JP6333704B2 - External power source cathodic protection device - Google Patents

Description

  The present invention relates to an external power source cathodic protection device that generates a direct current anticorrosion current for a cathodic protection target.

  The external power supply cathodic protection device uses an external power supply to generate an anticorrosion current from the anode into the electrolyte using the electrode provided in the electrolyte as the anode and the metal structure to be protected in the electrolyte as the cathode. The metal structure is subjected to cathodic protection. This external power source cathodic protection device measures the potential of the metal structure to be cathodic-protected and the coupon current flowing into the coupon connected to the metal structure. Or the output voltage of the external power source is controlled so that the coupon current density determined by the measured coupon current passes the cathodic protection standard.

  A DC power source obtained from a commercial AC power source is used as the external power source of such an external power source cathode anti-corrosion device. In the prior art described in Patent Document 1 below, an AC power source is transformed by a transformer circuit, its output is changed to a DC voltage by a rectifier circuit and a smoothing circuit, and the DC voltage is controlled to be turned on / off by a switching circuit. Output adjustment is performed by adjusting a duty ratio, which is a ratio between time and a switching period at a set frequency.

JP 2014-152346 A JP 2004-250779 A

  In recent years, metal structures to be protected against corrosion have been covered with a plastic coating having a high electrical resistivity, and as a result, the corrosion protection current output from the anode of the external power source cathode corrosion protection device has been reduced to about tens of mA to 10 A. There is a tendency. For this reason, in order to control the anticorrosion current with high accuracy, an external power source that outputs a direct current with a low ripple rate from the anode is required.

  In recent years, cases in which plastic coating pipelines are embedded in parallel with high-voltage AC power transmission lines and AC electric railway transportation routes are increasing. Measures may be taken to install an AC induction reducer with a built-in capacitor between the pipeline and a low grounded object as described in. When an anticorrosive current having a high ripple rate flows into such a pipeline, the ripple current passes through the capacitor, and thus the anticorrosive current that should flow into the pipeline is partly lost. An external power supply that outputs a direct current with a low ripple rate from the anode is also required in order to allow the anticorrosion current to flow into the pipeline effectively.

  In addition, while the anticorrosion current is miniaturized in this way, metal structures buried in urban areas are affected by stray currents with large time fluctuations such as rail leakage current of DC electric railway vehicles. Since the metal structure is exposed to an environment in which the potential to the electrolyte of the metal structure and the coupon inflow current density change frequently, it is required to control the anticorrosion current at high speed and with high accuracy.

  Further, the anode of the external power source cathode anticorrosion apparatus is generally installed by filling graphite powder and coke powder as a backfill around in order to efficiently output an anticorrosion current. As a result, the ground resistance of the anode is low, and under conditions where the anticorrosion current output is miniaturized, stray current may flow into the anode, or if lightning strikes the anode, lightning current will flow in. The external power supply could be damaged.

  The present invention has been proposed in order to cope with such a situation. In an external power source cathodic protection device, a DC current with a low ripple rate is output from a commercial AC power source, thereby reducing a miniaturized anticorrosive current at high speed. Further, it is an object of the present invention to control with high accuracy, to prevent stray current and lightning current flowing from the anode with low ground resistance.

In order to achieve such an object, the present invention comprises the following arrangement.
An external power supply cathodic protection device comprising an external power supply device, wherein the metal structure to be protected against corrosion present in the electrolyte is used as a cathode, and an anticorrosion current is generated from the anode disposed in the electrolyte to the metal structure. The external power supply device includes a first rectifier circuit that rectifies an AC voltage of a commercial AC power supply, a smoothing circuit that smoothes the voltage rectified by the first rectifier circuit, and chopper control of the voltage smoothed by the smoothing circuit A switching circuit to which the voltage turned on and off by the switching circuit is input to the primary side, a second rectifier circuit that rectifies the secondary voltage of the transformer circuit, and rectification by the second rectifier circuit a PWM circuit for controlling the LC circuit for obtaining a DC voltage from a voltage that is, the duty ratio before Symbol switching circuit, wherein an output voltage of the LC circuit circuit An arithmetic processing unit is provided that receives an output current of an anode side output and adjusts a feedback voltage for controlling a duty ratio of the switching circuit according to a total circuit resistance obtained by the output voltage and the output current, and the feedback An external power source cathodic protection device, wherein the output voltage of the LC circuit applied between the cathode and the anode is controlled by adjusting the voltage .

