JP5675488B2 - Apparatus and method for evaluating signal transmission path - Google Patents

Description

  The present invention relates to a high-frequency weak signal measurement system used in a nuclear power plant, and more particularly, to a signal transmission line evaluation apparatus and evaluation method for evaluating a construction state of a connection portion such as a connector from the viewpoint of influence on measurement due to noise. .

  In recent years, the need for energy saving has increased, and the introduction of high-efficiency inverters is progressing in various fields. In nuclear power plants as well, the ratio of using inverter power sources for large capacity pumps such as nuclear reactor recirculation systems is increasing to improve operating efficiency. The inverter generates a voltage having a desired amplitude and frequency by switching and smoothing and supplies the voltage to the load. In particular, recent switching elements can be switched at a very high speed in order to improve efficiency, and the resulting electromagnetic noise has a large amplitude and high-frequency noise on the order of MHz is generated. For this reason, the electromagnetic noise in a nuclear power plant tends to increase.

  On the other hand, a high-frequency weak signal measurement system such as a neutron instrumentation system and a radiation monitor system is provided in the nuclear power plant. Of these, the neutron instrumentation system needs to measure and monitor the neutron flux and power in the reactor during the entire period when the reactor is loaded with fuel. Monitors are susceptible to high frequency noise because they handle weak pulse signals. Recently, an activation region neutron monitor in which a neutron source region monitor and an intermediate region monitor are integrated is used.

  Since such a nuclear instrumentation system outputs an indicated value to the nuclear reactor safety protection system, if a noise is superimposed on the signal from the neutron detector, a false alarm or a false scrum may occur. Similarly, some radiation monitoring systems provide signals to the reactor safety protection system. For this reason, measures for suppressing the influence of high-frequency electromagnetic noise on these measurement systems and prior influence evaluation are important.

  Here, the noise influence from a power system such as a recirculation system to a high-frequency weak signal system such as a neutron instrumentation system can be evaluated by dividing it into two characteristics. The first characteristic is the ease of propagation from the noise source to the target weak signal system. This can be evaluated by measuring how much common mode current has propagated through the weak signal system. The second characteristic is the ease of influence on the measurement by the common mode current propagated to the weak signal system. This can be evaluated by measuring how much the common mode current is converted into a signal voltage generated between the core wire and the return wire. As for the first characteristic, Patent Document 1 discloses a method for measuring the ease of noise propagation in a state where it is constructed in a plant.

  FIG. 7 shows a mechanism by which a common mode current is converted into a signal voltage in the conventional example. In FIG. 7, the signal transmission path 101 has a coaxial structure of a core wire 102 and a shield 103. One end of the signal transmission path 101 is connected to the detector 105, and the other end is connected to the signal voltage measuring device 106. Further, the signal transmission path 101 is connected to the building ground line 104 with a certain impedance in high frequency to form a ground loop.

  For such a system, electromagnetic noise from the outside is normally applied to the ground loop in the form of a common mode current, that is, a signal current in the same direction in the core wire and shield wire of the signal transmission path.

At this time, if the voltage (external noise) applied to the ground loop from the outside is Vn, the voltage Vs applied to the shield 103 of the signal transmission path 101 is
[Equation 1]
Vs≈Z2 / (Z2 + Z5) × Vn (1)
It becomes. Here, Z2 is the impedance of the shield 103, Z5 is the impedance of the building grounding wire, and the impedance Z2 of the shield 103 is the core wire 102, the detector 105, the core wire impedance Z1 of the signal voltage measuring device 106, the detector impedance Z4, and It was assumed that it is smaller than Z5.

Furthermore, the voltage Vm measured by the signal voltage device 106 is
[Equation 2]
Vm≈Z3 / (Z1 + Z3 + Z4) × Vs (2)
It becomes. Z3 is a measuring instrument impedance.

  Usually, since the impedance Z2 of the shield 103 is small, the influence of the external noise Vn is very small and limited. However, if the impedance Z2 of the shield 103 increases for the same reason, the signal voltage Vm due to the external noise Vn increases. In FIG. 7, the signal transmission path 101 is shown by one line. However, for example, when the signal transmission path 101 is configured by two lines connected by a connector or the like, on the shield side of the connector portion. When the impedance increases due to oxidation or the like, a larger signal voltage Vm is generated for the same external noise Vn.

