What conditions must a 67 device see in order to close its contacts?

A 67 device, commonly referred to as an directional overcurrent relay, is designed to monitor electrical currents and detect conditions that could indicate faults. For the device to close its contacts, it specifically looks for overcurrent conditions that travel in a predetermined direction. This directional capability is crucial because it ensures that the protection relay only responds to faults that are relevant to its protection scheme, thereby avoiding unnecessary tripping due to currents that may not be harmful.

In an electrical system, the direction of current flow can signify whether a fault originates from within the protected area or from an external source. The 67 device uses this directional information to operate correctly and ensure it only trips when needed, ultimately increasing system reliability and safety.

On the other hand, options focusing on overvoltage may not provide the directional context required for the relay’s operation, while options that include both overcurrent and undervoltage, or simply overcurrent, do not incorporate the necessary directional aspect that is vital for a 67 device’s functionality. Thus, the ability to see overcurrent in a predetermined direction is the essential criterion that enables the relay to close its contacts.