JPS6124184A - Method of shortcircuiting electric furnace and preventing discharge - 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] [Industrial Application Field] The present invention provides a method for preventing short circuits or discharge accidents in electric furnaces, in particular detecting abnormalities in the electrical system before an accident occurs and implementing a series of operations. The present invention relates to a method for preventing short circuits and discharges in electric furnaces, which can eliminate short circuits and discharge phenomena by performing the following steps.

[Conventional technology]

Electric resistance heating type vacuum furnaces are prone to temporary short circuits or discharge phenomena because the furnace is in a vacuum and a high voltage electric heater is installed inside the furnace, but these abnormal phenomena are continuous. This can lead to short circuits and discharge accidents where large currents flow, so it is important to take early measures before accidents occur.

However, as a conventional countermeasure, as shown in Fig. 4, the power supply circuit (BLT-star connection) to each electric heater (tL) is connected, and the neutral point (c)' on the load side is connected to the earth (d) together with the furnace body (d).
e), and even with this measure, a potential difference equivalent to the secondary voltage ■ occurs between the furnace body (d) and the electric heater (α), which prevents discharge from occurring. [Problem to be solved by the invention] The present invention detects temporary short circuits and discharge phenomena at an early stage, and eliminates them at an early stage before these abnormal phenomena lead to accidents. The present invention relates to a method for suppressing and extinguishing short circuits and discharges in electric furnaces.

[Means for solving the problem] ゛A detailed observation of the mechanism and characteristics of temporary abnormal phenomena inside the vacuum furnace shows that discharge tends to occur where the distance between the discharge electrodes is small and the potential difference is large; As shown in Figure 2, it often occurs between the electric heater (6) that is close to the furnace body (8) or the connection terminal αO of the electric heater and the furnace body (8). Once a discharge occurs, the discharge phenomenon continues even after the potential difference decreases; however,
Once the power is turned off, it often does not occur again the next time the power is turned on.

In addition, short circuits are likely to occur due to poor insulation of high voltage parts such as the electric heater (6) or the connection terminal frame. In other words, these high-voltage parts are covered with an insulating material such as alumina insulator, but if a thin metal film is deposited on the surface of the insulating material and a thin metal film is deposited on the surface of the insulating material, the insulation becomes incomplete and short circuits occur. wake up However, this temporary short circuit phenomenon can be eliminated by incinerating or vaporizing the scratches or metal coating by passing an open current for a very short time.

The present invention focuses on the characteristics of the short circuit and discharge phenomenon described above, and detects the abnormality at an early stage when a short circuit or discharge occurs, cuts off the power supply, and then reduces the power supply to zero. This relates to a method for preventing short circuits and discharges in electric furnaces in which the power is turned on again and the power is gradually increased.
Since it suppresses and eliminates temporary short circuits or discharge circuits, it has the advantage of improving the safety and operating efficiency of the electric furnace.

〔Example〕

Hereinafter, embodiments of the present invention will be explained with reference to the drawings. 1st
The figure and FIG. 2 show a first embodiment of an apparatus for carrying out the present invention, and in the figure, reference numeral (1) is a power supply, and (2) is a power supply.
is a power breaker, (3) is a transformer, (4) (5) is the primary and secondary windings of the transformer, (6) is an electric heater, (7
) is a power supply circuit that supplies power to the electric heater (6), (8
) is the furnace body, (9) is the inner container, and QO is the electric heater (6).
connection terminal, αη is the vacuum pump, (2) is the power control unit, Q3 is the furnace body (8)
This is a grounding circuit that is grounded to the IO. FIG. 1 shows one phase of the three-phase AC power supply and the equipment and wiring related to the negative phase.

A device implementing the present invention includes, for example, a primary circuit of a transformer (
A current detector (to) for detecting abnormal current installed in g), a short circuit/discharge detection and removal device αη (hereinafter referred to as removal device), etc. that sends out a series of operation command signals according to a predetermined program when an abnormal phenomenon occurs. The removal device also has the ability to compare and judge the received signal with a predefined set value. Note that the symbol (2) is a signal circuit that sends a current signal from the current detector α0, Q9 is a signal circuit that sends a current signal from an overcurrent relay (not shown) in the thyristor unit (2), and the wire is a signal circuit that sends a current signal from the overcurrent relay (not shown) in the thyristor unit (2). A signal circuit that sends an electric signal to the thyristor in order to control the thyristor that does not operate, Q]) is a signal circuit that sends an electric signal to control the opening and closing of the power circuit breaker (2).

Next, we will describe the operation of one device, and also explain the removal device xt(lIη
The configuration of is explained. During operation of the electric furnace, if a metal film adheres to the insulating material surface of the connection terminal αO (see Figure 2), or if the potential difference between the connection terminal (10 and the furnace body (8) becomes excessive), the connection terminal αO and A small-scale short circuit (A) occurs between the furnace bodies (3) (see the analogy in Figure 1).As a result, part of the current supplied to the electric heater (6) is caused by the short circuit (C). Through the earth α, QK flow, the supply voltage V fluctuates, and this fluctuation further causes the primary side circuit a!1
This results in an increase in current of 9. - The increase in current in the next circuit a is detected by the current detector (to) and sent to the removal device 07 via the signal circuit (2) (arrow σ).

