JPH01112169A - Optical zero-phase current detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical zero-sequence current detector for detecting zero-sequence current with high sensitivity and reliability.

[Conventional technology]

When a ground fault occurs in an ungrounded power transmission/distribution line, a weak zero-sequence current flows due to the stray capacitance of the line.

In order to detect this weak zero-sequence current, a zero-sequence current detection device is required.

Zero-phase current transformers (ZCTs) have been used as zero-phase current detection devices for conventional high-voltage ungrounded power transmission and distribution lines.

However, in some cases, such as in high-voltage overhead distribution lines, where the three-phase wires are far apart, it is difficult to use ZCT, or when the capacity is large, ZCT is used due to the large area of through conductors and interphase insulation.
may become large.

In such cases, the accuracy is 1 to 1 compared to ZCTi.
Although slightly inferior, a 3CT system using three 0CTs (current transformers) is sometimes used because of its connectivity and ease of interphase insulation.

The fifth method for measuring the zero-sequence current of a three-phase circuit with a 3CT is
There is a secondary residual circuit system shown in FIG. 6, and a tertiary zero-phase shunt system shown in FIG.

The secondary residual circuit system is generally used for applications below 400A, and as shown in FIG. 5, three-phase electric wires 21a and 21b are used.

21C, each transformer 22a, 22b, 2 each has a single core as a primary circuit and a secondary winding thereon.
2c is attached, and these parallel circuits are short-circuited by a load 23. In this scheme, the secondary zero-sequence current component appears as a current (.2) passing through the burden 23, and the magnitude of the current also
If the number of secondary windings of c is N turns, -1 of the snowstorm phase current
/N becomes. However, each transformer 22a, 22b, 2
2c is a through-type CT, and the negative side winding thereof has one turn. The number of secondary windings N is determined by the secondary positive sequence current, and since this current is normally 5A, the -order rated current is 4
In the case of 00A, it becomes N-80 turns.

For example, if the primary zero-sequence current that defines the characteristics of ZCT is 200
+++ In the case of A, the secondary zero-sequence current to2 is 200/80
= Only 2.5mA flows. - When the secondary rated current becomes larger, the secondary positive sequence current is constant at 5A, so the number of secondary turns becomes larger, and therefore the secondary zero-sequence current t
02 becomes smaller and smaller.

Therefore, when detecting a large current of 400 A or more, a three-order zero-phase shunt system shown in FIG. 6 is generally used. In this method, three-phase electric wires 31a, 31b, and 31c each have a single core as a primary circuit, and are connected to secondary windings 33a, 33b, and 33c, and tertiary windings 34a,
34b.

34C transformers 32a, 32b, and 32c are installed. And secondary windings 33a, 33b
, 33c are short-circuited at both ends to cancel the positive phase currents, and the tertiary windings 34a, 34b, 34
A load 35 is connected to the series circuit of c.

In the method shown in FIG. 6, the tertiary winding 34a is independent of the secondary winding circuit for canceling the positive phase component.

Since the zero-phase component can flow through 34b and 34c, the number of turns of the tertiary windings 34a, 34b, and 34c can be freely selected.

Therefore, if the number of turns of the tertiary windings 34a, 34b, and 34c is reduced, the tertiary zero-sequence current t. 3, it is not so small and a relatively large zero-sequence current output can be obtained. However, even if the number of turns is gradually reduced, it cannot be reduced to less than one turn, and therefore, in principle, the current cannot be amplified to more than the -blizzard phase current.

For example, if the primary zero-sequence current that defines the characteristics of ZCT is 200mA, the tertiary zero-sequence output is 200mA.
This means that it cannot be higher than A. As a countermeasure for this,
Resistor 3 for burden of tertiary windings 34a, 34b, 34c
One possible method is to view the voltage proportional to the zero-sequence current generated across the terminals of 5 as an output signal, but in order to increase this output voltage, the burden resistor must be increased and the current in the tertiary winding circuit must be increased. There must be.

For this reason, it is necessary to increase the number of turns of the tertiary windings 34a, 34b, and 34c and to increase the core size, but there is a practical limit to this.

[Problem that the invention seeks to solve]

In this way, as the −Positive phase current increases, the tertiary zero-sequence shunt method becomes very effective as a method for measuring the zero-sequence current, but the disadvantage of this method is that the tertiary winding Since current flows through the line, a secondary shunt current occurs, the current transformation ratio fluctuates, and there is a problem that accurate zero-sequence current cannot be measured.

Furthermore, when an extremely large primary zero-sequence current flows, such as in the case of a different-phase ground fault, a proportionately large current also flows in the tertiary winding, resulting in a large winding size. Furthermore, since electromagnetic force is also applied, there is a drawback that the mechanical support of the windings must also be strong.

The present invention has been made in view of such conventional problems, and an object of the present invention is to detect zero-sequence current with high sensitivity and high reliability.

