JP4361923B2 - GPT addition type ground voltage suppression device - Google Patents

Description

  The present invention relates to an apparatus for suppressing an abnormal potential increase in a grounding potential transformer (hereinafter referred to as GPT). The present invention can be used by connecting to a GPT installed in a distribution substation facility operated by an electric power company or the like, for example.

  In Japan, a non-grounded three-phase distribution line is generally used as a distribution line that supplies electric power from a substation to homes. A non-grounded three-phase distribution line uses a GPT in order to detect a ground fault, electric leakage, or the like. For example, the following Patent Documents 1 and 2 are known as documents related to GPT.

  As shown in FIG. 8, the conventional GPT 800 includes an iron core 810 and primary to tertiary windings 811 to 813 wound around the iron core 810. As shown in FIG. 8, the primary winding 811 has a Y connection, the secondary winding 812 has a Y connection, and the tertiary winding 813 has an open Δ connection. The primary winding 811 is connected to the R phase, S phase, and T phase of a three-phase distribution line (not shown) at each end R1, S1, T1, and is grounded at a neutral point N. Each point R2, S2, and T2 of the secondary winding 812 is connected to an external device 830 such as a voltmeter, an overvoltage / undervoltage relay, and a voltage regulator. Further, between the open terminals O1 and O2 of the tertiary winding 813, for example, a 36 ohm load resistor 820 and a ground fault direction relay are connected.

  When the three-phase distribution line is normal (that is, when there is no ground fault or leakage), the R-phase, S-phase, and T-phase voltages of the three-phase distribution line are shifted by 1/3 period. This ensures that the voltage sum is always zero volts. Therefore, the potential at the neutral point N is also zero volts. For this reason, almost no current flows through the tertiary winding 813. Therefore, the voltage across the terminals of the load resistor 820 is substantially zero volts.

  On the other hand, when an abnormality occurs in the three-phase distribution line (that is, when one or two of the three distribution lines have a ground fault or leakage), the potential at the neutral point N increases. As a result, the inter-terminal voltage of the tertiary winding 813 also increases. Therefore, by measuring the voltage of the tertiary winding 813, the occurrence of abnormality in the three-phase distribution line can be detected.

  On the other hand, iron resonance has been known as one of the causes for increasing the potential of the three-phase distribution line. With iron resonance, a ground fault caused by a reactance component, for example, an LC series circuit is formed by a transformer winding (L) and a capacitance (C) of a wiring path, and magnetic saturation of the reactance component occurs. This is a phenomenon in which the voltage of the three-phase distribution line rises abnormally. For example, the following Patent Documents 3 and 4 are known as documents relating to iron resonance.

  As shown in the conceptual diagram of FIG. 9A, the pole transformer (not GPT) 900 has an iron core 910, and a primary winding 911 and a secondary winding 912 wound around the iron core 910. . Each end of the primary winding 911 is connected to one of the R phase, S phase, and T phase of the three-phase distribution line 930 via fuses 921 and 922. In addition, each end of the primary winding 911 is grounded via lightning protection equipment 931 and 932. Each end of the secondary winding 912 is connected to the device 940 but is unloaded.

  In such a pole transformer 900, the conceptual diagram of FIG. 9B shows a circuit configuration when the fuse 922 is cut and the lightning protection equipment 931 causes dielectric breakdown. The current I flowing through the three-phase distribution line 930 is discharged to the ground via the fuse 921 (not shown in FIG. 9B), the primary winding 911, and the lightning protection equipment 932. Therefore, the LC series circuit is configured by the capacitance 941 of the three-phase distribution line 930 and the primary winding 911.

Thus, in the case of a ground fault in the three-phase distribution line 930, an LC series circuit may be formed between the three-phase distribution line 930 and the ground. This LC series circuit generates iron resonance.
JP-A-8-275376 JP-A-9-222455 Japanese Patent Laid-Open No. 2005-295883 JP-A-5-300657

  When iron resonance occurs in a non-grounded three-phase distribution line, the potential of the three-phase distribution line rises abnormally. According to the study of the inventor of this application, in a ground fault involving iron resonance, the increase in ground potential of the three-phase distribution line is 10 kilovolts (3.8 kilovolts for distribution lines not connected to the LC series circuit) or More than that.

  An abnormal rise in distribution line ground potential due to iron resonance may damage lightning protection equipment such as arresters (lightning arresters), and may also cause damage to various devices connected to the three-phase distribution line and the distribution line itself.

