JP2003188005A - Resistive element and voltage sensor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resistive element and a voltage sensor using the resistive element, of high mass-productivity, excellent temperature characteristics, with no degradation in measurement precision depending on changes of surface resistance caused by contamination, moisture absorption, etc., to measure the voltage of a high-voltage main circuit of a high-voltage distribution panel, etc. <P>SOLUTION: The resistive element is manufactured by integrally molding a high-voltage resistor showing a negative temperature coefficient, a terminal electrically connected to both ends of the high-voltage resistor, and a guard electrode provided around one of the terminals, using a thermosetting resin. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance element for measuring the voltage of a high voltage main circuit such as a high voltage switchboard and a voltage sensor using the resistance element.

[0002]

2. Description of the Related Art Since a conventional wattmeter has a heavy load, a transformer for an instrument has been used to measure the voltage of a high-voltage main circuit such as a high-voltage switchboard. With the widespread use, a voltage sensor using a resistance element or the like has come to be used.

FIG. 9 is a sectional view showing the structure of a resistance element 110 used in a conventional voltage sensor disclosed in Japanese Patent Laid-Open No. 11-283801, in which 111 is a resistor, 112 is an insulator, and 113 is. Indicates an electrode. Resistor 11
1 is a thermoplastic polymer material such as polypropylene or polybutyl terephthalate. A conductive material, for example, conductive carbon or metal powder is uniformly mixed and stirred, and then the thermoplastic polymer material is melted and integrally molded into a cylindrical shape. Constitute. An electrode 11 made of Al, Ag, or Cu is formed on the entire one end face in the axial direction.
3 is provided, and an insulator 112 made of synthetic resin is stuffed around the entire side surface of the resistor 111 and the peripheral edge of the other end surface in the axial direction to form the resistor element 110. The voltage to be measured is obtained by inserting an impedance element between the other end of the resistance element 110 in which the electrode 113 is connected to the conductor to be measured and the ground, measuring the voltage at both ends, and calculating the voltage division ratio. The temperature correction of the resistance value uses a means for monitoring the temperature of the resistor 111 and performing a correction calculation from the relationship between the temperature and the resistance value measured in advance.

[0004]

The conventional voltage sensor has the following problems.
Since it is necessary to manufacture a dedicated resistance element, mass productivity is low, and a correction calculation circuit has to be provided for temperature-correcting the resistance value of the resistance element. Further, when the surface of the insulator of the resistance element is contaminated and absorbs moisture to reduce the surface resistance, there is a problem such as a measurement error of the voltage sensor.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a voltage sensor using a resistance element having high mass productivity and excellent temperature characteristics. Furthermore, it is an object of the present invention to provide a voltage sensor using a resistance element whose measurement accuracy does not decrease with respect to a change in surface resistance due to contamination, moisture absorption, or the like.

[0006]

The resistance element according to the first aspect of the present invention is a high voltage resistor having a negative temperature coefficient molded by a thermosetting resin.

The resistance element according to claim 2 of the present invention is the resistance element according to claim 1, wherein a resistor of 20 MΩ to 100 MΩ is used as the high voltage resistor exhibiting a negative temperature coefficient. It was what I had.

The resistance element according to claim 3 of the present invention is the resistance element according to claim 1 or 2, wherein the thermosetting resin is a thermosetting resin containing an inorganic filler. It is the one using the thing.

The resistance element according to claim 4 of the present invention is the resistance element according to any one of claims 1 to 3, wherein a high-voltage resistor and an electrical connection between both ends of this high-voltage resistor are provided. While integrally molding the terminals that are electrically connected,
A guard electrode is provided around one of the terminals.

The resistance element according to a fifth aspect of the present invention is the resistance element according to the fourth aspect, in which a surge arrester is provided between a terminal provided with a guard electrode on the periphery and the guard electrode. Is.

The voltage sensor according to a sixth aspect of the present invention uses the resistance element according to any one of the first to fifth aspects as a voltage dividing resistor for applying a high voltage.

