JPS6258221B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is mainly installed in a telephone subscriber's house to eliminate fault currents caused by lightning flowing in from telephone lines and power lines, thereby preventing electric shocks of subscribers and preventing household equipment such as telephones. This invention relates to a circuit for a telephone subscriber protector used to prevent fire damage.

Conventionally, this type of protector has the following features, as shown in Figure 1:
It is composed of fuses 4, 4' and lightning arresters 5, 5', and has outside line terminals 1, 1' connected to the telephone line, extension line terminals 2, 2' connected to domestic equipment, and ground terminal 3 connected to the ground. Fuses 4 and 4' interrupt persistent fault currents such as those that occur when telephone lines and power lines come into contact, and lightning arresters 5 and 5' discharge high voltage momentary fault currents such as lightning surges to the ground. Therefore, the fuses 4 and 4' need to have the ability to interrupt high-voltage sustained fault currents, and are connected in series to the telephone line as shown in the figure, and the lightning arresters 5 and 5' The circuit is arranged to discharge current and momentary fault currents to earth.

For this reason, fuses 4 and 4' may melt when a momentary fault current such as a large lightning surge occurs, and in areas where there is a lot of lightning, replacing fuses 4 and 4' requires a lot of work and becomes a problem. There is. In view of this, efforts have been made to develop cut-off mechanisms using electromagnetic coils and cut-off mechanisms using bimetals, but to date, no satisfactory devices have been developed. The main problem is that it is extremely difficult to interrupt high-voltage, continuous fault currents, and with conventional circuit disconnection methods, the arc that occurs during the disconnection process continues, causing damage to various parts and making it impossible to disconnect. For this reason, the fuses 4, 4' have a complicated structure as shown in FIG.

6 is a high strength thermosetting resin pipe, 7, 7'
8 is a metal cap, 8 is a fuse wire, 9 is a thermoplastic resin sleeve, 10 is a grain of silica sand, and the caps 7, 7' are fixed to both ends of the pipe 6. The fuse wire 8 is stretched inside the pipe, and the caps 7, 7' are attached to both ends of the pipe. 7', a sleeve 9 is inserted in the center, and the inside of the pipe is filled with silica sand grains 10, and the fuse wire 8 is instantaneously evaporated by a high voltage continuous fault current.
turns into metal vapor and adheres to the silica sand grains, and the central sleeve 9 generates an insulating gas to prevent "arc discharge".

As described above, the telephone protector not only discharges momentary fault currents to the ground, but also uses a fuse having the above-mentioned structure in order to interrupt high-voltage continuous fault currents.

However, as mentioned above, fuses can blow out due to high-voltage instantaneous fault currents, and fuses like the one described above must be used for each telephone line, so there is a limit to miniaturization, and this is proportional to the development of telephones. The challenge is to miniaturize collective security devices that combine multiple lines.

FIG. 3 is an embodiment of the circuit diagram of the telephone protector according to the present invention, in which 1 and 1' are external line terminals as before;
2 and 2' are extension terminals, 3 is a ground terminal, and 1
Reference numerals 1 and 11' designate a normally closed contact mechanism which transitions to disconnection when a high-voltage continuous fault current flows in, 12 a discharge mechanism, 13 a lightning arrester, and 14 a detection mechanism.

External line terminals 1, 1 are connected to telephone lines, internal line terminals 2, 2
is connected to the in-house equipment, and the ground terminal 3 is connected to the earth.

The normally closed terminals cannot be disconnected due to the inflow of a momentary fault current between the external line terminals 1, 1' and the internal line terminals 2, 2', but transition to disconnection due to the inflow of a high-voltage continuous fault current. The contact mechanisms 11, 11' are inserted, and a primary grounding circuit _A1 is provided on the extension terminal side of _the normally closed contact mechanisms 11, 11'. In addition to providing the above-mentioned lightning arrester 13 that discharges water to the ground, the above-mentioned normally closed contact mechanism 11, 1 is provided.
1' external line terminal 2, the normally closed contact mechanism 11 on the 2' side,
A secondary grounding circuit A ₂ is provided which starts discharging the above-mentioned continuous fault current to _the earth as _the circuit 11' disconnects. The fuse 15, which blows when a fault current flows in, is inserted through the discharge mechanism 12, and in the process of blowing the fuse, the normally closed contact mechanism is separated to a distance that can withstand high-voltage continuous fault current. .

The contact mechanisms 11, 11' are, for example, a primary grounding circuit A ₁
An example is shown in which the contact is disconnected by the detection mechanism 14 inserted into the terminal, and after the contact is disconnected, the structure is such that the contact portion is separated by a distance that has a sufficient withstand voltage. For example, the detection mechanism 14 is a heating coil, and the contact mechanisms 11 and 11' are configured to move to disconnection in conjunction with the heating coil. Alternatively, the detection mechanism may not be used, and the contact mechanism itself may be a heat-sensitive contact mechanism such as a non-returnable bimetal, or a contact mechanism may be used that senses the discharge heat of the lightning arrester 13 and shifts to disconnection.

Although the lightning arrester 13 is shown as a three-pole type arrester in the example, a two-pole type arrester may be used as shown in FIG. When the discharge mechanism 12 is connected in parallel with the surge arrester 13, a discharge gap with a discharge starting voltage higher than that of the surge arrester 13 is used so that no discharge occurs as long as the surge arrester 13 is connected, or a resin film 16 is inserted into the discharge gap to prevent discharge. It is designed to cause a delay.

