs to be closed again without load to verify whether the wiring modification is correct.

[0059] The present invention is beneficial to the polarity verification efficiency of the transformer zero-sequence differential protection, preventing the transformer from malfunctioning after the differential protection is put into operation, and can automatically verify the circuit problems that occur during the operation of the main transformer, promptly alarm and eliminate the faults, and reduce the inspection and maintenance costs.

[0060] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A transformer zero-sequence differential protection self-checking system, characterized in that The invention comprises a first current transformer module (1), a zero-sequence current transformer module (2), a second current transformer module (3), a signal conditioning module (4), a signal processing module (5), a power supply module (6), and a display and input module (7); the secondary current signal output ends of the first current transformer module (1), the zero-sequence current transformer module (2), and the second current transformer module (3) are respectively connected to the input end of the signal conditioning module (4); the output end of the signal conditioning module (4) is connected to the analog quantity sampling input port of the signal processing module (5); the communication port of the signal processing module (5) is connected to the communication end of the display and input module (7); and the power supply module (6) supplies power to the signal conditioning module (4), the signal processing module (5), and the display and input module (7); The first current transformer module (1) comprises three single-phase current transformers, respectively collecting the A, B and C phase currents on the line side of the transformer; the zero-sequence current transformer module (2) comprises a single-phase current transformer, collecting the single-phase current of the neutral point on the grounding side of the transformer; the second current transformer module (3) comprises three single-phase current transformers, respectively collecting the A, B and C phase currents on the neutral point side of the transformer; The signal processing module (5) collects the analog voltage signal output by the signal conditioning module (4), and restores the voltage signal into an actual current signal, checks the polarity of the transformer zero-sequence differential protection module according to the restored current signal, and the signal processing module (5) determines whether a ground fault occurs in the transformer through the transformer zero-sequence differential protection logic and a fixed value.

2. The transformer zero-sequence differential protection self-checking system according to claim 1 is characterized in that It also includes a digital signal input and output module (8), which is connected to the digital input and output ports of the signal processing module (5).

3. The transformer zero-sequence differential protection self-checking system according to claim 1 is characterized in that The output voltage level of the power module (6) is ±3.3V, ±5V, ±12V, ±24V.

4. The transformer zero-sequence differential protection self-checking system according to any one of claims 1 to 3, characterized in that The signal conditioning module (4) comprises a plurality of identical single-phase current signal conditioning circuits, the single-phase current signal conditioning circuits comprising a signal input port P2, a current transformer CT1, an operational amplifier OP1, an operational amplifier OP2, a signal output port P1, a variable resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R8 and capacitors C1 and C2; the first pin and the second pin of the signal input port P2 are connected in parallel to the primary end of the current transformer CT1, the two ends of the resistor R6 are connected in parallel to the secondary end of the current transformer CT1, the non-polarity end of the secondary end of the current transformer CT1 is connected to the power supply ground, the polarity end of the secondary end of the current transformer CT1 is connected to the second pin of the operational amplifier OP1 via the capacitor C2 and the resistor R4 in sequence, the third pin of the operational amplifier OP1 is connected to the middle tap end of the variable resistor R1 via the resistor R2, and one end of the variable resistor R1 is connected to the ground. The operational amplifier OP1 is connected to the power ground, and the other end is connected to the 5V power supply. The second pin of the operational amplifier OP1 is connected to the sixth pin of the operational amplifier OP1 via the resistor R8. The fourth pin of the operational amplifier OP1 is connected to the 5V power supply. The seventh pin of the operational amplifier OP1 is connected to the -5V power supply. The sixth pin of the operational amplifier OP1 is connected to the third pin of the operational amplifier OP2 via the resistor R3. One end of the capacitor C1 is connected to the third pin of the operational amplifier OP2, and the other end is connected to the power ground. The second pin of the operational amplifier OP2 is connected to the sixth pin. The fourth pin of the operational amplifier OP2 is connected to the 5V power supply. The seventh pin of the operational amplifier OP2 is connected to the -5V power supply. The sixth pin of the operational amplifier OP2 is connected to the first pin of the signal output port P1 via the resistor R5. The second pin of the signal output port P1 is connected to the power ground and then connected to the sixth pin of the operational amplifier OP2 via the resistor R7.

