Piston Trip Reset Lever for Circuit Breaker Debris Impediment
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Solution Overview
Problem
Molded case circuit breakers (MCCBs) with pressure-sensitive trip mechanisms often suffer from internal surface damage during arc fault events, leading to impaired movement of the movable surface and unintended tripping during normal operation due to fouling by hot gases and debris.
Innovation Solution
A mechanical linkage using a connecting element, such as a wedge-shaped lever, is introduced to transfer motion from a manual reset lever to the movable surface, ensuring proper resetting and avoiding tripping by linking the motion of the breaker handle to the movable surface, even when the surface is impeded by debris.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pressure sensitive trip mechanism is used to detect over current events, then the circuit breaker can automatically trip during over current conditions, but the interior surface can be damaged by hot gasses and molten metallic debris during arc fault events, impeding the movement of the movable surface
Solution Approach 1:
A reset lever is introduced as an intermediary component between the movable surface and the breaker handle. The reset lever acts as a mediator that transfers motion from the breaker handle to the movable surface, enabling the movable surface to overcome impediments caused by fouled interior surfaces and return to its normal operating position.
2Ease of operation
If the movable surface is biased to return to normal operating position after tripping, then the mechanism can reset automatically, but the fouled interior surface prevents the movable surface from returning to its normal operating position
Solution Approach 1:
The reset lever serves as a mechanical intermediary that amplifies and transfers the resetting motion from the breaker handle to the movable surface. This allows the movable surface to be forcibly returned to its normal position even when the interior surface is fouled, overcoming the limitation of simple bias-based automatic resetting.
3Reliability
If a mechanical linkage is introduced to connect the breaker handle to the movable surface, then the movable surface can be properly reset following a trip event, but the device complexity increases
Solution Approach 1:
The reset lever performs multiple functions: it acts as a mechanical linkage to transfer motion from the breaker handle to the movable surface, serves as a pivot point for motion transformation, and provides a means to overcome friction and fouling impediments. This multi-functionality reduces the need for additional separate components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively resets the piston trip mechanism, preventing unnecessary tripping and ensuring reliable operation by overcoming the impediments caused by arc fault debris, thus maintaining the MCCB in a safe and functional state.
Implementation Method 1
When the contacts separate, an arc occurs as the air between the contacts ionizes and electrical energy arcs between the contacts. The energy released during the arc heats the gas in the chamber and increases the pressure within the chamber.
Implementation Method 2
The energy released during the arc heats the gas in the chamber and increases the pressure within the chamber. The chamber housing the contacts is sometimes referred to as a breaking unit. The breaking unit is in fluid communication with a piston trip pressure sensitive unit, which is another chamber that includes a movable surface that moves in response to the pressure increase communicated from the breaking unit.
Implementation Method 3
An MCCB incorporating a pressure sensitive trip mechanism (also referred to as a piston trip module) generally incorporates a bias for biasing the movable surface in a normal operating position. A spring can be used to bias the movable surface. After the pressure has stabilized, the bias causes the movable surface to return to the normal operating position.
Data Source
AI summary
A device for transferring motion from a manual lever to a reset lever of a pressure trip mechanism in a molded case circuit breaker. The pressure trip mechanism is activated when hot gasses are released during an arc event and the resultant increase in pressure forces a piston in the mechanism to expand and thereby activate the breaker. In some interruption events, hot gasses, and occasionally fragments of molten metal, are responsible for marring the plastic piston surface of the pressure trip mechanism and prevent the mechanism from returning to its pre-interruption position even when it is biased to the pre-interruption position with a spring. A configuration disclosed herein provides for linking the motion of the hand-driven manual lever used to reset the breaker to the reset lever connected to the pressure trip mechanism in order to force the pressure trip mechanism to return to its pre-interruption position.