CHAPTER 3: INSTALLATION DIRECT INPUT AND OUTPUT COMMUNICATIONSG30 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL 3-433Figure 3-49: IEEE C37.94 connection to compliant digital multiplexerThe UR-series C37.94 communication module can be connected to the electrical interface (G.703, RS422, or X.21) of a non-compliant digital multiplexer via an optical-to-electrical interface converter that supports the IEEE C37.94 standard. Thefollowing figure shows the concept.Figure 3-50: IEEE C37.94 connection to non-compliant digital multiplexerIn 2008, GE Grid Solutions released revised modules 76 and 77 for C37.94 communication to enable multi-ended faultlocation functionality with firmware 5.60 release and higher. All modules 76 and 77 shipped since the change support thisfeature and are fully backward compatible with firmware releases below 5.60. For customers using firmware release 5.60and higher, the module can be identified with "Rev D" printed on the module and is to be used on all ends of G30communication for two and three terminal applications. Failure to use it at all ends results in intermittent communicationalarms. For customers using firmware revisions below 5.60, it is not required to match the revision of the modules installed.The UR-series C37.94 communication module has six switches to set the clock configuration. The following figure showsthe functions of these control switches.Figure 3-51: SwitchesFor the internal timing mode, the system clock is generated internally. Therefore, set the timing switch selection to internaltiming for relay 1 and loop timed for relay 2. There must be only one timing source configured.For the looped timing mode, the system clock is derived from the received line signal. Therefore, set the timing selection toloop timing mode for connections to higher order systems.The IEEE C37.94 communications module cover removal procedure is as follows:1. With power to the relay off, remove the IEEE C37.94 module (type 2I, 2J, 76, or 77 module) as follows. Record theoriginal location of the module to help ensure that the same or replacement module is inserted into the correct slot.2. Simultaneously pull the ejector/inserter clips located at the top and bottom of each module in order to release themodule for removal.3. Remove the module cover screw.4. Remove the top cover by sliding it towards the rear and then lift it upwards.
