US3425017A

US3425017A - Current sensor and short circuiting means therefor

Info

Publication number: US3425017A
Application number: US705251A
Authority: US
Inventors: Guenther G Schockelt
Original assignee: S&C Electric Co
Current assignee: S&C Electric Co
Priority date: 1966-06-30
Filing date: 1967-11-29
Publication date: 1969-01-28
Anticipated expiration: 1986-01-28

Description

Jan. 28, 1969 e. G. SCHOCKELT 3,425,017

CURRENT SENSOR AND SHORT CIRCUITING MEANS THEREFOR Original Filed June so, 1966 j I j /3.2

05 04 w m M M15 7 49/415 440 Q 63 /60 j M WM /55 62 /57 j I A I I l- 7 v g 6016/ A56 A37 /59 H6? m2 m 0/ 2 W5 United States Patent 7 Claims ABSTRACT OF THE DISCLOSURE A current sensor having contacts bridged by a fusible element operates on predetermined current flow to close these contacts and perform a mechanical control function.

This application is a division of application Ser. No. 561,839, filed June 30, 1966.

This invention relates to metal enclosed switchgear for application to alternating current circuits operating at voltages of the order of 13.2 kv. It can be employed for circuits operating at higher -or lower voltages and for different current ranges as may be required. It constitutes an improvement over the constructions disclosed in US. Beebe et al. Patent 3,055,996, issued Sept. 25, 1962, and in copending applications Ser. No. 552,282, filed May 23, 1966, and Ser. No. 561,839 filed June 30, 1966.

For electric power distribution at various locations, such as shopping centers, high rise buildings, industrial plants, etc., and at relatively high voltage, for example 13.2 kv., switching equipment is provided that must be reliable and safe. Such equipment is arranged for normal supervision and operation by personnel of limited skill whose capabilities extend only to routine operations involving opening and closing a circuit, changing blown current responsive means, such as fuse devices, etc. Because of competitive conditions, the cost of this switching apparatus is required to be held to a minimum consistent with proper and safe operation.

Among the objects of this invention are: To employ a current sensor with fusible means capable of carrying full load current continuously and arranged to blow on flow of excess current therethrough in accordance with the time-current characteristic of a fuse to release an operating member for opening a current interrupter; and to shunt the blown fusible means to maintain circuit continuity with respect only to the blown fusible means to permit opening of the circuit by the circuit interrupter.

In the drawing: FIG. 1 is a longitudinal sectional view, at an enlarged scale, of the current sensor. FIG. 2 is a vertical sectional view, taken generally along the line 2-2 of FIG. 1. FIG. 3 is a View in end elevation, looking from right to left, of the terminal member employed in the current sensor shown in FIG. 1. FIG. 4 is a view at a reduced scale and somewhat similar to FIG. 1 to show the current sensor in the operated condition.

In FIG. 1 a current sensor is indicated, generally, at 40 and it is arranged to be connected in series circuit relation with a switch blade and a current interrupter as disclosed in the application of which this application is a division. The current sensor 40' is mounted on a platelike lower end 74 of a conductor that forms a part of the series circuit to the current interrupter and switch blade. The current sensor 40 is mounted directly on an upper contact plate 75 which has a plate 76 of insulation between it and the plate-like lower end 74 of the conductor. It will be observed that the

conductor plates

74 and 75, with the insulating plate 76 therebetween, are

3,425,017 Patented Jan. 28, 1969 held together by flat head screws 131 which extend through insulating bushings 132 in the conductor plate 74. An internally threaded metallic guide bushing 133, preferably formed of copper, is secured to the upper contact plate and has threaded therein one end of a tubular metallic housing 134 that also is formed preferably of copper. At its distal end the tubular metallic housing 134 is provided with a cap 135 of copper and it has an inwardly extending annular contact portion 136 that is arranged to be engaged, in a manner to be described, by contact fingers 137, FIG. 2, which extend from a contact tube 138 that preferably is formed of copper and makes contact with the conductor plate 74. An insulating sleeve 139 serves to space the tubular metallic housing 134 from the contact tube 138.

In order to insulate normally the annular contact portion 136 from the contact fingers 137, an internal layer of insulation 140* is formed at one end of a metallic tension tube 141 which is slidably mounted within the contact tube 138: and extends outwardly therefrom. The metallic tension tube could be formed wholly of insulation. However, in order to provide the requisite strength within the limited confines of the contact tube 138, it has been found desirable to employ the metallic tension tube 141, preferably formed of steel, with the internal layer of insulation 140 in the manner described. Slotted openings 142 are located in diametrically opposite sides of the tension tube 141 and at the end opposite the layer of insulation 140. The inner ends of the slotted openings 142 form shoulders 143, FIG. 4, that are arranged to engage inner sides 144 of an end portion 145 of a terminal member 146, FIG. 3, which has a press fit with the outer end of the contact tube 138. The terminal member 146 preferably is formed of copper. The tension tube 141 extends past the end portion 145 of the terminal member 146 and through an opening 147 in the conductor plate 74. Its outer end is closed by a metallic end plug 148 that may be formed of aluminum. A coil compression spring 149 reacts between a shoulder 150 and the end surface of the end portion 145 for normally biasing the tension tube 141 outwardly.

