Field Trial of Optical Fibre Cable-TV System Optical Fibre System for ...

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CMUB PA — u q11 PA ~ U Q13 PA — U g12 Oi V^ > position 3 04I • position 2 ^» position 1 SWI SSC i MC AL4 AL3 AL2 AL1 PA — Ug 14 Fig. 5 Block diagram of CMUB, control and monitor unit for the inverter bridge, IB SWI SSC UBEF MAV MAC CSM EA OSC COMP AND BM PA MC u 2 CSPR U gii-Ug,4 AL1 AL2 AL3 AL4 Switch pos. 1: OFF pos. 2: ON pos. 3: CHARGING Start circuit for slow start Stable reference voltage Measurement amplifier, voltage Measurement amplifier, current Current distributor (distributes the load cur rent equally between rectifiers working in parallel) Error amplifier Oscillator, 40 kHz Comparator AND gate Bistable flip-flop Pulse amplifier Supervision and alarm circuits Rectifier output voltage Signal proportional to the current fed into the output filter Current signal from rectifiers working in parallel Control pulses to transistors in the inverter bridge Alarm signal: Rectifier failure Alarm signal: Overvoltage Alarm signal: No load Alarm signal: Mains voltage too low pacitors (C,) are charged via a resistor, which determines the magnitude of the start-up current. It is a maximum of 10 A, i.e. less than the rated current (25 A) for the input fuse, IFU. The voltage across the capacitors is monitored by a guard circuit. The guard lets the preregulator start working when the voltage has reached a certain value. The voltage is then further increased and regulated to a constant level. The control unit for the inverter bridge is then allowed to start up, i.e. to supply control pulses to the transistors in the bridge. During thestarting-up process and restarts (after control pulses have been blocked) the pulse width of the control pulses is slowly increased from zero to the value required in orderto obtain the normal output voltage. Voltage pulses are obtained across the windings in the main transformer (TR) when the inverter bridge starts operating. A turn on the transformer core feeds a circuit (CUTH) that triggers the thyristors in the mains rectifier bridge (DB). From then on the preregulator (PRU) is fed via this bridge. The supply voltage is supervised by a mains monitor which blocks the control unit in the preregulator (CMUP) in the case of unacceptably low mains voltage. After a mains break or an abnormal reduction of the supply voltage the mains monitor allows restart of control unit CMUP when the voltage has again risen to an acceptable value. The restart is carried out with slowly increasing pulse width. Control unit CMUB protects the inverter bridge against overload. If the current drawn tends to exceed the rated current (100 A), the control unit reduces the pulse width sufficiently to keep the rectifier output current constant (at approximately 102 A). If the output is shortcircuited the current is also effectively limited to the same value. Alarm and supervision circuits A circuit supervises the function of the rectifier by checking that it generates voltage pulses in the main circuit. If no pulses are obtained in spite of the input fuse being operated an alarm signal, "Rectifier fault", is initiated. A load indicator circuit, which interacts with the above circuit, checks that the rectifier supplies current (takes load). If the rectifier does not take any load the load indicator, after a delay of about a minute, will give an alarm indication, "No load", by lighting an LED on the front of the unit. An overvoltage monitor checks the output voltage of the rectifier and prevents it from generating an unacceptably high voltage. The monitor is selective. This means that it blocks the control pulses to the transistors in the inverter bridge only if the rectifier has remained active in spite of the voltage across its output having risen above the operating threshold of the monitor.
