US 3745369 A
Description (OCR text may contain errors)
United States Patent [191 Yamagata July 10, 1973 CIRCUIT BREAKER  inventor:
 Assignee: Mitsubishi Denki Kabushiki Kaisha,
Tokyo, Japan  Filed: June 5, 1972  Appl. No.: 259,870
Kiyoshi Yamagata, Tokyo, Japan  US. Cl 307/131, 317/22, 317/41  Int. Cl. H0lh 35/00  Field of Search 317/22, 23, 41, 37;
[5 6] References Cited UNITED STATES PATENTS 3,599,043 8/1971 Biedennann 317/41 X Primary Examiner-Herman J. l-lohauser A tt0rney- Norman F. Oblon. Marvin J. Spivuk et ill.
[5 7 ABSTRACT A circuit breaker includes the series combination of a breaker element and a self-restoring type current limiter in a feeder circuit. The self-restoring type current limiter responds to the current of the feeder circuit. A relay is provided and responds to the voltage between both of the terminals of the self-restoring type current limiter so as to cause a breaking operation of the breaker under abnormal operating conditions.
4 Claims, 1 Drawing Figure PAIENIEU JUL I cum 745,135 9 crncurr BREAKER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention generally relates to circuit breakers and more particularly to a circuit breaker which serially includes as circuit breaker and a current limiter such that any overcurrent will be limited by the current limiter and detected whereupon the ciruit breaker will be automatically restored for reuse after the overcurrent condition is eliminated.
2. Description of the Prior Art In the past, it was customary that when a conventional circuit breaker was operated by the voltage outgoing means provided in the circuit breaker the excitation of the coil of the voltage outgoing means was made through a contact of an induced overcurrent type relay or through a contact of other control type switches.
However, since the the induced overcurrent type relay or control type switches used did not themselves have a current limiting function, there was no means for protecting the circuit breaker. In order to overcome this dufficulty, a fusing element was provided in the conventional current limiting fuse having a silver alloy element, whereby the relay or control switches were operated to operate the voltage outgoing means of the circuit breaker.
Since in the prior art device the current limiting device was fused, it was necessary to change the current limiting fuse at each fusing. Such a procedure required a long time for restoring the circuit and it was inconvenient in that spare fuses had to be maintained.
SUMMARY OF THE INVENTION It is an object of this invention to provide a new and improved unique circuit breaker having a self-restoring type current limiter for accurately exciting the voltageoutgoing means thereof to cut off an abnormal current and to easily restore the circuit in a short time.
Briefly, these and other objects of this invention are attained by providing a circuit breaker which includes a breaker and self-restoring type current limiter in a feeder circuit. The self-restoring type current limiter responds to the current of the feeder circuit. A relay is provided and responds to the voltage across the selfrestoring type current limiter to cause a breaking operation of the breaker under abnormal or overcurrent conditions.
BRIEF DESCRIPTION OF THE DRAWING The foregoing object and advantages of this invention will become more readily appreciated by reference to the following detailed description, when considered in connection with the accompanying drawing, which is a circuit diagram of a circuit breaker according to the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawing, a circuit diagram of one preferred embodiment of the circuit breaker of this invention is shown as including a self-restoring type current limiter wherein an alkali metal such as sodium, potassium or a mixture thereof is packed in a case. The currenlimiter 10 has high conductivity at normal temperatures, but has a high electrical resistance when the alkali metal is vaporized by the Joule-heat of a current.
A detector coil 20 is provided and is excited by a high voltage as a result of an increase in the resistance between the terminals of the self-restoring type current limiter 10. A switch 30 is provided and is operated by the detector coil 20. The detector coil 20 and the operation switch 30 form a relay R.
A breaker 40 is connected in series with the selfrestoring type current limiter l0 and the combination constitutes a feeder circuit. A conventional voltageoutgoing means 50 which is connected to the operation switch 30 is provided and the same is excited by impressing a rated voltage thereacross. At such time the ratch mechanism of the breaker 40 is operated by a suction generated thereby to open the breaker 40. A voltage-power source-terminal 60 is provided for supplying the necessary voltage for operating the voltageoutgoing means 50 when the operation switch 30 is closed.
An electric power source terminal and a load terminal are provided for the breaker 40.
