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Arc Faults and Electrical Safety
Published in Paul G. Slade, Electrical Contacts, 2017
where εr is the relative permittivity of the cable insulation and L is wire inductance per unit length and C the wire capacitance per unit length. The velocity factor, VF, is a percentage of the speed of light, c, and for wire insulation made from PVC, the wave propagation velocity is approximately 50% that of the speed of light in free space. Meaning that for a given frequency, the wavelength is half as long as compared to the wavelength in free space making a given cable length effectively double as compared to the wave traveling at the speed of light. Knowing either the relative permittivity of the cable insulation or the L and C per unit length of the cable will allow for calculating VF.
Real-time remote energy consumption location for power management application
Published in Advances in Building Energy Research, 2021
Sam Moayedi, Hamed Nabizadeh Rafsanjani, Subhaditya Shom, Mahmoud Alahmad, Changbum R. Ahn
The basic concept of STDR is described using the Time Domain Reflectometry (TDR) method. Time Domain Reflectometry (TDR) is based on the reflective property of waveforms on a conducting medium. The principle of TDR is similar to the radar. TDR technique is used for locating short-circuits, faults or damage and discontinues or impedance mismatches on wires for electrical and communication systems (Iskander, 2000). In this method, a pulse signal injects to the wire and it reflects back when it reaches the end of the wire or when there is an impedance changes. The wave propagation along the transmission line depends on the velocity of propagation (VOP) or velocity factor (VF) of the medium. VF is the speed at which a wave travels through the wire, relative to the speed of light (Ulaby, Michielssen, & Ravaioli, 2010). Using the VOP of the desired wire, and measuring the signal’s time for travelling to the end and reflecting back, length of the wire or distance to the impedance mismatch can be determined.