CN110132361B - Superconducting current limiter state monitoring system and state monitoring method - Google Patents
Superconducting current limiter state monitoring system and state monitoring method Download PDFInfo
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- CN110132361B CN110132361B CN201910484962.1A CN201910484962A CN110132361B CN 110132361 B CN110132361 B CN 110132361B CN 201910484962 A CN201910484962 A CN 201910484962A CN 110132361 B CN110132361 B CN 110132361B
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Abstract
A state monitoring system and method of a superconducting current limiter, including the body of the superconducting current limiter, liquid nitrogen storage tank, cryogenic refrigeration system, sensor assembly, real-time data acquisition system and monitoring system; the sensor assembly comprises a voltage sensor, a temperature sensor, a pressure sensor and a liquid level sensor; the real-time data acquisition system comprises a voltage acquisition module, a temperature acquisition module, a pressure acquisition module and a liquid level acquisition module, and is used for converting sensor signals into corresponding digital quantities; the monitoring system analyzes and monitors the operating parameters of the superconducting current limiter; the state parameters of the superconducting current limiter in the operation process are collected and transmitted in real time, fault characteristic analysis is carried out on the superconducting current limiter based on the fault criterion of the superconducting current limiter, state evaluation on the superconducting current limiter is achieved, the problem of equipment defects is found and solved in advance, equipment and system faults are avoided, and reliability and stability of the whole system are improved.
Description
Technical Field
The invention belongs to the technical field of state monitoring, and particularly relates to a state monitoring system and a state monitoring method of a superconducting current limiter.
Background
The superconducting current limiter uses the physical property of superconductor in transition from superconducting state to normal state to limit current, and has very low loss in normal operation, automatic reset and ideal current limiting device. Once a fault occurs, the direct-current short-circuit fault current cannot be effectively limited, and the unplanned shutdown can be caused, so that the safe and stable operation of the power grid is directly threatened.
The superconducting current limiter is in an operation environment of ultralow temperature, high voltage and electromagnetic oscillation, which brings great difficulty to the state monitoring of the superconducting current limiter, the traditional sensor cannot work normally in the operation environment of ultralow temperature, high voltage and electromagnetic oscillation, and the problem of any part of the whole system can cause the superconducting current limiter to be incapable of operating normally. In the state monitoring of the superconducting current limiter, on one hand, various parameter signals such as temperature, pressure, liquid level and the like need to be synchronously acquired to ensure that a monitoring system carries out accurate fault analysis; on the other hand, the data storage and remote transmission are beneficial to improving the state monitoring efficiency of the superconducting current limiter, and the effective fusion of the internal and external state information of the superconducting current limiter is realized.
At present, one of the most key elements for realizing the practical application of the superconducting current limiter lies in the maintenance of a low-temperature environment, the state monitoring device of the conventional superconducting current limiter is difficult to ensure the maintenance-free operation of the whole current limiting system for more than one year, and cannot ensure the synchronous acquisition of the internal and external state information of the superconducting current limiter and the state evaluation and fault analysis of the whole system, so that the state monitoring device is very important for the online monitoring of the state parameters such as the liquid level, the pressure, the temperature and the like of the superconducting current limiter and a low-temperature container.
