CHAPTER 3: INSTALLATION
ELECTRICAL INSTALLATION
D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
65
Figure 36: Clock and data transitions
The RS422 interface utilizes NRZI-MARK modulation code and therefore does not rely on an
Rx clock to recapture data. NRZI-MARK is an edge-type, invertible, self-clocking code.
To recover the Rx clock from the data-stream, an integrated DPLL (digital phase lock loop)
circuit is utilized. The DPLL is driven by an internal clock, which is 16-times oversampled,
and uses this clock along with the data-stream to generate a data clock that can be used
as the SCC (serial communication controller) receive clock.
Fiber communications interface
The UR
Plus
-series communication module is designed to interface with IEEE C37.94
compliant digital multiplexers or an IEEE C37.94 compliant interface converter for use with
direct input and output applications when the
Protocol Encoding
setting is “C37.94” or for
direct fiber interfaces using the Differential Manchester protocol when the
Protocol
Encoding
setting is “Direct Fiber”. The IEEE C37.94 standard defines a point-to-point optical
link for synchronous data between a multiplexer and a teleprotection device. This data is
typically 64 kbps, but the standard provides for speeds up to 64
n
kbps, where
n
= 1, 2,…, 12.
The UR
Plus
-series C37.94 communication modules are either 64 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 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 × 64/128 kbps optical fiber interface.
•
Differential Manchester protocol: 2 × 64/128 kbps optical fiber interface.
•
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: 850 nm VCSEL laser.
•
Connection: as per all fiber optic connections, a Tx to Rx connection is required.
The UR
Plus
-series C37.94 communication module can be connected directly to any
compliant digital multiplexer that supports the IEEE C37.94 standard as shown below.
Figure 37: IEEE C37.94 connection to compliant digital multiplexer
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