According to a seventh aspect of the present invention, in the voltage sensor of the first aspect, when a high voltage is applied to the resistance element, the current flowing through the resistance element is converted into current-voltage. The circuit measures the high voltage by converting it into a voltage.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. 1 is a sectional view of a resistance element according to a first embodiment of the present invention. In FIG. 1, 1 is a high voltage resistor, 2 and 3 are terminals, and the high voltage resistor 1 and the terminals 2 and 3 are electrically connected by, for example, soldering. Hereinafter, in the present invention, the terminal 2 connected to the high voltage side of the main circuit of the high voltage switchboard is referred to as a high voltage terminal,
The terminal 3 connected to the signal processing circuit of the resistance element is called a low voltage terminal. Pre-connected high voltage resistor 1, high voltage terminal 2,
The low voltage terminal 3 is set in a mold and integrally molded with the thermosetting resin 4. 2 to 4 show the temperature characteristics of a high voltage resistor 1, for example, a GS type high voltage high resistance thick film resistor manufactured by Tama Electric Industry Co., Ltd., showing only the high voltage resistor 1 (before molding).
2 is 20 MΩ, FIG. 3 is 50 MΩ, and FIG.
Is a characteristic of 100 MΩ.

As shown in FIGS. 2 to 4, it can be seen that the temperature characteristics differ depending on the resistance value. Generally, the temperature characteristic of a resistor having a low resistance value (20 MΩ or less) is a metal property,
When the temperature rises, the resistance value increases and shows a positive temperature coefficient, and when the resistance value rises (20 MΩ or more), it is a property of the insulator, and when the temperature rises, the resistance value tends to decrease. 2-4 high voltage resistor 1 (before molding)
This tendency was recognized in the temperature characteristics of. Epoxy resin (Nagase Chemtex Co., Ltd .: XNR4153 / XNH4)
153) and mold at 80 ℃ for 16 hours + 130 ℃
The characteristics after heat curing for 16 hours (FIGS. 2 to 4) have a temperature coefficient of 30 ppm to 50 ppm reduced in each resistance value as compared with the high voltage resistor before molding (10
The resistance value decreases at a rate of 0.3% to 0.5% with respect to a temperature change of 0 ° C.). This is a decrease in the temperature coefficient resulting from the compressive strain applied to the high-voltage resistor 1 due to the thermal contraction of the epoxy resin, and as shown in FIGS. 2 to 4, the glass transition temperature (Tg) of the epoxy resin This phenomenon appears at low temperatures. 50 MΩ (FIG. 3) and 100 MΩ (FIG. 4), which show a negative temperature coefficient only with the high-voltage resistor 1, are molded with epoxy resin to obtain a resistance element having a smaller temperature coefficient than the high-voltage resistor 1 alone. You can

The voltage measuring accuracy of the resistance element used in the high voltage switchboard is required to be within ± 1% including the absolute accuracy (accuracy at 20 ° C.) and the temperature coefficient (range of 5 ° C. to 95 ° C.). The high-voltage resistor 1 having an absolute accuracy of ± 0.5% can be obtained at a relatively low cost, for example, the GS type manufactured by Tama Electric Co., Ltd. can be used, but the temperature coefficient may be large depending on the resistance value. On the other hand, a resistor having a small temperature coefficient is expensive. However, the high voltage resistor 1 has a resistance value of 20 MΩ.
By using a GS type resistor of ˜100 MΩ and molding with an epoxy resin, the temperature change of the resistance value at 5 ° C. to 95 ° C. can be kept within ± 0.5%. Further, as shown in FIG. 3, when the resistance value is 50 MΩ, it is possible to manufacture one having a very small temperature coefficient after molding, which is the optimum resistance value for integrally molding with epoxy resin to obtain a resistance element. .