Disclosure of Invention
In order to solve the problems in the prior art, the present invention provides a system and a method for monitoring the state of a superconducting current limiter, which can effectively detect the parameters of the entire system, and achieve the purpose of real-time state evaluation and fault monitoring of the superconducting current limiter.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a state monitoring system of a superconducting current limiter comprises a superconducting current limiter body 2, a liquid nitrogen storage tank 1, a low-temperature refrigeration system, a liquid discharge port 8, a sensor assembly 9, a deconcentrator 10, a real-time data preprocessing module 11 and a monitoring host 7; the method is characterized in that:
the liquid nitrogen storage tank 1 is connected with the superconducting current limiter body 2 through a pipeline and provides required liquid nitrogen for the superconducting current limiter body;
a liquid discharge port 8 is arranged at the lower part of the superconducting current limiter body 2;
a low-temperature refrigeration system is arranged at the upper part of the superconducting current limiter body 2 and is used for cooling the liquid nitrogen temperature in the superconducting current limiter body 2;
sensor components 9 are arranged in the liquid nitrogen storage tank 1, the superconducting current limiter body 2 and the supercooled liquid nitrogen dewar tank 5, wherein the sensor components 9 comprise a voltage sensor, a temperature sensor, a pressure sensor and a liquid level sensor and are used for detecting the voltage at two ends of the superconducting current limiter body 2, the temperature, the pressure and the liquid level of liquid nitrogen during operation and the liquid level of the liquid nitrogen in the liquid nitrogen storage tank 1 and the supercooled liquid nitrogen dewar tank 5;
the data acquisition output end of each sensor is connected to a real-time data preprocessing module 11 through a deconcentrator 10, and the real-time data preprocessing module 11 converts analog signals acquired from the sensor assembly 9 into digital signals and uploads the digital signals to the monitoring host 7;
in the steady-state operation process, the voltage, the strip temperature value, the pressure value and the liquid level value of the liquid nitrogen at two ends of the superconducting current limiter body 2 and the liquid level values of the liquid nitrogen in the liquid nitrogen storage tank 1 and the supercooled liquid nitrogen dewar 5 need to be kept within a preset range, if any monitoring parameter exceeds the early warning range, the monitoring host 7 sends out early warning, and corresponding relay protection measures are taken.
The present invention further includes the following preferred embodiments.
The liquid outlet 8 is provided with a remote control valve switch, when the liquid level of liquid nitrogen in the superconducting current limiter body exceeds the early warning liquid level, the monitoring host 7 sends out a valve opening signal, and when the liquid level falls to the safe liquid level, the valve is closed.
The liquid discharge port 8 adopts a stainless steel flange gate valve to discharge excessive liquid nitrogen in the superconducting current limiter body 2 to the outside, so that the liquid level of the liquid nitrogen in the superconducting current limiter body 2 is always in a safe liquid level interval.
The cryogenic refrigeration system comprises a cryogenic liquid nitrogen pump 3, a refrigerator 4 and a supercooled liquid nitrogen dewar tank 5, one end of the refrigerator 4 is connected to the superconducting current limiter body 2 through a pipeline, the other end of the refrigerator is connected to the supercooled liquid nitrogen dewar tank 5 through a pipeline, the cryogenic liquid nitrogen pump 3 extracts liquid nitrogen from the supercooled liquid nitrogen dewar tank 5, the liquid nitrogen is pressed into the superconducting current limiter body 2 through a pipeline, the supercooled liquid nitrogen dewar tank 5 is connected with air through an exhaust port 6, a safety valve is arranged on the exhaust port 6, and the valve is opened when the pressure in the supercooled liquid nitrogen dewar tank 5 is higher than a set value of a nitrogen release valve. The refrigerating machine 4 is a Stirling cycle refrigerating machine and is fixed on the inner wall of the cold liquid nitrogen Dewar tank 5 through a flange plate, the Stirling cycle refrigerating machine pressurizes, cools and liquefies nitrogen in the supercooled liquid nitrogen Dewar tank 5, liquid nitrogen obtained through a separation tower is stored in the supercooled liquid nitrogen Dewar tank 5, then the low-temperature liquid nitrogen pump 3 extracts the liquid nitrogen and circulates the liquid nitrogen to the superconducting current limiter body 2 through a pipeline, and the temperature of the superconducting current limiting unit is enabled to be at the normal working temperature.
The exhaust port 6 is provided with a nitrogen discharge valve which adopts an internal feedback structure, and when the internal pressure of the subcooled liquid nitrogen dewar tank 5 is higher than a set value of the nitrogen discharge valve, the valve core moves upwards to open the valve and discharge nitrogen to the outside; when the pressure in the tank is reduced to a set value, the valve is closed.
