3-36 D60 Line Distance Protection System GE Multilin3.3 DIRECT INPUT AND OUTPUT COMMUNICATIONS 3 HARDWARE33.3.8 IEEE C37.94 INTERFACEThe UR-series IEEE C37.94 communication modules (modules types 2G, 2H, 76, and 77) are designed to interface withIEEE C37.94 compliant digital multiplexers or an IEEE C37.94 compliant interface converter for use with direct input andoutput applications for firmware revisions 3.30 and higher. The IEEE C37.94 standard defines a point-to-point optical linkfor synchronous data between a multiplexer and a teleprotection device. This data is typically 64 kbps, but the standardprovides for speeds up to 64n kbps, where n = 1, 2,…, 12. The UR-series C37.94 communication modules are either64 kbps (with n fixed at 1) for 128 kbps (with n fixed at 2). The frame is a valid International Telecommunications Union(ITU-T) recommended G.704 pattern from the standpoint of framing and data rate. The frame is 256 bits and is repeated ata 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 1 × 128 kbps optical fiber interface (for 2G and 2H modules) or C37.94 for 2 × 64 kbps opti-cal fiber interface (for 76 and 77 modules).• Fiber optic cable type: 50 mm or 62.5 mm core diameter optical fiber.• Fiber optic mode: multi-mode.• Fiber optic cable length: up to 2 km.• Fiber optic connector: type ST.• Wavelength: 830 ±40 nm.• Connection: as per all fiber optic connections, a Tx to Rx connection is required.The UR-series C37.94 communication module can be connected directly to any compliant digital multiplexer that supportsthe IEEE C37.94 standard as shown below.The UR-series C37.94 communication module can be connected to the electrical interface (G.703, RS422, or X.21) of anon-compliant digital multiplexer via an optical-to-electrical interface converter that supports the IEEE C37.94 standard, asshown below.In 2008, GE Digital Energy 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 D60 communi-cation for two and three terminal applications. Failure to use it at all ends results in intermittent communication alarms. Forcustomers using firmware revisions below 5.60, it is not required to match the revision of the modules installed.