  The external power source cathodic protection device having such features can output a direct current with a low ripple rate from a commercial alternating current power source, and can control the miniaturized anticorrosion current at high speed and with high accuracy, and has a low grounding resistance. The stray current and the lightning current flowing from the anode can be effectively prevented.

It is explanatory drawing which showed the whole structure of the external power supply cathode anticorrosion apparatus which concerns on one Embodiment of this invention. It is explanatory drawing which showed the circuit structure of the external power supply device in the external power supply cathode anticorrosion apparatus which concerns on one Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing the overall configuration of an external power source cathode anticorrosion device according to an embodiment of the present invention. Here, the metal structure to be protected against corrosion will be described as a pipeline embedded in the soil that is an electrolyte, but is not particularly limited thereto.

  The external power supply cathodic protection device 1 includes an external power supply device 2 and an anode 3, and one output terminal 2A of the external power supply device 2 is connected to a pipeline P existing in the soil as an electrolyte via an electric wire L1. The other output terminal 2B of the external power supply device 2 is connected to the anode 3 disposed in the electrolyte near the pipeline P via the electric wire L2. The external power supply device 2 includes input terminals 2C and 2D. A commercial AC power supply AC is connected to the input terminals 2C and 2D, and an AC voltage is input.

  The pipeline P is connected to the reference electrode 4 and the coupon 5 installed in the electrolyte via the electric wires L3 and L4, and the voltage value measured by the voltmeter 6 connected to the electric wire L3 or the electric wire L4. The current value measured by the connected ammeter 7 is input to the arithmetic processing unit 8, and the tube-to-ground potential (electrolyte potential) P / S and the coupon current density Ic obtained by the arithmetic processing unit 8 are determined by the external power supply 2. Has been entered.

  Further, the arithmetic processing unit 8 has a wireless or wired communication function, and by this communication function, monitoring information including a tube-to-ground potential P / S and a coupon current density Ic in a remote monitoring / control center (described later). Output voltage V, output current I, total circuit resistance R, etc.) and a control signal from the monitoring / control center.

  The external power supply device 2 applies a direct-current output voltage V between the pipeline P, which is a cathode, and the anode 3, and supplies the anticorrosion current generated in the electrolyte from the anode 3 to the pipeline P. The circuit configuration shown in FIG. 2 is provided.

  This external power supply device 2 converts AC voltage input to the input terminals 2C and 2D into DC voltage, and outputs it from output terminals 2A and 2B connected to the anode 3 and the pipeline P. The line filter 10 , An inrush current prevention circuit 11, a first rectifier circuit 12, a power factor correction circuit 13, a smoothing circuit 14, a switching circuit 15, a transformer circuit 16, a second rectifier circuit 17, and an LC circuit 18, and an output voltage to the switching circuit 15. As a feedback circuit for feeding back V, an error amplification circuit 19, a phase compensation circuit 20, and a PWM circuit 21 are provided.

  The basic operation of the external power supply device 2 will be described. The AC voltage input to the input terminals 2 </ b> C and 2 </ b> D has its noise removed by the line filter 10, and is rectified to a voltage without polarity reversal by the first rectifier circuit 12 via the inrush current prevention circuit 11. As the first rectifier circuit 12, a bridge-type full-wave rectifier circuit as shown in the figure can be used.

  The voltage rectified by the first rectifier circuit 12 is smoothed by the smoothing circuit 14 via the power factor correction circuit 13, and the smoothed voltage is turned on / off by the switching circuit 15 including a switching transistor such as a MOSFET. Chopper controlled. The voltage chopped by the switching circuit 15 is input to the primary side of the transformer circuit 16 formed of a high-frequency transformer, and the secondary side voltage of the transformer circuit 16 is half-wave rectified by the second rectifier circuit 17 configured by one diode. , And output as a DC voltage via the LC circuit 18.

  The output voltage V of the LC circuit 18 is detected by the output voltage detection means 22 and is input to the arithmetic processing device 8 via the AD converter 23, and the feedback voltage Vf output from the arithmetic processing device 8 is in the feedback circuit. It is sent to the error amplification circuit 19.