In order to restrain the outward movement of the tension tube 141 as urged by coil compression spring 149, fusible means, shown generally at 152, are employed. Under normal operating conditions the fusible means 152 shunts the contact portion 135 and the contact fingers 137 extending from the contact tube 138. The fusible means 152 includes a fusible element 153 which may be a coil of silver wire. One end of the fusible element 153' is secured to the inner end of a terminal member 154, preferably in the form of a copper rod, which extends through the cap 135 and contact portion 136 and is secured thereto by a set screw 155. The other end of the fusible element 153 is secured to a hexagonal head 156 of a fuse element fitting, shown generally at 157', which is threaded at 158 into the adjacent end of a stem 159 which forms a part of the terminal member 146. The fusible means 152 also includes a strain element 160, preferably in the form of nichrome wire, with one end being secured to the terminal member 154 and the other end extending through the fitting 157 and through the terminal member 146. The outer end of the strain element 160 extends through the metallic end plug 148 and is secured thereto by a set screw 161. Extending outwardly from the end plug 148 is a quick detachable fitting 162 the purpose of which will be described presently.

Normally the current path from the conductor plate 75 to the conductor plate '74 is as indicated by the line with arrow heads and extends through the metallic guide bushing 133, tubular metallic housing 134, cap 135, terminal member 154, fusible means 152, fuse element fitting 1'57, terminal member 146, and contact tube 13-8 to the conductor plate 74. The fusible means 152 are arranged and constructed to carry the normal current flow of the circuit in which the current sensor 40 is connected and also to withstand the flow of overload current in accordance with conventional fuse practice. The timeourrent characteristic for the fusible means 152 is selected in accordance with the circuit requirements. When the current flow exceeds the rating of the current sensor 40', the fusible element 153 melts and the entire current flow then is transferred to the strain element 160 which promptly melts and releases the end plug 148 for movement outwardly to the position shown by broken lines in FIG. 1 under the influence of the coil compression spring 149. This is accompanied by endwise movement of the tension tube 141 and by withdrawal of the layer of insulation 140 from between the annular contact portion 135 and the adjacent ends of the contact fingers 137. Their inherent resiliency is sufficient to move them into contact engagement with the contact portion 136, aided by the magnetic forces generated by current flow in the closely adjacent housing 134 and contact fingers 137, with the result that the gap formed by blowing of the fusible means 152 is promptly shunted. The reason for this shunting arrangement is that the current sensor 40 is not intended to have any current interrupting capacity. The current flow then, as shown by the broken line in FIG. 12, is transferred to flow directly from the conductor plate 75' through the metallic housing 134 and the contact fingers 137 of the contact tube 138 to the conductor plate 74. Here the tension tube 141 is moved to its outermost position as limited by engagement of the shoulders 143 with the inner sides 144 of the end portion 145.

Instead of providing the layer of insulation 140 on the inside of metallic tension tube 141, the outer surface of the contact portion 136: can be coated with a suitable insulating material which can be readily punctured when the voltage resulting from the blowing of the fusible means 152 is applied between the contact portion 135 and the contact fingers 13-7. However, the tension tube 141 still is employed, although not of the same length, to provide a member that moves from one position to another as a result of blowing of the fusible means 152.

As described in the application of which this application is a division, the outward movement of the tension tube 141 accompanied by corresponding movement of the quick detachable fitting 162 is employed to trip a spring biased linkage which is arranged to open the circuit interrupter and thereafter move the series connected switch blade to the open circuit position.

What is claimed as new is:

1. Current responsive means for controlling a circuit interrupter connected in series therewith comprising:

fusible means for connection in series with said circuit interrupter, 1 operating means biased for movement from one position to another position for opening said circuit interrupter and restrained by said fusible means, contact means arranged to shunt said fusible means on blowing thereof,

means biasing said contact means toward contact engagement, and

insulating means biased for movement from a position holding said contact means in said open position to another position permitting closure of said contact means, said insulating means being restrained by 5 said fusible means.

2. Current responsive means comprising:

first and second conductor means,

means holding said first and second conductor means in insulated spaced relation,

a tubular metallic housing connected at one end to said first conductor means and extending laterally therefrom,

contact means carried by said tubular metallic housing at its distal end and extending inwardly thereof, contact tube connected at one end to said second conductor means, telescoped within said tubular metallic housing, and having a plurality of contact fingers biased toward contact engagement with said contact means,

fusible means interconnecting said contact means and said contact tube and providing a path along which current normally flows therebetween, and

insulating means interposed between said contact means and said contact fingers and arranged to be removed on blowing of said fusible means whereby the current flow is shifted from said path to another path through said contact means and said contact fingers.

3. Current responsive means according to claim 2 30 wherein:

said insulating means at least forms a part of a tubular member telescoped with said contact tube and movable endwise thereof,

a spring biases said tubular member in a direction to remove said insulating means from between said contact means and said contact fingers, and means responsive to blowing of said fusible means restrains said tubular member. 4. Current responsive means according to claim 3 wherein:

said first and second conductor means are in the form of metallic plates in overlying relation, and said means holding them in insulated spaced relation includes a plate of insulation interposed therebetween. References Cited UNITED STATES PATENTS 974,109 10/1910 Auel et al 200ll6 BERNARD A. GILHEANY, Primary Examiner.

HAROLD BROOME, Assistant Examiner.

US. Cl. X.R. 337-221