Power line with power shutdown device including detection line

ABSTRACT

A less expensive power cord with a safety device detects the damage of the power lines in a cord at an earlier stage, shuts off the power, and guarantees the safety of an electric appliance and its environment. The power cord has two power lines and a detection line provided between them, and the sheath portion between the detection line and the power line is thinner than the insulating sheath material of the cord contact portion. When the power line becomes half-broken and damaged by the fatigue with the passage of time due to bendings and pulls, the broken ends of the thin lines of the power line are untwisted and contact the thin sheath portion of the detection line, a current flows through the detection line, a current difference occurs in the power line, the power shutdown device detects the difference, releases a latch, and opens a constant close interlocking switch, thereby shutting off the power.

INFORMATION

DETAILED DESCRIPTION OF THE INVENTION

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention are described, below by referring to the attached drawings.

FIG. 2A is a typical sectional view of the wiring configuration of the power cord with a safety device according to an embodiment of the present invention, and FIG. 2B is an enlarged view showing an actual configuration of the sectional view along the line A-A′ indicated by the arrow. As shown in FIG. 2A or B, a power cord is formed by covering the cord contact portion with an insulating sheath material , two power lines and are arranged in parallel in the insulating sheath material , a detection line is provided between the power lines and , and a plug is connected to one end of the cord contact portion.

The plug contains a power shutdown device operating when it detects a current flowing through the detection line when the power is supplied from the other end of the power lines and to the electric appliance by plugging the plug in the commercial power receptacle. The power shutdown device is obtained by connecting the detection line according to the present invention to a normal leakage detecting power shutdown device.

The power shutdown device comprises a sensor core , a sensor coil wound around the sensor core , a switch drive unit operating based on the output of the sensor coil , constant close interlocking switches and released by the switch drive unit in an abnormal state, and a test circuit comprising a constant open switch and a resistor .

The power lines and connected to the two plug terminals and of the plug through the constant close interlocking switches and are inserted into the sensor core . The detection line passes outside the sensor core , and is connected to the plug terminal through a resistor and the constant close interlocking switch

In a normal state, since the same amount of currents flow in the opposite directions through the power lines and inserted into the sensor core , the induced magnetic force is offset, thereby generating no magnetic force line in the sensor core . Therefore, no current flows through the sensor coil . However, if there occurs a leakage in the electric appliance not shown in the drawings attached to the other end of the power cord due to a careless or mistaken handling such as a drop into a bathtub, etc., then there arises a current difference by an amount of leakage between the power line (or ) on the leakage side and the power line (or ) on the non-leakage side. In response to the amount of the current difference, a magnetic force line is generated in the sensor core . In response to the magnetic force line, a current is generated in the sensor coil . The current is detected by the switch drive unit .

The switch drive unit is not shown in the attached drawings, but comprises, for example, an amplifier circuit, a latch type solenoid, etc., and a weak current from the sensor coil is detected by the amplifier circuit. That is, the output of the amplifier circuit closes the energized circuit in the switch drive unit , and passes the power current to the latch type solenoid. Thus, the latch type solenoid operates, and the constant close interlocking switches and are released, thereby shutting off the power.

The test circuit is used to confirm that the power shutdown device correctly operates by shutting off the power by the above mentioned effect through an artificial short-circuit of the portion subsequent to the sensor core of the power line and the portion preceding to the sensor core of the power line by setting the constant open switch in a close state by a manual external operation or a jig after connecting the plug terminals and to a testing power circuit after assembly in the factory or before shipment from the factory.

Thus, the power cord has the function of shutting off the power when there occurs a leakage due to common careless or mistaken handling, and further has the function of shutting off the power by early detecting an internal half-broken state due to the fatigue with the passage of time. That is, the cord contact portion of the power cord is formed such that the thickness of a sheath portion - covering the entire unit can be 1.0 mm as shown in FIG. 2B, and the thickness (distance) of a sheath portion - covering the detection line through the power line or can be 0.6 mm. That is, the sheath portion - between the detection line and the power line or is formed thinner than the sheath portion - of the cord contact portion.

In the example shown in FIG. 2B, the sheath portion - between the detection line and the power line or is about ⅔ times as thick as the sheath portion -. However, the thickness is not limited to this value. For example, the relationship between them can be arbitrarily set so far as the thickness of the sheath portion - is smaller than the thickness of the sheath portion -.

Thus, if the power line or enters the half-broken state and damaged due to the fatigue with the passage of time, etc. by bendings and pulls while using the line, then the damaged and broken ends of the thin lines of the power line or normally formed by twisting a number of thin lines are untwisted and easily contact the detection line through the damaged portion of the sheath portion - between the detection line and the power line or normally thinner than the sheath portion -.

When the detection line contacts the power line , the power is shut off by the above mentioned effect of the short circuit between the power lines and . Furthermore, when the detection line contacts the power line , the current from the plug terminal flows separately through the inside (power line ) and the outside (detection line ) of the sensor core . Also in this case, a small current difference occurs between the power lines and encompassed by the sensor core . Therefore, if the sensor core and the sensor coil can be configured as a zero-phase current transformer (ZCT) using a toroidal coil having a sensitive magnetic core, and the value of the resistor can be set to an appropriate value, then the above mentioned small current difference can be detected, thereby also successfully shutting off the power by the similar effect described above.

