JPH05316184A - Lightning resistance test method for telephone set with extension function - Google Patents

Abstract

PURPOSE:To execute the lightning test excellent fault reproducibility by connecting an impedance equivalent to an earth feedback circuit while taking the earth feedback circuit of an extension cable together with a subscriber line and a power source line into consideration. CONSTITUTION:An impedance element 11 having an impedance equivalent to earth return impedance is inserted to a power source earth line 48, a resistor 12 simulating an earth resistance of a 3rd class ground to a 3rd class connection line 49 and an impedance element 13 equivalent to an earth feedback impedance of an extension cable is connected between the extension cable 43 and ground. Furthermore, since the resistor 12 simulates the 3rd class grounding for protection of a human body, when the device adopts a double insulation structure, the connection is not required because no frame ground terminal is used, and when the double insulation structure is not adopted, the earth connection is required. Furthermore, the most severe condition for the ground resistance of the 3rd class ground has the resistance of 100 ohms by taking the potential rise in the telephone set frame into account.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightning resistance test method for a telephone with an extension function for testing the proof strength of the telephone with an extension function against a lightning surge.

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing a configuration of a conventional lightning protection test circuit for a telephone with an extension function.

In the figure, a main telephone 4 having an extension function
A subscriber circuit 42 simulating an exchange is connected to 0 through a subscriber line 41, and a sub telephone 44 is connected through an extension cable 43. Further, the main telephone 40 is supplied with power of AC 100 V through a power switch 45, an insulating transformer 46 and a power line 47. One line of the power line 47 is grounded via a power ground line 48, and the frame of the main telephone 40 is grounded via a third type ground line 49. In contrast to the basic configuration of such a telephone, the lightning surge generator 50, one end of which is grounded, applies a lightning surge to the subscriber line 41 via a coupling circuit 51. The subscriber circuit 42 simulating the exchange is operated by a battery and is sufficiently insulated from the ground.

In this lightning protection test circuit, first, the subscriber circuit 4
2 is operated to set the subscriber line 41 side of the main telephone 40 to the power supply state, and the power switch 45 is turned on to turn on the AC.
The 100V power supply system is also in the power supply state. Next, the lightning surge generated by the lightning surge generator 50 is applied to the subscriber line 41 via the coupling circuit 51. Since the lightning surge applied to the subscriber line 41 does not have an outflow route from the subscriber circuit 42 side, it all flows into the main telephone 40 and is grounded via the power supply ground line 48 and the third type ground line 49. It flows out and returns to the lightning surge generator 50.

[0005]

By the way, in the conventional lightning protection test circuit, the lightning surge is applied from the subscriber line 41, but the power supply ground line 48 and the third type ground line 49 are the outflow paths. , The extension system is configured so that the lightning surge current does not flow into it. That is, even if the lightning protection test is performed with such a circuit, no lightning surge current flows in the extension interface circuit of the main telephone 40 or the sub telephone 44.

However, when looking at the failure situation when the telephone with extension function is damaged by lightning in a real environment such as a general home, a factory, an office, etc., the most frequent location is the main telephone 4
It was 0 extension interface circuit. That is, in the conventional lightning protection test circuit configuration, the actual situation at the site does not match the lightning protection test result, and the failure reproducibility due to the lightning protection test is extremely low.

It is an object of the present invention to provide a lightning protection test method for a telephone with an extension function, which can obtain good failure reproducibility according to the actual situation at the site.

[0008]

According to the present invention, a first impedance element corresponding to a ground return impedance of a power supply line is connected between one line of a power supply line for supplying power to a main telephone and ground, and an extension line is connected. A lightning resistance test is performed by connecting a second impedance element corresponding to the earth return impedance of the extension cable between the cable and the ground.

[0009]

In the present invention, the ground of the power supply line is grounded with a more realistic impedance, and the extension cable, which has been conventionally insulated from the ground, is also grounded with the earth return impedance, so that the extension function telephone It is possible to set electrical circuit conditions close to the actual installation conditions.
Therefore, it is possible to reproduce the actual lightning damage situation of the telephone with extension function in the lightning resistance test.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an embodiment configuration of a lightning protection test circuit for implementing the lightning protection test method of the present invention.

In the figure, main telephone 40 and subscriber line 4
1, subscriber circuit 42, extension cable 43, sub telephone 4
4, power switch 45, isolation transformer 46, power line 4
7, the power supply ground line 48, the third type ground line 49, the lightning surge generator 50, and the coupling circuit 51 have the same arrangement as the conventional one.

A feature of the present invention is that in this embodiment, the impedance element 11 corresponding to the ground return path impedance is inserted in the power source ground line 48, and the third type ground line 4 is inserted.
A resistor 12 simulating the grounding resistance of the third type ground is inserted in 9 and an impedance element 13 corresponding to the ground return impedance of the extension cable is connected between the extension cable 43 and the ground.

Since the resistor 12 simulates the third type grounding for human body safety, when the device has a double insulation structure, the grounding terminal of the frame is not provided, so that the connection is not made. It is not necessary, but it must be connected if the device does not have a double insulation structure. In addition, the ground resistance of this type 3 ground is defined as 100Ω or less according to the electrical equipment technical standard, so the resistance value of the resistor 12 is 0 to 100Ω.
However, considering the rise in the potential of the telephone frame, the most severe condition is to set the resistance value to 100Ω.