The thermosetting resin 4 may be any of silicone resin, polyurethane resin and polyester resin other than epoxy resin. Further, the thermosetting resin may contain any one of silicon dioxide, alumina, aluminum hydroxide, calcium carbonate, glass short fibers (also generally called glass chop), or a mixture thereof as an inorganic filler. By adjusting the compounding ratio of the thermosetting resin and the inorganic filler to change the compressive strain applied to the high voltage resistor 1 after thermosetting, the temperature coefficient of the high voltage resistor 1 after molding can be freely set. It is possible to obtain a resistance element having an optimum temperature coefficient.

Embodiment 2. FIG. 5 is a sectional view of a resistance element according to the second embodiment of the present invention. The same or corresponding parts as in FIG. 1 are designated by the same reference numerals. In FIG. 5, 5
Is a guard electrode. The guard electrode 5 is provided so as to surround the outer circumference of the low-voltage terminal 3, and is integrally molded with the high-voltage resistor 1, the high-voltage terminal 2 and the low-voltage terminal 3 with a thermosetting resin 4.

Normally, the resistance element used in the high-voltage switchboard in the air is not cut off from the outside air, and it is polluted by the outside air (salt damage in the land adjacent to the coast, nitrogen oxides in exhaust gas, sulfur oxides in factory flue gas, etc.). Due to the effects of dust and humidity, the insulation resistance of the mold surface may decrease after long-term use. This decrease in insulation resistance causes an error in the resistance value of the resistance element. This embodiment is for preventing the error, and the low voltage terminal 3
By shielding the low voltage terminal 3 by providing the guard electrode 5 around the area, the influence of the surface resistance can be eliminated and the resistance value error can be reduced.

Although the case where the guard electrode 5 is provided separately from the low voltage terminal 3 has been described in the present embodiment, the same effect can be obtained by using a commercially available integrated coaxial terminal as the low voltage terminal.

Embodiment 3. FIG. 6 is a sectional view of a resistance element according to a third embodiment of the present invention. The same or corresponding parts as in FIG. 5 are designated by the same reference numerals. In FIG. 6, 6
Is a surge arrester. The surge arrester 6 is electrically connected between the low voltage terminal 3 and the guard electrode 5 and is integrally molded with the thermosetting resin 4.

Since the high-voltage terminal 2 of the resistance element is connected to the high voltage side of the main circuit of the high-voltage switchboard, impulse surge voltage due to lightning, breaker in the switchboard, and switching surge voltage from the disconnector intrude into the resistance element. There is. On the other hand, since the low voltage terminal 3 is connected to the signal processing circuit of the resistance element, it is necessary to protect the surge voltage. If a surge arrester 6 such as an NV type varistor manufactured by Tama Electric Industry Co., Ltd. is used between the low voltage terminal 3 and the guard electrode 5, the voltage between the low voltage terminal 3 and the guard electrode 5 is limited and the signal processing circuit is protected. It will be possible.

In this embodiment, the case where the surge arrester 6 is provided in the resistance element in which the guard electrode 5 and the low voltage terminal 3 are separate has been described, but a commercially available integrated coaxial terminal is used as the low voltage terminal and the coaxial terminal is used. Even if a surge arrester is provided between the central conductor and the outer conductor, the same effect can be obtained.

Fourth Embodiment FIG. 7 is a configuration diagram of a voltage sensor using a resistance element according to the fourth embodiment of the present invention. The same or corresponding parts as in FIG. 5 are designated by the same reference numerals. In FIG. 7, 7 is a shield wire (coaxial cable),
Reference numeral 8 is an operational amplifier (OP amplifier), 9 is a feedback resistor, and the OP amplifier 8 and the feedback resistor 9 form a current-voltage (IV) conversion circuit 10. The center conductor at one end of the shield wire is connected to the low voltage terminal 3, the sheath is connected to the guard electrode 5, and the center conductor at the other end of the shield wire is O.
The sheath is connected to the inverse input (-) of the P amplifier 8 and the ground of the OP amplifier 8.

