CHAPTER 3: INSTALLATION DIRECT INPUT AND OUTPUT COMMUNICATIONSG30 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL 3-473The connections shown in the figure are for multiplexers configured as data communications equipment (DCE) units.3.4.7 G.703 and fiber interfaceThe following figure shows the combined G.703 plus fiber-optic interface configuration at 64 kbps. The 7E, 7F, 7G, 7Q, and75 modules are used in configurations where channel 1 is employed via the G.703 interface (possibly with a multiplexer)and channel 2 via direct fiber. AWG 24 twisted shielded pair wiring is recommended for external G.703 connectionsconnecting the shield to pin 1a at one end only. For the direct fiber channel, address power budget issues properly. Seeprevious sections for details on the G.703 and fiber interfaces.Figure 3-54: G.703 and fiber interface connection3.4.8 IEEE C37.94 interfaceIEEE C37.94 is a standard interface between teleprotection equipment and digital multiplexers.The UR-series IEEE C37.94 modules (module types 2I, 2J, 76, and 77) are designed to interface with IEEE C37.94 compliantdigital multiplexers or an IEEE C37.94 compliant interface converter for use with direct input and output applications. TheIEEE C37.94 standard defines a point-to-point optical link for synchronous data between a multiplexer and a teleprotectiondevice. Data speed is typically 64 kbps, but the standard provides for speeds up to 64n kbps, where n = 1, 2,…, 12. The UR-series C37.94 communication modules are either 64 kbps (with n fixed at 1) or 128 kbps (with n fixed at 2). The frame is avalid International Telecommunications Union (ITU-T) recommended G.704 pattern from the standpoint of framing anddata rate. The frame is 256 bits and is repeated at a frame rate of 8000 Hz, with a resultant bit rate of 2048 kbps.The specifications for the module are as follows:• IEEE standard — C37.94 for 2 × 64 kbps optical fiber interface (for 76 and 77 modules)• Fiber-optic cable type — 50 nm or 62.5 μm core diameter optical fiber• Fiber-optic mode — multimode• Fiber-optic cable length — up to 2 km• Fiber-optic connector — type ST• Wavelength — 820 ±40 nm• Connection — as per all fiber-optic connections, a Tx-to-Rx connection is requiredThe UR-series C37.94 module can be connected directly to any compliant digital multiplexer that supports the IEEE C37.94standard. The figure shows the concept.When using a laser interface, attenuators can be necessary to ensure that you do not exceed themaximum optical input power to the receiver.