JP 2009-293931 A

  Evaluating the influence of noise on the high-frequency weak signal system in advance leads to minimizing the rework of the construction work and can improve the construction efficiency. According to Patent Document 1, it is possible to evaluate in advance the ease of propagation of common mode current from a specific facility to a high-frequency weak signal system. However, Patent Document 1 does not disclose an evaluation of the rate at which common mode noise is converted into a signal voltage in a high-frequency weak signal system.

  As described above, the construction state of the connector or the like greatly affects the rate at which noise that has entered as a common mode current is converted into a signal voltage. Conventionally, however, there has been only an evaluation method based on DC electrical characteristics such as loop resistance and insulation resistance for evaluating the construction state of the connector and the like. Such a small resistance value measured by the conventional method is not important at high frequencies, but rather the inductance component plays a larger role. Therefore, it is effective to directly evaluate how easily the measurement signal is affected by electromagnetic noise that has entered in the common mode, including the influence of the inductance component on the high frequency.

  It is an object of the present invention to provide a measuring apparatus and a measuring technique that solve such problems.

  The present invention relates to a high-frequency weak signal measurement system for a nuclear power plant provided with a signal transmission path for transmitting a high-frequency weak signal of a radiation detector, and a current injection device for injecting a high-frequency common mode current into the signal transmission path, and a current injection device. A current generator for supplying a high-frequency common mode current of a predetermined frequency, a current measuring device for measuring a common mode current flowing in the signal transmission path, and a core wire and a return line of the signal transmission path by the common mode current flowing in the signal transmission path A signal voltage measuring device that measures the voltage generated between the current value and the current value measured by the current measuring device and the voltage value measured by the signal voltage measuring device are input and the ratio of the measured value of the current value and the voltage value And a conversion ratio calculating device for calculating a conversion ratio.

  In the signal transmission path evaluation apparatus, the conversion ratio calculation apparatus includes a first synchronization component extraction unit that extracts a signal from the current measurement device, and a second synchronization component extraction unit that extracts a signal from the signal voltage measurement device. And a control device that changes the measurement frequency band of the signal current and signal voltage of the first and second synchronization component extraction units, and the signal current and signal that have passed through the first synchronization component extraction unit and the second synchronization component extraction unit An arithmetic circuit for calculating a conversion ratio, which is a voltage ratio, is provided.

  Further, in the signal transmission path evaluation device, the control device receives the high-frequency common mode current frequency information transmitted from the current generator and measures the measurement frequency band of the current and voltage signals to be measured in synchronization with the received frequency. It is characterized by changing.

  In the signal transmission path evaluation apparatus, the first synchronization component extraction unit and the second synchronization component extraction unit are composed of bandpass filters.

  In the signal transmission path evaluation apparatus, an A / D conversion circuit and an effective value calculation circuit are provided between the first synchronization component extraction unit, the second synchronization component extraction unit, and the calculation circuit.

  In the signal transmission line evaluation apparatus, the current generator includes a signal generator that generates a signal current by changing a frequency in accordance with a predetermined pattern, and a switching device that outputs or stops the signal current to the current injection apparatus. And a control device that transmits the frequency and amplitude information of the signal current to the conversion ratio calculation device.

  In the signal transmission path evaluation apparatus, the current measurement apparatus and the signal voltage measurement apparatus include a voltage measurement apparatus and a transmission apparatus.

  Further, in the signal transmission path evaluation apparatus, a simulated ground capacity for connecting the return line and the plant building ground line is provided at the end opposite to the end where the signal voltage measurement apparatus of the signal transmission path is connected. And

Furthermore, in a high-frequency weak signal measurement system including a signal transmission path having a core wire and a return line for transmitting a high-frequency weak signal of a radiation detector of a nuclear power plant,
Injecting a high-frequency common mode current from the outside into a signal transmission path for transmitting a radiation detector signal for detecting neutron flux, gamma rays, etc. as a high-frequency signal;
Measuring the current value of the common mode current flowing in the signal transmission path;
Measuring a voltage value generated between the core line and the return line of the signal transmission path by the common mode current;
Calculating a conversion ratio that is a ratio of a current value and a voltage value;
A step of comparing a predetermined reference value with a conversion ratio.

