Electricity: electrical systems and devices – Control circuits for electromagnetic devices – For relays or solenoids
Patent
1990-10-04
1991-12-31
Stephan, Steven L.
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
For relays or solenoids
307326, 307113, H01H 926, H02H 1100
Patent
active
050776312
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a door interlock system and method and relates particularly but not exclusively, to a door interlock system and method for controlling the energization of power to an explosion protected electrical installation and/or enclosure that may be of a fixed or mobile nature.
A system of interlocking enclosure doors on an electrical enclosure so the electrical supply is disconnected from the electrical equipment therein if the doors are opened is a statutory requirement for explosion protection in a hazardous zone. A hazardous zone may be defined as a specified area in which there may be a dangerous concentration of flammable gases, vapours or dusts or other materials. Such areas may be in the coal mining or other mining environments, in the petroleum industry or other industries.
To prevent an explosion which may occur within an explosion proof enclosure from being communicated to the hazardous zone such as a flammable atmosphere, the enclosure must be satisfactorily explosion proof and this is statutorily controlled by ensuring the enclosure is of adequate strength and has special design at the joints. In order that the effectiveness of the joints will be preserved over the life of the equipment, and in particular that such effectiveness will not be impaired by repeated removal of doors or other parts for maintenance or inspection of the equipment within the enclosure, jointing or sealing devices such as gaskets, gland packing and the like, are not generally used. Instead, a minimum width of joint face (flame path) and maximum opening of gap according to the volume of the enclosure and the characteristics of the flammable atmosphere concerned are specified at the joints, shafts, openings, venting devices and the like. This is to ensure that if an explosion occurs within the enclosure, a flame will be restricted or cooled sufficiently during any passage across the joint face so that ignition of the surrounding flammable atmosphere will not occur.
STATEMENT OF PRIOR ART
In known electrical installations in explosion proof enclosures in hazardous environments, mechanical door interlock linkages are used which ensure that before the doors or covers to the enclosures are removed, electrical power is interrupted. Such mechanical door interlocks are generally awkward to use and with time reliability is suspect due to wear, corrosion or distortion of the linkages. More importantly, however, is that it is possible for persons to deliberately override the mechanical interlock linkages so that the enclosure doors can be opened so that the electrical energization will not be interrupted.
Throughout the present specification the term "door" will be used to describe any barrier used to cover an opening for access to an enclosure whether hinged or not.
OBJECTS AND STATEMENT OF THE INVENTION
The present invention has been devised with the object of providing a more reliable door interlock system which is less susceptible to being circumvented by personnel, and which can therefore ensure improved safety in hazardous environments.
According to the present invention there is provided a door interlock system for controlling the electrical energization of components within an enclosure which is closed by a door, the door being openable to permit access to said components, the system comprising:
a power supply circuit breaker connected with a pilot circuit relay means which will trip-out said supply circuit breaker in the event of a current disruption to said pilot circuit relay means, both said power supply circuit breaker and said pilot circuit relay means being external of said enclosure, said pilot circuit relay means being electrically connected to the up-line side of said supply circuit breaker
a power supply lead extending from said supply circuit breaker to an enclosure circuit breaker within said enclosure to supply power to energize said components within said enclosure through said enclosure circuit breaker and said supply circuit breaker,
a further lead extend
REFERENCES:
patent: 4048666 (1977-09-01), Irie et al.
patent: 4140929 (1979-02-01), Somerville
patent: 4260904 (1981-04-01), Horie et al.
patent: 4355269 (1982-10-01), Burton et al.
patent: 4378507 (1983-03-01), Root
patent: 4655634 (1987-04-01), Loy et al.
patent: 4835657 (1989-05-01), Parkhomenko et al.
Davidson Ben
Kembla Coal & Coke Pty. Ltd.
Stephan Steven L.
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