Method for avoiding ferromagnetic resonance of medium-voltage plant power system in nuclear power plant

Abstract

The invention provides a method for avoiding ferromagnetic resonance of a medium-voltage auxiliary power system of a nuclear power plant. The method comprises the following steps: step 1, changing a V / V wiring mode formed by connecting two single-phase voltage transformers from star wiring of a voltage transformer of the medium-voltage auxiliary power system; step 2, acquiring and measuring the voltage to ground of each phase; and step 3, generating a bus zero sequence voltage. According to the invention, the electromagnetic voltage transformer adopts V / V wiring and has no primary neutral point, so that a grounding problem does not exist, and ferromagnetic resonance between the electromagnetic voltage transformer and a grounding capacitor is avoided. The problem of ferromagnetic resonance is fundamentally solved, and the threat of ferromagnetic resonance to safe and stable operation of plant power of the nuclear power plant is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of medium-voltage power supply detection in nuclear power plants, and in particular to a method for preventing ferromagnetic resonance in a medium-voltage power supply system in a nuclear power plant. Background Art

[0002] Failures caused by ferromagnetic resonance in the medium-voltage power supply system of nuclear power plants occur from time to time. For example, when the civil construction excavation of the No. 05 plant building of a nuclear power plant was carried out, the B-phase cable on the high-voltage side of the No. 05 reactor transformer was accidentally broken, causing single-phase grounding, which then triggered the resonance of the 6kV plant I section, causing the primary two-phase fuses of the 6kV public 1 section and safety 1 section PT to melt (both A / C phases), and the dedicated power-off A channel was activated, and the unit reduced the load. Another example is that the A phase of the 002TU transformer of the 1LGA bus voltage transformer of a nuclear power plant was cracked, and the B and C transformers were not obviously damaged.

[0003] The causes of resonance include: Figure 1 As shown in the figure, when the C phase of 1SEC003MO is grounded, the A / B phase voltage rises to the line voltage. After the motor is shut down, the ground fault is removed, and the three-phase voltage suddenly changes, which excites the system ground capacitance and PT inductance to produce ferromagnetic resonance, eventually causing PT damage. The starting point of the fault is the creepage of the insulator on the incoming line side of 1SEC003MO, which causes the C phase of the motor to be grounded. The reason is the insulation degradation of the motor insulator; the cause of the fault of the 1LGA bus voltage transformer 002TU is the ferromagnetic resonance caused by the shutdown of the motor, which eventually causes PT damage.

[0004] The voltage transformer currently configured in the medium-voltage power supply system of a nuclear power plant with an ungrounded neutral point is a neutral point directly grounded method. The voltage transformer and the secondary microcomputer detuning device cannot avoid the ferromagnetic resonance of the medium-voltage system. Resonance failures occur from time to time, posing a certain threat to the safe and stable operation of the power supply of the nuclear power plant.

[0005] To address the above problems, the technologies currently used are: first, adding resistance in the zero-sequence loop to damp the generation and development of resonance; second, trying to change the reactance of the transformer or the capacitive reactance of the power supply to the ground to avoid matching the resonance parameters. There are two specific methods:

[0006] First, connect a resistor or detuning device to the open delta winding port of the voltage transformer: In the factory power supply where the neutral point is not grounded, single-phase grounding is allowed to run for up to 2 hours. If the R0 resistance is too small, long-term connection to the open delta winding will cause the transformer to overheat and burn. Therefore, the selection of R0 must not only meet the requirements of eliminating saturation overvoltage, but also ensure that the capacity of the transformer does not exceed the allowable range when single-phase grounding.

[0007] Second, the neutral point of the voltage transformer high-voltage side is grounded through a resistor: To limit resonance, the neutral point of the transformer high-voltage measurement is grounded through a resistor R0. The larger the R0 value, the greater the damping effect and the better the overvoltage limiting effect. If R0→∞, the equivalent inductance L does not participate in the zero-sequence circuit, and there is no overvoltage problem caused by the saturation of the mutual inductance. However, if the R0 value is too large, when the factory power is single-phase grounded, most of the zero-sequence voltage drops on R0, and the open delta winding voltage will be too low, affecting the action of the protection device.

[0008] However, the prior art has the following two defects:

[0009] First, when the resistor or detuning device is connected to the open delta winding port of the voltage transformer: if the R0 resistance is too small, the transformer will overheat and burn out. At the same time, it is impossible to correctly distinguish between fundamental resonance and single-phase grounding, because in these two cases, the voltage and waveform at both ends of the open delta winding are almost the same, and the detuning measures cannot be identified, and it cannot be guaranteed that they will only act at the fundamental resonance.