According to the present invention, in a high-frequency weak signal measurement system for a nuclear power plant including a signal transmission path for transmitting a high-frequency weak signal of a radiation detector, a current injection device for injecting a high-frequency common mode current into the signal transmission path, and a current injection A current generator for supplying a high-frequency common mode current of a predetermined frequency to the device, a current measuring device for measuring a common mode current flowing in the signal transmission path, a core of the signal transmission path by the common mode current flowing in the signal transmission path, and A signal voltage measuring device that measures a normal mode voltage generated between the return lines, a current value measured by the current measuring device, and a normal mode voltage value measured by the signal voltage measuring device are input, and the current value and voltage A high frequency that simulates noise by providing a conversion ratio calculation device that calculates a conversion ratio that is a ratio of measured values The common mode current is applied to the signal transmission path of a high-frequency weak signal system, it is possible to measure the effect on the measurement signal when the direct.

  Thereby, before the power equipment etc. which become a noise source are installed in a plant, it is possible to determine a construction state of a joint portion such as a cable or a connector by a single high frequency weak signal system.

  Conventionally, the influence of noise cannot be evaluated in such a determination, and reworking such as cleaning the connector again after a problem has occurred has occurred, but the present invention solves these problems. Work efficiency can be improved.

It is a schematic diagram which shows the system configuration | structure in Example 1 of this invention. It is a block diagram which shows the simulation electric current generator in Example 1 of this invention. It is a block diagram which shows the electric current measurement apparatus in Example 1 of this invention. It is a block diagram which shows the signal voltage measuring apparatus in Example 1 of this invention. It is a block diagram which shows the conversion ratio measuring apparatus in Example 1 of this invention. It is a schematic diagram which shows the system configuration | structure in Example 2 of this invention. It is a schematic diagram which shows the signal voltage conversion mechanism in the common mode current of a prior art example.

  Embodiments of the present invention will be described below with reference to the drawings.

  Example 1 shows an example of an evaluation apparatus that evaluates the influence of noise in a high-frequency weak signal system.

  FIG. 1 illustrates a system configuration of a signal transmission path evaluation apparatus according to the first embodiment. In the nuclear power plant, the reactor pressure vessel 1, the detector collecting tube 2 inserted into the reactor pressure vessel 1, and the detector collecting tube 2 are accommodated by the thermal neutrons in the reactor pressure vessel 1. A neutron detector 3 that generates a weak current by ionizing action, a cable 4 that transmits a weak current signal from the neutron detector 3, and a connector 5 that connects the cable are provided.

  What is evaluated in Example 1 is a signal transmission path including the neutron detector 3, the cable 4, and the connector 5. Normally, during operation of a nuclear power plant, a neutron instrumentation system is connected to a cable 4 with a preamplifier and a signal processing unit to measure and monitor the neutron flux. Instead of an amplifier or a signal processing device, a signal transmission line evaluation device 6 including a current injection device 7, a current generation device 8, a current measurement probe 9, a current measurement device 10, a signal voltage measurement device 11, and a conversion ratio calculation device 12 is connected. Has been.

  The cable 4 has one end of the shield connected to the building ground line 13 in the signal voltage measuring device 11, and the other end has a capacity with respect to the reactor pressure vessel 1 to which the neutron detector 3 is grounded and the ground of the cable itself. A large ground loop is formed by being connected to the building ground line 13 in a high frequency manner through a capacitor or the like.

  In the signal transmission line evaluation device 6, the current generator 8 applies a signal current whose frequency is changed according to a preset pattern to the current injection device 7. The current injection device 7 is for injecting a high-frequency current applied from the current generator 8 into the ground loop formed by the cable 4 and the building grounding wire 13, such as a ferrite formed in a substantially ring shape. A magnetic body, which is composed of a core that is ring-shaped when coupled, a coil wound around the core body, and a lead cable (not shown) that connects the coil and the current wave generator 8. 7 The cable 4 is arranged so as to pass through the main body.

  The current injection device 7 injects a high frequency current corresponding to the applied high frequency signal into the cable 4 by electromagnetic induction. At the same time, the current generator 8 transmits signal current information having a predetermined frequency applied to the current injection device 7 to the conversion ratio calculation device 12.

