Optical fibers will transmit visible light less efficiently, so there may be a loss of signal when measuring absorbance through optical fibers, especially due to the increased distance traveled.
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Insertion Loss is defined as the reduction in optical power between the input and output of a fiber optic link. It is expressed in decibels (dB) and calculated using the formula: IL = –10 log (Pout / Pin) Where: Lower insertion loss values indicate better optical performance. To be able to judge whether a fiber optic cable plant is good, one does a insertion loss test with a light source and power meter and compares that to an estimate of what is a reasonable loss for that cable plant.
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Loss of excitation protection is used to protect the synchronous machine (alternator or generator) acts as induction motor when the excitation fails. It is caused by accidental tripping of field breaker, short circuit in the field circuits, poor brush contact or operating errors. Abstract-- This paper was written by a Working Group of the IEEE Power System Relay Committee to provide guidance to the industry to better coordinate generator protection with generator control. The protection function includes detection of overcurrent and undercurrent as well as supervision of the ripple.
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This part of IEC 60255 specifies common rules and requirements applicable to measuring relays and protection equipment, including any combination of equipment to form a distributed protection scheme for power system protection such as control, monitoring and process. Measuring, protecting, controlling and maintaining electricity power networks in a smart grid world requires intelligent electronic devices (IED), such as smart energy meters, measuring relays, protection systems, control and automation devices. Protective relays and devices have been developed over 100 years ago to provide "lastline"of defense for the electrical systems. They are intended to quickly identify a fault and isolate it so the balance of the system continue to run under normal conditions. The basic functions are to receive input signals, monitor and determine them, and output an alarm signal if a set.
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SEL relays detect faults and other abnormal conditions in electric power systems and initiate protective actions to maintain system stability and safety. They are used in a wide range of applications, from transmission and distribution to industrial power systems. Selectivity is a mandatory requirement for all protection, but the importance of it depends on the application. For example, unselective protection operation during a medium voltage network fault will cause an outage for an unnecessarily large number of consumers. Types of Protective Relays: Protective relays are categorized by their mechanism (electromagnetic, static, mechanical) and function.
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