JP2010062419A - Zero-phase current transformer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zero-phase current transformer easily installable on an existing power distribution line, and capable of minimizing a residual current. <P>SOLUTION: An iron core 11 is formed annularly by jointing a plurality of circular-arc-like iron core members 13 to one another, a plurality of divided secondary coils 12 are mounted by moving arrangement positions to the iron core 11, and the divided secondary coils 12 are serially connected to one another to output currents generated in the divided secondary coils 12 from output terminals 19. The divided secondary coils 12 are moved along the iron core 11 to identify positions of the divided secondary coils 12 for minimizing residual currents generated in the secondary coils 12, and the divided secondary coils 12 are arranged at the identified positions. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a zero-phase current transformer that detects a zero-phase current.

  For example, the ground fault current of a three-phase 6 kV distribution line is detected by a three-phase zero-phase current transformer (ZCT). That is, the zero-phase current transformer detects a zero-phase current that is generated when a ground fault occurs in the distribution line, and inputs it to the ground fault direction relay. The ground fault direction relay determines a ground fault in the distribution line based on the zero phase current detected by the zero phase current transformer.

  FIG. 6 is a system diagram showing an example of a distribution system in a distribution substation. The distribution transformer 21 steps down the voltage of the primary transmission line and supplies power to the secondary distribution line. Usually, a plurality of distribution lines are connected to the secondary bus 22. ing. FIG. 6 shows a case where three distribution lines 23a to 23c are connected. Each distribution line 23a-23c supplies electric power to a load via the circuit breakers 24a-24c. Zero-phase current transformers 25a to 25c are arranged in the respective distribution lines 23a to 23c, and zero-phase currents detected by the zero-phase current transformers 25a to 25c are respectively input to the ground fault direction relays 26a to 26c. . The ground fault direction relays 26a to 26c determine the ground fault of the distribution lines 23a to 23c based on the zero phase current detected by the zero phase current transformers 25a to 25c. The circuit breakers 24a to 24c of the distribution lines 23a to 23c that have been determined to have a tie-up accident are opened.

  A three-phase zero-phase current transformer is configured by winding a secondary coil around an annular iron core and penetrating a three-phase conductor in a space surrounded by the annular iron core on the primary side. Then, the secondary current corresponding to the vector sum of the currents flowing through the primary-side three-phase conductor is taken out from the secondary-side coil as a zero-phase current.

  In such a zero-phase current transformer, the ground fault current (leakage current) is influenced by the magnetic permeability of the iron core material, the position of the primary side conductor and the winding and arrangement of the secondary side coil, the magnetic saturation of the iron core, etc. Even if it is not, a residual current may be output to the secondary coil. The residual current has a characteristic that changes in proportion to the load current, and since a current containing many harmonic components flows through the distribution line, the residual current also contains harmonic components. Further, the residual current changes depending on the tilt of the iron core or the change in the distance between the iron core and the conductor. This is because the magnetic path is changed by changing the positional relationship between the iron core and the primary conductor, and the residual current is changed by the change of the magnetic path.

  As described above, the signal detected by the zero-phase current transformer is input to the ground fault relay and used to determine the ground fault, so when the residual current is output from the zero-phase current transformer May cause the ground fault direction relay to malfunction. Since the ground fault direction relay is set with high sensitivity, the ground fault direction relay may malfunction even with a small residual current. In order to prevent malfunction, the sensitivity of the ground fault direction relay is made dull, but in this case, it becomes impossible to detect a micro ground fault.

  Therefore, a high-magnetic material such as permalloy is used for the iron core, and the secondary coil is distributedly wound while maintaining the distance between the conductors through which the load current flows at a predetermined size, so that the zero phase change is prevented. I'm making a fluency.

In addition, the through-type zero-phase current transformer has an annular iron core, and a conductor must be penetrated through the annular iron core, so that it is difficult to install it later in an existing distribution line. Therefore, there is a split-type zero-phase current transformer that is configured by dividing the iron core and joining the split iron core so as to sandwich an existing conductor. As such a split-type zero-phase current transformer, the secondary coil is divided into six coils having the same number of turns and the same length, and two of them are arranged at the center of each semicircular iron core, There are those in which the other four cores are located close to the positions that do not reach the meshing portion, the skill is not required for production, the man-hours are reduced, and the residual current is also reduced (for example, see Patent Document 1) .
JP-A-1-214003

  However, in the thing of patent document 1, since the arrangement | positioning position of six divided coils is a predetermined position, a residual current is not necessarily the minimum. As described above, the residual current is affected by the magnetic permeability of the iron core material, the position of the primary side conductor, the winding and arrangement of the secondary side coil, the magnetic saturation of the iron core, etc. Residual current is not minimized just by placing it at a different position.

