JP2009025242A - Power supply device for energizing cable fault point measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply device for energizing fault point measuring device, capable of stably measuring a fault point, by using commercial power supply for a DC power supply of the cable fault point measurement device, at all times. <P>SOLUTION: The power supply device 30 for energizing the cable fault point measuring device equipped with an AC/DC converter 32 generated from the AC commercial power supply 31 a DC voltage applied to the cable as a fault point measurement object includes a power supply protection circuit 40 for blocking inductive current by a live cable, other than the fault point measurement object flowing backward to the AC/DC converter 32 and a load resistive circuit 50 consuming the inductive current blocked by the power supply protection circuit 40, wherein a voltage limiter circuit 60 limits the abnormal rise in the output DC voltage of the AC/DC converter 32 due to the effect of the induction voltage and protects the fault point measuring device 20, thereby stabilizing the fault point measurement operation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a DC power supply device used for an accident point measuring device that measures the position of a ground fault point that occurs in a cable having an insulation coating such as a three-phase AC underground power transmission cable.

  A power cable having an insulation coating such as a three-phase AC underground power transmission cable laid in a power plant or substation may cause a ground fault due to breakage or deterioration of the insulation coating. The three-phase AC underground power transmission cable has one set of three-phase three-wires juxtaposed in the underground cable conduit. In this case, the three-phase three-wire cables are individually juxtaposed in the ground, or the three-phase three-wire cables are juxtaposed in the ground as an integrated cable combined into one cable. In addition, normally, multiple other sets of underground power transmission cables and communication cables are juxtaposed in the cable conduit, and these cables are live when measuring the fault point of the cable subject to the fault point measurement. Is in a state. If a ground fault occurs in any one of the three-phase one set of underground transmission cables, the three-phase three-wire one set of underground transmission cables cannot transmit power. When a ground fault occurs in this way, the underground power transmission cable is buried underground.To find the location where the ground fault occurred, it is usually necessary to use a measuring instrument from the ground to ground the accident phase cable. The location of the fault is measured.

  There is a Murray loop method using the conductor resistance of the cable as a method of measuring the fault point of the fault phase cable in the three-phase AC underground transmission cable. In the Murray loop method, a fault circuit cable and a healthy one-phase cable that does not cause a ground fault (sound phase cable) constitute a loop circuit, and a DC voltage is applied to the loop circuit to cause a fault in the fault phase cable. Measure the location of the accident point. As a cable fault point measuring device based on the Murray loop method, there is an fault point measuring device using a DC constant voltage of a storage battery as a power supply voltage (for example, see Patent Document 1). The outline of this accident point measuring instrument will be described with reference to FIG.

  The accident point measuring instrument 20 shown in FIG. 3 uses a 6V storage battery 10 similar to a lead storage battery applied to a battery of an automobile as a power source. The cables 1a and 1b shown in FIG. 3 are two-phase three-phase three-wire one set of three-phase AC, one of which is a healthy phase cable 1a that has not caused a ground fault, and the other that has caused a ground fault. The accident phase cable 1b. The sound phase cable 1a and the accident phase cable 1b are two wires having the same structure, and the conductors 2a and 2b are respectively covered with insulating layers 3a and 3b, and the outer peripheries of the insulating layers 3a and 3b are protected by metal sheaths 4a and 4b. is doing. The sheaths 4a and 4b of the cables 1a and 1b are grounded. The accident point P shown in the accident phase cable 1b is a location where a ground fault has occurred due to dielectric breakdown. The accident phase cable 1b is specified because the insulation resistance between the conductor 2b and the sheath 4b rapidly decreases at the accident point P. By specifying the accident phase cable 1b, power transmission of the three-phase three-wire one set is stopped, and the position of the accident point P of the accident phase cable 1b is measured as follows.

  A loop circuit is configured by connecting one end of the accident phase cable 1b and one end (far end) of the healthy phase cable 1a, which is one of the other two phases, with a jumper wire 5. The fault voltage measuring device 20 is used to apply the 6V DC voltage E of the storage battery 10 to the other ends of the healthy phase cable 1a and the accident phase cable 1b, and a loop current is passed through the two-wire loop circuit. Further, the polarity reversing switch 21 of the accident point measuring instrument 20 is operated to reverse the polarity of the DC voltage E applied to each cable 1a, 1b. Each time a loop current is passed through the loop circuit of each cable 1a, 1b, the ground voltage V1 of the conductor 2a of the sound phase cable 1a is measured by the first voltmeter 6, and the conductor 2b of the accident phase cable 1b is measured by the second voltmeter 7. The ground voltage V2 is measured. The cables 1a and 1b have the same length, and the cable length is L. Moreover, when the distance from the other end where the DC voltage E of the accident phase cable 1b is applied to the accident point P is X, the distance X is calculated by the following equation.

