JP3859217B2 - Low voltage distribution system protection device in high magnetic field environment - Google Patents

Description

  The present invention relates to a low voltage distribution system protection device that operates normally even in a high magnetic field environment and a method for selecting a low voltage distribution system protection device.

In the nuclear fusion experimental reactor, a strong magnetic field is required to confine the plasma, so a leakage magnetic field is generated, affecting surrounding equipment. The leakage magnetic field at the outer wall of the cryostat in this experimental furnace has reached 2000 gauss or more, but it is necessary to provide a low-voltage distribution line for measuring equipment or the like in such a place.
On the other hand, in a normal low-voltage distribution system, a protection device for protecting wiring and a control protection device for controlling and protecting the load are installed between the power source and the load.

  This simplified low voltage distribution system is shown in FIG. In Japan, a circuit breaker (MCCB: Molded Case Circuit Breaker) is generally used as a protective device for protecting wiring. MCCB has a function to automatically detect and shut off overcurrent in order to prevent the wire from fusing or burning out due to a short circuit current or overload current at the time of an accident. An electromagnetic contactor (MC: Magnetic Contactor) is generally used for load control, and this is a device that opens and closes contacts by exciting magnets, and for load control purposes, The short-circuit current cannot be interrupted, and the interruptable current is up to the overload region. When a motor is used as a load, an electromagnetic switch (MS: Magnetic Switch) in which a MC is combined with a thermal relay (THR: Thermal Relay) is generally used in order to prevent burning of the motor due to overload. The THR is a thermal overload detection relay using a bimetal, and when an overload current flows, the MC excitation is turned off to open the circuit and prevent the motor from burning.

These protection devices for low-voltage distribution systems and control / protection devices that control and protect the load are not suitable for use in a high magnetic field environment of 2000 gauss, such as around the above-mentioned fusion experimental reactor. We confirmed this by experiment.
According to the experiment, the circuit breaker for wiring was about 160 gauss or more, and the magnetic contactor was about 130 gauss or more.
"Mitsubishi No-fuse Circuit Breaker Technical Data", page 67, created by Mitsubishi Electric Corporation, published in March 2002

  Therefore, there is no such protection equipment for low-voltage distribution systems that normally operate in a high magnetic field environment, nor control protection equipment that controls and protects loads. It is. In addition, it is conceivable to magnetically shield each protective device of the low voltage distribution system, but it is not possible to adopt it in terms of cost, and the possibility of magnetic shielding was examined by simulating the magnetic shield to the protective device, Since the magnetic field could not be lowered sufficiently, it was necessary to consider other means.

  The present invention has been made in view of these points, and can control and protect a load protection device and a load of a low-voltage distribution system that normally operates even in a high magnetic field environment without magnetic shielding of the protection device. It is an object of the present invention to provide a simple protection device and protection method having a control protection device to perform, and to solve the above-mentioned problems.

The invention of claim 1 is a low voltage distribution system protection device in a high magnetic field environment of 2000 gauss or more, wherein the distribution line is provided with a high magnetic field application fuse, a high magnetic field application switch and a high magnetic field application thermal relay, An element made of silver ribbon or a single metal is stretched in an insulating cylinder, and the surroundings are filled with arc-extinguishing sand. The high-field application switch is a solid-state contactor, and the high-field application thermal relay is A low-voltage distribution system protection device in a high magnetic field environment, characterized in that an iron member used for a movable part other than a bimetal is a non-magnetic material.

  According to the first to fourth aspects of the invention, the low-voltage distribution system can be protected even in a high magnetic field or without a magnetic shield. Further, the protection device or method of the present invention can deal with a magnetic field in any direction and not only a static magnetic field but also a variable magnetic field.

  Each device of the low-voltage distribution system protection device was selected or improved so as not to be affected in a high magnetic field.

  FIG. 1 shows a schematic configuration of a low-voltage distribution system protection device according to the present invention, which is a simple system in which a power source and a load are in a one-to-one correspondence. The present invention is characterized by a high magnetic field application fuse 4 as a short-circuit current protection function, a high magnetic field application switch 5 as an overload current protection function and a switching function, and an overload in a distribution line 3 from the power source 1 to the load 2. A high magnetic field application thermal relay 6 is provided as a current detection function.

