Motor Protector Cover Barriers for Arc Containment
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Solution Overview
Problem
Conventional enclosed break devices, such as the 4TM and 5TM, do not meet the requirements of the second edition IEC Standard 60079-15, which demands that they pass a make-and-break test 10 times without communicating an internal explosion to external flammable gas or vapor, due to gaps between the cover and base allowing flammable gas to enter and ignite.
Innovation Solution
The modification of the cover with multiple wall barriers to impede arc travel and reduce the volume for potential explosions, combined with sealing openings in the housing with epoxy to prevent explosion propagation, ensures compliance with the standard by minimizing the entry of flammable gases and preventing ignition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional 4TM/5TM device design is used with gaps between cover and base, then ease of manufacture is improved, but reliability deteriorates due to flammable gas entry and ignition risk
Solution Approach 1:
The cover is segmented into multiple wall barriers (first wall, second wall, third wall) that create separate compartments. This segmentation blocks the arc path and prevents flammable gas from reaching the electrical contacts through the gaps between cover and base, thereby improving reliability while maintaining the simple manufactured design
Solution Approach 2:
Multiple wall barriers are introduced as intermediary structures between the electrical contacts and the external environment. These walls act as mediators that intercept and block the arc path, preventing ignition of flammable gas that enters through gaps, thus resolving the contradiction between easy manufacture and reliability
2Reliability
If multiple wall barriers are added to the cover, then reliability is improved by blocking arc paths, but device complexity increases
Solution Approach 1:
The multiple wall barriers are merged into a single integrated cover structure. The first wall, second wall, and third wall are formed as one piece with the cover, combining multiple protective functions into a single component. This reduces assembly complexity while maintaining the reliability benefits of multiple barriers
Solution Approach 2:
The cover with integrated multiple wall barriers serves multiple functions simultaneously: it encloses the electrical contacts, blocks arc paths in multiple directions, reduces internal volume, and prevents flammable gas entry. This multi-functionality justifies the added structural complexity by delivering comprehensive protection
3Object-affected harmful factors
If cover volume is reduced by multiple wall barriers, then harmful factors are reduced by minimizing fuel supply, but manufacturing precision requirements increase
Solution Approach 1:
The multiple wall barriers are positioned strategically at specific locations where arc paths are most likely to escape. The walls are not distributed uniformly but placed locally where needed to block arcs from the contacts to the openings. This localized approach minimizes the volume reduction requirement while maintaining manufacturing feasibility
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
The modified design effectively prevents the ignition of external flammable gases by blocking arc paths and reducing fuel volume, enabling the device to withstand multiple make-and-break tests without external ignition, thus meeting the revised IEC Standard 60079-15 requirements.
Implementation Method 1
The sealing can be utilized by itself or along with the cover modifications noted above
Implementation Method 2
The modification of the cover with multiple wall barriers to impede arc travel and reduce the volume for potential explosions
Implementation Method 3
The disc is adapted to snap from one dished configuration to an opposite dished configuration upon being heated to a preselected temperature
Implementation Method 4
a heater is disposed therein in heat transfer relation to a thermostatic disc seated in the base over the well
Data Source
AI summary
An enclosed motor protector has a housing formed by a base (10) and a cover (12) received on the base and enclosing a recess (10a) formed in the base. A first terminal (14) extends through an opening in the housing and mounts a stationary contact (14c) within the recess. An elongated movable contact arm (18) is cantilever mounted at one end in the recess and mounts a second movable contact (18a) on a free end of the arm which is adapted to move into and out of engagement with the stationary contact. A heater (20) is mounted in the recess in heat transfer relation with a snap acting thermostatic disc (22) disposed adjacent to the movable contact arm so that upon reaching a preselected temperature the disc will snap from one dished configuration to an opposite dished configuration with its motion transferred to the movable contact arm to move the contacts out of engagement. The cover is formed with a first multiple wall barrier (122) in the form of a triangular body when seen in a lateral cross section closing a first terminal receiving opening and a second multiple wall barrier (124) closing a second terminal receiving opening to interrupt the travel of arcs and the inlet of explosive gas to the enclosure. These features also diminish air supply in the enclosure to thereby weaken any combustion.