As described in the prior art, an impedance element is inserted between the low voltage terminal 3 and ground, and the voltage across the voltage is measured to measure the voltage division ratio. There is a method to ask from. If the resistance element described in the first to third embodiments is used as the voltage dividing resistance for applying a high voltage, it is possible to perform a measurement that is superior to the conventional technique in temperature characteristics and is less affected by the surface resistance of the resistance element. However, in this method, in addition to the impedance element, a floating impedance of a signal line from the impedance element to the signal processing circuit, for example, is included in the configuration of the component, which causes an error in voltage division with the resistance element. In the present embodiment, since the current flowing through the resistance element is converted into a voltage by the IV conversion circuit 10 including the OP amplifier 8 and the feedback resistor 9 and measured, the input voltage of the OP amplifier 8 (inverse input (- )
(The voltage between the ground and the ground) becomes almost 0 (the amplification factor of the OP amplifier 8 is 100 dB or more, so if the feedback circuit shown in FIG. 7 is configured, the input voltage is 1/10 of the output voltage.
It becomes 10,000 and can be regarded as almost 0). Therefore, the floating impedance of the shield wire 7 can be ignored, and only the current flowing through the resistance element can be accurately measured.

The OP amplifier 8 is, for example, AD741 manufactured by Analog Devices Co., Ltd., and the feedback resistor 9 is, for example, a JF type metal film resistor manufactured by Tama Electric Co., Ltd. (absolute accuracy ± 0.1%, temperature). Coefficient ± 10ppm)
When the IV conversion circuit 10 is configured by using, the inexpensive and accurate signal processing circuit can be configured. When the accuracy of voltage measurement was measured using this signal processing circuit, the accuracy within ± 1% required for the voltage sensor of the high-voltage switchboard was obtained.

In this embodiment, as the current-voltage conversion circuit, the circuit composed of the OP amplifier 8 and the feedback resistor 9 has been described. However, if only the current flowing through the resistance element can be accurately measured, what kind of current It may be a voltage conversion circuit. Although the resistance element according to the second embodiment is used in the present embodiment, the resistance element according to another embodiment may be used.

Embodiment 5. FIG. 8 is a configuration diagram of a voltage sensor using a resistance element according to the fifth embodiment of the present invention. The same or corresponding parts as in FIG. 7 are designated by the same reference numerals. In FIG. 8, 11 is a surge protection element, for example, a metal oxide varistor or a clamping diode, which is connected between the inverse input (-) of the OP amplifier 8 and the ground.

As described in the third embodiment, the surge protection element is used because the impulse surge voltage due to lightning, the circuit breaker in the switchboard, the switching surge voltage from the disconnector, etc. enter the resistance element used in the high voltage switchboard. By limiting the input voltage (voltage between the inverse input (-) and the ground) of the OP amplifier 8 by using 11, it is possible to protect the signal processing circuit from the aforementioned surge voltage. In addition, the fourth embodiment
As described above, since the input voltage of the OP amplifier 8 is almost 0, even if the surge protection element 11 is inserted in the input of the OP amplifier 8, there is almost no measurement error.

If, for example, an NV type varistor manufactured by Tama Electric Industry Co., Ltd. is used as the surge protection element 11, the input voltage of the OP amplifier 8 is limited and the IV conversion circuit 10 can be protected. As the surge protection element 11, for example, two diodes MC-301 manufactured by Mitsubishi Electric Corp. are connected in parallel so that their polarities are opposite to each other so that they are clamped by a drop voltage of a forward current. If it is connected between the inverse input (-) of the OP amplifier 8 and the ground, sufficient protection becomes possible.

Even if the resistance element according to the third embodiment is used to form the voltage sensor according to the fourth embodiment, the same effect can be obtained.

[0031]

According to the resistance element of the first aspect of the present invention, since the high voltage resistor exhibiting a negative temperature coefficient is molded with the thermosetting resin, the temperature coefficient is smaller than that of only the high voltage resistor. A resistance element can be obtained.

According to the second aspect of the present invention, the resistance element according to the second aspect is a high voltage resistor having a negative temperature coefficient.
Since a resistor of 0 MΩ to 100 MΩ was used, 5 ° C to 95
The temperature change of the resistance value at ℃ can be kept within ± 0.5%.

