1. Field of the Invention
This invention relates to switches used in electric power distribution systems such as circuit breakers, disconnects and transfer switches. More particularly, it relates to the operating mechanism for opening and closing the contacts of molded case power switches, and specifically an operating mechanism which uses energy stored in a spring and delivered through a cam assembly to close and open the switch contacts.
2. Background Information
Switches used in electric power distribution systems are well known. Such switches include circuit breakers which provide overcurrent and short circuit protection. Similar switches without such protection are used as disconnects to isolate a particular load or section of the distribution system and as transfer switches to switch between sources such as a utility and an emergency power generator.
Different types of switching mechanisms are used for such power switches in different parts of the power distribution system depending in part upon the current to be handled by the particular switch. The various switches are designed to handle up to a specified "rated" current. One of the factors related to the rated current is the amount of force needed to close the switch and hold it closed against the magnetic repulsion force generated by the current.
Molded case switches, so named because the mechanism is mounted in a molded, electrically insulative resin housing, typically have a rated current of from 3 to 2,500 amperes. Conventionally, such molded case switches have a spring powered toggle mechanism which opens the contacts. The opening spring is charged by closing of the switch. This is performed manually by a handle or can be effected remotely with a motor operator.
Larger power switches which are required to withstand the larger magnetic repulsion forces generated at the higher current ratings, require larger forces to close the contacts. Typically, such higher closing forces cannot be generated by a direct acting manual handle. Thus, the larger power switches have a closing spring which releases stored energy to close the contacts. This closing spring may be charged manually, usually by a handle acting through a rachet mechanism, or electrically by a motor operator. Typically, these power switches have a closing cam driven by the closing spring which rotates a pole shaft to in turn close the contacts. Separate latches are used to close and open the contacts.
Improvements in molded case switches for electric power distribution systems have resulted in switches with higher current ratings. However, the closing forces required for these molded case switches with higher current ratings cannot be conveniently generated by the direct acting handle or the conventional motor operators designed for such switches. Furthermore, the conventional spring driven closing mechanisms of the larger circuit breakers, with their pole shaft and other components are too large for adaptation to molded case switches with higher rated currents.
Therefore, there is a need for improved molded case switches for electric power distribution systems with extended current ratings.
More particularly, there is a need for such improved molded case switches which incorporate a closing spring.
There is an additional need for a mechanism with a closing spring which can be accommodated in the conventional molded casing.
There is a further need for such a molded case switch which incorporates a close spring but which does not require complete redesign of the entire switch.