In the above mentioned embodiment, the sheath portion - between the detection line and the power line or is formed thinner than the sheath portion -. However, the relationship between the sheath portion for the detection line and the sheath portion for the power line or (sheath portion of the cord contact portion) is not limited to this so far as the broken thin line of the power cord can easily contact the detection line when the power cord has fatigue with the passage of time and enters the half-broken state

FIGS. 3A, B, and C show examples of another configuration in which the broken thin line of the power line or can easily contact the detection line when the power line or enters a half-broken state by the fatigue with the passage of time of the power cord . FIG. 3A shows an example of the configuration in which a sheath portion of the detection line is, for example, polyvinyl chloride normally used as the sheath portion for the power cord, and the sheath of the power lines and is cross-linked polyethylene which is more heat-resistant than the polyvinyl chloride.

With the configuration, if the power cord has fatigue with the passage of time or it is carelessly or mistakenly handled, the power line or enters the half-broken state, and the user is not aware of the situation and continues using the electric appliance, then the portion in the half-broken state is heated with increasing electric resistance. The heat melts the less heat-resistant sheath portion between the detection line and the power line or before the more heat-resistant sheath portion of the cord contact portion melts. Therefore, also in this case, the half-broken portion of the thin line easily contacts the detection line .

Thus, the fatigue with the passage of time of the power cord can be detected and the power can be shut off before a disaster takes place due to an electric shock accident of a user or a fire caused by a broken cord contact portion.

FIG. 3B shows the configuration of a sheath portion of a conductive resin containing carbon grains around the detection line . Also in this case, if the power cord has fatigue with the passage of time or it is mistakenly handled, the power line or enters the half-broken state, and the broken thin line contacts the conductive sheath portion nearby, then the half-broken power line or are easily connected to the detection line , the power shutdown device operates as described above, and the power is shut off.

FIG. 3C has the structure of a detection cover rather than a detection line. That is, it comprises the two power lines and arranged in parallel; an insulating internal sheath portion covering the power lines and ; a conductive sheath portion replacing the detection line around the internal sheath portion ; and an insulating external sheath portion forming the cord contact portion by covering the conductive sheath portion . The above mentioned is a flexible cylindrical sheath material in the form of a net or a twisted cord.

Also in this case, if the power cord has fatigue with the passage of time or it is mistakenly handled, the power line or enters the half-broken state, and the broken thin line contacts the conductive sheath portion , then a current flows through the conductive sheath portion by which amount a current difference occurs relating to the power line or , and the current difference is detected by the power shutdown device , thereby shutting off the power.

With the configuration of the present embodiment, when the power line or is damaged, the damaged power line or contacts the conductive sheath portion before breaking the sheath portion of the cord contact portion, and the power shutdown device shuts off the power. Therefore, it is the optimum configuration when safety is specifically required, that is, in designing a medical appliance and an electric appliance to be used near water facilities where a leakage and an electric shock accident can cause a serious disaster.

FIG. 4A is a typical sectional view of the configuration of the wiring of the power cord with a safety device according to another embodiment. FIG. 4B shows the configuration of the circuit of a power shutdown device ′. The power shutdown device ′ embedded in a plug ′ of a power cord ′ is an example of a wet detecting power shutdown device, and an example of a semiconductor detection circuit used in the device as shown in FIG. B. In the example shown in FIG. 4B, the detection line is connected to the gate of a semiconductor switching device (for example, a thyristor) . With the configuration, when a current flows through the detection line , the switching device is turned on for the circuit in the arrow B direction, a solenoid is driven by the current flowing through a bridge circuit , the latch is released to open the constant close interlocking switch and , and the current is shut off in a moment on both sides.

A method of detecting a current flowing through the detection line (or the conductive sheath portion ) from the power line or can be realized by various examples other than those shown in FIGS. 2A and 4B. That is, as described above by referring to the embodiments of the present invention, each type of power shutdown device can be appropriately combined with the cord having the detection line (or the conductive sheath portion ) shown in FIG. 2B or A through C. When a current flows through the detection line (or conductive sheath portion ), a current difference of a power line or a voltage change of a detection line (or a conductive sheath portion) is detected to open an interlocking switch with a latch. Thus, when an internal damage occurs before a cord contact portion is damaged, the damaged portion of a power line contacts the detection line, thereby shutting off the power.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the power cord provided with a conventional cord protector;

FIG. 2A is a typical sectional view of the wiring configuration of the power cord with a safety device according to an embodiment of the present invention, and FIG. 2B is an enlarged view showing an actual configuration of the sectional view along the line A-A′ indicated by the arrow;

FIGS. 3A, B, and C show examples of other configurations in which the power line of the power cord is in a half-broken state and a broken thin line can easily contact the detection line;

FIG. 4A is a typical sectional view of the wiring configuration of the power cord with a safety device according to another embodiment of the present invention, and

FIG. 4B shows the configuration of the circuit of the power shutdown device.

CLAIMS

1. A power cord with a safety device for supplying power from a commercial power receptacle to an electric appliance in which a cord contact portion is covered with an insulating sheath material, the cord contains two power lines and a detection line, a plug includes a power shutdown device for operating upon detection of a current flowing through the detection line, wherein: the detection line is provided between two power lines arranged in parallel; and sheath portion between each of the two power lines and the detection line is thinner than the sheath portion between each of the power lines and an exterior of the cord at the cord contact portion.

2. The cord according to claim 1, wherein the detection line is covered with a sheath material having a lower melting point than a sheath material of the power lines.

3. The cord according to claim 1, wherein the detection line is covered with a conductive sheath material.

4. The cord according to claim 1, wherein said power shutdown device can be a leakage detecting power shutdown device.

5. The cord according to claim 1, wherein said power shutdown device can be a wet detecting power shutdown device.

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