  The error amplification circuit 19 in the feedback circuit generates an error signal by inverting and amplifying the difference between the feedback voltage Vf sent from the arithmetic processing unit 8 and the reference voltage Vr. The generated error signal is phase compensated by the phase compensation circuit 20, and the phase compensated error signal is supplied to the PWM comparator 21 </ b> C in the PWM circuit 21. The PWM comparator 21C compares the phase compensated error signal with a triangular wave 21a output from a triangular wave oscillator (not shown) to generate a PWM signal. The generated PWM signal is supplied to the switching circuit 15.

  When the phase-compensated error signal is larger than the triangular wave 21a, the PWM signal is high and the switching circuit 15 is turned on. When the phase-compensated error signal is smaller than the triangular wave 21a, the PWM signal is low. Since the switching circuit 15 is turned off, the ON / OFF duty ratio by the switching circuit 15 is controlled according to the magnitude of the error signal, and feedback control is performed so that the output voltage V matches the reference voltage Vr.

  The arithmetic processing unit 8 that sends the feedback voltage Vf to the error amplifying circuit 19 is not only inputted with the output voltage V of the LC circuit 18 via the AD converter 23 but also measured by the voltmeter 6 or the ammeter 7. The measured value is input via the A-D converter 23. Then, the arithmetic processing unit 8 obtains the pipe ground potential P / S (electrolyte potential) or the coupon current density Ic of the pipeline P from these measured values, and based on the pipe ground potential P / S or the coupon current density Ic. The feedback voltage Vf is adjusted. By adjusting the feedback voltage Vf in this way, the output voltage V is controlled according to the measured tube-to-ground potential P / S and the coupon current density Ic, and the anticorrosion current generated from the anode 3 can be appropriately controlled. it can.

  Further, a shunt resistor 24 is provided on the anode side output wiring of the LC circuit 18, and the external power supply device 2 includes an output current detection means 25 that detects the output current I from the shunt resistor 24. Then, the output current I detected by the output current detection means 25 is input to the arithmetic processing device 8 via the AD converter 23, and the arithmetic processing device 8 receives the input output current I and the output voltage V. Thus, the total circuit resistance R is obtained. Here, the feedback voltage Vf output from the arithmetic processing unit 8 can be appropriately adjusted by the output current I and the total circuit resistance R.

  Between the anode and the shunt resistor 24 for detecting the output current, an anode inflow current preventing means 26 composed of a fast recovery diode is inserted. The fast recovery diode operates at high speed, and the operation time for preventing backflow after stray current or lightning current flows into the anode and the potential of the anode becomes higher with respect to the output terminal (output plus terminal) 2B of the external power supply 2 Is very short, and after this phenomenon has subsided, the time for returning to the forward direction is very short. In addition, since the reverse voltage is high (for example, reverse withstand voltage 800V), even when a high lightning voltage is applied to the anode and the external power supply device 2, the fast recovery diode prevents the lightning current from flowing.

  Here, in order to reduce the ripple rate of the direct current output from the anode, it is necessary to increase the switching frequency of the switching circuit 15, but if it is too high, a switching loss is induced. Further, since the data sampling frequency of the output voltage V, the output current I, and the control pipe ground potential P / S output in analog is 10 kHz, the switching frequency is set to 100 kHz in consideration of these.

  According to the external power source cathodic protection device 1 including the external power source device 2 having such a circuit configuration, after first rectifying the AC voltage of the commercial AC power source AC to obtain a voltage without polarity inversion, and smoothing it. Since the switching circuit 15 converts the frequency into a high frequency, the transformer circuit 16 can be reduced in size and weight. Further, by adopting chopper control by turning on / off the switching circuit 15, it becomes possible to operate with low power consumption and high efficiency.

  Since the output voltage V is detected and input to the arithmetic processing unit 8 and the duty ratio of the switching circuit 15 is controlled at high speed according to the feedback voltage Vf output from the arithmetic processing unit 8, high-speed and high-precision output voltage control It can be performed.

  Since the first rectifier circuit 12 and the smoothing circuit 14 are provided in the preceding stage of the switching regulator composed of the switching circuit 15 and the transformer circuit 16, and the second rectifier circuit 17 and the LC circuit 18 are provided in the subsequent stage of the switching regulator described above, low ripple The DC voltage output of the rate can be stepped down or boosted to an arbitrary height. As a result, a stable anticorrosion current without polarity reversal can be output from the anode 3.