188 Fig. 6 The rectifier with the outer steel cover removed. It contains, from the left, the printed board with control and supervision circuits, main transformer, the electrolyte capacitor in the input circuit, the inductor in the input circuit and the printed board with the preregulator control and supervision circuits. Behind these components is the large, wiring unit printed board with power transistors, their drive circuits and current supply circuits for the electronics. The angle brackets on which the power semiconductors are mounted can be seen behind the board. The brackets are screwed to the large heat sink, whose flanges can be seen at the top of the rear of the unit Theovervoltage monitor allows the control unit to make one restart attempt. If the rectifier gives too high a voltage once again within a certain time the control unit is blocked. Such blocking is followed by the alarm indications "Overvoltage" and "Rectifier failure". Indications on the front panel of the rectifier Light emitting diodes in different colours and with clear labelling indicate the following operating modes and alarm signals: Colour Red Red Red Red Yellow Yellow Green Label Rect. Failure Overvoltage No Load Mains Failure Current Limit Charge On The operation of the rectifier can be controlled manually by means of a toggle switch on the front panel: Position On Significance The control unit circuits are working if the input fuse is operated Off/Reset The control unit curcuits are blocked, i.e. the rectifier does not generate any voltage across its output (even if the input and output fuses are operated). In the case of blocking by the overvoltage monitor the switch must be briefly switched from "On" to "Off/Reset" in order to reset the monitor (break the blocking state). Charge Instrument In this position the rectifier voltage level is raised. (In certain cases this function is removed, namely in systems containing battery cells equipped with circuits for equalization charging.) The front panel contains a liquid crystal digit indicator. It can be switched to show either the output voltage or the output current of the rectifier. Special dimensioning problem The demands for compact structure, large variation range for the supply voltage, little interference and the ability to withstand transients, both on the input and the output, have greatly influenced the dimensioning and the mechanical construction. Great attention has been paid to the mechanical construction in ordertoensure efficient cooling of the semiconductors in the main circuit. This has resulted in a rectifier with a high heat exchange capacity at a low temperature difference, and good electrical insulation between live parts and the large heat sink that transfers the heat to the cooling air. The cooling flanges have been designed to give the best possible heat transfer with self-circulation of the cooling air through the rack. The ability to withstand transients from the mains supply is obtained by means of a combination of interference suppression filters, metal oxide varistors and electrolyte capacitors that can store a large amount of energy. The requirements specification defines what type of overvoltage transients the rectifier must be able to withstand. This property of the rectifier was tested using a transient generator with carefully defined characteristics (Schaffner type NSG223). The output filter protects the rectifier against transients on the output side. Polypropylene capacitors, placed adjoining the connector, have low impedance in order to be able to cope with any rapid voltage changes. The electrolyte capacitor in the output filter can absorb the energy from any transients. Electrical safety The rectifier has been designed to meet the electrical safety standardsof IEC435 and BT, Technical Guide No. 25. This means, for example, that an insulating barrier has been arranged between components connected to the mams and components in the output circuit on the low voltage side.
Page 1 and 2: ERICSSON REVIEW 4 1985 Field Trial
Page 3 and 4: Trial of Optical Fibre Cable-TV Sys
Page 5 and 6: Head end (HC] 280 Mbit/s Farsta aut
Page 7 and 8: 158 Switching equipment Fig. 7 Futu
Page 9 and 10: 160 Fig. 10 The teleconference room
Page 11 and 12: GERHARD GOBL Public Telecommunicati
Page 13 and 14: Fig. 5, above left Two-channel A/D
Page 15 and 16: Digital input signals Digital outpu
Page 17 and 18: Power ZAV 280/4 has individual powe
Page 19 and 20: Wavelength Division Multiplexing fo
Page 21 and 22: 172 Subscriber side BP-890 Controll
Page 23 and 24: Fig. 8 Transmission characteristics
Page 25 and 26: Most computer cabinets are 19" wide
Page 27 and 28: 178 Fig. 5 Modems in Series 7 Modem
Page 29 and 30: Computer Aided Production of Plasti
Page 31 and 32: Fig. 4 Product geometry displayed o
Page 33 and 34: Rectifier for Mobile Telephone Syst
Page 35: I OR | OFU OS I CMUP HlsHi W±±±h
Page 39 and 40: Fig. 9 Rectifier BMJ A01 001 with t
Page 41 and 42: The Renewal of the London Undergrou
Page 43 and 44: 194 Rickmansworth, and the Loughton
Page 45 and 46: 196 Fig. 5 Optical fibre cable rout
Page 47 and 48: 198 In planning the optical fibre n
Page 49 and 50: Fig. 9 The digital telephone DIAVOX
Page 51 and 52: 202 Fig. 11 Transmission equipment
Page 53 and 54: 204 Fig. 2 Automatic testing of mul
Page 55 and 56: 206 Relative occurrence for F Fig.
Page 57 and 58: Fig. 5 Field testing of a 140 Mbit/
Page 59 and 60: 210 Fig. 7 The system down time as
Page 61 and 62: MTBF (years) Equipment 2-5 Transmul

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