5. The transformer zero-sequence differential protection self-checking system according to claim 4 is characterized in that The signal processing module (5) comprises an STM32F103 microprocessor U203, a capacitor C212, a capacitor C213, a capacitor C210, a capacitor C208, a capacitor C231, a capacitor C230, a capacitor C232, a capacitor C207, a capacitor C209, a capacitor C202, a capacitor C206, a capacitor C200, a capacitor C201, a capacitor C203, a resistor R214, a resistor R215, a resistor R202, a crystal oscillator Y200, a crystal oscillator Y201, a TPS73233 voltage regulator chip U210, a diode D201, a diode D200 and a battery BT200; the STM32F103 microprocessor U203 No. 64 The pin is connected to a 3.3V power supply, the two ends of the capacitor C212 are connected in parallel to the 64th and 63rd pins of the STM32F103 microprocessor U203, the 60th pin of the STM32F103 microprocessor U203 is connected to the power ground via a resistor R214, the two ends of the capacitor C213 are connected in parallel to the 48th and 47th pins of the STM32F103 microprocessor U203, the negative polarity end of the battery BT200 is grounded and connected to one end of the capacitor C203, the other end of the capacitor C203 is connected to the 1st pin of the STM32F103 microprocessor U203, the positive polarity end of the battery BT200 is connected to the STM3 after the anode and cathode of the diode D200 respectively. The anode of the diode D201 is connected to the 3.3V power supply, and the cathode is connected to the cathode of the diode D200. Both ends of the crystal oscillator Y200 are connected in parallel to the 3rd and 4th pins of the STM32F103 microprocessor U203. One end of the crystal oscillator Y200 is connected to the power ground via the capacitor C200, and the other end of the crystal oscillator Y200 is connected to the power ground via the capacitor C201. After the resistor R202 is connected in parallel with the crystal oscillator Y201, both ends are connected to the 5th and 6th pins of the STM32F103 microprocessor U203 respectively. One end of the capacitor C202 and one end of the capacitor C206 are grounded. The capacitor C207 and the capacitor C209 are connected in parallel, and one end of the capacitor C207 and the capacitor C209 are connected to the power ground and the 12th pin of the STM32F103 microprocessor U203, and the other end of the capacitor C207 and the capacitor C209 are connected to the 13th pin of the STM32F103 microprocessor U203. The two ends of the capacitor C230 are connected in parallel to the 1st and 2nd pins of the TPS73233 voltage regulator chip U210, and the 1st and 3.3V, the 2nd pin of the TPS73233 voltage regulator chip U210 is connected to the power ground, the 3rd pin of the TPS73233 voltage regulator chip U210 is connected to the 1st pin, the 4th pin of the TPS73233 voltage regulator chip U210 is connected to the power ground via capacitor C231, the 5th pin of the TPS73233 voltage regulator chip U210 is connected to the 13th pin of the STM32F103 microprocessor U203, the 28th pin of the STM32F103 microprocessor U203 is connected to the power ground via resistor R215, the two ends of the capacitor C210 are connected in parallel to the 31st and 32nd pins of the STM32F103 microprocessor U203; the 20th pin of the STM32F103 microprocessor U203 is connected to the 1st pin of the signal output port P1. .

6. A transformer zero-sequence differential protection self-checking system according to claim 5, characterized in that The display and input module (7) adopts an industrial-grade integrated touch display screen, and the display and input module (7) is connected to the signal processing module (5).

7. A transformer zero-sequence differential protection self-checking method, characterized in that The steps include: 1) The first current transformer module (1) collects the three-phase current on the line side of the transformer, the zero-sequence current transformer module (2) collects the neutral point current of the transformer, and the second current transformer module (3) collects the three-phase current on the neutral point side of the transformer; 2) The signal conditioning module (4) converts the secondary current signals output by the first current transformer module (1), the zero-sequence current transformer module (2) and the second current transformer module (3) into analog voltage signals compatible with the signal processing module (5); 3) The signal processing module (5) collects the analog voltage signal output by the signal conditioning module (4), and restores the voltage signal into an actual current signal, and checks the polarity of the transformer zero-sequence differential protection module according to the restored current signal. The signal processing module (5) determines whether a ground fault occurs in the transformer through the transformer zero-sequence differential protection logic and fixed value.

8. The transformer zero-sequence differential protection self-checking method according to claim 7 is characterized in that The signal processing module (5) further confirms the correctness of the polarity of the transformer zero-sequence differential protection current transformer by cross-comparing the self-generated zero-sequence current on the line side and the self-generated zero-sequence current on the neutral point side with the measured zero-sequence current of the neutral point.

9. The transformer zero-sequence differential protection self-checking method according to claim 7, characterized in that The signal processing module (5) is also connected to a display and input module (7), and the display and input module (7) is used to display the current signals of the first current transformer module (1), the zero-sequence current transformer module (2), and the second current transformer module (3) and the polarity information of the transformer zero-sequence differential protection module. When a ground fault occurs in the transformer or the zero-sequence differential protection polarity is wrong, an alarm message is displayed in time to remind the staff to take corresponding measures; the display and input module (7) is also used to set the transformer zero-sequence differential protection setting value.

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