Circuit breaker having hall effect sensors

The load lugs electrically connecting circuit breakers employing electronic trip units with associated electrical distribution circuits are shaped to provide magnetic flux concentration to Hall effect current sensors within the electronic trip unit circuit. The Hall effect sensor is positioned within the shaped region of the load lug for optimum focus of the magnetic flux within each phase of a multi-phase electrical distribution system.

BACKGROUND OF THE INVENTION 
Circuit interrupters currently employed within industrial electrical 
distribution systems include separable contacts arranged for interrupting 
circuit current on command from an electronic trip unit. Current 
transducers such as current transformers as described within U.S. Pat. No. 
4,672,501 entitled "Circuit Breaker and Protective Relay Unit" are often 
used to provide the trip unit with sample indication of circuit current. 
Such current transformers require space within the circuit breaker 
enclosure and increase in size with respect to the circuit breaker ampere 
rating. The increased size results in an increase in the size of the 
circuit breakers used in higher ampere-rated applications. 
Hall effect devices such as described in U.S. Pat. No. 5,615,075 entitled 
"AC/DC Current Sensor for a Circuit Breaker" are much smaller in size than 
current transformers and allow for reduced space within the circuit 
breaker enclosure. Such Hall effect devices require some sort of a 
magnetic flux enhancer or concentrator to increase the Hall effect 
response at a further increase in the overall cost of the circuit breaker 
components. 
An additional problem with use of Hall effect devices, particularly within 
multi-phase circuits, is the sensitivity of the Hall effect device to the 
magnet flux developed within adjoining phases. An overcurrent occurrence 
within one phase, for example, could generate substantial magnetic flux to 
increase the sensitivity of the Hall effect device in an immediately 
adjacent phase resulting in a false indication of an overcurrent 
occurrence in the adjacent phase. 
The purpose of the invention is to describe an arrangement whereby Hall 
effect devices can be used with multi-pole circuit breakers without 
incurring cost increases over standard current transformers and without 
being subject to interphasal magnetic conditions. 
SUMMARY OF THE INVENTION 
The load lugs electrically connecting circuit breakers employing electronic 
trip units with associated electrical distribution circuits are shaped to 
provide magnetic flux concentration to Hall effect current sensors within 
the electronic trip unit circuit. The Hall effect sensor is positioned 
within the shaped region of the load lug for optimum focus of the magnetic 
flux within each phase and for optimum shield of the Hall effect sensor in 
one phase from magnetic flux generated in the adjoining phases. The 
shaping of the load lugs eliminates the need of additional magnetic flux 
concentrators as well as obviating the further need of an interphasal 
magnetic shield.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A molded case circuit breaker 10 is depicted in FIG. 1 and includes a 
thermoset plastic case 11 to which a cover 12 of similar material is 
attached. A movable contact 14 on a movable contact arm 15 adjoins a fixed 
contact 16 on a contact support 17 for transport of circuit current 
between a line lug 18 and a load lug 19 within each phase of a three phase 
electrical distribution circuit. The ON and OFF conditions of the contacts 
are controlled by means of an electronic trip circuit 32 carried by a 
printed circuit board 21 located under the circuit breaker cover. The 
condition of the contacts is manually controlled by means of the operating 
handle 13 extending from the top surface of the cover. A rating plug 23 
accessible from the top surface of the circuit breaker cover allows the 
ampere rating of the electronic trip circuit to be field-selectable as 
described in the aforementioned U.S. Pat. No. 4,672,501. 
In accordance with the invention, the load lug 19 comprises a metallic 
strap shaped to form a central radial projection 20 within which the Hall 
effect device, hereinafter "Hall sensor" 24 is positioned. The Hall sensor 
is a type GH 600 obtained from F.W. Bell Co., Orlando, Fla. and connects 
with the trip circuit 32 by means of a pair of conductors, one of which is 
illustrated at 22, for inputting an electric signal to the trip circuit in 
proportion to the current flow through the load lug 19 in the manner 
described within the aforementioned U.S. Pat. No. 5,615,075. 
The load lug 19 is now depicted in FIG. 2 to illustrate the positioning of 
the radial projection 20 with respect to the front 25 and rear 26 portions 
of the load lug. It is thus seen that the thickness t and the width w of 
the load lug remains constant throughout the front, rear and radial 
projection thereof to insure a uniform magnetic flux distribution within 
the linear extent x defined about the center of the radius R. 
The magnetic flux lines 29 about a representative electrical conductor 28 
having a defined radial projection 20 are illustrated in FIG. 3 wherein 
the Hall sensor 24, shown in phantom, is situated within the center 27 of 
the radial projection 20. The concentrated magnetic flux is illustrated by 
the number of flux lines 29' in the vicinity of the radial projection 20 
producing the magnetic lines of force through the Hall sensor, as 
indicated at 31. It has been determined that not only is the magnetic flux 
increase within the radial projection 20, but the positioning of the Hall 
sensor within the radial projection 20 shields and protects the Hall 
sensor from stray magnetic fields produced by adjacent conductors in a 
manner similar to that provided by a Faraday cage. 
The electrical circuitry within the circuit breaker 10 of FIG. 1 is shown 
in FIG. 4 to include the printed circuit board 21 upon which the trip 
circuit 32 is mounted. The electric contacts 14, 16 are shown connected 
within a three phase electrical distribution system that includes 
conductors 33, 34, 35 and the shaped load lugs 19 depicted in phantom, 
encompass the corresponding Hall sensor 24 within the shaped radial 
projection 20 within each separate phase. Three miniature current 
transformers 36-38 are connected within each phase to provide operating 
power to input ports 14, 15 of the trip unit circuit 32 by means of three 
separate bridge rectifiers 39-41, conductors 42, 43 and 44, diode D1, FET 
Q1 and capacitor C1. 
The conditioning circuit 45 connects between the Hall sensors 24 and the 
input ports I.sub.1 -I.sub.3 of the trip unit and includes current 
limiting resistors R1-R6, feedback resistors R7, R9, R11 and ground 
resistors R8, R10, R12 connecting with the OP AMPs 46-48 in amplifying 
stage of the conditioning circuit. The OP AMPs 46-48 connect with OP AMPs 
49-51 through limiting resistors R13-R15 and feed-back resistors R16-R18 
in the rectification stage and the OP AMPs 52-54 connect the input ports 
I.sub.1 -I.sub.3 of the trip unit 32 through feed back resistors Rl9-R21, 
R22-R24, rectifying diodes D2-D4 and conductors 55-57 to complete the 
inverter stage of the conditioning circuit 45. 
The signals inputted from the Hall sensors 24 through the conditioning 
circuit 45 are processed within the trip unit circuit 32 to determine 
instantaneous, short time and long time overcurrent conditions in the 
manner described within the recent aforementioned U.S. Pat. No. 5,615,075 
and a trip signal is outputted over conductor 60 to the gate of switching 
transistor Q2 to energize the trip solenoid 58 via output port 01. The 
cathode of Q2 connects with ground through conductor 61 and output port 02 
to complete the circuit to the trip solenoid. The solenoid operates over 
the connector 59 to separate the contacts 14, 16 within each of the 
conductors 33-35 to interrupt the circuit within each pole. 
A circuit breaker of reduced component size and expense has herein been 
disclosed whereby a Hall sensor and supplemental miniature current 
transformer within each phase of a multi-phase circuit is able to both 
power up the circuit breaker electronic trip unit as well as provide 
sample current to the trip unit without magnetic interference between the 
respective Hall sensors within adjoining phases.