[0010] Second, the neutral point on the high-voltage side of the voltage transformer is grounded through a resistor: but the R0 value is too large. When single-phase grounding occurs in the plant power supply, most of the zero-sequence voltage drops on R0, and the open delta winding voltage will be too low, affecting the action of the protection device, causing the protection device to malfunction or refuse to operate, posing a threat to the safety of the nuclear power plant.

[0011] It can be seen that the current medium-voltage power supply system of nuclear power plants with ungrounded neutral points adopts suppression or restriction measures. When ferromagnetic resonance occurs, the remedial measures are to increase damping and destroy the resonance conditions. In practical applications, the detuning resistor and secondary detuning device cannot play a good role, resulting in the burning of the voltage transformer, which has a great impact on the safe and reliable operation of the power supply system of nuclear power plants and needs to be solved urgently. Summary of the invention

[0012] The purpose of the present invention is to provide a method for avoiding ferromagnetic resonance in a medium-voltage power supply system of a nuclear power plant, thereby solving the problem that ferromagnetic resonance is prone to occur during the operation of the medium-voltage power supply system, leading to burning of the voltage transformer.

[0013] In order to achieve the above object, the present invention provides the following technical solutions:

[0014] A method for avoiding ferromagnetic resonance in a medium-voltage power system of a nuclear power plant, comprising the following steps:

[0015] Step 1: Change the voltage transformer of the medium voltage auxiliary power system from star connection to V / V connection of two single-phase voltage transformers;

[0016] Step 2: Collect and measure each relative ground voltage;

[0017] Step 3: Generate bus zero-sequence voltage.

[0018] Step 1 specifically includes: two voltage transformers are connected to the line voltage U UV , U VW The primary winding is not grounded, and one end of the secondary winding is grounded, where U UV Refers to the voltage between phases U and V, U VW Refers to the voltage between V and W phases.

[0019] Step 2 specifically includes:

[0020] Step 2.1: Use an electronic voltage transformer to measure the relative voltage to ground;

[0021] Step 2.2: The secondary three-phase voltage acquisition and processing module of the electronic voltage transformer is connected to the MCU module to monitor the busbar relative to ground voltage, and then perform insulation monitoring and alarm on the medium-voltage auxiliary power system.

[0022] The parameters used in step 2.1 are: voltage level 10kV, rated frequency 50Hz, power frequency withstand voltage 42kV / 1min, lightning impulse withstand voltage 75kV, partial discharge ≤10pC, rated primary voltage Load impedance ≥ 2MΩ, rated secondary output is phase voltage Zero sequence voltage 6.5V / 3.

[0023] Furthermore, after the busbar relative voltage is collected, 3U0 = U U +U V +U W Generates self-generated zero-sequence voltage 3U0, where U U Refers to the voltage U relative to ground, U V Refers to the voltage V relative to ground, U W Refers to the voltage W relative to ground.

[0024] In step 3, the amplitude and frequency of the phase-to-ground voltage and the zero-sequence voltage are analyzed by using the wavelet transform method through the frequency tracking technology.

[0025] Compared with the prior art, the method for avoiding ferromagnetic resonance in the medium-voltage power system of a nuclear power plant provided by the present invention has the following beneficial effects:

[0026] The present invention adopts V / V wiring through the electromagnetic voltage transformer, has no primary neutral point, and thus does not have a grounding problem, thereby avoiding ferromagnetic resonance between the electromagnetic voltage transformer and the grounding capacitor. The present invention fundamentally solves the occurrence of ferromagnetic resonance and avoids the threat of ferromagnetic resonance to the safe and stable operation of power supply in nuclear power plants.

[0027] Furthermore, the present invention develops intelligent grounding monitoring logic, which can determine the phase difference and abnormal nature and promptly alarm when the plant power system is grounded abnormally, reminding the operating personnel to deal with it in time, and ensuring the safe and reliable operation of the nuclear power plant power supply and plant power. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 System configuration diagram provided for the prior art;

[0030] Figure 2 This is a schematic diagram of the V / V wiring method of the voltage transformer provided by the present invention;

[0031] Figure 3 This is a principle block diagram of the three-phase-to-ground voltage acquisition and processing provided by the present invention;

[0032] Figure 4 This is a schematic diagram of the main electrical wiring and voltage transformer layout of a nuclear power plant provided by the present invention. DETAILED DESCRIPTION

[0033] The following is further explained in detail through specific implementation methods.