The application also discloses a superconducting current limiter state monitoring method based on the monitoring system, which is characterized by comprising the following steps:
step 1: acquiring voltage values at two ends of the superconducting current limiter, temperature signals, pressure signals and liquid level values of liquid nitrogen through a sensor assembly arranged on the superconducting current limiter body, and acquiring liquid nitrogen level values of a liquid nitrogen storage tank and a supercooled liquid nitrogen dewar tank through liquid level sensors arranged in the liquid nitrogen storage tank and the supercooled liquid nitrogen dewar tank;
step 2: when the superconducting current limiter body enters an operating state, the voltage signal, the temperature signal, the liquid nitrogen pressure signal and the liquid level value measured by the sensor assembly in the step 1 are subjected to analog-to-digital conversion by the real-time data preprocessing module and then uploaded to the monitoring host;
and step 3: recording the ranges of the temperature, the pressure and the liquid level value of the liquid nitrogen of the current limiter body when the current limiter body operates in a steady state, namely when the voltage at two ends of the current limiter body is 0, and taking the ranges of the liquid level values in the liquid nitrogen storage tank and the supercooled liquid nitrogen dewar as steady state early warning ranges;
and 4, step 4: in the monitoring host, estimating the temperature T of the superconducting current limiting unit strip based on a convective heat transfer and heat flow density formula, and the steps are as follows:
wherein c is the specific heat capacity of liquid nitrogen, d is the distance between the sensor and the strip, T1Is the initial temperature of liquid nitrogen, T2The temperature at the time of liquid nitrogen measurement, T is T1To T2K is the thermal conductivity coefficient;
and 5: measuring voltage values at two ends of the superconducting current limiter, a temperature signal, a pressure signal and a liquid level value of liquid nitrogen and liquid nitrogen level values of a liquid nitrogen storage tank and a supercooled liquid nitrogen dewar tank respectively for 20 times under four states of superconducting strip damage, refrigeration system abnormity, power grid overcurrent fault and normal current limiting, calculating the temperature of the strip in the superconducting current limiter body each time according to a calculation formula in the step 4, and simultaneously recording a strip temperature peak value, voltage values at two ends of the current limiter body, liquid nitrogen pressure values and liquid level values when the strip temperature reaches the peak value, and liquid level values in the liquid nitrogen storage tank and the supercooled liquid nitrogen dewar tank;
step 6: inputting six characteristic values of the strip temperature peak value, the voltage value at two ends of the current limiter, the liquid nitrogen pressure value and the liquid level value, and the liquid level value in the liquid nitrogen storage tank and the supercooled liquid nitrogen dewar tank, which are obtained by calculation in the step 5, into a BP neural network model for training, wherein an output vector can be expressed as
Wherein: x is the number ofi(i ═ 1, 2, …, 6) is an input feature value; w is aiTheta respectively represents a connection weight value and a threshold value, and is generated by a random number function, and the range of the connection weight value and the threshold value is [ -1,1]In the training process, the automatic adjustment can be carried out according to the requirement of the set output error; f (I)i) Expressing a transfer function by adopting an S-shaped logarithmic function;
and 7: when the current limiter operates in a steady state, namely when the voltage at two ends of the current limiter body is 0, and any monitoring value is not in the range of the steady-state early warning value, starting an early warning program; and (4) in a current limiting state, namely when the voltage at two ends of the current limiter body is not 0, transmitting the monitoring value to the monitoring host in real time, obtaining an output value through the BP neural network model, comparing the output value with the output value in the step (6), and judging the state of the current limiter.
Compared with the prior art, the invention has the following advantages:
1. for the operating environment of ultralow temperature, high voltage and electromagnetic oscillation of the superconducting current limiter, a sensor assembly capable of quickly responding is arranged to monitor the whole current limiting system, so that the online synchronous detection of various physical signals is realized, and the state monitoring accuracy of the superconducting current limiter is improved.
2. The designed communication mode of the on-line monitoring system ensures that the state information of the superconducting current limiter can be transmitted in real time, and the signal data of the whole current limiting system is uploaded to a measurement result display screen through IEC61850, so that the centralized display of the data is realized.
3. For temperature, pressure and liquid level signals, after being processed by the IED, the results can be directly displayed in a display screen in real time, the multi-dimensional fault analysis function of the superconducting current limiter is realized based on fault criteria, and advanced application functions such as monitoring, early warning, evaluation and analysis of equipment states are completed.
Drawings
FIG. 1 is a schematic diagram of a superconducting current limiter state monitoring system according to the present invention;
fig. 2 is a schematic flow chart of a state monitoring method of a superconducting current limiter according to the present invention.
Reference numerals: 1. a liquid nitrogen storage tank; 2. a superconducting current limiter body; 3. a cryogenic liquid nitrogen pump; 4. a refrigerator; 5, supercooling liquid nitrogen Dewar; 6. an exhaust port; 7. a monitoring system; 8. a liquid discharge port; 9. a sensor assembly; 10. a wire divider; 11. a data preprocessing module; 12. a data transfer bus.
