Clapper armature system for a circuit breaker

Details Clapper armature system for a circuit breaker Clapper armature system for a circuit breaker

1999-09-23

2001-12-04

Donovan, Lincoln (Department: 2832)

Electricity: magnetically operated switches, magnets, and electr

Electromagnetically actuated switches

Automatic circuit-interrupting devices

C335S172000

Reexamination Certificate

active

06326869

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to electrical equipment protective devices generally and more particularly, to a circuit breaker, operating under low current conditions, that includes a clapper armature system for tripping the circuit breaker in response to a short circuit condition.
Circuit breakers typically provide protection against persistent overcurrent conditions and against very high currents produced by short circuits. This type of protection is provided in many circuit breakers by a thermal-magnetic trip mechanism having a thermal trip portion and a magnetic trip portion, similar to that shown in FIG.
1
. The trip mechanism
10
of
FIG. 1
includes a conductor
12
that carries current from a load terminal to the pair of contacts for interrupting current in response to an overcurrent or short circuit condition.
The thermal trip portion
13
of the trip mechanism
10
includes a bimetallic strip
14
having one end
16
attached to the conductor
12
. The bimetallic strip is formed of two metals having different coefficients of expansion such that a free end
15
of the bimetallic strip bends or deflects counterclockwise when the temperature exceeds a predetermined temperature. As shown, the bimetallic strip
14
is disposed adjacent and substantially parallel to a portion of the conductor
12
. When an overcurrent condition occurs, the conductor generates heat, which in turn increases the temperature of the bimetallic strip. If the temperature of the bimetallic strip exceeds the predetermined set point, the free end
15
of the bimetallic strip deflects to actuate a linkage interconnected to the pair of separable contacts. The linkage then opens the pair of contacts to interrupt the current and thereby, protect the load from the overcurrent condition.
The magnetic trip portion
17
of the trip mechanism
10
includes a clapper
18
having one end
20
pivotally connected to the housing of the circuit breaker and a free end
22
that engages the linkage to open the pair of separable contacts in response to a short circuit condition. As shown in
FIG. 1
, the clapper is disposed adjacent the bimetallic strip
14
. A generally U-shaped yoke
24
is disposed about the conductor
12
and the bimetallic strip. Arms
26
and
28
of the yoke extend proximate the clapper
18
. When a short circuit condition occurs, a magnetic field in the yoke is generated proportional to the current passing through the conductor. When the magnetic force attracting the clapper
18
is greater than a predetermined level, the clapper pivots clockwise to engage the yoke
24
and actuate the linkage to open the contacts.
The trip mechanism
10
of
FIG. 1
is commonly used to protect loads that operate under high current conditions, but not for low operating current conditions. Generally these thermal-magnetic trip mechanisms
10
are unable to afford protection with electric current in the range of 16 to 60 amperes. Such current level is unable to induce a magnetic field of the intensity required for clapper movement when short current protection is required. Typically, the magnetic trip portion
17
of current trip mechanisms
10
for circuit breakers includes a solenoid that is substantially more sensitive to the low current operating conditions.
BRIEF SUMMARY OF THE INVENTION
In an exemplary embodiment of the invention a clapper armature system for a circuit breaker includes a heater having a heater element and a pair of electrical conductors. The heater element is electrically connected to and disposed between the conductors. The conductors are spaced from the heater element to provide a pair of slots between the conductors and the heater element. A heat sensitive strip having one end electrically connected to at least one conductor is disposed proximate the heater element. A yoke has a pair of arms with each arm passing through a respective slot of the heater. The heater element and heat sensitive strip are disposed between the arms and provide a plurality of current paths between the arms. A clapper is disposed pivotally proximate the arms. The clapper pivots to the arms of the yoke to open a pair of separable contacts of the circuit breaker in response to a predetermined current passing through the heater and heat sensitive strip.


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