  A current measuring probe 9 is connected to the current measuring device 10 and measures the current value injected into the cable 4. The current measurement probe 9 has a shape similar to that of the current injection device 7, and has a magnetic core such as a ferrite that is formed in a ring shape and becomes a ring shape when coupled, and a coil wound around the core body. A voltage proportional to the signal current flowing through the cable 4 inserted through the measurement probe 9 is output. The signal voltage output by the current measurement probe 9 is converted into a current value in the current measurement device 10 and transmitted to the conversion ratio calculation device 12.

  The signal voltage measurement device 11 measures the signal voltage generated between the core wire of the cable 4 and the shield when the signal current is injected from the current injection device 7. The measured signal voltage is transmitted from the signal voltage measuring device 11 to the conversion ratio calculating device 12.

The conversion ratio calculation device 12 receives the current value and the voltage value transmitted from the current measurement device 10 and the signal voltage measurement device 11. The conversion ratio calculation device 12 also receives a signal current having a predetermined frequency that is a reference value transmitted from the current generator 8, and receives a current value and a signal voltage value transmitted from the current measurement device 10 and the signal voltage measurement device 11. Only the frequency component included in is extracted, and its effective value is calculated. Then, a conversion ratio K between the current value and the signal voltage value is calculated from the calculated current value effective value Ie and the signal voltage effective value Ve and displayed.
[Equation 3]
K = Ve / Ie (3)
FIG. 2 shows the configuration of the current generator 8. The current generator 8 includes a signal generator 16 that generates a sine wave of an arbitrary frequency, a solid state relay (SSR) 17 that outputs or stops the signal current generated by the signal generator 16 to the outside, and a signal current The storage device 14 stores the frequency and amplitude in advance, and the control device 15 controls the amplitude and frequency of the signal current generated by the signal generator 16 based on the data stored in the storage device 14.

  In order to apply the signal current generated by the current generator 8 to the current injector 7, the output terminal of the SSR 17 and the current injector 7 are connected by a lead cable (see FIG. 1). Further, the frequency and amplitude information of the noise current applied to the opening / closing of the SSR 17 and the current injection device 7 are transmitted from the control device 15 to the conversion ratio calculation device 12 via a signal transmission path such as serial communication, for example. .

  FIG. 3 shows the configuration of the current measuring device 10. The current measuring device 10 includes a voltage measuring device 18 and a transmission device 19. The voltage measuring device 18 amplifies a voltage signal proportional to the current value output from the current measuring probe 9 with a predetermined gain. The amplified voltage signal is transmitted to the conversion ratio calculation device 12 by the transmission device 19.

  FIG. 4 shows the configuration of the signal voltage measuring device 11. A cable 4 is connected to the signal voltage measuring device 11, and a voltage generated between the core wire 20 of the cable 4 and the shield 21 is measured by the voltage measuring device 18 and transmitted to the conversion ratio calculating device 12 by the transmission device 19. The shield 21 is connected to the building grounding wire 13 through a housing formed of a conductor of the signal voltage measuring device 11, and a ground loop similar to the original neutron instrumentation system is formed so that a common mode current flows. It is like that.

  FIG. 5 shows the configuration of the conversion ratio calculation device 12. The conversion ratio calculation device 12 receives a measured current value and a signal voltage from two systems of the current measuring device 10 and the signal voltage measuring device 11, and passes a signal in a frequency band set for each system. 22, an A / D conversion circuit 24 that converts the current value that has passed through the band-pass filter into a digital value, and an effective value calculation device 25 that converts this digital value into effective value data.

  Further, from the control device 23 that sets the passband of the bandpass filter 22 to the input current frequency, and the current value effective value Ie and the signal voltage effective value Ve output from the effective value calculation device 25, the conversion ratio = Ve / An arithmetic circuit 26 that calculates Ie and a display device 27 that displays the conversion ratio calculated by the arithmetic circuit 26 are configured.

  Next, operation | movement of the influence evaluation apparatus of the electric motor system in a plant mentioned above is demonstrated using FIGS.