  An object of the present invention is to provide a zero-phase current transformer that can be easily installed in an existing distribution line and that can minimize the residual current.

  The zero-phase current transformer of the present invention includes a core formed in an annular shape by joining a plurality of arc-shaped core members, and a plurality of divided secondary sides on which the arrangement position on the core is movably mounted. A coil and an output terminal for outputting the current generated in the divided secondary coil by connecting the divided secondary coil in series, and moving the divided secondary coil along the iron core; The position of the divided secondary coil that minimizes the residual current generated in the secondary coil is specified, and the divided secondary coil is arranged at the specified position.

  According to the present invention, since a plurality of arc-shaped iron core members are joined to form an annular iron core, it can be easily installed on an existing distribution line. Further, the secondary coil to be mounted on the iron core is divided into a plurality of pieces and arranged on the iron core so as to be movable, and the divided secondary coil is moved along the iron core to generate a residual in the secondary coil. Since the position where the current becomes the smallest is specified and the divided secondary coil is arranged at the specified position, a zero-phase current transformer with a small residual current can be provided. Therefore, it is possible to prevent malfunction of the ground fault direction relay that operates using the output of the zero phase current transformer as an input, and it is possible to detect a micro ground fault with high sensitivity.

  FIG. 1 is a configuration diagram of a zero-phase current transformer according to an embodiment of the present invention. As shown in FIG. 1, the zero-phase current transformer is configured by mounting a plurality of divided secondary coils 12 a to 12 d on an iron core 11. FIG. 1 shows a case where four divided secondary coils 12a to 12d are mounted. The iron core 11 includes a plurality of iron core members 13a and 13b and a fixture 14 that fixes the plurality of iron core members 13a and 13b in a ring shape. In FIG. 1, the case where it is the two iron core members 13a and 13b is shown. The fixture 14 is arranged by winding one circumference of the outer peripheral surfaces of the two divided iron core members 13 a and 13 b, and fastening portions 15 a and 15 b are formed at the ends of the fixture 14. And by fixing between the fastening parts 15a and 15b with the volt | bolt 16 and the nut 17, the two iron core members 13a and 13b divided | segmented with the fixing tool 14 are fixed, and the iron core 11 is formed.

  On the iron core 11 formed in this way, four divided secondary coils 12a to 12d to which the arrangement position on the iron core 11 is movably mounted are mounted. The four divided secondary coils 12a to 12d are connected in series by the wiring 18, and are output to the outside from an output terminal 19 that outputs a current generated in the divided secondary coils 12a to 12d.

  FIG. 2 is a perspective view of the iron core member of the zero-phase current transformer according to the embodiment of the present invention. The plurality of iron core members are formed by dividing an annular iron core member into a plurality of pieces. FIG. 2 shows a case where the core member is divided into two iron core members 13a and 12b. Since these two iron core members 13a and 13b are formed by dividing an annular iron core member into two, each iron core is formed. The members 13a and 13b are formed in an arc shape. And the divided | segmented part is joined and it is set as a cyclic | annular iron core member.

  FIG. 3 is a perspective view of the iron core of the zero-phase current transformer according to the embodiment of the present invention. As shown in FIG. 3, the two divided core members 13 a and 13 b are joined to form an annular core member, and the annular core member is joined by a fixture 14 to form the annular core 11. The fixture 14 is arranged by winding one circumference of the outer peripheral surfaces of the two divided iron core members 13a and 13b, and is fixed by bolts 16 and nuts 17 by fastening portions 15a and 15b.

  Next, how to install the divided secondary coil 12 on the iron core 11 will be described. FIG. 4 is a perspective view of the process of forming the iron core of the zero-phase current transformer according to the embodiment of the present invention, and FIG. 5 is a perspective view of the divided secondary coil 12.

  As shown in FIG. 4, in the process of forming the iron core 11 with the fixture 14 in contact with the outer peripheral surface of one iron core member 13a, the openings of the fastening portions 15a and 15b of the fixture 14 are shown in FIG. The split secondary coil 12 shown is inserted.

  As shown in FIG. 5, the divided secondary coil 12 is formed in a square cylinder shape, and a conductor 27 with an insulation coating is wound around the surface of the cylinder body. The through-hole 20 of the cylindrical body of the divided secondary coil 12 is formed larger than the cross-sectional area of the iron core member 13a and the fixture 14, and has a size through which the iron core member 13a and the fixture 14 can pass. Therefore, the through-hole 18 of the divided secondary coil 12 is passed through the iron core member 13a and the fixture 14, and the four divided secondary coils 12 are sequentially inserted into the iron core member 13a and the fixture 14. Thereafter, the other core member 13b is disposed inside the fixture 14, and the four divided secondary coils 12 are inserted into the core members 13a, 13b and the fixture 14, and the fastening portions 15a, 15b. Are fixed with bolts 16 and nuts 17. Thereby, the zero phase current transformer shown in FIG. 1 is obtained.

