GE Multilin D60 Line Distance Protection System 3-393 HARDWARE 3.3 DIRECT INPUT AND OUTPUT COMMUNICATIONS33.3.9 C37.94SM INTERFACEThe UR-series C37.94SM communication modules (2A and 2B) are designed to interface with modified IEEE C37.94 com-pliant digital multiplexers or IEEE C37.94 compliant interface converters that have been converted from 820 nm multi-modefiber optics to 1300 nm ELED single-mode fiber optics. The IEEE C37.94 standard defines a point-to-point optical link forsynchronous data between a multiplexer and a teleprotection device. This data is typically 64 kbps, but the standard pro-vides for speeds up to 64n kbps, where n = 1, 2,…, 12. The UR-series C37.94SM communication module is 64 kbps onlywith n fixed at 1. The frame is a valid International Telecommunications Union (ITU-T) recommended G.704 pattern fromthe standpoint of framing and data rate. The frame is 256 bits and is repeated at a frame rate of 8000 Hz, with a resultant bitrate of 2048 kbps.The specifications for the module are as follows:• Emulated IEEE standard: emulates C37.94 for 1 × 64 kbps optical fiber interface (modules set to n = 1 or 64 kbps).• Fiber optic cable type: 9/125 μm core diameter optical fiber.• Fiber optic mode: single-mode, ELED compatible with HP HFBR-1315T transmitter and HP HFBR-2316T receiver.• Fiber optic cable length: up to 10 km.• Fiber optic connector: type ST.• Wavelength: 1300 ±40 nm.• Connection: as per all fiber optic connections, a Tx to Rx connection is required.The UR-series C37.94SM communication module can be connected directly to any compliant digital multiplexer that sup-ports C37.94SM as shown below.It can also can be connected directly to any other UR-series relay with a C37.94SM module as shown below.In 2008, GE Digital Energy released revised modules 2A and 2B for C37.94SM communication to enable multi-ended faultlocation functionality with firmware 5.60 release and higher. All modules 2A and 2B 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.