  In order to prevent such an abnormal increase in the distribution line ground potential, for example, the three-phase distribution line may be changed to a resistance grounding system or a reactor grounding system. However, in Japan, the secondary windings of distribution transformers used in substations are usually configured with delta connections, so such a change in equipment is accompanied by a significant change in equipment. Cost is required.

  The subject of this invention exists in the point which provides the apparatus which suppresses the abnormal electric potential rise of a distribution line at low cost.

(1) GPT additional type ground voltage suppression device according to the invention, a primary winding of Y-connection that is connected and the neutral point ungrounded system three-phase distribution lines are grounded, are applied to the primary winding and a secondary winding for outputting to another device with a transformer for three-phase voltage, and the tertiary winding Oh Pun Δ connection, connecting the open terminal of the tertiary winding, for measuring the potential of the neutral point The present invention relates to a GPT-added ground voltage suppressing device connected in parallel with a burden resistor between open terminals of a GPT including a burden resistor .

And it has the discharge circuit which starts electricity supply when the voltage between open terminals exceeds the electricity supply start voltage , and the voltage control resistance connected in series with the discharge circuit.

(2) The discharge circuit may include a discharge gap that starts energization when the inter-terminal voltage exceeds the energization start voltage .

(3) The discharge circuit may be a thyristor circuit that starts energization when the inter-terminal voltage exceeds the energization start voltage .

  (4) The energization start voltage of the discharge circuit is desirably 290 volts or more and 500 volts or less as a peak value.

  (5) The resistance value of the voltage control resistor is desirably 2 ohms or more and 8 ohms or less.

  In the present invention, when the neutral point potential of the primary winding rises due to an abnormal rise in the wire voltage, the inter-terminal voltage of the tertiary winding also rises. And when the voltage across the terminals of the burden resistor provided in the tertiary winding exceeds the discharge start voltage of the discharge circuit, the discharge circuit is energized, so that the burden resistor and the voltage control resistor are connected in parallel. Become. For this reason, since the resistance value between the open terminals of a tertiary winding falls, the electric current which flows into a tertiary winding increases. As a result, the amount of current discharged from the electric wire to the ground via the neutral point increases, and the potential drop of the electric wire is promoted.

  Therefore, according to the present invention, when an abnormal rise in the electric potential of the electric wire is started, such as when iron resonance occurs due to the LC series circuit of another transformer, etc., the GPT promotes the electric discharge of the electric wire, The abnormal increase can be suppressed.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the size, shape, and arrangement relationship of each component are shown only schematically to the extent that the present invention can be understood, and the numerical conditions described below are merely examples. .

  FIG. 1 is a conceptual diagram showing a schematic configuration of the GPT 100 according to this embodiment. As shown in FIG. 1, the GPT 100 includes an iron core 110, primary to tertiary windings 111 to 113, a load resistor 120, and a ground voltage suppression device 130.

  The iron core 110 is an iron core for generating a magnetic flux corresponding to the current flowing through the primary to tertiary windings 111 to 113, and may be the same as the iron core used in a normal GPT.

  The primary winding 111 is a Y-connected winding. Each end R1, S1, T1 of the primary winding 111 is connected to the R phase, S phase, and T phase (not shown) of the non-grounded three-phase distribution line. Further, the neutral point N of the primary winding 111 is grounded. The number of turns of the primary winding 111 is, for example, “6600”.

  The secondary winding 112 transforms the voltage of the three-phase distribution line and supplies the voltage to the external device 140 (for example, a voltmeter, an overvoltage / undervoltage relay, a voltage regulator, etc.) from each end R2, S2, T2. . In addition, although the connection structure of the secondary winding 112 is not particularly limited, in this embodiment, the Y connection is used. The number of turns of the secondary winding 112 is, for example, “110”.

  The tertiary winding 113 is an open Δ-connected winding. Between the open terminals O1 and O2 of the tertiary winding 113, the burden resistor 120 and the ground voltage suppression device 130 are connected in parallel. The number of turns of the tertiary winding 113 is, for example, “110”.

  The burden resistor 120 is a resistance element for stabilizing the measurement potential. As will be described later, when the potential of the three-phase distribution line rises abnormally, the terminal voltage of the burden resistor 120 rises according to the potential. When the GPT 100 is installed in a substation, the resistance value of the burden resistor 120 is generally preferably 36 to 40 ohms, but in this embodiment, it is 36 ohms.

