JPH029414B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit protection sensor applied to circuit breakers and the like.

In order to protect loads from fault currents such as so-called overcurrents and short-circuit currents, circuit breakers and the like have a built-in circuit protection sensor that detects the above-mentioned current and operates to interrupt the circuit. Various types of sensors of this type have already been provided.

FIG. 1 shows a conventional example of a bimetal system. In this structure, when a fault current flows through a bimetal 3 consisting of a low expansion metal 1 and a high expansion metal 2, the bimetal 3 bends in the direction of the arrow due to the heat generated, and as a result, the well-known latch placed opposite the bimetal 3 It is designed to operate a mechanism or a tripping mechanism (not shown) to interrupt the circuit.
A sensor with such a configuration has the disadvantage that it can only provide its protective function against a single fault current.

Furthermore, FIG. 2 shows a conventional example of a sensor consisting of an oil dumppot, and when an overcurrent occurs, the plunger 4 gradually moves upward, and when it reaches the upper part, the movable iron piece 4' is attracted to the lid part 5. On the other hand, when a short circuit current occurs, the movable iron piece 4' is directly attracted, thereby operating the latch mechanism, but in this configuration, the suction force is small and high speed is lacking, so sufficient protection against short circuits cannot be expected. There's a problem.

Figure 3 shows a conventional example of a plunger type short circuit sensor.
When a short-circuit current or an extremely large overcurrent flows, the magnetic flux around the solenoid 6 increases, and the plunger 7 begins to advance when the attraction force due to the overcurrent exceeds the spring force, and as the plunger 7 advances, The gap decreases and pushes pin 8 outside, and the output of pin 8 is transmitted to the latch mechanism to operate the tripping mechanism, but if you try to deal with both overcurrent and short circuit current, it will be impossible. The disadvantage is that it is difficult to create a compact configuration.

The present invention was proposed in view of the above points, and
The object of the present invention is to provide a compact circuit protection sensor that can handle both overcurrent and short-circuit current, is fast, has a large attraction force, and is compact.

Hereinafter, one embodiment of the present invention will be described based on FIG. 4.

9 is a yoke made of magnetic material, and this yoke 9
A hollow cylindrical coil tube 10 is disposed inside. A coil 11 is wound around the outer periphery of this coil tube, which is inserted in series in an electric path when applied to a circuit breaker or the like. This coil 11 has a rated current of
It has a heater function that does not raise the temperature of the spring to its transformation temperature when energized at 100%, and raises the temperature above the transformation temperature at 125% energization. Rapidly displace the plunger.

Reference numeral 12 denotes a fixed iron core, which is fixed to one opposing piece of the yoke 9 and arranged at one end inside the coil tube 10. This fixed iron core 12 has a through hole 12a in the center.
The drive pin 13 is slidably disposed in the through hole 12a.

Reference numeral 14 denotes a plunger, which is disposed within the coil tube 10 in such a manner that it can be attracted to the fixed iron core 12. Therefore, this plunger 14 has an operating stroke within a range in which the leftward movement in the figure is restricted by the end face of the fixed iron core 12, and the rightward movement is restricted by the other opposing piece of the yoke 9.

Reference numeral 15 denotes a return spring, which is compressed between the large-diameter step portion 14a of the plunger 14 and the step portion 12b of the fixed iron core 12. The return spring 15 applies a bias spring force to the plunger 14, and normally presses the plunger 14 to the right in the figure.

Reference numeral 16 denotes a spring made of a unidirectional shape memory alloy such as a nickel-titanium (Ni-Ti) alloy. The other opposing piece is disposed around the plunger. The spring 16 is molded at a high temperature to have a predetermined spring force that overcomes the spring force of the return spring 15, and is set to be smaller than the spring force of the return spring 15 at room temperature. Therefore, at room temperature, the plunger 14 is pressed by the spring force of the return spring 15 and is in the position shown in FIG. 4A. When 125% of the rated current is applied to the coil 11, the temperature of the spring 16 rises to a transformation temperature (for example, 80°C).
The spring force overcomes the spring force of the return spring 15 and the plunger 1 returns to the state at the time of high temperature molding.
4 to the position shown in FIG. 4B, and the drive pin 13 is made to protrude.

Next, the operation will be explained. Since the spring 16 is below the transformation temperature when energized at 100% or less of the rated current, its spring force is smaller than the return spring 15 and is at the position shown in FIG. 4A.

If an overcurrent, that is, 125% of the rated current, is applied in this state, the temperature of the coil 11 will rise and the spring 1
6 is heated, and when the spring 16 eventually exceeds its transformation temperature, its spring force overcomes the spring force of the return spring 15, displacing the plunger 14 to the position shown in FIG. 4B. Therefore, the drive pin 13 protrudes to the outside and drives a known tripping mechanism to interrupt the electrical circuit.