[0034] like Figures 2 to 4 As shown, the present invention provides a method for avoiding ferromagnetic resonance in a medium-voltage power system of a nuclear power plant, comprising the following steps:

[0035] Step 1: The voltage transformer of the medium voltage auxiliary power system is changed from the original star connection to a V / V connection of two single-phase voltage transformers. Figure 2 , the two voltage transformers are connected to the line voltage U UV , U VW The primary winding does not need to be grounded, where U UV Refers to the voltage between phases U and V, U VW Refers to the voltage between V and W phases.

[0036] For safety reasons, one end of the secondary winding needs to be grounded. Using only two single-phase voltage transformers can obtain three symmetrical line voltages, but the phase voltage cannot be measured. In order to monitor the insulation between each phase and the ground of the system, it is necessary to be able to measure the voltage between each phase and the ground.

[0037] Step 2: Collection and measurement of each relative ground voltage.

[0038] Step 2.1: Use an electronic voltage transformer based on the resistor voltage division principle to measure the voltages of each phase to ground. The present invention designs parameters that must be met in practical applications, and the specific technical parameters are shown in Table 1.

[0039] Table 1 Specific technical parameters

[0040]

[0041] The composition and advantages of the electronic voltage transformer based on the resistance voltage division principle:

[0042] (1) Based on the principle of resistor voltage division, the output signal is a voltage quantity, which is proportional to the voltage of the measured system. It has a wide frequency response range, a large measurement range, and good linearity;

[0043] (2) When the secondary output terminal of the voltage is short-circuited, no overcurrent will be generated. Since it does not contain an iron core and has resistance damping performance, there is no magnetic saturation phenomenon in the entire measurement range, the output is linear, the measurement accuracy is high, and no ferromagnetic resonance will be generated;

[0044] (3) Directly output small voltage signals, simplifying the system structure and reducing error sources.

[0045] Step 2.2: The secondary three-phase voltage acquisition and processing module of the electronic voltage transformer is connected to the MCU module to monitor the busbar relative to ground voltage, and then perform insulation monitoring and alarm on the medium-voltage auxiliary power system.

[0046] like Figure 3 As shown in FIG. 1 , the principle block diagram of three-phase-to-ground voltage acquisition and processing includes: an electronic voltage transformer (composed of R1 to R6: U phase is composed of R1 and R2; V phase is composed of R3 and R4; W phase is composed of R5 and R6); a core circuit board and a power supply module, an MCU module, a clock module, a WIFI module, a 4G module and an ESAM module connected to the core circuit board; a GPS module and a storage chip, etc. The principle diagram is shown in FIG. Figure 3 .

[0047] Step 3: Generate bus zero-sequence voltage.

[0048] After the busbar voltage relative to ground is collected through step 2, 3U0 = U U +U V +U W (U U , U V and U W All in phasor format) to generate the self-generated zero-sequence voltage 3U0, where U UV Refers to the voltage between phases U and V, U VW Refers to the voltage between V and W phases.

[0049] Through frequency tracking technology and wavelet transform method, the amplitude and frequency of relative ground voltage and zero-sequence voltage are analyzed, and intelligent prompts are given for grounding phase difference, metal and non-metal grounding, voltage transformer disconnection monitoring, etc.

[0050] For example, Figure 4 As shown in the schematic diagram of the electrical main wiring and voltage transformer arrangement of a nuclear power plant, the present invention includes the following steps:

[0051] like Figure 4 As shown, the operation mode is: No. 1 high-voltage transformer operates with power load, and the two auxiliary transformers operate without load. The operation modes of circuit breakers, disconnectors, voltage transformers, etc. are as follows: the medium-voltage power equipment 1LGA, 1LGB, 1LGC, 1LGD, 1LHA, 1LHB bus power supply incoming line circuit breakers are all closed; 1LGB102JA, 1LGC102JA circuit breakers are disconnected; medium-voltage bus voltage transformers (1LGA001TU, 1LGA002TU, 1LGB001TU, 1LGC001TU, 1LGD001TU, 1LGD002TU, 1LHA001TU, 1LHB001TU) are all put into operation.

[0052] Through step 1, all the medium-voltage auxiliary power system voltage transformers (1LGA001TU, 1LGA002TU, 1LGB001TU, 1LGC001TU, 1LGD001TU, 1LGD002TU, 1LHA001TU, 1LHB001TU) in the embodiment are changed from the original star connection to a V / V connection mode formed by two single-phase fully insulated voltage transformers, which can reduce 8 voltage transformers. The two voltage transformers are respectively connected to the line voltage U UV , U VW Up(U UV Refers to the voltage between phases U and V, U VW Refers to the voltage between phases V and W) For safety reasons, one end of the secondary winding is grounded, and only two single-phase voltage transformers are used to measure the three symmetrical line voltages.