Detailed Description
The invention is described in further detail below with reference to the following figures and specific embodiments.
As shown in fig. 1, the present invention discloses a superconducting current limiter state monitoring system,
a state monitoring system for a superconducting current limiter comprises a superconducting current limiter body 2, a liquid nitrogen storage tank 1, a low-temperature refrigeration system, a liquid discharge port 8, a sensor assembly 9, a deconcentrator 10, a real-time data preprocessing module 11 and a monitoring host 7. The liquid nitrogen storage tank 1 is connected with the superconducting current limiter body 2 through a pipeline and provides required liquid nitrogen for the superconducting current limiter body; a liquid discharge port 8 is arranged at the lower part of the superconducting current limiter body 2; the liquid outlet is provided with a remote control valve switch, when the liquid level of liquid nitrogen in the superconducting current limiter body exceeds the early warning liquid level, the monitoring host 7 sends out a valve opening signal, and when the liquid level is reduced to the safe liquid level, the valve is closed; a low-temperature refrigeration system is arranged at the upper part of the superconducting current limiter body 2 and is used for cooling the liquid nitrogen temperature in the superconducting current limiter body 2; the low-temperature refrigeration system comprises a low-temperature liquid nitrogen pump 3, a refrigerator 4 and a supercooled liquid nitrogen dewar tank 5, one end of the refrigerator 4 is connected to the superconducting current limiter body 2 through a pipeline, the other end of the refrigerator is connected to the supercooled liquid nitrogen dewar tank 5 through a pipeline, the low-temperature liquid nitrogen pump 3 extracts liquid nitrogen from the supercooled liquid nitrogen dewar tank 5 and presses the liquid nitrogen into the superconducting current limiter body 2 through a pipeline, the supercooled liquid nitrogen dewar tank 5 is connected with air through an exhaust port 6, a safety valve is arranged on the exhaust port 6, and when the pressure in the supercooled liquid nitrogen dewar tank 5 is larger than a set threshold value, the valve is opened; sensor components 9 are arranged in the liquid nitrogen storage tank 1, the superconducting current limiter body 2 and the supercooled liquid nitrogen dewar tank 5, wherein the sensor components 9 comprise a voltage sensor, a temperature sensor, a pressure sensor and a liquid level sensor and are used for detecting the voltage at two ends of the superconducting current limiter body 2, the temperature, the pressure and the liquid level of liquid nitrogen during operation and the liquid level of the liquid nitrogen in the liquid nitrogen storage tank 1 and the supercooled liquid nitrogen dewar tank 5; the data acquisition output end of each sensor is connected to a real-time data preprocessing module 11 through a deconcentrator 10, and the real-time data preprocessing module 11 converts analog signals acquired from the sensor assembly 9 into digital signals and uploads the digital signals to the monitoring host 7; in the steady-state operation process, the voltage, the strip temperature value, the pressure value and the liquid level value of the liquid nitrogen at two ends of the superconducting current limiter body 2 and the liquid level values of the liquid nitrogen in the liquid nitrogen storage tank 1 and the supercooled liquid nitrogen dewar 5 need to be kept within a preset range, if any monitoring parameter exceeds the early warning range, the monitoring host 7 sends out early warning, and corresponding relay protection measures are taken.
In the preferred embodiment of the invention, the liquid nitrogen storage tank 1 is connected with the superconducting current limiter body 2 through a low temperature resistant stainless steel pipeline, liquid nitrogen is supplemented for the superconducting current limiter body when the liquid nitrogen is insufficient, a liquid discharge port 8 is arranged at the lower part of the superconducting current limiter body 2, a remote control valve switch is arranged on the liquid discharge port, when the liquid level of the liquid nitrogen in the superconducting current limiter body exceeds the early warning liquid level, a monitoring host sends a valve opening signal, and when the liquid level falls to the safe liquid level, the valve is closed. Preferably, the liquid discharge port 8 is a stainless steel flange gate valve, and excess liquid nitrogen in the superconducting current limiter body 2 is discharged to the outside when necessary, so that the liquid level of the liquid nitrogen in the superconducting current limiter body 2 is always in a safe liquid level interval.