[Means for solving problems]

In order to achieve this objective, the optical zero-phase current detector of the present invention has an annular iron core placed on each of the three-phase power transmission and distribution lines, and a secondary winding and a tertiary winding wound around each iron core. A transformer is provided, a resistor is connected as a load for the secondary residual circuit of these transformers, the tertiary windings of each phase are connected in series, and a voltage sensor is provided between both terminals of the series circuit to obtain a zero voltage. It is characterized by comprising means for detecting a voltage proportional to the phase current.

As this voltage sensor, by using an electro-optic crystal element, such as a Pockels element, in which the refractive index of the medium changes depending on the electric field, signal extraction that is not affected by external noise becomes possible.

[Effect]

Since the present invention has the above-described configuration, if the primary winding, which is a three-phase-order conductor, does not include a zero-phase component and the transformation ratios of the three transformers are equal, the sum of the secondary currents is zero. becomes. Therefore, in this case, no voltage is generated across the burden resistor connected to the secondary residual circuit, no voltage is induced in the tertiary winding, and the voltage sensor does not operate.

On the other hand, when a zero-sequence current flows through the primary winding of a transformer, a current proportional to the zero-sequence current flows through the secondary residual circuit of this transformer, and the burden resistor connected to both ends of this secondary residual circuit flows. , a voltage proportional to the generated zero-sequence current is generated. This voltage is amplified by the tertiary winding and output as a voltage across the voltage sensor. When the voltage sensor is constructed of a dielectric material such as an electro-optic crystal element, a voltage output can be obtained without passing a tertiary zero-sequence current to the tertiary circuit. Therefore, if you increase the number of tertiary windings, you can easily obtain a large voltage output.
Moreover, since no current flows through the tertiary winding, all the drawbacks of the tertiary zero-phase shunt method described above are eliminated. In other words, the tertiary winding can be wound with extremely thin wire that has a high resistance per unit length.
Even if it is wound many times, the size does not become large and the load can be reduced.

Therefore, the core size becomes smaller, and a compact high-sensitivity aCT method can be realized.

〔Example〕

Hereinafter, the present invention will be specifically described based on embodiments shown in the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, 1 is an optical transmitter that sends out light, 2 and 3 are optical transmission paths and optical reception paths using optical fibers, 5 is a signal processing circuit, and 6 is a display device. 7 is a switch filled with arc-extinguishing gas, and switching electrodes 7a, 7b, and 7c connected to three-phase power transmission and distribution lines are housed inside the switch. 8, 9.10 is a transformer, switch electrode 7a
, 7b, 7c, annular iron cores 8a, 9a are disposed surrounding the electrodes, respectively.

10a are provided, and these iron cores 8a, 9a, 10
a, the secondary windings 8b, 9b, 10b and the tertiary winding 3c such that the transformation ratios of the respective transformers 8, 9, 10 are equal.

9c, IOC is wound. the secondary winding 8b;
9b.

A load resistor 11 is connected in parallel to 10b, and the secondary windings 3c, 9c, and IOC are connected in series, and the terminals on both sides are connected to the electrodes of the optical voltage sensor 12, respectively. This optical voltage sensor 12 includes an electric field operated element such as a Pockels element, for example LiTa0. ,, LiN
bO3゜KDP (KN, PO,), BGO (Bi, 2
Ferroelectric materials such as Ge12o) and B50 (Bi, 2Si02o) are mainly used.

The voltage detection system using this optical voltage sensor 12 is
As shown in the figure. IA is a pulse generator, and its output pulses are converted into optical pulses by an electro-optical conversion element IB, and sent to an optical voltage sensor 12 via an optical transmission path 2 using an optical fiber.
given to. These pulse generator IA and electro-optical conversion element IB are provided within the optical transmitter 1.

The optical voltage sensor 12 includes an electric field-operated element 13 having a transparent electrode 14.14 on its end face, and a polarizer 15. ! It is composed of a /1 wavelength plate 16 and an analyzer 17. Transparent electrode 14
．． 14 is the tertiary winding 3c in FIG.

It is electrically connected to both ends of the series circuit of 9c and 10c. The optical output from the analyzer 17 is transmitted via an optical receiving path 3 using an optical fiber to an optical receiver 4 equipped with an optical-to-electrical conversion element, where it is converted into an electrical signal and sent to a signal processing circuit 5. It will be done.

Next, the operation of the block diagram in FIG. 1 will be explained. When the power transmission and distribution lines (not shown) connected to the switching electrodes 7a, 7b, 7c of the switch 7 are normally energized, the secondary windings 8b, 9b, 101 of the transformer 8.9.10 ]
Since the sum of the secondary currents induced in each becomes zero, no voltage is generated across the burden resistor 11, and the tertiary windings 3c,
9c, no voltage is generated at IOC. Therefore, the continuous light transmitted from the optical transmitter 1 to the optical transmission path 2 passes through the optical voltage sensor 12 to which no voltage is applied, and passes through the optical receiving path 2.
The signal is output from the optical receiver 4 to the optical receiver 4. The optical receiver 4 converts the optical signal into an electrical signal and outputs it to the signal processing circuit 5. The signal processing circuit 5 amplifies the manually generated electrical signal, performs signal processing, and outputs the signal to the display device 6.

