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Digital recording and transmission principles
Published in John Watkinson, The Art of Digital Audio, 2013
In cable transmission, also known as line signalling, and in telemetry, the starting point was often the speech bandwidth available in existing telephone lines and radio links. There was no DC response, just a range of frequencies available. Figure 6.32(a) shows that a pair of frequencies can be used, one for each state of a data bit. The result is frequency shift keying (FSK) which is the same as would be obtained from an analog frequency modulator fed with a two-level signal. This is exactly what happens when two-level pseudo-video from a PCM adaptor is fed to a VCR and is the technique used in units such as the PCM F-1 and the PCM-1630. PCM adaptors have also been used to carry digital audio over a video landline or microwave link. Clearly FSK is DC-free and self-clocking.
Comparative Analysis of Some Remarkable Islanding Detection Techniques in Inverter-Based Distributed Generation Systems
Published in Electric Power Components and Systems, 2021
Bineeta Soreng, Raseswari Pradhan
There are broadly three types of techniques such as local, remote, and hybrid techniques. Again, local are grouped into passive and active techniques. In passive method the control variables are based on the threshold set value and can be frequency, voltage, current and phase angle etc. These are directly controlled by measuring their values at PCC. If values of these measured parameters are not within the range of that of threshold value, then islanding is detected and the DG unit is disconnected from the load. In the active method, the detection is done directly with the introduction of a small disturbance signal into the line to any of the parameters and monitoring its variation. Similarly, in impedance method, a small signal of current is injected and variation in voltage is noticed. This small injection of current shows large change in voltage, thus showing islanding. Remote techniques are utility based where DG’s inverter is monitored. If there are disturbances then trip signal is sent to DG. Here, SCADA system and power line signaling schemes are used.
A Hybrid Islanding Detection Method For Distribution Systems
Published in Distributed Generation & Alternative Energy Journal, 2018
Aref Pouryekta, Vigna K. Ramachandaramurthy
Communication based methods are the most reliable methods. Theoretically, communication based method is the most accurate method. On the other hand, they suffer from nuisance tripping. As long as the signal detector (SD) senses the generated signal from signal generator (SG), DG unit is considered as grid connected. Once islanding takes place or any switch operation causes lost communication between the SG and SD, islanding will be detected. In comparison to active methods, Power Line Signaling (PLS) sends one signal to down-stream DG units through the transmission line to detect the islanding. By implementation of PLS, the signal interface caused by different active methods is solved. The weakness of this method is the high cost of installation and its sensitivity to noise [14, 23–28].