  First, when the user activates the current generator 8 shown in FIG. 2, the frequency and amplitude pattern of the signal current to be injected into the current injector 7 is received from the storage device 14 to the controller 15 according to a read command from the controller 15. Is included. The control device 15 sets the value of the frequency and amplitude of the common mode current, which is the noise current to be generated by the signal generator 16, and controls the opening and closing of the SSR 17 at a predetermined timing. The high frequency current output from the current generator 8 is applied to the current injector 7. As a result, a common mode current according to a predetermined pattern can be injected into the cable 4. Further, the control device 15 of the current generator 8 outputs the frequency and amplitude information of the generated common mode current to the conversion ratio calculation device 12.

  When a signal current is applied to the current injection device 7 by the current generator 8, a common mode current is generated in the cable 4 shown in FIG. The common mode current is measured as a voltage signal by the voltage measuring device 18 of the current measuring device 10 through the current measuring probe 9, amplified by a predetermined gain, and then transmitted from the transmission device 19 to the conversion ratio calculating device 12.

  The voltage measured by the voltage measuring device 18 of the signal voltage measuring device 11 is amplified with a predetermined gain and transmitted from the transmission device 19 to the conversion ratio calculation device 12.

  In the conversion ratio calculation device 12, as shown in FIG. 5, these current measurement values are input to the band-pass filters 22 and 22 for each system. At the same time, frequency and amplitude signal data from the current generator 8 are input to the controller 23. The control device 23 sets the passband of the bandpass filters 22 and 22 to the frequency transmitted from the current generator 8 and calculates the frequency and amplitude information of the signal current applied to the current injector 7 to the arithmetic circuit 26. Transmit to.

  The current value and the signal voltage value that have passed through the band pass filters 22 and 22 are converted into digital values by the A / D conversion circuits 24 and 24, and converted into effective value data by the effective value arithmetic units 25 and 25. This effective value data is transmitted to the arithmetic circuit 26 together with the frequency / amplitude data.

  The arithmetic circuit 26 calculates the conversion ratio = Ve / Ie from the current value effective value Ie and the signal voltage effective value Ve output from the effective value calculation device 25, and the conversion ratio is displayed on the display device 27 together with the frequency and amplitude information. Send. The display device 27 displays the frequency, amplitude value, and conversion ratio as one set.

  As described above, according to the apparatus for evaluating a signal transmission path of the first embodiment, by applying the common mode current to the same path as the high frequency noise, it is possible to directly evaluate the susceptibility to the influence of the noise. In particular, by checking the degree of noise effect in the absence of an actual noise source, it is possible to determine whether the connector and other joints are in good working condition. Such reworking can be prevented.

  Further, according to the form of the first embodiment, the conversion ratio can be calculated using only the same frequency component as the frequency of the signal current to be applied, and high-precision measurement is possible even in an actual plant where various noise currents meditate. Is possible.

  FIG. 6 shows an example in which a simulated detector 30 and a simulated ground capacitance 31 are connected in place of the original neutron detector in the second embodiment of the present invention. A simulated detector 30 is connected to the end of the cable 4 opposite to the signal voltage measuring device 11. The simulated detector 30 connects the core wire 20 and the shield 21 with a capacitor having a predetermined capacity. Usually, the fission ionization chamber used as the neutron detector 3 can be simulated as a capacitance from the viewpoint of impedance with respect to a high frequency, and thus has such a configuration. Further, the shield side of the simulated detector 30 and the building grounding wire 13 are connected by a simulated ground capacitance 31 formed of a capacitor having a predetermined capacity. Thereby, the stray capacity between the neutron detector 3 and the reactor pressure vessel 1 and the stray capacity between the cable and the ground can be simulated.

  With this configuration, even when no neutron detector 3 is installed in the reactor pressure vessel 1, prior evaluation of the influence of noise on the signal transmission path such as a cable / connector that does not include a neutron detector alone. This makes it possible to further improve the efficiency of construction work.

