While this could be made into a separate mode of operation, this is usually most expediently handled via voltage failure simulation test switches whilethe system is the automatic mode. For the same reason overcurrent trip switches for low-voltage circuit breakers or lockout relays for medium-voltage circuit breakers are also required.Īnother question that frequently arises is that of a “test” mode of operation. Of necessity, to make this mode logic arrangement function properly the breaker status must consist both of breaker open-closed indication and, for drawout circuit breakers, circuit breaker cell switch indication.Ĭircuit breaker cell switches are a feature which must not be overlooked as they are essential for the proper function of an automatic transfer scheme with drawout circuit breakers. This arrangement provides a high level of security for the transfer scheme, i.e., undesired or “nuisance” operations are minimized, enhancing safety, maintainability, and reliability of the system. To leave this mode of operation, the system must be placed into manual mode. ![]() For automatically-controlled circuit breakers, only manual tripping (or trip due to a fault) is allowed. Such manual or fault-driven operations will result in the system being placed into Auto Mode Failure. In Automatic Mode, operations for certain circuit breakers (such as main and tie circuit breakers) are automatic, however manual tripping (or breaker trip due to a fault) of automatically-controlled circuit breakers is allowed. Attempting to enter automatic mode if the system conditions are not correct places the system into Auto Mode Failure. ![]() Selected via a selector switch position or other pre-determined user input via the user interface. Selected via a selector switch position or other pre-determined user input via the user interface. The three modes of operation then typically work as follows: In fact, they necessitate, in a well-designed automatic transfer system, the inclusion of a third mode of operation, typically known as auto mode failure. Such questions are not always easy to answer.
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