  [X / L] = [2 × V1] / [V1 + V2]

The above measurement of the accident point distance X is repeated a plurality of times under the same conditions. The average value of the distances measured a plurality of times is specified as the distance X. When the distance X is specified, the jumper wire 5 and the accident point measuring instrument 20 are removed from the cables 1a and 1b. After that, the cable with the accident point P is exchanged, and the power transmission by the three-phase AC three-wire one set is resumed.
JP-A-57-184983

  The above-mentioned accident point measuring instrument and the storage battery, which is a power supply device for energizing the same, are designed to have a size and weight that can be easily carried to various cable accident point measurement sites. In a three-phase AC underground power transmission cable, the time and time zone when a ground fault occurs are indefinite, and the rate of occurrence is negligible, once a year. For this reason, an electric power company that performs cable fault point measurement needs to be charged constantly in anticipation of spontaneous discharge of the storage battery that is the power source of the fault point measuring device, which has a problem in maintainability.

  Further, the energization current (loop current) that flows from the storage battery to the cable that is the target of the accident point measurement depends on the conductor resistance determined by the thickness and length of the cable. Therefore, for example, when a storage battery is used as a DC power source for a cable fault point measuring device for an ultra-high voltage underground transmission line of 77 kV or higher, a large current of several tens of amperes or more flows with a DC voltage of several volts depending on the line conditions. A large voltage drop may occur in the storage battery, which may adversely affect the accident point measurement results. Furthermore, even if the storage battery 10 is always charged, the performance deteriorates with aging, and a voltage drop may occur during a plurality of accident point measurement operations, making it difficult to measure the accident point with high accuracy.

  Note that it is conceivable to use a DC power source obtained by converting an AC commercial power source into a DC power source as the DC power source for the accident point measuring instrument. However, this has the following problems.

  In the case of a three-phase AC underground power transmission cable, normally, a live cable such as another underground power transmission cable or communication cable is juxtaposed in the vicinity of the cable to be measured at the fault point. For this reason, during an accident point measurement operation for the cable subject to the accident point measurement, an induced voltage is induced in the cable subject to the accident point measurement by a nearby live cable, and an induced current flows. Since this induced current flows into a storage battery that is a DC power source of the accident point measuring instrument and is stored, there are few problems. However, if a DC power source obtained by converting an AC commercial power source is used as the DC power source of the fault point measuring instrument, the DC power source causes fluctuations in the output voltage due to the influence of the induced current, making it difficult to measure a stable cable fault point. The influence of such an induced current is large in a cable in which three-phase three-wire underground power transmission cables are singly arranged in the ground.

  The present invention has been made in view of such circumstances, and an object of the present invention is to use an AC commercial power source as a DC power source of a cable fault point measuring instrument, and to always perform stable cable fault point measurement. To provide an apparatus.

  In order to achieve the above object, the present invention connects one end of each of a pair of cables juxtaposed to each other and applies a DC voltage to the other end of the pair of cables to cause a ground fault accident that occurred in one of the pair of cables. A power supply for energizing an accident point measuring instrument that measures points, an AC / DC converter that generates a DC voltage to be applied to a cable from an AC commercial power supply, and a cable that is separate from the cable when the accident point measuring instrument is in operation A power protection circuit for preventing an induced current induced by another live line cable laid on the AC / DC converter and a load resistance circuit for consuming the induced current blocked by the power protection circuit It is characterized by comprising. In this power supply device, a voltage limiter circuit for regulating the upper limit of the output DC voltage of the AC / DC converter due to the induced current based on the rated voltage of the accident point measuring device can be attached.