DESCRIPTION OF SYMBOLS 3 Neutron detector 4 Cable 5 Connector 6 Signal transmission line evaluation apparatus 7 Current injection apparatus 8 Current generation apparatus 9 Current measurement probe 10 Current measurement apparatus 11 Signal voltage measurement apparatus 12 Conversion ratio calculation apparatus 13 Building ground line 15 Control apparatus 16 Signal generation Device 17 Solid state relay 18 Voltage measuring device 19 Transmission device 20 Core wire 21 Shield 22 Band pass filter 23 Control device 24 A / D conversion circuit 25 RMS value calculation device 26 Calculation circuit 27 Display device 30 Simulation detector 31 Simulation ground capacity 101 Signal Transmission path 102 Core wire 103 Shield 104 Building ground wire 105 Detector 106 Signal voltage measuring device

Claims (9)

In the evaluation method of the signal transmission path of a high circumferential wave signal No. measuring system of a nuclear plant including a signal transmission line for transmitting a high frequency No. wave signal of the radiation detector,
A current injection device for injecting a high frequency common mode current the signal transmission path to the signal cable includes a coil wound a magnetic material in the body of the core and the core formed in a ring shape is disposed so as to pass through the A current generator for supplying a high frequency common mode current of a predetermined frequency to the current injection device; a current measuring device for measuring a common mode current flowing in the signal transmission line; and the signal by the common mode current flowing in the signal transmission line. A signal voltage measuring device for measuring a normal mode voltage generated between a core wire and a return line of a transmission line, a current value measured by the current measuring device, and a normal mode voltage value measured by the signal voltage measuring device are input. And a conversion ratio calculation device that calculates a conversion ratio that is a ratio of the measured values of the current value and the voltage value. Evaluation apparatus of the road.   2. The signal transmission path evaluation device according to claim 1, wherein the conversion ratio calculation device extracts a first synchronization component extraction unit that extracts a signal from the current measurement device, and a signal from the signal voltage measurement device. A second synchronization component extraction unit; and a control device that changes a measurement frequency band of the signal current and the signal voltage of the first and second synchronization component extraction units, the first synchronization component extraction unit and the second synchronization component An apparatus for evaluating a signal transmission line, comprising: an arithmetic circuit that calculates a conversion ratio that is a ratio of a signal current and a signal voltage that have passed through an extraction unit. 3. The signal transmission path evaluation apparatus according to claim 2, wherein the control device receives high-frequency common mode current frequency information transmitted from the current injection device and measures current and voltage in synchronization with the received frequency. An apparatus for evaluating a signal transmission path, characterized by changing a measurement frequency band of a signal.   3. The signal transmission path evaluation apparatus according to claim 2, wherein the first synchronization component extraction unit and the second synchronization component extraction unit include a band-pass filter.   3. The signal transmission path evaluation apparatus according to claim 2, wherein an A / D conversion circuit and an effective value calculation circuit are provided between the first synchronization component extraction unit, the second synchronization component extraction unit, and the calculation circuit. An apparatus for evaluating a signal transmission path. 6. The apparatus for evaluating a signal transmission path according to claim 1, wherein the current injection device generates a signal current by changing a frequency according to a predetermined pattern, and the signal current. An apparatus for evaluating a signal transmission line, comprising: a switching device for outputting or stopping to a current injection device; and a control device for transmitting frequency and amplitude information of the signal current to the conversion ratio calculation device.   7. The signal transmission path evaluation apparatus according to claim 1, wherein the current measurement apparatus and the signal voltage measurement apparatus comprise a voltage measurement apparatus and a transmission apparatus. Evaluation device. In the evaluation device of the signal transmission apparatus as claimed in any of claims 1 to 7, the end connected to the signal voltage measuring device of the signal transmission line at the opposite end, the return line and the plant building ground line An apparatus for evaluating a signal transmission path, comprising a simulated ground capacity for connecting the two. In Radiation detector high frequency wave signal No. Evaluation Method of signal transmission line of the high circumferential wave signal No. measurement system nuclear power plant having a signal transmission path having a core wire and a return line for transmitting the,
A signal transmission path for transmitting a signal of a radiation detector for detecting neutron flux, gamma rays, etc. as a high frequency signal has a core formed of a magnetic material in a ring shape and a coil wound around the main body of the core , and a signal cable is inserted therethrough. Injecting a high frequency common mode current from the outside by means of a current injection device arranged as follows:
Measuring a current value of a common mode current flowing in the signal transmission path;
Measuring a normal mode voltage value generated between the core line and the return line of the signal transmission path by the common mode current;
Calculating a conversion ratio that is a ratio of the current value and the voltage value;
A method for evaluating a signal transmission path, comprising a step of comparing a predetermined reference value with the conversion ratio.

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