The cryogenic refrigeration system is used for providing ultralow temperature operation environment (about 78K) for superconducting current limiter, the cryogenic refrigeration system includes cryogenic liquid nitrogen pump 3, refrigerator 4 and supercooling liquid nitrogen dewar jar 5, supercooled liquid nitrogen dewar jar 5 one end is passed through pipe connection to superconducting current limiter body 2, cryogenic liquid nitrogen pump 3 draws the liquid nitrogen from supercooling liquid nitrogen dewar jar 5 and impresses the liquid nitrogen into superconducting current limiter body 2 through the pipeline, supercooled liquid nitrogen dewar jar 5 links to each other with the air through gas vent 6, 6 installation relief valves in gas vent, the valve is opened when supercooling liquid nitrogen dewar jar 5 internal pressure is greater than the settlement threshold value, can discharge unnecessary nitrogen gas, prevent the incident that the unusual continuous rise of emergence pressure probably causes.
In the preferred embodiment of the present application, the refrigerator is a stirling cycle refrigerator, and is fixed on the inner wall of the cold liquid nitrogen dewar tank 5 by using a flange plate, the stirling cycle refrigerator pressurizes, cools and liquefies the nitrogen in the supercooled liquid nitrogen dewar tank 5, obtains liquid nitrogen through a separation tower and stores the liquid nitrogen in the supercooled liquid nitrogen dewar tank 5, and then the low-temperature liquid nitrogen pump 3 extracts the liquid nitrogen and circulates the liquid nitrogen to the superconducting current limiter body 2 through a pipeline, so that the temperature of the superconducting current limiting unit is at the normal operating temperature.
Because the superconducting system generates a large amount of heat when in instant quench under the load condition, liquid nitrogen volatilizes, the volume rapidly expands, and the overpressure safety protection needs to be considered. The method mainly comprises three safety protections, wherein the first safety protection is that the pressure margin of the low-temperature container and the welding process are strictly implemented according to the standard of the low-temperature vacuum container. The second aspect is the control protection of the operation process, the deformation factor in the manufacturing process is controlled, the welding process is evaluated according to the standard, and the supervision and inspection of the process are made. A third aspect is overpressure protection, including safety valve protection, allowing nitrogen to vent directly to the atmosphere through a pressure protection device-to-atmosphere vent path.
Set up sensor assembly 9 in liquid nitrogen storage tank 1, superconducting current limiter body 2 and supercooled liquid nitrogen dewar jar 5, sensor assembly 9 includes temperature sensor, pressure sensor and level sensor, and temperature sensor can use PT100 thermal resistance sensor, and pressure sensor can use low temperature film pressure sensor, and level sensor can use capacitanc sensor for detect liquid nitrogen temperature, pressure, the liquid level of superconducting current limiter body 2 when superconducting current limiter moves, the liquid level of liquid nitrogen in liquid nitrogen storage tank 1 and supercooled liquid nitrogen dewar jar 5.
The lead wires of the sensors are anti-interference wires with high insulation performance, collected data are connected to a real-time data preprocessing module 12 through a wire divider 11, and the real-time data preprocessing module 12 converts analog signals collected from the sensor assembly 9 into digital signals and uploads the digital signals to the monitoring host 7.
The fault early warning scheme is mainly divided into two parts: steady state operation early warning and current-limiting operation early warning.
In the steady-state operation process, namely when the voltage at the two ends of the current limiter body is 0, the temperature value, the pressure value and the liquid level value of the liquid nitrogen in the superconducting current limiter body 2, and the liquid level values of the liquid nitrogen in the liquid nitrogen storage tank 1 and the supercooled liquid nitrogen dewar 5 need to be kept within a preset range, if any monitoring parameter exceeds the early warning range, the monitoring host 7 gives out early warning, and certain measures are taken. The invention takes a 160kV superconducting current limiter as an example, sets a steady-state early warning data range and sets a maintenance scheme, and if the liquid level value of liquid nitrogen in a superconducting current limiter body is too low, the liquid nitrogen in a liquid nitrogen storage tank is sent to the superconducting current limiter.
