JP4446993B2 - Electric heater for liquid - Google Patents

Description

The present invention relates to an in-liquid electric heater that can reliably detect the penetration of liquid into the vicinity of a heating element and shut off a power source.
JP-A-2005-44740

  For heating a plating solution or the like that needs to be heated to a temperature higher than that of water, an electric heater that incorporates a heating wire that is immersed in the solution and used is known (see Patent Document 1). FIG. 4 is a diagram for explaining the submerged electric heater device disclosed in Patent Document 1. FIG. As shown in the figure, the submerged heater is installed and used in a liquid tank. The liquid level sensor detects the liquid level, and the liquid temperature sensor detects the liquid temperature. The control unit controls the power source of the submerged heater based on the temperature detected by the liquid temperature sensor.

  FIG. 5 is a diagram showing an example of a submerged heater that has been conventionally used. When the submerged heater is installed in the liquid tank in a proper use state and operating under proper conditions, the heating element operates at a temperature of about 600 to 800 ° C., and the outer tube surface temperature is 60 to When used in a liquid at 100 ° C., the temperature near the inner side of the outer tube is stable at 200 to 300 ° C. Such a submerged heater is provided with a leakage detection sensor for detecting that the liquid has permeated inside and shutting off the power supply. As this sensor, a ground metal wire for detecting the leakage current is placed near the heat insulating material, and the heat insulating material uses the fact that the leakage current increases due to the insulation deterioration between the power supply conductor and the ground metal wire due to the penetration of the liquid. The earth leakage breaker was shut off at a current value above a certain value.

  However, in this method, although the penetration of the liquid near the conductor holding part can be detected, there is a case where the leakage detection sensor does not function when the liquid penetrates only in the vicinity of the heating element.

  An object of the present invention is to solve such problems, and to reliably detect not only the penetration of liquid into the vicinity of the conductor holding part but also the penetration of liquid into the vicinity of the heating element, and shut off the power supply. Yes.

  The submerged electric heater according to the present invention is a heat generating body constituted by a heat-resistant insulating bobbin and a heating wire wound thereon, an outer tube for housing the heating element, and led into the outer tube. A conductor holding portion made of a heat insulating material that holds the conductor. The outer tube is made of a non-metallic material. The bobbin has a generally cylindrical shape having a central through hole, and a metal wire is disposed and fixed in the central through hole. The entire metal wire functions as a sensor that detects leakage current, and when the liquid enters the outer tube, the leakage current that flows through the metal wire is detected to shut off the power supply.

  According to the present invention, since the metal wire is disposed so as to penetrate the bobbin in the central portion of the bobbin constituting the heating element, the liquid penetrates into either the heating element or the conductor holding part in which the heat insulating material is disposed. Even if the insulation is reduced, the leakage breaker can be tripped by detecting the leakage current. If the power supply is connected to the heating wire, the current from the power supply immediately flows to the ground metal wire and the earth leakage breaker inserted in the ground circuit through the ground terminal can be operated to shut off the heater power supply. Can be prevented.

  Hereinafter, the present invention will be described based on examples. FIG. 1 is an overall configuration diagram of an in-liquid electric heater embodying the present invention. The non-metallic outer tube has a long cylindrical shape to widen the contact area with the liquid and prevent the liquid and the heating element from coming into direct contact, and its tip is closed. Has the shape. As the outer tube, a non-metallic material such as quartz glass or Teflon (registered trademark) resin is used. If the outer tube that houses the heating element is made of metal, it is possible to detect accidents due to abnormalities in the internal heating element by directly grounding the outer tube, but depending on the liquid composition, a non-metallic outer tube may be used. I have to. Thus, when the outer tube is non-metallic such as quartz glass or Teflon (registered trademark) resin, it is impossible to detect abnormality of the heating element due to liquid penetration by directly grounding the outer tube.

  The heating element is composed of a cylindrical bobbin and a heating wire such as a nichrome wire wound on the cylindrical bobbin for heating the liquid. The heating wire is wound so that a plurality of heating wires are wound around the outer periphery of the cylindrical body bobbin at intervals, and the surface of the cylindrical body is covered as a whole. A power supply wire connected to the heating wire at the bobbin entrance (outside the bobbin collar) is connected via a power supply provided outside the outer tube, a power supply cord, and a power supply connection terminal. The conductor holding part using the heat insulating material is made of a heat-resistant insulator that closes the opening of the outer tube, and holds not only the power supply conductor but also the ground conductor.

  Copper wires, etc., which are common materials for power supply conductors and ground conductors, lack long-term reliability. For example, power conductors connected to heating wires use tin-plated annealed copper wires as the conductors, and glass double horizontal winding silicone Use double coated wire of lower insulation layer of varnish baking and upper insulation layer of glass single braided silicone varnish baking. The heat resistance is 180 ° C. The ground metal wire that enters the bobbin must use Ni-Cr or Fe-Cr-Al materials with high heat resistance used for the heating wire, but outside the bobbin during normal use Since the temperature is 150 ° C. or lower, the ground conductor connected to the ground metal wire is insulated by using an ordinary insulated conductor such as a double-coated tin-plated annealed copper wire or by covering with an insulating tube. The connection between the bare ground metal wire inside the bobbin and the ground lead wire outside the bobbin is made outside the bobbin collar, similarly to the connection between the heating wire wound around the bobbin and the power supply lead.

