JPS61263080A - Electrically heating furnace apparatus - 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 electric heating furnace apparatus equipped with a mechanism for guarding against leakage current.

[Conventional technology and problems]

The leakage current of an electric heating furnace is mainly influenced by the electrical insulation properties of the thermal insulator that constitutes the furnace wall, and generally exhibits a large value compared to other electrical equipment. For this reason, electric heating furnaces require a mechanism to protect the human body from leakage current for safety reasons.

Currently, earth leakage circuit breakers are used as this guard mechanism, and the circuit is cut off when an excessive earth leakage current flows, but in reality, this circuit breaker is not necessarily designed rationally for use. It's hard to say that it is.

For example, during initial drying after manufacturing an electric heating furnace, the furnace wall thermal insulation still contains moisture, which often causes excessive leakage current and activates the earth leakage circuit breaker, which hinders work execution. often occurs.

In addition, the insulation properties of this furnace wall thermal insulation material generally tend to decrease as the temperature rises, and the degree of this decrease becomes greater as the period of use passes, so leakage current increases as the furnace temperature rises, and the most There is always a risk that the leakage current will exceed the set current value of the earth leakage breaker during heating near the required rated operating temperature and the circuit will be interrupted, and this often actually occurs.

Of course, one way to eliminate this drawback is to increase the thickness of the furnace wall thermal insulator, but this is undesirable because it increases the size and weight of the furnace body. Another method is to set the current value of the earth leakage breaker to a large value in advance, but this weakens the significance of using the earth leakage breaker from a safety standpoint and should be avoided as much as possible.

The present invention has been made in view of the above problems, and even if the set current value of the earth leakage breaker is set to a low value based on normal safety standards, the above problems will not occur. The aim is to provide an electric heating furnace with excellent safety and usability characteristics.

[Means for solving problems]

As a result of intensive research into the above-mentioned problem, the present inventor has created the following mechanism.

That is, (a) an electric heating furnace having a furnace wall having a thermally insulating inner layer, a thermally insulating outer layer, a conductive layer interposed between the inner layer and the outer layer, and an electric heating load, and (b) an earth leakage interrupter. (c) a zero-phase current transformer, wherein the electric heating load wire passes through the earth leakage breaker and the zero-phase current transformer, and the wire connected to the conductive layer passes through the zero-phase current transformer. A device characterized by being grounded through a flow vessel.

[Examples and effects]

In FIG. 1, the apparatus of the present invention has an electric heating furnace 1, an earth leakage breaker 2, and a zero-phase current transformer 3. The electric heating furnace 1 has a furnace wall having an inner thermally insulating layer 4 , a conductive layer 5 , an outer thermally insulating layer 6 and a furnace shell 7 , and an electric heating load 8 .

The conductive layer 5 can be a box made of a steel plate, and its thickness is preferably about 0.5 to 1 mm. Thermal insulation inner layer 4
Although the inner layer 4 and the outer layer 5 can be formed of the same material, it is more effective to form the inner layer 4 with a material that has particularly high heat resistance, and to form the outer layer 5 with a material that has particularly high electrical insulation. From the viewpoint of thermal insulation and electrical insulation, it is desirable that the inner layer 4 is sufficiently thicker than the outer layer 6. For example, if the total thickness of the insulating layer is 250 mm in an electric furnace with a maximum heating temperature of 1100° C., then the inner layer 4 has a thickness of 200 mm.

The outer layer 6 can be made of 50u+, the inner layer 4 can be made of a ceramic material, and the outer layer 6 can be made of a rock wool thread material.

In this embodiment, the earth leakage breaker 2 includes a power source 9 and three three-phase AC electric wires 10, 11. '12 is inserted, and one of the wires 11 is grounded.

The three electric wires that have passed through the earth leakage breaker 2 then pass through a zero-phase current transformer 3 and are connected to an electric heat load 8.

Further, the electric wire 13 tangential to the conductive layer 5 passes through the zero-phase current transformer 3 and is connected to the ground type Na1l.

Furthermore, the output line 14 of the zero-phase current transformer 3 is input to the earth leakage breaker 2. The furnace shell 7 of the electric furnace 1 is grounded.

The zero-phase current transformer 3 can be constructed of an iron core with a secondary winding. An electric wire of 10°11.12 passes through the inside of the iron core. When current flows through each wire, magnetic flux is generated in the iron core, and a secondary current flows through the secondary winding. However, since all the wires pass through each wire, the sum of the induced secondary currents is O under normal conditions. , no current flows through the output line 14 after all. Here, if there is an earth leakage, a zero-sequence current flows, and a corresponding secondary current is input to the earth leakage breaker 2 via the output 'a14. If the input level exceeds the rated sensitivity current value, the earth leakage breaker 2 is shut off.

In this embodiment, the electric wire 13 connected to the conductive N5
passes through the zero-phase current transformer 3 and is grounded, so even if a leakage current occurs, it is collected by the conductive layer 5, passes through the zero-phase current transformer 3, and is transferred from the zero-phase current transformer 3 to the ground. No secondary current is generated. Therefore, the leakage current can be effectively grounded without operating the leakage circuit breaker 2. If the leakage current crosses the conductive layer 5 and reaches the furnace shell, since the furnace shell is grounded,
When the zero-sequence current flows and reaches a certain reference level, the leakage circuit breaker operates to cut off the input current.

〔Effect of the invention〕

In the device of the present invention, a conductive layer is provided within the furnace wall and is grounded through the zero-layer current transformer, so even if there is a leakage current, the surface of the electric furnace will not be affected. Not only can it be effectively grounded without reaching the ground, but the input current will not be cut off by a leakage breaker. Also,
Since the leakage circuit breaker is activated only when a certain level of leakage current reaches the furnace shell and flows to the ground, the set current value of the leakage circuit breaker can be set low from the viewpoint of safety. Furthermore, even in such a case, the circuit breaker will not operate too frequently and prevent electrical heating. Further, by forming the inner layer of the furnace wall of the electric heating furnace thickly with a heat-resistant material and forming the outer layer thinly with an electrically insulating material, heat insulation and leakage prevention can be effectively achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the electric heating furnace apparatus of the present invention. DESCRIPTION OF SYMBOLS 1... Electric heating furnace, 2... Leakage circuit breaker, 3... Zero-phase current transformer, 4... Thermal insulation inner layer, 5... Conductive layer, 6...
・Thermal insulation outer layer, 7... Furnace shell, 8... Electric heating load, 9.
...Power supply, 10-14...Electric wire.

Claims (4)

[Claims] (1) (a) a furnace wall having a thermally insulating inner layer, a thermally insulating outer layer, and a conductive layer interposed between the inner layer and the outer layer;
an electric heating furnace having an electric heating load; (b) an earth leakage breaker; and (c) a zero-phase current transformer. The device is characterized in that the electric wire connected to the conductive layer passes through the zero-phase current transformer and is grounded. (2) The apparatus according to claim 1, wherein the thermally insulating inner layer of the electric furnace has high heat resistance, and the thermally insulating outer layer has high electrical insulation. (3) In the device according to claim 1 or 2, the electric heating load electric wire is composed of three three-phase alternating current electric wires, one of which is grounded; An apparatus characterized in that an electric wire connected to the conductive layer passes through the zero-phase current transformer and is connected to the ground electric wire. (4) The apparatus according to any one of claims 1 to 3, wherein the electric heating furnace has a furnace shell that covers the thermally insulating outer layer, and the furnace shell is grounded. A device that does this.