The detection mechanism 14 detects whether the flowing fault current is an instantaneous fault current such as a lightning surge or a continuous fault current,
Normally closed contact mechanism 11,1 in case of persistent fault current
1', and as mentioned above, one example of a detection method is a method of discrimination based on heat generated within the detection mechanism. For example, 10 for lightning that is close to direct lightning.
In the ×200μs waveform, the peak value of the lightning surge (instantaneous fault current) that melts the 0.3φ copper wire is as high as 1000A, but the energy in this case is W = I ² Rt = 200R even if it is a 200μs rectangular wave. Since the fuse blowing start current is specified as 6A within 10 seconds, a continuous fault current will result in W = 360R, and this difference can be detected and linked to the normally closed contact mechanism by melting the solder.

Further, as described above, the heat generated by the lightning arrester 13 may be used without using the detection mechanism 14 in particular. In this case, since the lightning arrester 13 exhibits negative resistance, the residual voltage during discharge is approximately 50V regardless of the current.
Then, for lightning surge, W = VIt = 50 × 1000 × 200 × 10 ^-6 = 10, and for sustained fault current, W = VIt = 50 × 6 × 10 = 300, and the difference between lightning surge and sustained fault current is extreme. can be determined. Therefore, it is also effective to use a lightning arrester as a detection mechanism and add one with a structure that discriminates based on its heat. If such a determination is made, the heat generated by the continuous fault current melts the solder or moves the bimetal to open the normally closed contact mechanisms 11, 11'.

Due to this structure, a momentary fault current flows from the telephone line and is discharged from the lightning arrester 13 to the ground through the normally closed contact mechanism, but in the case of a sustained fault current, the normally closed contact mechanisms 11 and 11' are disconnected. The persistent fault current flows through discharge mechanism 12 and fuse 15 to ground, causing fuse 15 to blow.

Since the normally closed contact mechanisms 11 and 11' have been disconnected by the time the fuse 15 is disconnected, the voltage generated during the disconnection process is only the residual voltage during discharge of the discharge mechanism 12, and no arc that causes a sustained discharge occurs. do not have. Therefore, a continuous fault current can be interrupted without blowing out the fuse 15 due to an instantaneous fault current such as a lightning surge.

Note that this system requires only one fuse 15 even if multiple lines are grouped together as shown in Figure 4.
Since no individual fuses are required, it can be made extremely compact. In addition, as shown in Fig. 5, the normally closed contact mechanism is of a two-contact switching type, and in the process of switching from one contact a constituting the normally closed contact to the switching contact b on the fuse 15 side constituting the normally closed contact, contact b If contact a is opened after switching to the side, high voltage will not be applied to the normally closed contact mechanisms 11, 11' during the switching process.

As mentioned above, the normally closed contact mechanism is significantly smaller than a fuse because it only needs to have a sufficient withstand voltage after the current of about 1000 A flows through momentary fault currents such as lightning surges and is shut off. Therefore, it has the feature that the fuse, which is the most problematic for downsizing, can be reduced to one by combining appropriate lines into one block.

In addition, in the case of instantaneous fault currents such as those caused by lightning, the normally closed contact mechanisms 11 and 11' properly flow the fault current to the primary grounding circuit without causing a fuse-like blowout, thereby obtaining a discharge from the lightning arrester 13 and ensuring that the current is discharged to the ground. have them do it. Therefore, it is possible to effectively eliminate the disadvantage that fuses are blown out inadvertently by the instantaneous fault current, which occurs when a fuse is inserted into a line.

In addition, in the case of sustained fault currents such as high voltage cross-contact, by opening the normally closed contact mechanism inserted into the line, a good insulation cut-off state is created between the inner and outer line terminals of the line, and the protection of the equipment on the inner line side is further improved. It becomes certain. In addition, after the normally closed contact mechanisms 11, 11' are opened, the secondary grounding circuit functions to discharge the continuous fault current, so arc discharge after the normally closed contact mechanisms are opened can be reliably prevented, and the fuse is then disconnected. 15 is fused to ensure that the continuous fault current is interrupted.

As described above, the present invention effectively achieves security objectives such as preventing electric shock to telephone subscribers and damage to household equipment.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional security circuit for telephone subscribers, FIG. 2 is a schematic sectional view of a fuse used in the security circuit, and FIGS. 3 and 4 are security circuits for telephone subscribers of the present invention. 3 shows an embodiment in which the present invention is applied to a single protector circuit, and FIG. 4 shows an embodiment in which the present invention is applied to a collective protector circuit.
FIG. 5 is a circuit diagram showing an embodiment of the normally closed contact mechanism of the same circuit. 1, 1'...external terminal, 2, 2'...internal terminal, 1
1, 11'... Normally closed contact mechanism, 13... Lightning arrester, 15
…Hyuse.

Claims (1)

[Claims] 1. A normally closed contact mechanism is inserted between the external line terminal and the internal line terminal, which cannot be disconnected by the inflow of a momentary fault current, but transitions to disconnection by the inflow of a continuous high voltage fault current, and the normally closed contact mechanism is A primary grounding circuit is provided on the internal line terminal side of the contact mechanism, and a lightning arrester is provided in the primary grounding circuit to discharge fault current and discharge it to the earth. A secondary grounding circuit is provided that starts discharging the continuous fault current to the earth as the contact mechanism is disconnected, and the secondary grounding circuit is equipped with a discharge mechanism having a higher discharge starting voltage than the lightning arrester of the primary grounding circuit. A fuse that blows when the continuous fault current flows into the secondary grounding circuit is inserted in series, and the normally-closed contact mechanism is separated by a distance that can withstand high-voltage continuous fault current during the process of blowing the fuse. A security circuit for telephone subscribers characterized by the following.