FIG. 3 shows a characteristic diagram of the detection signal when the power transmission and distribution line is normally energized, and when the vertical axis is the output and the horizontal axis is the time, the detection signal has a horizontal signal characteristic.

Next, when one phase of the power transmission and distribution line has a ground fault and a zero-sequence current flows through the switching electrode 7a of the switch 7, a secondary current and A transformer 9.10 in which a secondary voltage is generated and provided on the other switching electrodes 7b, 7c
The same secondary voltage is applied to each of the secondary windings 9b, 10b, and a detection voltage is induced in the tertiary windings 8c, 9c, 10c of the respective transformers 8, 9.10. Tertiary windings 8c, 9c of these transformers 8, 9.10.

10C are connected in series, the detected voltages are added and applied to the electrodes of the optical voltage sensor 12. As a result, the light transmitted through the optical voltage sensor 12 is polarized, and a polarized optical signal is transmitted from the optical receiving path 3 to the optical receiver 4.

The optical receiver 4 converts the optical signal into an electrical signal and outputs it to the signal processing circuit 5. The signal processing circuit 5 amplifies the manually generated electrical signal, performs signal processing, and outputs it to the display device 6.

Figure 4 shows the characteristics of the detection signal when a zero-sequence current flows when a ground fault occurs.If the vertical axis is the output and the horizontal axis is the time, the detection signal will be as shown in the figure. Displayed as a sine wave waveform.

In this embodiment, a ring-shaped iron core is arranged around the switching electrode of the switch, but a current transformer may be arranged around the power transmission and distribution line, and as a voltage sensor,
It is not limited to an optical voltage sensor using an electro-optic crystal, but any type of voltage sensor with high input impedance may be used.

〔Effect of the invention〕

As explained above, in the present invention, a transformer is provided with an annular core arranged around a primary conductor that is a three-phase power transmission and distribution line, and a secondary winding and a tertiary winding are wound around this annular core. A burden resistor is connected to the secondary residual circuit of these transformers, the tertiary winding is connected in series, and the terminals on both sides are connected to the electrodes of a voltage sensor to detect weak voltages on ungrounded power transmission and distribution lines. I am trying to measure the zero-sequence current. This eliminates the drawbacks of the conventional tertiary zero-phase shunt system, such as increased size due to passing current through the tertiary winding, irregularities in the current transformation ratio, and low tertiary output current or output voltage. This problem can be easily resolved, making it possible to create a compact current transformer with a small core size and winding diameter, allowing accurate zero-sequence current measurement. Furthermore, by using an electro-optic crystal element as a voltage sensor, measurements can be made without being grounded, so there is no malfunction due to stray current flowing through a multi-point grounded circuit, and it is not affected by external noise, improving reliability. It becomes possible to build a sophisticated system.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing the structure of the optical voltage sensor, Fig. 3 is a characteristic diagram of the detection signal when the power transmission and distribution line is normally energized, and Fig. Figure 4 is a characteristic diagram of the detection signal when a zero-sequence current flows when a ground fault occurs, Figure 5 is a connection diagram of the conventional secondary residual circuit method, and Figure 6 is a connection diagram of the three-flight shunt method. It is a diagram. 1: Optical transmitter, 1-eight pulse generator IB: Electrical-optical conversion element 2: Optical transmission path 3: Optical reception path 4
: Optical receiver 5: Signal processing circuit 6: Display device 7: Switch 7a, 7b, 7c: Switching electrode 8.9, 1.0: Transformer 8a, 9a, lQ
a+ iron core 8b, 9b, lQb: secondary winding 8c,
9c, 10c: Tertiary winding 11: Load resistance
12: Photovoltage sensor 13; Electric field operated element 14: Transparent electrode 15' polarizer 16; Z wavelength plate 17;
Analyzer patent applicant Anyo Electric Manufacturing Co., Ltd. Agent
Masu Kobori (and 2 others) Publication g Publication g -5/

Claims (1)

[Claims] 1. A ring-shaped iron core is arranged on each of the three-phase power transmission and distribution lines, and a transformer with a secondary winding and a tertiary winding wound around each iron core is provided, and the secondary winding of these transformers is Next, a resistor is connected as a burden on the residual circuit, and the tertiary windings of each phase are connected in series, and a voltage sensor is provided between both terminals of the series circuit to detect a voltage proportional to the zero-sequence current. An optical zero-sequence current detector characterized by: 2. The optical zero-sequence current detector according to claim 1, characterized in that an electro-optic crystal element is used as the voltage sensor.