  The ground voltage suppression device 130 includes a discharge gap 131 and a voltage control resistor 132. The discharge gap 131 is used as a discharge circuit of the present invention, and one end is connected to the open terminal O1. The voltage control resistor 132 is provided between the other end of the discharge gap 131 and the open terminal O2. In order to prevent destruction of an arrester (lightning arrester) or the like due to iron resonance, it is desirable to set the energization start voltage of the discharge gap 131 to a peak value of 290 volts to 500 volts, and the resistance value of the voltage control resistor 132 is It is desirable to be 2 ohms or more and 8 ohms or less. In this embodiment, a discharge gap (product number Y20-425-C, manufactured by Sankosha Co., Ltd.) having an energization start voltage of 425 volts was used as the discharge gap 131. In this embodiment, the voltage control resistor 132 is configured by connecting five resistance elements (GRZG1B 120 1RO K, manufactured by Nippon Resistor Mfg. Co., Ltd.) in series of 180 watts and 1 ohm.

  FIG. 2A shows an equivalent circuit of the GPT 100 shown in FIG.

  In FIG. 2A, AC power supplies 211 to 213 and capacitances 221 to 223 correspond to the distribution voltage and capacitance of each wire constituting the three-phase distribution line. That is, the AC power supply 211 and the electrostatic capacity 221 correspond to any one electric wire in the distribution line, the AC power supply 212 and the electrostatic capacity 222 correspond to another one electric wire in the distribution line, and The AC power supply 213 and the electrostatic capacity 223 correspond to the last one electric wire in the distribution line.

The burden resistance 230 corresponds to the burden resistance 120 in FIG. In FIG. 1, the turn ratio between the primary winding and the tertiary winding is 6600: 110 (= 60: 1), and the generated voltage of the open Δ is tripled. Therefore, in the equivalent circuit of FIG. The resistance value of the burden resistance 230 is (60/3) ² = 400 times that of the burden resistance 120, that is, 14.4 kilohms.

  The discharge gap 241 corresponds to the discharge gap 131 in FIG. The energization start voltage of the discharge gap 241 is 20 times that of the discharge gap 131, that is, 8.5 kilovolts.

  The voltage control resistor 242 corresponds to the voltage control resistor 132 in FIG. The resistance value of the voltage control resistor 242 is 400 times that of the voltage control resistor 132, that is, 2 kilohms, for the same reason as that of the burden resistor 230.

  FIG. 2B is a circuit diagram illustrating another configuration example of the ground voltage suppression device. 2B, the same reference numerals as those in FIG. 1 denote the same elements as those in FIG.

  The discharge circuit 250 in FIG. 2B includes a bidirectional thyristor (ie, triac) 260 and Zener diode circuits 270 and 280.

  In the bidirectional thyristor 260, one main electrode is connected to the open terminal O1, and the other main electrode is connected to the voltage control resistor 132.

  The Zener diode circuit 270 has one or more stages of Zener diodes (in this embodiment, three stages of Zener diodes 271, 272, and 273) connected in series. The anode of the first stage Zener diode 271 is connected to the gate of the bidirectional thyristor 260.

  The Zener diode circuit 280 has one or more stages of Zener diodes (in this embodiment, three stages of Zener diodes 281, 282, and 283) connected in series. The anode of the Zener diode 281 is connected to the anode of the Zener diode 273. Further, the anode of the Zener diode 283 is connected to the open terminal O1.

  In the discharge circuit 250 having such a configuration, when the open terminal O1 is at a positive potential, the Zener diodes 271, 272, and 273 are connected in the forward direction, and the Zener diodes 281, 282, and 283 are connected in the reverse direction. For this reason, when the potential of the open terminal O1 rises and the potential difference between both ends of the Zener diodes 281, 282, 283 exceeds a predetermined threshold value, the gate potential of the bidirectional thyristor 260 rises, thereby causing the bidirectional thyristor. 260 is energized.

  On the other hand, when the open terminal O1 has a negative potential, the Zener diodes 271, 272, and 273 are connected in the reverse direction, and the Zener diodes 281, 282, and 283 are connected in the forward direction. For this reason, when the potential of the open terminal O1 falls and the potential difference between both ends of the Zener diodes 271, 272, and 273 exceeds a predetermined threshold value, the gate potential of the bidirectional thyristor 260 falls, thereby causing the bidirectional thyristor. 260 is energized.

  As described above, in the discharge circuit 250 of FIG. 2B as well, like the discharge gap 131, energization can be performed only when the inter-terminal voltage exceeds a predetermined value.