  In the zero-phase current transformer shown in FIG. 1, the four divided secondary coils 12 a to 12 d are slidable on the iron core 11, and the arrangement position is movable on the iron core 11. The arrangement positions of the divided secondary coils 12a to 12d are positions where the residual current generated in the secondary coils 12a to 12d connected in series is the smallest.

  The position where the residual current generated in the secondary side coils 12a to 12d becomes the smallest is specified as follows. A three-phase conductor is passed through the space surrounded by the annular core 11 of the zero-phase current transformer shown in FIG. 1, and a current is passed through the three-phase conductor. In this state, a synchroscope is connected to the output terminal 19, and the residual current generated in the secondary coils 12a to 12d is measured. The four divided secondary coils 12a to 12d are moved along the iron core, and the position where the measured residual current is minimized is specified. For example, of the four divided secondary coils 12a to 12d, two divided secondary coils are fixed, and another two divided secondary coils are moved so that the measured residual current is Specify the smallest position. After that, move the two divided secondary coils that were fixed first and check if there is a position where the measured residual current is the smallest. Then, the two divided secondary coils moved later are fixed at the positions.

  In the above description, the case of the four divided secondary coils 12a to 12d has been described. However, five or more divided secondary coils 12 may be used, or two or three divided secondary coils 12 may be used. It is good. Moreover, although the iron core 11 demonstrated the case of the two iron core members 13a and 13b, you may divide | segment into three or more. Furthermore, when the arrangement position of the divided secondary coil 12 is specified, if the harmonic component included in the residual current to be measured cannot be ignored, the residual current may be measured using a filter.

  According to the embodiment of the present invention, since a plurality of arc-shaped iron core members 13 are joined to form the iron core 11 in an annular shape, it can be easily installed on an existing distribution line. Further, the secondary coil 12 to be mounted on the iron core 11 is divided into a plurality of pieces and arranged on the iron core 11 so as to be movable. The divided secondary coil 12 is moved along the iron core 11 to move to the secondary side. Since the position where the residual current generated in the coil 12 becomes the smallest is specified and the divided secondary coil 12 is arranged at the specified position, a zero-phase current transformer with a small residual current can be provided.

  At that time, the position where the three-phase conductors of the distribution line pass through the space surrounded by the annular core 11 may be any position in the space surrounded by the annular core 11. This is because the residual current generated in the secondary coil 12 is the largest when the divided secondary coil 12 is moved along the iron core 11 after the three-phase conductor is passed through the space surrounded by the annular iron core 11. This is because the position to be reduced is specified.

  For a zero-phase current transformer in which a residual current of a secondary current of 10 mA (primary conversion value 4 A) is generated by a secondary coil having a load current of 230 A and a winding number of 400 turns in a conductor of a distribution line, When the embodiment of the present invention is applied using four divided secondary coils having 125 windings, the secondary current can be set to 0.028 mA (residual current having a primary conversion value of 14.0 mA). In this situation, when the zero-phase current component is energized with 50 mA, the current value (waveform) can be confirmed with certainty. It is possible to prevent malfunction of the ground fault direction relay that operates using the output of the current transformer as input, and to detect a micro ground fault with high sensitivity.

The block diagram of the zero phase current transformer concerning embodiment of this invention. The perspective view of the iron core member of the zero phase current transformer concerning an embodiment of the invention. The perspective view of the iron core of the zero phase current transformer concerning an embodiment of the invention. The perspective view of the formation process of the iron core of the zero phase current transformer concerning embodiment of this invention. The perspective view of the division | segmentation secondary coil of the zero phase current transformer concerning embodiment of this invention. The system diagram which shows an example of the power distribution system in the substation for power distribution.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Iron core, 12 ... Split secondary coil, 13 ... Iron core member, 14 ... Fixing tool, 15 ... Fastening part, 16 ... Bolt, 17 ... Nut, 18 ... Wiring, 19 ... Output terminal, 20 ... Through-hole, 21 ... Distribution transformer, 22 ... Busbar, 23 ... Distribution line, 24 ... Circuit breaker, 25 ... Zero phase current transformer, 26 ... Ground fault relay, 27 ... Conductor

Claims (1)

  An iron core formed in an annular shape by joining a plurality of arc-shaped iron core members, a plurality of divided secondary coils that are movably mounted on the iron core, and the divided secondary coils An output terminal for outputting a current generated in the split secondary coil by connecting in series, and moving the split secondary coil along the iron core so that the residual current generated in the secondary coil is the highest. A zero-phase current transformer characterized in that a position of the divided secondary side coil that becomes smaller is specified, and the divided secondary side coil is arranged at the specified position.

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