  As shown in FIG. 2, this high magnetic field applied fuse 4 has a structure in which a ceramic cylinder 41 is filled with a fuse element 42 made of a silver ribbon and the surroundings are fully filled with arc extinguishing sand 43. Caps 44 and 44 are put on both ends of 41, terminals 45 and 45 are provided on the outside of each cap, and each of these terminals 45 and the fuse element 42 are electrically connected. At the time of overcurrent energization, the fuse element 42 melts and evaporates the metal vapor collides with the fully filled cinnabar 43 and is prevented from diffusing into the energizing path, and the energizing path becomes an insulator, thereby interrupting the current.

  Conventionally, fuses for low-voltage power distribution systems filled with arc-extinguishing sand and made of elements as alloys have been used in the past. In addition, since there was no high magnetic field of 2000 gauss, the knowledge that it was hardly affected by the high magnetic field has never been used so far, and it has never been used for a high magnetic field.

  In order to find a device that can be used as a protective device for a low-voltage distribution system in a high magnetic field, the present inventor is in the process of screening various electrical devices, and the behavior of the fuse element in the low-voltage distribution system, that is, a normal field without a magnetic field. The behavior in the environment and the behavior in the high magnetic field are completely different, that is, in the low voltage distribution system without magnetic field, the fuse element is not affected at all, whereas in the high magnetic field of 2000 Gauss, the fuse The element noticed that it vibrates greatly due to electromagnetic force, and adopted a fuse element configuration filled with arc-extinguishing sand as means for suppressing this vibration.

In the present invention, the fuse element is not an alloy, but a silver ribbon or a single metal. However, when a characteristic test of the alloy element fuse in a high magnetic field environment is performed, a magnetic field applied to the fuse in the overload current region is obtained. This is because the result that the fusing time varies greatly depending on the direction of the film was obtained.
When such an alloy element fuse is used in a high magnetic field environment, it is necessary to measure and evaluate the range of change in fusing time depending on the magnetic field direction of the fuse, and the fuse selection becomes complicated. Therefore, there is a problem in using the alloy element fuse in a high magnetic field environment, and a fuse of an element using a silver ribbon or a single metal which has a quick disconnection with respect to both an overload current and a short circuit current.

  As the fuse, specifically, 500GA50 and 500GB100 manufactured by Hinoide Electric Manufacturing Co., Ltd. were tested in a high magnetic field of 2000 gauss. As a result, it was confirmed that they normally operated in the magnetic field. Since arc extinguishing sand is fully filled, the arc extinguishing sand receives vibrations caused by electromagnetic force applied to the element in the magnetic field. A certain effect can be expected for deterioration. Other fuses are considered to work in the same way as long as the low-voltage current-limiting fuse has a structure in which a fuse element made of a single metal or a silver ribbon is fully filled with sand. Further, the fuse holder is also made of a nonmagnetic material.

  The high magnetic field application switch 5 is a solid state contactor (SSC). This solid state contactor uses a thyristor connected in reverse parallel as a semiconductor, and controls the thyristor with a DC12-24V control signal. Although it is an element without a protecting function, the present invention has another feature in that such a simple switch is used as a high magnetic field breaker by using it together with a high magnetic field thermal relay. Actually, an SSC operation test was performed in a high magnetic field of 2000 gauss. The SSC used for the test is US-K20SSTE manufactured by Mitsubishi Electric and its drive unit UA-SH1. The test items are switching characteristics, non-energization time at the current zero point in the closed state, main circuit leakage current in the open state, and main circuit current waveform.

There was no difference in the operation of the SSC with or without a magnetic field, and the operation was normal even in a magnetic field. The SSC operation confirmation test in a magnetic field was performed with a small main circuit current of several amperes. However, in principle, it is not considered that the magnetic field affects the semiconductor, and it can be said that the SSC can be used even in the magnetic field.
The SSC (US-K20SSTE) for which the operation check test has been performed is a small-capacity product, so that the thyristor is naturally cooled by air, but a cooling fan is usually used for a large-capacity SSC. Since use of a fan utilizing an electromagnetic phenomenon is not suitable in a magnetic field, it is necessary to take measures such as increasing the size of the radiation fin. Furthermore, it can also cool using a piezoelectric element and a Peltier element.