Sample training is carried out for 20 times respectively on four states of damage of a superconducting strip, abnormity of a refrigerating system, overcurrent fault of a power grid and normal current limiting, the temperature of the strip in a superconducting current limiter body at each time is calculated according to a formula, the peak value of the temperature of the strip is recorded, when the temperature of the strip reaches the peak value, the voltage value, the liquid nitrogen pressure value and the liquid level value at two ends of the current limiter body, and the liquid level values in a liquid nitrogen storage tank and a supercooled liquid nitrogen dewar tank are input into a BP neural network model for training. And (4) in the actual current-limiting operation process, namely when the voltage at two ends of the current limiter body is not 0, transmitting the monitoring value to the monitoring host in real time, obtaining an output value through a BP neural network model, comparing the output value with the output value in the step (6), judging the state of the current limiter, and performing fault maintenance.
The invention also discloses a state monitoring method of the superconducting current limiter based on the monitoring system, which is characterized by comprising the following steps of:
step 1: acquiring voltage values at two ends of the superconducting current limiter, temperature signals, pressure signals and liquid level values of liquid nitrogen through a sensor assembly arranged on the superconducting current limiter body, and acquiring liquid nitrogen level values of a liquid nitrogen storage tank and a supercooled liquid nitrogen dewar tank through liquid level sensors arranged in the liquid nitrogen storage tank and the supercooled liquid nitrogen dewar tank;
step 2: when the superconducting current limiter body enters an operating state, the voltage signal, the temperature signal, the liquid nitrogen pressure signal and the liquid level value measured by the sensor assembly in the step 1 are subjected to analog-to-digital conversion by the real-time data preprocessing module and then uploaded to the monitoring host;
and step 3: recording the ranges of the temperature, the pressure and the liquid level value of the liquid nitrogen of the current limiter body when the current limiter body operates in a steady state, namely when the voltage at two ends of the current limiter body is 0, and taking the ranges of the liquid level values in the liquid nitrogen storage tank and the supercooled liquid nitrogen dewar as steady state early warning ranges;
and 4, step 4: in the monitoring host, estimating the temperature T of the superconducting current limiting unit strip based on a convective heat transfer and heat flow density formula, and the steps are as follows:
wherein c is the specific heat capacity of liquid nitrogen, d is the distance between the sensor and the strip, T1Is the initial temperature of liquid nitrogen, T2The temperature at the time of liquid nitrogen measurement, T is T1To T2K is the thermal conductivity coefficient;
and 5: measuring the damage of the superconducting strip, the abnormality of a refrigerating system, the overcurrent fault of a power grid and the normal current limiting for 20 times respectively, calculating the temperature of the strip in the superconducting current limiter body every time according to the calculation formula in the step 3, and simultaneously recording the peak value of the temperature of the strip, wherein when the temperature of the strip reaches the peak value, the voltage value, the liquid nitrogen pressure value and the liquid level value at two ends of the current limiter body, and the liquid level values in a liquid nitrogen storage tank and a supercooled liquid nitrogen dewar tank are measured;
step 6: inputting six characteristic values of the strip temperature peak value, the voltage value at two ends of the current limiter, the liquid nitrogen pressure value and the liquid level value in the liquid nitrogen storage tank and the supercooled liquid nitrogen dewar tank in the step 4 into a BP neural network model for training, wherein the output vector can be expressed as
Wherein: x is the number ofi(i ═ 1, 2, …, 6) is an input feature value; w is aiTheta represents the connection weight and the threshold respectively, and is generated by a random number function, and the range of the value is [ -1,1]In the training process, the automatic adjustment can be carried out according to the output error so as to meet the output requirement; f (I)i) The transfer function is expressed, and an S-type logarithmic function is used here.
And 7: when the current limiter operates in a steady state, namely when the voltage at two ends of the current limiter body is 0, and any monitoring value is not in the range of the steady-state early warning value, starting an early warning program; and (4) in a current limiting state, namely when the voltage at two ends of the current limiter body is not 0, transmitting the monitoring value to the monitoring host in real time, obtaining an output value through the BP neural network model, comparing the output value with the output value in the step (6), and judging the state of the current limiter.
While the best mode for carrying out the invention has been described in detail and illustrated in the accompanying drawings, it is to be understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the invention should be determined by the appended claims and any changes or modifications which fall within the true spirit and scope of the invention should be construed as broadly described herein.