  The power factor correction circuit 13 inserted between the first rectifier circuit 12 and the smoothing circuit 14 is a phase loss due to the phase difference between the current waveform and the voltage waveform of the AC power supply input during full-wave rectification through the first rectifier circuit 12. The power factor is adjusted so that is minimized. By providing this power factor correction circuit 13, the harmonic current generated by the switching circuit 15 can be made lower than the limit value.

Furthermore, since the shunt resistor 24, the anode inflow current prevention means (diode) 26, and the anode 3 are connected in series to the anode side output of the LC circuit 18, the output current I obtained from the shunt resistor 24 as the load of the anode 3 is connected. Can be directly evaluated. The anode 3 has a permissible current density. Generally, the permissible current density of the composite oxide-coated electrode used as the anode of the external power source cathodic protection device 1 is 100 A / m ² or less, but the output current I obtained from the shunt resistor 24 is By controlling the output voltage V by the above, the load of the anode 3 can be accurately within the allowable range.

  The external power supply cathodic protection device 1 including such an external power supply device 2 can obtain a DC voltage with a low ripple rate from the commercial AC power supply AC and can control the miniaturized anticorrosion current at high speed and with high accuracy. Further, stray current and lightning current flowing from the anode 3 having a low ground resistance can be prevented by the anode inflow current preventing means 26. Further, since the output current I is detected immediately before the output terminal 2B connected to the anode 3, the load of the anode 3 can be accurately kept within the allowable range.

1: External power source cathodic protection device,
2: external power supply, 2A, 2B: output terminal, 2C, 2D: input terminal,
3: anode, 4: reference electrode, 5: coupon, 6: voltmeter, 7: ammeter,
8: arithmetic processing unit,
10: line filter, 11: inrush current prevention circuit, 12: first rectifier circuit,
13: Power factor correction circuit, 14: Smoothing circuit, 15: Switching circuit,
16: Transformer circuit, 17: Second rectifier circuit, 18: LC circuit, 19: Error amplifier circuit,
20: Phase compensation circuit,
21: PWM circuit, 21a: triangular wave, 21C: PWM comparator,
22: output voltage detection means, 23: AD converter, 24: shunt resistor,
25: output current detection means, 26: anode inflow current prevention means,
AC: AC power supply,
P: pipeline, V: output voltage, I: output current, R: total circuit resistance,
P / S: tube-to-ground potential (vs. electrolyte potential), Ic: coupon current density,
Vf: feedback voltage, Vr: reference voltage,
L1, L2, L3, L4: Electric wire,

Claims (3)

An external power supply cathodic protection device that includes an external power supply device and uses a metal structure to be protected against corrosion present in the electrolyte as a cathode, and generates a corrosion protection current from the anode disposed in the electrolyte to the metal structure,
The external power supply includes a first rectifier circuit that rectifies an AC voltage of a commercial AC power supply, a smoothing circuit that smoothes a voltage rectified by the first rectifier circuit, and a chopper that smoothes the voltage smoothed by the smoothing circuit. A switching circuit to be controlled, a transformer circuit in which a voltage turned on / off by the switching circuit is input to a primary side, a second rectifier circuit that rectifies a secondary voltage of the transformer circuit, and the second rectifier circuit an LC circuit from rectified voltage obtained DC voltage, a PWM circuit for controlling the duty ratio before Symbol switching circuit, the output current of the anode side output of the output voltage and the LC circuit of the LC circuit is input, the output An arithmetic processing unit for adjusting a feedback voltage for controlling a duty ratio of the switching circuit by a total circuit resistance obtained by a voltage and the output current; For example,
An external power source cathodic protection device, wherein an output voltage of the LC circuit applied between the cathode and the anode is controlled by adjusting the feedback voltage . 2. An external power source cathodic protection device according to claim 1, wherein anode inflow current preventing means is provided at the anode side output of the LC circuit . The arithmetic processing unit adjusts the feedback voltage based on one or both of a counter-electrolyte potential and a coupon current density of the metal structure, thereby adjusting an output voltage of the LC circuit applied between the cathode and the anode. external power cathodic protection system of claim 1, wherein the controller controls.

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