When the removal device (17) receives the abnormal current signal,
Send a power cutoff signal to the power breaker (2) (arrow h), then send a signal to the thyristor unit (2) so that the power in the primary circuit (to) becomes zero (arrow c), and then Afterwards, the power circuit breaker (2) is closed again, and the thyristor unit is controlled to gradually increase the power supplied to the electric furnace at a predetermined speed.

During the above operation, the power of the negative side circuit a0 is once reduced to zero because there is a possibility that the short circuit (2) has expanded and the resistance has become zero. Further, the rate of increase in power is selected to be a value suitable for the device.

When the power is gradually increased, current flows through the short circuit wire first. If the formation of a short circuit is caused by a temporary insulation failure due to adhesion of a thin metal film or graphite whiskers on the surface of the insulating material, the above-mentioned energization will overheat and remove the adhesion, resulting in a short circuit (e). Disappear. Also, abnormal current generation.

Even if the failure is due to the formation of a similar discharge circuit, there is a strong possibility that the discharge circuit will disappear because the discharge circuit is unlikely to reoccur once the power is turned off.

Therefore, at the time when the power is increased, most of the temporary short circuit or discharge phenomenon is removed and the normal state is restored, so the power is increased to the specified maximum value and normal operation is continued.

If the scale of the temporary short circuit or discharge phenomenon is large and an abnormal current that exceeds the specified value is detected even after performing all of the power increase operations described above, shut off the power and perform the series of operations described above, that is, zero power. setting,.

Repeat the operations of shutting off the power and slowly increasing the power. This repeated operation can be repeated as many times as necessary until related devices such as the thyristor unit (6) are adversely affected by overheating. However, it is practical to repeat the operation about 5 times, and if the abnormality is not resolved even after 5 times, it is likely that the abnormality has occurred somewhere in the force rather than a temporary short circuit or discharge. As a precaution, the power circuit breaker is opened to stop the electric furnace from operating, and an alarm such as a buzzer is sounded.

In addition, if a large-scale short circuit or discharge phenomenon occurs from the beginning, the IT-style vertical relay (not shown) in the CYRIS and TAUNI SOTO (2) will operate, and the removal device a'h will issue a signal for the cut-off engine.

A second embodiment of the invention is illustrated in FIG. In this example, a current detector (16 cL) is installed with a ground wire (2ffj K) connected to the center tap (c) of the transformer secondary winding (5), and an extremely small-scale similar discharge circuit ( Even if c) occurs, the voltage balance at the center tap % will be disrupted and current will flow through the ground circuit (c), so the detection operation will be sensitive, and the potential difference between the electric heater (6) and the furnace body (8) will be Since it is half of the power supply voltage V (=V/2), it has the advantage of being less likely to cause in-furnace discharge t', but other than that there is no difference from the first embodiment.

Note that the present invention is not limited to the above-described embodiments; for example, the current detector may be provided on the secondary side of the transformer or another ground circuit (not shown); It is possible to detect electrical fluctuations in
It goes without saying that various other changes may be made without departing from the gist of the present invention.

〔Effect of the invention〕

As described above, the method for preventing short circuits and discharges in electric furnaces according to the present invention detects abnormalities at an early stage when short circuits or discharges occur, cuts off the power supply, then reduces the supplied power to zero, and then restarts the electric furnace. Since the power is turned on and the power is gradually increased, temporary short circuits or discharge circuits can be suppressed and eliminated, providing excellent effects such as improving the safety and operating efficiency of electric furnaces. .

[Brief explanation of drawings]

1 and 2 show a first embodiment of an apparatus for carrying out the method of the present invention, FIG. 1 is a circuit diagram of the apparatus for the electric furnace electric heater phase, and FIG. 2 is a circuit diagram of the apparatus for the electric furnace electric heater phase. Is the cutaway side view, Figure 3, the invention? A circuit configuration diagram showing a second embodiment of the device to be implemented, and FIG. 4 is an explanatory diagram of conventional discharge countermeasures. In the figure, (2) is the power supply breaker, (4) is the negative side winding, 0Q
(16cL) is a current detector, Q71 is a short circuit/discharge detection/removal device, and (C) is a ground wire.

Claims (1)

[Scope of Claims] 1) Detecting an abnormality in the electric system of the electric furnace, and when the abnormality is detected, immediately shutting off the power supply, reducing the power supply to the electric furnace to zero, and closing the power supply again to supply the electric furnace. A method for preventing short circuits and discharges in electric furnaces, which comprises gradually increasing power and confirming that the abnormality has been resolved. 2) The method for preventing short circuits and discharges in an electric furnace according to claim 1, wherein the same operation is repeated multiple times if the abnormality is still not resolved. 3) If the abnormality still persists even after repeating the procedure several times,
A method for preventing short circuit and discharge in an electric furnace according to claim 2, characterized in that the power source is kept open. 4) A method for preventing short circuits and discharges in an electric furnace according to claims 1) to 3), wherein the abnormality in the electric system is detected by detecting an abnormality in the power supply system. 5) A method for preventing short circuits and discharges in an electric furnace according to claims 1) to 3), wherein abnormalities in an electrical system are detected by detecting abnormalities in a ground circuit.