Claims (7)
1. A state monitoring method of a superconducting current limiter comprises the steps that a liquid nitrogen storage tank is connected with a superconducting current limiter body through a pipeline, a low-temperature refrigeration system is arranged on the upper portion of the superconducting current limiter body, sensor assemblies are arranged in the liquid nitrogen storage tank, the superconducting current limiter body and a supercooled liquid nitrogen Dewar tank and used for detecting voltage at two ends of the superconducting current limiter body, temperature, pressure and liquid level of liquid nitrogen during operation, and liquid level of the liquid nitrogen in the liquid nitrogen storage tank and the supercooled liquid nitrogen Dewar tank is detected; the state monitoring method is characterized by comprising the following steps of:
step 1: acquiring voltage values at two ends of the superconducting current limiter, temperature signals, pressure signals and liquid level values of liquid nitrogen through a sensor assembly arranged on the superconducting current limiter body, and acquiring liquid nitrogen level values of a liquid nitrogen storage tank and a supercooled liquid nitrogen dewar tank through liquid level sensors arranged in the liquid nitrogen storage tank and the supercooled liquid nitrogen dewar tank;
step 2: when the superconducting current limiter body enters an operating state, the voltage signal, the temperature signal, the liquid nitrogen pressure signal and the liquid level value measured by the sensor assembly in the step 1 are subjected to analog-to-digital conversion by the real-time data preprocessing module and then uploaded to the monitoring host;
and step 3: recording the ranges of the temperature, the pressure and the liquid level value of the liquid nitrogen of the current limiter body when the current limiter body operates in a steady state, namely when the voltage at two ends of the current limiter body is 0, and taking the ranges of the liquid level values in the liquid nitrogen storage tank and the supercooled liquid nitrogen dewar as steady state early warning ranges;
and 4, step 4: in the monitoring host, estimating the temperature T of the superconducting current limiting unit strip based on a convective heat transfer and heat flow density formula, and the steps are as follows:
wherein c is the specific heat capacity of liquid nitrogen, d is the distance between the sensor and the strip, T1Is the initial temperature of liquid nitrogen, T2The temperature at the time of liquid nitrogen measurement, T is T1To T2K is the thermal conductivity coefficient;
and 5: measuring voltage values at two ends of the superconducting current limiter, a temperature signal, a pressure signal and a liquid level value of liquid nitrogen and liquid nitrogen level values of a liquid nitrogen storage tank and a supercooled liquid nitrogen dewar tank respectively for 20 times under four states of superconducting strip damage, refrigeration system abnormity, power grid overcurrent fault and normal current limiting, calculating the temperature of the strip in the superconducting current limiter body each time according to a calculation formula in the step 4, and simultaneously recording a strip temperature peak value, voltage values at two ends of the current limiter body, liquid nitrogen pressure values and liquid level values when the strip temperature reaches the peak value, and liquid level values in the liquid nitrogen storage tank and the supercooled liquid nitrogen dewar tank;
step 6: inputting six characteristic values of the strip temperature peak value, the voltage value at two ends of the current limiter, the liquid nitrogen pressure value and the liquid level value, and the liquid level value in the liquid nitrogen storage tank and the supercooled liquid nitrogen dewar tank, which are obtained by calculation in the step 5, into a BP neural network model for training, wherein an output vector can be expressed as
Wherein: x is the number ofiIs an input characteristic value, and the value of i is 1 to 6; w is aiTheta respectively represents a connection weight value and a threshold value, and is generated by a random number function, and the range of the connection weight value and the threshold value is [ -1,1]In the training process, the automatic adjustment can be carried out according to the requirement of the set output error; i isiFor intermediate variables, y characterizes the superconducting current limiter state, f (I)i) Expressing a transfer function by adopting an S-shaped logarithmic function;
and 7: when the current limiter operates in a steady state, namely when the voltage at two ends of the current limiter body is 0, and any monitoring value is not in the range of the steady-state early warning value, starting an early warning program; and (4) in a current limiting state, namely when the voltage at two ends of the current limiter body is not 0, transmitting the monitoring value to the monitoring host in real time, obtaining an output value through the BP neural network model, comparing the output value with the output value in the step (6), and judging the state of the current limiter.
