IEEE Std 1458 pdf free download
IEEE Std 1458 pdf free download.Selection, Field Testing, and Life Expectancy of Molded-Case Circuit Breakers for Industrial Applications.
3.6.3 Over-toggle
In a circuit breaker with an over-toggle mechanism, a manual handle on the circuit breaker is operated to set the mechanism in motion. The handle is moved to open or close the circuit breaker until a point is reached where the handle goes over-toggle (past the point of no return), and the spring-assisted mechanism automatically opens or closes the circuit breaker. This toggle mechanism is called the quick-make, quick-break type, meaning that the speed with which the contacts open or close is independent of how fast the handle is moved. A motor operator can be used to operate the handle automatically in lieu of manually going through the motion. The design is such that the circuit breaker would trip open when called upon to provide its expected protection, even if the man ual handle were to he held in the ON (closed) position.
3.6.4 Two-step stored energy
The closing springs in this type of mechanism are used to store energy for use when needed. The process of’
storing energy and closing the circuit breaker is separated into the following two steps:
I ) Closing springs are charged with the circuit breaker open. The circuit breaker is then closed.
2) The closing springs are re-charged with the circuit breaker closed, providing tbr an open-close-open sequence.
Storing the energy in the springs is accomplished through the use of a manual-charging handle, an automatic means through the use of a small electric motor, or both. By having the ability to re-charge the closing springs, the circuit breaker can rapidly and remotely reclose after a fault. This ability to attempt a reclosure if a fault causes the circuit breaker to trip is designed to provide the user with a high degree of service continuity. Closing the circuit breaker can be accomplished by using a manual pushbutton or an electrical closing solenoid.
Insulated-case circuit breakers typically have a two-step stored-energy mechanism. Insulated-case circuit breakers are certified to the standard fbr molded-case circuit breakers.
3.6.5 Electromagnetic assistance
Many molded-case circuit breaker designs achieve high interrupting ratings by being designed to take full advantage of certain natural facts of physics to assist the operating mechanism with the opening process. This concept centers on a natural repulsion between two parallel conductors with current running in them in opposite directions.
3.7 Means to extinguish an arc
3.7.1 Introduction
An arc is defined as a discharge of electric current crossing a gap between two contacts. Arcs are formed when the contacts of a circuit breaker are opened under load. Arcs can be very destructive and vary greatly in size and intensity. The size of the arc depends on the amount of current present when the contacts are pulled apart. For example, the arc formed when a normal load current is broken would be insignificant in comparison to the arc formed when a short-circuit current is broken. Since arcs cannot be prevented, circuit breakers arc designed to control them.
The heat associated with an arc creates an ionized gas environment. The bigger the arc, the more heat created. The more heat created, the more ionization that takes place. The more ionization, the better the conditions are for an arc to be maintained and grow. Obviously, this is the condition that must be dealt with quickly and effectively by a circuit breaker. The important thing to remember is that the ability of the circuit breaker to control the arc is the key to its short-circuit interrupting capability. Of all overcurrent conditions, the short circuit is potentially the most devastating.
IEEE Std 1458 pdf download.