  Here, the cable to be measured for the accident point is a cable having an insulation coating such as a three-wire AC and three-wire one-set underground transmission cable or a submarine cable. Measure (specify) the ground fault point based on the insulation breakdown of this cable with the fault point measuring instrument. An accident point measuring instrument is a device that applies a DC voltage to a pair of cables that are subject to loop fault point measurement to cause a loop current to flow, and measures the position of the fault point of the cable that caused the ground fault. Applicable. An AC / DC converter that converts an AC commercial voltage of 100 V into, for example, a DC voltage of 6 V is applied as a DC power source for this accident point measuring instrument. As the AC / DC converter itself, a commercially available product can be applied. As the power source protection circuit, a protection diode circuit that prevents an induced current from flowing back from the cable to be measured to the AC / DC converter can be applied. As the load resistance circuit, a resistance circuit that uses an induced current blocked by the power supply protection circuit and consumes it by heat generation can be applied. By preventing the backflow of the induced current with the power supply protection circuit and consuming the blocked induced current with the load resistance circuit, the output DC voltage of the AC / DC converter is stabilized, and the cable fault point can always be measured stably.

  Also, in order to prevent the output DC voltage of the AC / DC converter from rising abnormally due to the influence of the induction current, the AC / DC converter regulates the upper limit of the output DC voltage based on the rated voltage of the fault point measuring instrument. It is desirable to provide a limiter circuit. When the rated output voltage of the AC / DC converter is, for example, 6V, if the upper limit of the output DC voltage is regulated to, for example, 8V by the voltage limiter circuit, the abnormal increase of the output DC voltage is prevented, and the accident point due to the abnormal increase of the power supply voltage is prevented. The malfunction and failure of the measuring instrument can be avoided, and stable cable fault point measurement can be performed.

  In the present invention, the AC / DC converter is provided with a constant current circuit that regulates the upper limit of the direct current output from the AC / DC converter to the fault point measuring device based on the rated current of the fault point measuring device. be able to. The constant current circuit here detects the output DC current of the AC / DC converter, and when the detected output DC current exceeds the rated current of the fault point measuring device and rises abnormally, this abnormal rise is rated for the fault point measuring device. Restrict to the upper limit determined by the current. This regulation prevents an abnormal increase in the output DC current of the AC / DC converter, protects the accident point measuring instrument, and makes it possible to always perform stable cable fault point measurement.

  According to the present invention, since the AC commercial power source is used as the DC power source of the fault point measuring device that applies a DC voltage to the cable and measures the ground fault point of the cable, the cable fault point measurement is always performed with a stable DC voltage. This eliminates the need for maintenance such as always charging a conventional storage battery. In addition, when measuring the fault point of a cable such as an underground power transmission cable, even if an induced current flows through the cable subject to the fault point measurement by another live wire cable and tries to flow backward to the AC / DC converter, the power protection circuit This prevents the backflow of the induced current, and the blocked induced current is consumed by the load resistor circuit, so that the output DC voltage of the AC / DC converter is stable, and the cable fault point can always be measured stably. Can play. The effectiveness of such an effect is particularly great in underground transmission cables in which three-phase three-wire cables that are easily affected by induced currents are individually juxtaposed in the ground.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 shows a circuit configuration of a power supply device 30 according to the present invention. FIG. 2 is a circuit diagram when the power supply device 30 is used as a DC power source of the fault point measuring device 20 shown in FIG. 2 that are the same as or equivalent to those in FIG.

  A power supply device 30 in FIG. 1 includes an AC / DC converter 32 that generates a DC voltage E to be applied to a pair of cables 1 a and 1 b to be measured at an accident point from an AC commercial power supply 31. The AC / DC converter 32 converts the AC commercial voltage of AC 100V into a DC voltage E of 6V, for example, and outputs the DC voltage E to the accident point measuring instrument 20. Between the AC / DC converter 32 and the accident point measuring device 20, a power protection circuit 40, a load resistance circuit 50, and a load resistance circuit 50 for dealing with an induced current flowing from the cables 1a and 1b to be measured when the accident point measuring device 20 operates. A voltage limiter circuit 60 is installed. A constant current circuit 70 is attached to the AC / DC converter 32.

  The AC / DC converter 32 may be a commercially available product with stable quality. A cooling fan 34 that operates with the AC commercial power supply 31 is wired to the input circuit 33 of the AC / DC converter 32. The cooling fan 34 is used for air cooling of the load resistance circuit 50. The 6V output DC voltage E of the AC / DC converter 32 becomes the input voltage of the accident point measuring device 20, and the accident point measuring device 20 operates in the same manner as in FIG. 3 to measure the accident point of the accident phase cable 1b. Do. During this accident point measurement operation, the cable 1a, 1b to be measured from the cable (not shown) in a live state such as another underground power transmission cable near the cables 1a, 1b to be measured. Inductive voltage is induced by electromagnetic induction and induced current flows. This induced current flows backward in the direction of flowing into the AC / DC converter 32 via the fault point measuring device 20. When the induced current flows backward to the AC / DC converter 32, the output DC voltage E may fluctuate in an increasing direction, which may affect the fault point measurement accuracy.