The impedance element 11 inserted in the power ground line 48 has a resistance of 50 Ω / similar to the case of the high frequency interference wave.
Although a pseudo power supply network of 50 μH may be used, the power supply line 47
Is the path through which lightning surge currents are most likely to flow out, so the shortest condition is the most severe condition.

The impedance element 13 connected to the extension cable 43 includes a ground return circuit resistance r (Ω / km), a ground return circuit inductance l (H / km), and a ground return circuit leakage amount g (mho / km). ), Capacitance of earth return circuit c
If (F / km), the characteristic impedance Z ₀ is Z ₀ = {(r + jωl) / (g + jωc)} ^1/2 (1)

Frequency range of lightning surge voltage is from several tens of kHz to several
100 kHz, and in this frequency band, r <jωl, g
Since there is a relation of = 0, the equation (1) can be approximated as Z ₀ = (1 / c) ^1/2 + r / jω2 (lc) ^1/2 (2). As shown in FIG. 2, the equation (2) is obtained by using the resistance R having a value of (1 / c) ^1/2 and 2 (lc) ^1/2 / r.
It can be approximated by the impedance of the series circuit of the capacitor C having the value of.

Conductor diameters of 0.4
Since a cable of ~ 0.65mmφ is used, r,
The values of l and c are 53-139 (Ω / km), 0.3-
It is considered to be in the range of 0.7 (H / km) and 50-100 (nF / km).

Further, when the values of the resistor R and the capacitor C of FIG. 2 are obtained from the relationship of the equation (2), they are 50 to 120, respectively.
(Ω), in the range of 0.08 to 0.2 (μF). Here, FIG. 3 shows an experimental result when the present invention is applied to an actual telephone. Three types of home telephones, A, B, and C, are selected as telephones with extension functions, and one auxiliary telephone and one intercom are connected to each extension system to configure a lightning protection test circuit as shown in Fig. 1, and an extension cable As a ground return impedance of, the lightning surge withstand capability was compared between the case where the circuit shown in FIG. 2 was connected and the case where it was not connected. The resistance to lightning surges when connected and the resistance to lightning surges when not connected (insulated).

In the telephones A and B used in the experiment, lightning surge countermeasures are implemented only between the subscriber line 41 and the power line 47, and the extension interface circuit is not treated. In the conventional lightning resistance test, 20 to 30 (kV) ) It had the lightning surge resistance above,
It was a telephone that was frequently damaged by lightning when it was introduced to the site. On the other hand, the telephone set C is a telephone set which has taken measures against lightning surges both between the subscriber line 41 and the power supply line 47 and in the extension system interface circuit, and has been less prone to damage due to lightning even after being introduced to the site.

Impedance element 13 used in this experiment
, R = 50 (Ω) and C = 0.2 (μF) were selected in consideration of the condition that the impedance is smallest and the current easily flows. Since all the home telephones used in this experiment have the double insulation structure, the third type grounding is unnecessary, and the experiment was conducted without connecting the resistor 12. Further, the impedance element 11 to be inserted into the power supply ground line 48 is short-circuited assuming the most severe condition.

The results of this experiment show that when the impedance element 13 is not connected to the extension cable 43, the telephone set A,
Both B and C have a lightning surge resistance of 20 to 30 (kV), but when the impedance element 13 is connected, the telephones A and B have only a lightning surge resistance of 4 to 5 (kV),
It can be seen that the yield strength is reduced to about 1/5 as compared with the telephone C. The failure condition at the time of applying the lightning surge is mainly a power supply circuit failure such as a fuse disconnection when the impedance elements 13 are not connected to all the telephones A, B, and C. However, when the impedance element 13 is connected, the extension interface circuit fails. It was confirmed that the number increased and that it was in good agreement with the on-site failure situation.

From this, it is understood that in the case of a telephone with an extension function, it is necessary to consider the ground return circuit of the extension cable 43 and connect an impedance corresponding to it.

[0023]

As described above, in carrying out the lightning resistance test, the present invention takes into consideration the ground return circuit of the extension cable as well as the subscriber line and the power line which are the direct inflow and outflow paths of the lightning surge. Since the impedance corresponding to that is connected, the circuit configuration becomes closer to the installation state at the site compared to the conventional configuration, and a lightning resistance test with extremely good failure reproducibility can be performed.

Further, the present lightning resistance test method can be applied not only to lightning surge, but also to a test method for conducting an immunity test such as conducted interference waves.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment configuration of a lightning protection test circuit for realizing a lightning protection test method of the present invention.

FIG. 2 Impedance element 1 connected to an extension cable
3 is an equivalent circuit diagram.

FIG. 3 is a diagram showing an experimental result when the present invention is applied to an actual telephone.

FIG. 4 is a diagram showing a configuration of a conventional lightning protection test circuit for a telephone with an extension function.

[Explanation of symbols]

 11 Impedance element 12 Resistor 13 Impedance element 40 Main telephone 41 Subscriber line 42 Subscriber circuit 43 Extension cable 44 Sub telephone 45 Power switch 46 Insulation transformer 47 Power line 48 Power ground line 49 Third type ground line 50 Lightning surge occurrence Device 51 coupling circuit

Claims (1)

[Claims] 1. A lightning protection test method for applying a lightning surge from a subscriber line to test the proof strength of a telephone with an extension function, to which a sub telephone is connected via an extension cable. A first impedance element corresponding to the earth return impedance of the power supply line is connected between one line of the power supply line to be supplied and the ground, and corresponds to the earth return impedance of the extension cable between the extension cable and the ground. A lightning protection test method for a telephone with extension function, comprising performing a lightning protection test by connecting a second impedance element.