According to the third aspect of the present invention, since the thermosetting resin containing the inorganic filler is used as the thermosetting resin, the thermosetting resin and the inorganic filling material are used. By adjusting the compounding ratio of the materials, it is possible to obtain a resistance element having an optimum temperature coefficient.

According to a fourth aspect of the present invention, the high voltage resistor and the terminals electrically connected to both ends of the high voltage resistor are integrally molded, and Since the guard electrode is provided around one of the terminals, it is possible to reduce the error in the resistance value of the resistance element due to the decrease in the insulation resistance on the mold surface.

Further, according to the resistance element of the fifth aspect of the present invention, since the surge arrester is provided between the terminal provided with the guard electrode on the periphery and the guard electrode, the voltage between the low voltage terminal and the guard electrode is limited. As a result, the signal processing circuit can be protected.

According to the voltage sensor of the sixth aspect of the present invention, the resistive element according to any one of the first to fifth aspects is used as the voltage dividing resistor for applying a high voltage.
Highly accurate measurement with little influence of temperature change can be performed.

According to the voltage sensor of the seventh aspect of the present invention, when a high voltage is applied to the resistance element, the current flowing through the resistance element is converted into a voltage by the current-voltage conversion circuit to generate the high voltage. Since the measurement is performed, the floating impedance of the signal line can be ignored, and the measurement can be performed with higher accuracy.

[Brief description of drawings]

FIG. 1 is a sectional view of a resistance element according to a first embodiment of the present invention.

FIG. 2 is a temperature characteristic diagram of a 20 MΩ high voltage resistor before and after molding.

FIG. 3 is a temperature characteristic diagram of a high voltage resistor of 50 MΩ before and after molding.

FIG. 4 is a temperature characteristic diagram of a 100 MΩ high voltage resistor before and after molding.

FIG. 5 is a sectional view of a resistance element according to a second embodiment of the present invention.

FIG. 6 is a sectional view of a resistance element according to a third embodiment of the present invention.

FIG. 7 is a configuration diagram of a voltage sensor using a resistance element according to a fourth embodiment of the present invention.

FIG. 8 is a configuration diagram of a voltage sensor using a resistance element according to a fifth embodiment of the present invention.

FIG. 9 is a sectional view of a conventional resistance element.

[Explanation of symbols]

1 high voltage resistor, 2 terminal, 3 terminal, 4 thermosetting resin, 5 guard electrode, 6 surge arrester, 10 current-voltage conversion circuit.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tadahiro Yoshida             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. F-term (reference) 2G025 AA02 AA09 AB05 AC04                 2G035 AA03 AA06 AB08 AC01 AC03                       AD10 AD20 AD54                 5E028 BB01 BB15 EA13                 5E034 BA09 BB01 BB04 BC01 DA02                       DE05 GA04

Claims (7)

[Claims] 1. A resistance element characterized in that a high voltage resistor having a negative temperature coefficient is molded with a thermosetting resin. 2. The resistance element according to claim 1, wherein a resistor having a resistance of 20 MΩ to 100 MΩ is used as the high voltage resistor having a negative temperature coefficient. 3. The resistance element according to claim 1 or 2, wherein a thermosetting resin containing an inorganic filler is used as the thermosetting resin. 4. A high voltage resistor and terminals electrically connected to both ends of the high voltage resistor are integrally molded, and a guard electrode is provided around one of the terminals. The resistance element according to any one of claims 1 to 3. 5. The resistance element according to claim 4, wherein a surge arrester is provided between the terminal around which a guard electrode is provided and the guard electrode. 6. A voltage sensor using the resistance element according to claim 1 as a voltage dividing resistance for applying a high voltage. 7. When a high voltage is applied to the resistance element according to claim 1, the current flowing through the resistance element is converted into a voltage by a current-voltage conversion circuit to measure the high voltage. A voltage sensor characterized in that