GE Power ManagementL90 Line Differential Relay2-112 PRODUCT DESCRIPTION 2.5 OTHER FUNCTIONS22.5 OTHER FUNCTIONS 2.5.1 ALARMSThe relay contains a dedicated alarm relay, the Critical Failure Alarm, housed in the Power Supply module. This outputrelay is not user programmable. This relay has Form-C contacts and is energized under normal operating conditions. TheCritical Failure Alarm will become de-energized if the relay self test algorithms detect a failure that would prevent the relayfrom properly protecting the transmission line.2.5.2 LOCAL USER INTERFACEThe relay’s local user interface (on the faceplate) consists of a 2 × 20 vacuum florescent display (VFD) and a 22 button key-pad. The keypad and display may be used to view data from the relay, to change settings in the relay, or to perform controlactions. Also, the faceplate provides LED indications of status and events. The operation of the keypad is discussed in theHUMAN INTERFACES chapter.2.5.3 TIME SYNCHRONIZATIONThe relay includes a clock which can run freely from the internal oscillator or be synchronized from an external IRIG-B sig-nal. With the external signal, all relays wired to the same synchronizing signal will be synchronized to within 0.1 millisecond.2.5.4 FUNCTION DIAGRAMSFigure 2–3: L90 BLOCK DIAGRAM