  As the high magnetic field application thermal relay 6, an improved THR improved from a conventional thermal relay (THR) was used. THR is a thermal overcurrent relay, and is used for motor overload protection. In THR, when the overcurrent flows for a certain period of time, the bimetal is bent due to the temperature rise due to the heat generation, and the overcurrent is detected. Since THR does not use electromagnetic action in principle, normal operation is expected even in a magnetic field. However, in the THR standard product, an iron part, which is a magnetic material, is used as a movable part in the mechanism part, and there is a risk that the iron parts are magnetized and attracted to each other in a magnetic field, thereby hindering the operation. Therefore, instead of the iron part of the movable part of the THR, this is made of a non-magnetic material to obtain an improved THR.

  As an improved THR that has confirmed normal operation in a high magnetic field of 2000 gauss, it can be handled by simply changing the movable part of the TH-N20 manufactured by Mitsubishi Electric to a nonmagnetic material. It was possible. Common bimetals use magnetic iron and nickel alloys, and THR bimetals are also used. Considering use in a magnetic field, the bimetal should be changed to a non-magnetic material. However, changing the bimetal material requires redesign of the THR, resulting in the development of a new model. Due to the structure of the TH-N20, it is considered that there is little influence even if a magnetic field acts on the bimetal that is a magnetic material. Therefore, the bimetal material was not changed, but this improved THR operated normally even in the magnetic field. It has become clear that TH-N20 can cope with high magnetic fields only by demagnetizing the iron member of the movable part without demagnetizing the bimetal.

A system composed of a combination of the above devices was constructed and an evaluation test was conducted. The equipment combinations used in the test are as follows.
・ Hinoide Electric Mfg. Fuse 500GA50A
・ Mitsubishi Electric Solid State Contactor US-K50SSTE
(With drive unit UA-SH1)
・ Mitsubishi Electric thermal relay TH-N20 (improved type)
In the combined system this time, the protection is shared mainly by the solid-state contactor in the overload current region and by the fuse in the short-circuit current region.
The conditions of the combination test were as shown in Table 1, and an overload current interruption test and a protection coordination test were conducted.

As a result of the test, it was confirmed that the abnormal current could be normally cut off without any damage of the thermal relay and the solid state contactor under any condition. In addition, no significant change in cutoff characteristics was observed depending on the presence or absence of a magnetic field and the direction of application.
From the result of the combination test, overload current protection in a high magnetic field of 2000 gauss is possible by the above combination system.
In addition, as a result of the interruption test in a high magnetic field of 2000 gauss with a single fuse, no significant difference in the interruption characteristics depending on the presence or absence of the magnetic field and the application direction was found, so it is also possible to protect the short circuit current by the above combination system it is conceivable that.
Furthermore, the situation does not change even if the power distribution system becomes complicated, the wiring from the power source to the load branches, and a plurality of loads correspond to one power source. In this case, there is a protection device (fuse + SSC + THR) on the upper side of the bus, and each branch circuit requires a lower-order protection device. It is possible to achieve timed protection coordination.

It is a schematic block diagram of the embodiment of this invention. It is sectional drawing of the fuse used for the Example of this invention. It is a schematic block diagram of the conventional low voltage distribution system protection apparatus.

Explanation of symbols

1 Power supply
2 Motor 3 Distribution line
4 High magnetic field applicable fuse 5 High magnetic field applicable switch
6 Thermal relay with high magnetic field

Claims (1)

In a low voltage distribution system protection device in a high magnetic field environment of 2000 gauss or more, a high magnetic field application fuse, a high magnetic field application switch and a high magnetic field application thermal relay are provided on the distribution line, and the high magnetic field application fuse is silver in an insulating cylinder. A ribbon or single metal element is stretched and the surrounding area is fully filled with arc-extinguishing sand. The high-field application switch is a solid-state contactor. The high-field application thermal relay is used for moving parts other than bimetal. A low-voltage distribution system protection device in a high magnetic field environment, characterized in that the iron member used is made of a non-magnetic material.

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