Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Tripping means
Reexamination Certificate
2000-02-24
2001-04-17
Barrera, Ray (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Tripping means
C335S042000, C335S172000, C335S174000, C335S179000, C335S229000
Reexamination Certificate
active
06218921
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to actuators for electrically operating switches in electric power circuits, and to electric power switches incorporating such actuators. The actuator is a flux transfer shunt trip actuator in which a coil is pulsed to generate a field which bucks the holding force generated by permanent magnets so that the spring drives the actuator to an actuated position to trip the operating mechanism of the electric power switch. More particularly, it relates to an arrangement for adjusting the response of the flux transfer shunt trip actuator.
Background Information
Electric power switches, such as for example, circuit breakers, transfers switches, network protectors, disconnects, and the like, typically have a stored energy powered operating mechanism that is tripped to rapidly open the power contacts of the switch. It is common to have electrically actuated devices actuating or tripping the operating mechanism. Even in the case of a circuit breaker with a thermal-magnetic trip unit, an electrically actuated device is often also provided to alternatively actuate the operating mechanism from a remote location or for other conditions, such as under voltage, loss of phase, or off frequency. In many cases, an electronic trip circuit is used instead of a thermal-magnetic mechanism for overcurrent protection.
It is becoming wide spread for the electronic circuits now used to actuate these trip devices to generate logic levels signals which have insufficient energy to actuate solenoids previously used for these purposes. A low energy device which has been developed to trip the operating mechanism of an electric power switch in response to logic level signals, is the flux transfer shunt trip actuator. These devices utilize a spring to bias a plunger to an actuated position. Permanent magnets generate sufficient magnetic force to override the actuating force generated by this spring and hold the plunger in an unactuated, typically a retracted, position. The actuating signal is applied to a coil to generate an electromagnetic force which bucks the force generated by the permanent magnets. With the permanent magnet field at least partially cancelled, the spring actuates the plunger. A short duration pulse applied to the coil is sufficient to actuate the plunger and trip the operating mechanism of the switch.
While these flux transfer shunt trip devices are very effective, slight variations in the strength of the magnets, springs, or even plating thicknesses can affect the current required to release the plunger. U.S. Pat. No. 5,886,605 discloses a flux transfer shunt trip actuator which incorporates an arrangement for calibrating the device. In this patented actuator, the spring biasing the plunger to the tripped position is mounted inside the cylindrical plunger. A screw threaded into the free end of the plunger bears against the spring to adjust the spring preload. While this is effective for calibrating the device, it results in changing the effective length of the plunger, and therefore, varies the spacing between the plunger and a trip button on the operating mechanism of the electric power switch.
Accordingly, there is room for improvement in flux transfer shunt trip actuators and electric power switch incorporating them.
In fact, there is a need for a flux transfer shunt trip actuator and an electric power switch incorporating such an actuator, which provides an improved arrangement for calibrating the actuator.
More particularly, there is a need for such an actuator and electric power switch incorporating the actuator, in which the actuator can be calibrated without affecting the spacing between the actuator plunger and the operating mechanism of the electric power switch.
There is a more specific need, for an improved flux transfer shunt trip device and an electric power switch incorporating the actuator, in which the preload on a spring biasing the actuator plunger can be adjusted without affecting the positioning or length of the plunger.
SUMMARY OF THE INVENTION
These needs and others are satisfied by the invention which is directed to a flux transfer shunt trip actuator in which the actuator can be calibrated by adjustment of the preload biasing spring without changing the position or length of the actuator plunger biased by this spring. More particularly, the invention relates to a flux transfer shunt trip actuator which includes a housing having a magnetically permeable seat, a magnetically permeable plunger mounted by the housing for movement between a retracted position with a first end seated against the seat and an actuated position with the magnetically permeable plunger spaced from the seat. A biasing spring biases the plunger toward the actuated position. One or more permanent magnets generate a permanent magnet force sufficient to overcome the biasing spring to hold the magnetically permeable plunger in a retracted position seated against the magnetically permeable seat. A coil generates an electromagnetic field when energized which bucks the permanent magnet field so that the biasing spring moves the plunger to the actuated position. An adjustment device adjusts the preloading on the biasing spring without adjusting the position or length of the plunger.
More specifically, the housing comprises a magnetically permeable U-shaped frame having a bight and a pair of legs spaced apart and extending from the bight. The permanent magnet or magnets are mounted between the legs and define a gap. A magnetically permeable seat member projecting from the bight toward the gap terminates in a free end which forms the seat. The first end of the magnetically permeable plunger extends into the gap when seated in the retracted position against the seat. The biasing spring has a first end bearing against the magnetically permeable plunger and the adjusting device comprises an adjusting member and a mount mounting the adjusting member for movement relative to the bight toward and away from the magnetically permeable plunger. The adjusting member bears against the second end of the biasing spring to adjust the preload. Thus, the actuator is calibrated through adjustment of the preload on the biasing spring, yet the plunger length and position do not change.
Even more specifically, the mount for the adjusting member is a threaded shaft which is coaxial with the seat member. The adjusting member is moved along the threaded shaft by a threaded member which engages the threaded shaft and bears against the adjustment member to set the position of the adjusting member on the threaded shaft and, therefore, the preload on the spring. In a preferred embodiment of the invention, the threaded shaft projects from the bight of the frame in a direction opposite the orientation of the legs of the frame. The adjusting member has at least one projection extending toward and engaging the first end of the biasing spring. In a particularly preferred embodiment, these projections extend through apertures in the bight of the frame and are a pair of opposed cylindrical sections each bearing against the biasing spring which is a helical compression spring coaxially mounted on the seat member together with the coil.
The invention also embraces the electric power switch incorporating such an adjustable flux transfer shunt trip actuator.
It is therefore, an object of the invention to provide an improved flux transfer shunt trip actuator and an electric power switch incorporating such an actuator.
It is a further object of the invention to provide such an improved actuator and electric power switch incorporating the actuator in which the actuator can be calibrated without affecting the length of the actuator plunger.
It is a more specific object of the invention to provide such actuator and electric power switch which can be calibrated by adjusting the preload on the biasing spring without changing the position or length of the plunger.
REFERENCES:
patent: 4489295 (1984-12-01), Altenhof, Jr. et al.
patent: 4639701 (1987-01-01), Shimp
patent: 5453
Eberts William George
Everett James Russell
Slepian Robert Michael
Barrera Ray
Eaton Corporation
Moran Martin J.
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