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Circuit Breakers Technical Information
作者:admin  來源:本站  發表時間:2010-8-2  點擊:10952

Who invented them? When? Why? The history of circuit breakers is the history of electricity. Circuit breakers appeared at about the same time as electrical power for industrial use. That would be at the end of the 1800s and beginning of the 20th Century.

Until very recently, electrical circuit breakers were very basic devices. If the current through the circuit breaker exceeded a certain level (rating), the circuit breaker would eventually "trip" open. It may surprise you to learn that circuit breakers do not trip immediately when the current exceeds their overload rating. In some cases the time delay can be several minutes, depending on how much the current exceeds the circuit breaker rating. Circuit breakers are manufactured with an intentional time delay. Most breakers also have an "instantaneous" function. But the instantaneous function does not trip the breaker unless the current through the circuit breaker is extremely high, possibly 20 times the circuit breaker's overload rating. The actual operation of some molded case circuit breakers was unpredictable. The trip delay of most molded case circuit breakers had a very wide range. As much as 50 to 300 seconds. Air circuit breakers had a variety of methods to provide protective trip rating and time delay. Some circuit breakers had oil dashpots. Some used springs and gears. Many modern molded case circuit breakers, insulated case circuit breakers, power circuit breakers, and low voltage air circuit breakers use electronic controls to monitor the current and trip the circuit breaker. These circuit breakers are very accurate and provide a major improvement in the quality of protection provide by a circuit breaker.