  Here, the discharge gap and the thyristor circuit are shown as an example of the discharge circuit, but the voltage between the open terminals O1 and O2 may be used in other circuits (for example, a circuit using a semiconductor element other than the thyristor). Any circuit that starts energization when the (peak value) exceeds a predetermined value can be used as the discharge circuit of this embodiment.

  FIG. 3 shows an external configuration of the GPT 100 according to this embodiment.

  As shown in FIG. 3, the bottom surface 301, the front surface 304, and the back surface 305 of the GPT 100 are covered with a phenol resin substrate, and the two side surfaces 302, 303 and the top surface 306 are covered with punching metal having good air permeability. A terminal block 307 is provided on the front surface 304. In this terminal block, the potentials of the open terminals O1 and O2 of the tertiary winding 113 are taken out and used to detect the occurrence of abnormality.

  Hereinafter, the operation principle of the GPT 100 according to this embodiment will be described with reference to FIG.

  As described above, the case where the three-phase distribution line is normal (that is, when no ground fault or electric leakage occurs) will be described.

  In this case, the R-phase, S-phase, and T-phase voltages (corresponding to the output voltages of the AC power supplies 211 to 213 in FIG. 2A) of the three-phase distribution lines are shifted from each other by 1/3 period. For this reason, since the sum of these voltages is zero volts, the potential at the neutral point N is also zero volts. Therefore, since the voltage applied to the discharge gap 241 is also zero volts, the discharge gap is not energized. As a result, the resistance element connected between the neutral point N and the ground is only the burden resistor 230, and thus the resistance value between the neutral point N and the ground is 14.4 kilohms. Further, since the potential at the neutral point N is zero volts, no current flows between the neutral point N and the ground, and the voltage across the load resistor 230 is zero volts.

  Subsequently, a case where one of the three distribution lines constituting the three-phase distribution line is completely grounded (that is, a ground fault not accompanied by iron resonance) will be described.

  In this case, the sum of the R-phase, S-phase, and T-phase voltages of the three-phase distribution line is not zero volts, and therefore the potential at the neutral point N also increases. In the case of a normal Japanese three-phase distribution line (the potential of each distribution line is 6600 volts), if one distribution line is completely grounded, the potential at the neutral point N is 3800 volts in terms of effective value and about 5400 in terms of peak value. Bolt (3800 × √2). At this time, the discharge gap 241 (energization start voltage 8.5 kilovolts) is not energized. For this reason, discharge is performed from the neutral point N to the ground only through the burden resistor 230 (resistance value: 14.4 kOhm).

  Next, consider the case where iron resonance occurs in a three-phase distribution line.

  As described above, iron resonance may occur in the three-phase distribution line due to a failure of another transformer (for example, a pole transformer) connected to the three-phase distribution line (see FIG. 8). When iron resonance occurs, the ground potential of each phase of the three-phase distribution line is 10 kilovolts or more as described above. Thereby, in GPT100, the peak value of the neutral point N becomes 10 kilovolts or more. In this case, the discharge gap 241 is energized because the applied voltage exceeds the energization start voltage (8.5 kilovolts). Therefore, the resistance value between the neutral point N and the ground is a combined resistance (about 1.75 kilohms) of the burden resistors 230 and 242. Discharge is performed from the neutral point N to the ground through this combined resistor.

  As described above, in the GPT 100 according to this embodiment, in the case of a ground fault without iron resonance or the like (that is, when the peak value of the neutral point N is less than 8.5 kilovolts), the neutral point N and the ground When the discharge resistance is large (14.4 kilohms) and a ground fault involving iron resonance occurs (ie, when the peak value of the neutral point N is 8.5 kilovolts or more), the neutral point N Discharge resistance between the ground and the ground becomes small (about 1.75 kilohms). Therefore, when the potential at the neutral point N increases abnormally due to the occurrence of iron resonance or the like, the discharge from the neutral point N to the ground is quickly performed.

  The inventor of the present invention reproduced the iron resonance using the simulated distribution line, and compared the characteristics of the conventional GPT800 (see FIG. 8) and the GPT100 according to this embodiment.

4 and 5 show the characteristics of the conventional GPT 800. FIG. 4A shows the R-phase potential of the secondary winding 812, FIG. 4B shows the S-phase potential of the secondary winding 812, and FIG. 5C shows the T-phase potential of the secondary winding 812, FIG. 5A shows the potential at the neutral point N (V ₀ ), and FIG. 5B shows the flow from the neutral point N of the primary winding 811 to the ground. Current. 6 and 7 show the characteristics of the GPT 100 according to this embodiment. FIG. 6A shows the R-phase potential of the secondary winding 112, and FIG. 6B shows the S phase of the secondary winding 112. FIG. 6C shows the T-phase potential of the secondary winding 112, FIG. 7A shows the potential (V ₀ ) at the neutral point N (see FIG. 1) of the primary winding 111, and FIG. ) Is a current flowing from the neutral point N of the primary winding 111 to the ground.