[0053] According to step 2.1, electronic voltage transformers based on the resistance voltage division principle (with the function of live indicator) are added between the 1LGA, 1LGB, 1LGC, 1LGD, 1LHA and 1LHB bus voltage transformers to measure the relative voltages of the busbars to the ground. At the same time, a certain resistance damping is added to the medium-voltage auxiliary power system.

[0054] According to step 2.2, the secondary three-phase voltage of the electronic voltage transformer is connected to the intelligent measurement module for collection, and the busbar relative voltage is monitored to generate a self-generated zero-sequence voltage, thereby performing insulation monitoring and alarming on the factory power system. When the secondary output terminal of the voltage is short-circuited, no overcurrent will be generated, and safety and reliability are guaranteed.

[0055] Step 3 uses the collected busbar relative voltage to generate a self-generated zero-sequence voltage (3U0 = U U +U V +U W ). The wavelet transform method is used through frequency tracking technology to analyze the amplitude and frequency of the phase-to-ground voltage and zero-sequence voltage. According to the fault properties and characteristics shown in Table 2, intelligent prompts for grounding phase difference, metal and non-metal grounding, and phase failure monitoring are developed. The voltage monitoring function of the medium-voltage power supply system of the nuclear power plant is improved and the occurrence of ferromagnetic resonance is avoided, so that the safe and stable operation of the medium-voltage power supply system of the nuclear power plant is technically guaranteed.

[0056] Table 2 Voltage transformer fault properties and characteristics

[0057]

[0058]

[0059] The present invention is suitable for voltage monitoring, single-phase grounding alarm and intelligent analysis and judgment of the medium-voltage plant electrical system of a nuclear power plant under normal operation, effectively solves the ferromagnetic resonance caused by voltage transformer saturation, and improves the continuous power supply capacity and safe and stable operation of the medium-voltage plant electrical system.

[0060] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for avoiding ferromagnetic resonance in a medium voltage power system of a nuclear power plant. It is characterized in that The following steps are involved: Step 1: Change the voltage transformer of the medium voltage auxiliary power system from star connection to V / V connection of two single-phase voltage transformers; Step 2: Collect and measure each relative ground voltage; Step 3: Generate bus zero-sequence voltage.

2. The method for avoiding ferromagnetic resonance in a medium voltage power system of a nuclear power plant according to claim 1, It is characterized in that Step 1 specifically includes: two voltage transformers are connected to the line voltage U UV , U VW The primary winding is not grounded, and one end of the secondary winding is grounded, where U UV Refers to the voltage between phases U and V, U VW Refers to the voltage between V and W phases.

3. The method for avoiding ferromagnetic resonance in a medium voltage power system of a nuclear power plant according to claim 1, It is characterized in that Step 2 specifically includes: Step 2.1: Use an electronic voltage transformer to measure the relative voltage to ground; Step 2.2: The secondary three-phase voltage acquisition and processing module of the electronic voltage transformer is connected to the MCU module to monitor the busbar relative to ground voltage, and then perform insulation monitoring and alarm on the medium-voltage auxiliary power system.

4. The method for avoiding ferromagnetic resonance in a medium voltage power system of a nuclear power plant according to claim 3, It is characterized in that The parameters used in step 2.1 are: voltage level 10kV, rated frequency 50Hz, power frequency withstand voltage 42kV / 1min, lightning impulse withstand voltage 75kV, partial discharge ≤10pC, rated primary voltage Load impedance ≥ 2MΩ, rated secondary output is phase voltage Zero sequence voltage 6.5V / 3.

5. The method for avoiding ferromagnetic resonance in a medium voltage power system of a nuclear power plant according to claim 4, It is characterized in that After the busbar relative voltage is collected, the 3U 0 =U U +U V +U W Generate self-generated zero-sequence voltage 3U 0 , where U U Refers to the voltage U relative to ground, U V Refers to the voltage V relative to ground, U W Refers to the voltage W relative to ground.

6. The method for avoiding ferromagnetic resonance in a medium voltage power system of a nuclear power plant according to claim 1, It is characterized in that In step 3, the amplitude and frequency of the phase-to-ground voltage and the zero-sequence voltage are analyzed by using the wavelet transform method through the frequency tracking technology.

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