Furthermore, when the electric circuit is cut off, the coil 11 no longer generates heat and the temperature of the spring 16 decreases, and when the spring 16 reaches the reverse transformation temperature, the spring force also decreases.
Due to the spring force of the return spring 15, the plunger 14 returns to the position shown in FIG. 4A.

Furthermore, if a short circuit current flows in the state shown in FIG. Regardless, the plunger 14 is rapidly attracted to the fixed iron core 12.

Next, an experimental example will be explained using a plunger rated at 2A with a plunger stroke of 3.5mm and a driving force of 50g.

Coil 11 is made of polyurethane copper wire 0.65φmm, 140
It was a turn.

The return spring 15 is made of stainless steel copper wire 0.4φmm, effective number of turns 9, winding diameter 6φmm, free length 12.8mm, stroke 0.
Spring length 8.7mm (spring force 50g), stroke 3.5
The spring length in mm was 5.2 mm (spring force 93 g).

The spring 16 is a Ni-Ti unidirectional shape memory alloy
0.6φmm, effective number of turns 9, winding diameter 6φmm, free length 18.8mm,
Spring length at transformation temperature 80℃ and stroke 0 at room temperature
7.5mm (spring force 50g or less), spring length at stroke 1.3mm (when tripping mechanism is activated) exceeding the transformation temperature
8.8mm (spring force 183g).

When such a circuit protection sensor is used in an atmosphere with an ambient temperature of 25°C and 100% of the rated current is applied to the coil 11, the current of the coil 11 is 38.3°C and the temperature of the spring 16 is 29.0°C.
℃ temperature rise, therefore the temperature of the spring 16 itself is 54℃.
However, the transformation temperature is not reached and the plunger 14 is not displaced.

Next, when 125% of the rated current is applied to the coil 11, the temperature of the coil 11 rises to 76.3°C and the temperature of the spring 16 rises to 59.9°C.Therefore, the temperature of the spring 16 itself reaches 84.9°C, reaching the transformation temperature, and the plunger 14 Displaced. At this time, when the tripping mechanism is activated, the return spring 15
is 1.3 mm shorter than the spring length at stroke 0, but its spring force is smaller than 93 g, and the spring force of the spring 16 is sufficiently large even when 50 g of the tripping mechanism driving force is applied.

Furthermore, looking at the spring force-temperature characteristics of the spring 16 when the tripping mechanism is activated, that is, at a stroke of 1.3 mm, it appears that the predetermined spring force is suddenly generated at the transformation temperature (80°C in this example). The spring force begins to increase from around 65℃, and increases almost linearly until the transformation temperature. In addition, when the temperature decreases after exceeding the transformation temperature, the spring force does not decrease immediately when it falls below the transformation temperature, but begins to decrease from around 60℃ (reverse transformation temperature) and decreases almost linearly until around 45℃. This shows hysteresis. That is, in order to expand the operating temperature range of such a circuit protection sensor, it is desirable that the difference between the transformation temperature and the reverse transformation temperature be small, or that the slope of the spring force-temperature characteristic curve be steep.

FIG. 5 shows a circuit breaker to which the circuit protection sensor of the present invention is applied, in which the tip of the drive pin 13 presses and rotates the drive rod 17, operating a tripping mechanism including an appropriate link mechanism. The movable contact 18 is separated from the fixed contact 19 to interrupt the electric circuit.

As described above, according to the present invention, a spring made of a shape memory alloy that expands due to heat from the coil in the event of overload is arranged opposite to the return spring between the fixed iron core around which the coil is arranged and the plunger. Because of this structure, it can be used as a circuit protection sensor against both overcurrent and short-circuit current, and during short-circuit operation, high-speed operation can be achieved by electromagnetic attraction force regardless of the shape-memory alloy spring. Since it is simple, it has advantages such as being able to realize compactness.

[Brief explanation of drawings]

Fig. 1 shows a conventional bimetal type electric circuit protection sensor, Fig. 2 shows a conventional oil dump pot type electric circuit protection sensor, Fig. 3 shows a conventional plunger type sensor, and Fig. 4 shows an electric circuit protection sensor according to the present invention. In an embodiment of the sensor, Fig. A is a cross-sectional view of the same as above, Fig. B is a cross-sectional view showing an operating state, and Fig. 5 is an explanatory cross-sectional view when the present invention is applied to a circuit breaker. 9... Yoke, 10... Coil tube, 11... Coil, 12... Fixed iron core, 13... Drive pin, 1
4... Plunger, 15... Return spring, 16...
Shape memory alloy.

Claims (1)

[Claims] 1. A yoke, a coil provided around a coil tube disposed within the yoke, a fixed iron core disposed within the coil tube, and a coil disposed within the coil tube that can be attracted to the fixed iron core. the plunger,
It comprises a return spring compressed between the plunger and the fixed iron core, and a spring made of a shape memory alloy that faces the return spring and is provided around the plunger so as to be able to press the plunger. Electric circuit protection sensor.