2. A superconducting current limiter state monitoring system using the superconducting current limiter state monitoring method according to claim 1, comprising a superconducting current limiter body, a liquid nitrogen storage tank, a cryogenic refrigeration system, a liquid outlet, a sensor assembly, a deconcentrator, a real-time data preprocessing module and a monitoring host; the method is characterized in that:
the liquid nitrogen storage tank is connected with the superconducting current limiter body through a pipeline and provides required liquid nitrogen for the superconducting current limiter body;
a liquid discharge port is arranged at the lower part of the superconducting current limiter body;
a low-temperature refrigeration system is arranged at the upper part of the superconducting current limiter body and is used for cooling the liquid nitrogen temperature in the superconducting current limiter body;
sensor components are arranged in the liquid nitrogen storage tank, the superconducting current limiter body and the supercooled liquid nitrogen dewar tank, and each sensor component comprises a voltage sensor, a temperature sensor, a pressure sensor and a liquid level sensor and is used for detecting the voltage at two ends of the superconducting current limiter body, the temperature, the pressure and the liquid level of liquid nitrogen during operation and the liquid level of the liquid nitrogen in the liquid nitrogen storage tank and the supercooled liquid nitrogen dewar tank;
the data acquisition output end of each sensor is connected to a real-time data preprocessing module through a deconcentrator, and the real-time data preprocessing module converts analog signals acquired from the sensor assembly into digital signals and uploads the digital signals to a monitoring host;
in the steady-state operation process, the voltage at two ends of the superconducting current limiter body, the temperature value of the strip material, the pressure value and the liquid level value of liquid nitrogen, and the liquid level values of the liquid nitrogen in the liquid nitrogen storage tank and the supercooled liquid nitrogen dewar tank need to be kept within a preset range, if any monitoring parameter exceeds the early warning range, the monitoring host computer sends out early warning, and corresponding relay protection measures are taken.
3. A superconducting current limiter condition monitoring system according to claim 2, wherein:
the liquid outlet is provided with a remote control valve switch, when the liquid level of liquid nitrogen in the superconducting current limiter body exceeds the early warning liquid level, the monitoring host sends a valve opening signal, and when the liquid level falls to the safe liquid level, the valve is closed.
4. A superconducting current limiter condition monitoring system according to claim 3, wherein:
the liquid discharge port adopts a stainless steel flange gate valve to discharge excessive liquid nitrogen in the superconducting current limiter body to the outside, so that the liquid level of the liquid nitrogen in the superconducting current limiter body is always in a safe liquid level interval.
5. A superconducting current limiter state monitoring system according to claim 2 or 3, wherein:
the low-temperature refrigeration system comprises a low-temperature liquid nitrogen pump, a refrigerator and a supercooled liquid nitrogen dewar tank, one end of the refrigerator is connected to the superconducting current limiter body through a pipeline, the other end of the refrigerator is connected to the supercooled liquid nitrogen dewar tank through a pipeline, the low-temperature liquid nitrogen pump extracts liquid nitrogen from the supercooled liquid nitrogen dewar tank, the liquid nitrogen is pressed into the superconducting current limiter body through a pipeline, the supercooled liquid nitrogen dewar tank is connected with air through an exhaust port, a safety valve is arranged on the exhaust port, and when the pressure in the supercooled liquid nitrogen dewar tank is higher than a set value of a nitrogen release valve, the valve is opened.
6. A superconducting current limiter condition monitoring system according to claim 5, wherein:
the refrigerating machine is a Stirling cycle refrigerating machine, a flange plate is fixed on the inner wall of the cold liquid nitrogen Dewar tank, the Stirling cycle refrigerating machine pressurizes, cools and liquefies nitrogen in the super-cooled liquid nitrogen Dewar tank, liquid nitrogen obtained through a separation tower is stored in the super-cooled liquid nitrogen Dewar tank, then a low-temperature liquid nitrogen pump extracts the liquid nitrogen and circulates the liquid nitrogen to the superconducting current limiter body through a pipeline, and the temperature of the superconducting current limiting unit is enabled to be at the normal working temperature.
7. A superconducting current limiter condition monitoring system according to claim 6, wherein:
the exhaust port is provided with a nitrogen discharge valve which adopts an internal feedback structure, and when the internal pressure of the super-cooled liquid nitrogen Dewar tank is higher than a set value of the nitrogen discharge valve, the valve core moves upwards to open the valve and discharge nitrogen to the outside; when the pressure in the tank is reduced to a set value, the valve is closed.
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