The operation of the apparatus for the circuit breaker as set forth above can be explained as follows:
Under normal operating conditions, the self-restoring type current limiter 10 has good electrical conductivity and, accordingly, the voltage between the terminals of the detector coil 20 is small. Thus, the relay R is not operated and the operation switch 30 will remain in an open condition. Accordingly, the circuit of the voltageoutgoing means 50 will be in open circuit so that electric power is supplied from the electric-power sourceterminal 70 through the breaker 40 and the selfrestoring type current limiter 10 to the load through terminal 80.
When an overcurrent occurs due to a shot-circuit accident in the load or the like, the current limiting material in the self-restoring type current limiter 10 will be vaporized by the Joule-heat caused by the overcurrent. A high electrical resistance will thereby exist across the current limiter 10 and a high voltage will thus be impressed between the terminals of the current limiter 10 and the short-circuit current caused by the accident will thereby be limited. The detector coil 20 will be excited by the high voltage across the current limiter l0 and the relay R will be operated to shut the operation switch 30 and thereby impress a voltage from the voltage-power source-terminal 60 to the voltage-outgoing means 50. The voltage-outgoing means will cause operation of the ratch mechanism of the breaker 40 (not shown in the drawing) by suction in response to the voltage which is impressed on the coil of the voltageoutgoing means 50, whereby the breaker 40 will be opened and break the supply of electric power from the power source at terminal 70 and thereby protect the circuit from the overcurrent.
When the cause of the accident is removed, the current limiting material of the current limiter 10 will be cooled to the normal temperature and the current limiting material will then again become a good electrical conductor. Accordingly, the voltage drop across the current limiter 10 will be quite small whereby the operation switch 30 of the relay R is opened, the voltageoutgoing circuit of the voltage-outgoing means 50 is opened, and the breaker will again be ready to receive a continuous current at the terminal 70.
It should be noted that while in the above embodiment the operation switch of the relay R is shown as exciting the coil of the voltage-outgoing means 50, the invention is not so limited and it is possible to use a normally closed contact as the operation switch with the excitation of the coil of the short-voltage-outgoing means being extinguished in order to break the circuit for protection from an over-current.
It should now be apparent that, in accordance with this invention, a self-restoring type current limiter is provided when a short-circuit accident is caused. Accordingly, after a short-circuit condition, the breaker 40 is again allowed to operate without the need for changing a fuse, when the cause of the short-circuit is removed. The restoration operation of the present invention is quite simple, and since the short-circuit current is limited by the current limiting effect of the current limiter, the breaker can be easily broken.
Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. Thus, for example, since the operation of the breaker of the present invention is conducted by a voltage-outoing means or a short-voltage-outgoing means, it is possible to remotely control the opening of the breaker. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
1 claim 1. A circuit breaker which comprises:
a breaker in a feeder circuit which is located between a power source and a load;
a self-restoring type current limiter located in said feeder circuit and which responds to the current thereof; and,
a relay for responding to the voltage across said selfrestoring type current limiter to break said breaker under abnormal operationconditions;
wherein said self-restoring type current limiter comprises an electrically conducting material which, due to Joule-heat, vaporizes during an overcurrent condition, and condenses after said overcurrent condition is removed.
2. A circuit breaker which comprises:
a breaker having a mechanism for operating an out going means by excitation or extinction of an excltation coil;
a self-restoring type current limiter connected in series to said breaker; and,
a relay connected in parallel to said self-restoring type current limiter, said relay being connnected to said coil of said outgoing means in order to electrically detect a current limiting operation of said self-restoring type current limiter and in accordance therewith to operate to cause said breaker to break; wherein said self-restoring type current limiter comprises an electrically conducting materlal which, due to Joule-heat, vaporizes during an overcurrent condition, and condenses after said overcurrent condition is removed.
3. The circuit breaker of claim 2, wherein said selfrestoring current limiter is made of an alkali metal, wherein said relay includes a detecotr coil WhlCh is connected across said self-restoring type current limiter and wherein said outgoing means is operated by a voltage generated in said detector coil.
4. A circuit breaker which comprises:
a first circuit for connecting a breaker and a selfrestoring type current limiter in series between a power source terminal and a load terminal; and, second circuit for connecting a detecor coil of a relay which is connected in parallel to selfrestoring type current limiter of the first circuit and an operation switch which is operated by a voltage of the detector coil f0 said relay and a voltageoutgoing means of said breaker; wherein said selfrestoring type current limiter comprises an electrically conducting material which, due to Joule-heat, vaporizes during an over-current condition, and condenses after said overcurrent condition is removed.