  As can be seen from FIGS. 4 and 5, in the conventional GPT 800, when iron resonance occurs, the peak value of the secondary winding rises to 10 to 15 kilovolts and does not converge. Thereby, the external device 830 (see FIG. 8) and the like are easily damaged.

  On the other hand, as can be seen from FIGS. 6 and 7, in the GPT 100 according to this embodiment, the value of the current flowing from the primary winding to the ground when the crest value at the neutral point N exceeds 8.5 kilovolts. Increases rapidly (see FIG. 7B), the potential at the neutral point N decreases (see FIG. 7A), and the iron resonance converges.

  As described above, according to this embodiment, the resistance value between the neutral point N and the ground can be switched according to the amount of increase in the potential of the neutral point N, so that it is connected to the three-phase distribution line. There is little possibility of causing damage to various devices and distribution lines themselves.

  In addition, the GPT 100 according to this embodiment is very inexpensive because it is only necessary to add the ground voltage suppression device 130 to the existing GPT.

  As a method for promoting discharge from the neutral point N to the ground, it is conceivable to reduce the resistance value of the burden resistor 230 (see FIG. 2A) without providing the ground voltage suppression device 130. However, when the resistance value of the burden resistor 230 is lowered, the neutral point N is changed from the neutral point N to the ground in the case where the potential at the neutral point N slightly increases during normal operation or in the case of a ground fault without iron resonance. The flowing current will increase. For this reason, since it becomes necessary to enlarge the burden capacity of GPT, it is not realistic. On the other hand, according to this embodiment, since it is not necessary to increase the burden capacity of GPT, it is inexpensive.

It is a circuit diagram which shows the circuit structure of GPT which concerns on embodiment. (A) is a circuit diagram which shows the equivalent circuit of FIG. 1, (B) is a circuit diagram which shows the other example of a ground voltage suppression apparatus. It is a perspective view which shows the external appearance structure of GPT which concerns on embodiment. It is a graph which shows the characteristic of conventional GPT. It is a graph which shows the characteristic of conventional GPT. It is a graph which shows the characteristic of GPT which concerns on embodiment. It is a graph which shows the characteristic of GPT which concerns on embodiment. It is a circuit diagram which shows notionally the structure of the conventional GPT. It is a conceptual diagram for demonstrating an iron resonance phenomenon.

Explanation of symbols

100 GPT
DESCRIPTION OF SYMBOLS 110 Iron core 111 Primary winding 112 Secondary winding 113 Tertiary winding 120,230 Burden resistance 130 Ground voltage suppression device 131,241 Discharge gap 132,242 Voltage control resistance 211-213 AC power supply 221-223 Capacitance 250 Discharge circuit 260 Bidirectional thyristor 270,280 Zener diode circuit 271-273, 281-283 Zener diode 301-303 Phenolic resin substrate 304-306 Punching metal 307 Terminal block

Claims (4)

A primary winding of Y connection connected to a non-grounded three-phase distribution line and having a neutral point grounded;
A secondary winding that transforms and outputs the three-phase voltage applied to the primary winding to another device;
A tertiary winding with an open Δ connection,
A burden resistance for measuring the potential of the neutral point, connecting between the open terminals of the tertiary winding;
A GPT addition type ground voltage suppression device connected between the open terminals of the GPT in parallel with the burden resistor,
A discharge circuit that starts energization when the voltage between the open terminals exceeds the energization start voltage ; and
A voltage controlled resistor connected in series to the discharge circuit;
Equipped with a,
The energization start voltage, GPT addition type ground voltage suppression device according to claim der Rukoto 290 volts to 500 volts at a peak value. The GPT-added ground voltage suppression device according to claim 1, wherein the discharge circuit includes a discharge gap that starts energization when a voltage between terminals exceeds the energization start voltage . The GPT-added ground voltage suppression device according to claim 1, wherein the discharge circuit includes a thyristor circuit that starts energization when a voltage between terminals exceeds the energization start voltage . The resistance value of the said voltage control resistance is 2 ohms or more and 8 ohms or less, The GPT addition type ground voltage suppression apparatus in any one of Claims 1-3 characterized by the above-mentioned.

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