  The power supply protection circuit 40 prevents the backflow of the induced current. The power supply protection circuit 40 is a protection diode circuit including backflow prevention diodes 41 and 42 that block an AC induced current that attempts to flow back to the AC / DC converter 32. The induced current blocked by the power supply protection circuit 40 flows through the plurality of resistance elements 51 of the load resistance circuit 50, and the resistance elements 51 generate heat to consume the induced current. By the action of the power source protection circuit 40 and the load resistance circuit 50, the influence of the AC / DC converter 32 due to the induced current is reduced, the fluctuation of the output DC voltage E is suppressed, and the fault point measurement accuracy of the fault point measuring device 20 is stable. To do.

  In addition, depending on the line condition of the fault point measurement target cable, the output DC voltage E of the AC / DC converter 32 may abnormally rise due to the influence of the induced voltage. Therefore, this abnormal rise is prevented by the voltage limiter circuit 60. When the rated output voltage of the AC / DC converter 32 is 6V, the voltage limiter circuit 60 limits the upper limit of the output DC voltage E to, for example, 8V based on the rated voltage of the accident point measuring device 20 by the voltage limiter circuit 60. In this way, an abnormal increase in the output DC voltage E is prevented, damage and failure of the accident point measuring instrument 20 are avoided, and measurement accuracy is stabilized.

  In addition, depending on the line condition of the fault point measurement target cable, the output DC current of the AC / DC converter 32 may abnormally rise due to the action of an induced current or the like. Therefore, the AC / DC converter 32 is provided with a constant current circuit 70 that regulates the upper limit of the direct current output to the accident point measuring device 20 based on the rated current of the accident point measuring device 20. The constant current circuit 70 includes a shunt resistor 71 that detects an output direct current of the AC / DC converter. When the output DC current detected by the shunt resistor 71 exceeds the rated current of the accident point measuring device 20 and rises abnormally, the abnormal rise is restricted to an upper limit value determined by the rated current of the accident point measuring device 20. By doing so, an abnormal increase in the output direct current of the AC / DC converter 32 is prevented, the fault point measuring device 20 is protected, and stable cable fault point measurement can always be performed, and the fault point measurement accuracy is stabilized. .

  It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

It is a circuit diagram which shows embodiment of the power supply device which concerns on this invention. It is a circuit diagram of the cable fault point measuring device using the power supply device of FIG. It is a circuit diagram of the conventional cable fault point measuring device.

Explanation of symbols

1a cable (healthy phase cable)
1b Cable (Accident phase cable)
20 Accident point measuring device 30 Power supply device 31 AC commercial power supply 32 AC / DC converter 40 Power supply protection circuit 41, 42 Backflow prevention diode 50 Load resistance circuit 60 Voltage limiter circuit 70 Constant current circuit 71 Shunt resistance E DC voltage P Accident point

Claims (4)

For connecting the one end of each of the pair of cables arranged side by side, applying a DC voltage to the other end of the pair of cables, and measuring the ground fault point generated in one of the pair of cables A power supply unit,
Inductive current induced by an AC / DC converter that generates the DC voltage from an AC commercial power source, and a cable in another live state installed on the cable at a position different from the cable when the accident point measuring device is operated And a load resistance circuit for consuming the induced current blocked by the power supply protection circuit. Power supply.   The cable fault point measurement according to claim 1, further comprising a voltage limiter circuit that regulates an upper limit of an output DC voltage of the AC / DC converter by the induced current based on a rated voltage of the fault point measuring device. Power supply unit   The constant current circuit which regulates the upper limit of the output direct current of the AC / DC converter based on the rated current of the fault point measuring device is attached to the AC / DC converter. Power supply device for energization of cable fault point measuring instrument.   The cable fault point measuring instrument energizing power supply device according to any one of claims 1 to 3, wherein each of the cables is a three-phase AC underground power transmission cable that is independently juxtaposed in the ground.

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