  As described above, since the insulation coated conductor is used as the power supply conductor and the ground conductor, the insulation layer is insulated between the power supply conductor and the ground conductor in the dry state, but liquid or water penetrates into the heat insulating material. When it penetrates, it easily penetrates into the insulating layer and the insulation between the power supply conductor and the ground conductor is lowered.

  The grounded metal wire that is bare inside the bobbin passes through the bobbin and is fixed to the insulating sheet on the tip side of the bobbin. The ground metal wire is not electrically connected anywhere on the tip side. The entire ground metal wire inside the bobbin functions as a sensor for detecting the leakage current. The insulating sheets provided on both sides of the bobbin are for separating and insulating so that the lead wire of the heating wire and the ground metal wire do not contact each other. For example, mica can be used.

  FIG. 2 is a side view (A) and a front view (B) showing the configuration of the ceramic bobbin. The bobbin material rises to around 800 ° C during operation, so alumina and silica ceramic materials, which are heat-resistant insulators with little decrease in insulation resistance at high temperatures, are selected to ensure insulation during heat generation. To do. The illustrated bobbin has a heating wire groove formed on the outer surface, and is provided with flanges on both sides of the bobbin. Here, a power supply wire hole into which three power supply wires exemplified as three phases are introduced, and grounding A central through hole into which the metal wire is introduced is provided.

  FIG. 3A is a diagram for explaining power supply to a heating element, and FIG. 3B is a diagram for explaining leakage current detection. The heater is industrial and is usually operated with AC200V3 phase, but a single-phase power source can also be used. In the case of a three-phase power supply, it has three power supply lines, one ground conductor, and four connection terminals for these conductors. In the case of a three-phase heater, as shown, the heating wire can be connected in either a star connection or a Δ connection. The heating wire in FIG. 1 is illustrated as a star connection.

  The power supply circuit including the heating wire and the ground metal wire are completely insulated inside the heater. If the chemical solution (or water) penetrates into the heater's heating element due to any accident, the insulation will drop rapidly. The present invention attaches a ground metal wire to the inside of the bobbin of the heating element and connects it to the ground terminal of an external power source through a grounding conductor connected to the metal wire, thereby preventing leakage of liquid due to liquid intrusion into the bobbin. Sensing can be detected very quickly, contributing to safety. The heating wire and the ground metal wire (sensor) inside the bobbin are normally insulated by the bobbin, but when the liquid enters the heater, the insulation of the bobbin decreases at a stretch and current flows from the heating wire to the ground metal wire. This is detected by the leakage current detection sensor, and operates the earth leakage breaker to shut off the power supply. As the earth leakage breaker itself, a conventionally known breaker can be used.

  In addition, even if liquid penetrates into the lead wire holding part (see FIG. 1), the insulation between the power supply lead wire and the ground lead wire is lowered, and a current flows in the same manner as the insulation drop generated inside the bobbin to operate the earth leakage breaker. I can do it. Since the grounding conductor also has an insulation coating structure similar to the power supply conductor, if the liquid penetrates, the insulation immediately decreases.

1 is an overall configuration diagram of an in-liquid electric heater embodying the present invention. It is the side view (A) and front view (B) which show the structure of a ceramic bobbin. It is the figure (A) explaining the power supply to a heat generating body, and the figure (B) explaining the leakage current detection. It is a figure explaining the electric heater apparatus for liquids of a prior art. It is a figure which shows an example of the heater for liquid used conventionally.

Claims (3)

A heating element composed of a heat-resistant insulating bobbin and a heating wire wound on the bobbin, an outer tube for housing the heating element, and a heat insulating material for holding a conducting wire led into the outer tube. A submerged electric heater comprising:
The outer tube is made of a non-metallic material,
The bobbin has a generally cylindrical body shape having a central through hole, and only one metal wire that is not electrically connected anywhere on the tip side is disposed in the central through hole. Fixing and winding a plurality of heating wires connected to a three-phase power supply line around the bobbin,
Liquid, characterized in that said comprises a sensor for detecting a leakage current flowing through the metal wire from the heating wire, to detect the leakage current flowing through the metal line when the liquid in the outer tube portion intrudes to cut off the power supply Medium electric heater. The submerged electric heater according to claim 1, further comprising insulating sheets on both sides of the bobbin for separating and insulating the lead wire connected to the heating wire and the metal wire so as not to contact each other. The submerged electricity according to claim 2, wherein a three-phase power source is used as a power source to be supplied to the heating wire, and flanges having power supply wire holes into which three power supply wires are introduced are provided on both sides of the bobbin. heater.

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