The majority occurs at 15 Kv and lower</li></li></ul><li>Different Methods<br />Mechanical detection methods, <br /> Comprise devices that provide a low impedance ground path by catching the falling conductor . This causes the conventional relaying to operate. <br />The main drawbacks of these methods are the high installation and maintenance costs.<br />
Electrical Detection Methods<br />Open Conductor Detection<br />This electrical HIF detection method detects loss of voltage to determine a broken conductor. <br />The system measures the phase voltage at each end of a single phase lateral.<br />When the voltage of any phase drops below the specified threshold, a signal is sent to upstream device. The upstream device opens if voltage is present at the upstream device.<br />
Ratio RelaysThe ratio of the negative sequence or zero sequence to positive sequence current is calculated and when this ratio exceeds a predetermined value, a trip signal is produced<br />
Phase current rate of change <br />The phase current rate of change is high (quick ) at the moment of fault, while the current changes progressively with load variation. <br />This algorithm monitors the sample difference at the corresponding sampling point of two subsequent cycles<br />
Harmonic Based Detection<br />Second harmonic detection<br /><ul><li>Second Harmonic detection, this algorithm is based on sensing the variation of the second-order harmonic current.
Normally the second harmonic component is very small.</li></li></ul><li>Third harmonic detection<br />1-The variations in amplitude of the third-order harmonic current and the variations of ratio of third–order harmonic to fundamental are monitored<br />2-The changes in both the third-order harmonic current magnitude and the third-order harmonic current phase angle with respect to the system voltage are monitored<br />
3rd ,5th and 7th harmonic detection<br />The variations in amplitudes and phase angles of the third, fifth and seventh order harmonic currents are monitored<br />
High frequency harmonics<br /><ul><li>The arcing fault on the feeder primary can be detected from an increase in the 2－10 kHz harmonic components of the feeder neutral line current.
These harmonic components often lasts longer than that from normal switching operations</li></li></ul><li>Digital based techniques used for extracting signal signature<br /><ul><li>Fast Fourier Transform
Particle Swarm</li></ul>Ii(actual) − Ii(calculated ) = errori<br />Fitness Function to be minimized based on the error <br />(absolute or square)<br />
High Impedance Fault Detection and Relaying Scheme<br />Data Collection, CT& PT<br />Sampling Waveforms<br />Genetic Algorithm<br />Signal Analysis (GA) <br />ANN Based Detection<br />
Input Data<br />Fundamental Component<br />Lower Harmonics<br />Higher Harmonics<br />GR<br />Current before the highest transient value<br />Current after the highest transient value<br />Current Rate of change cycle to cycle<br />
Electrical </li></li></ul><li>Mechanical techniques can not protect the whole distribution system<br />Electrical techniques use digitized samples of the Current and voltage signals. These techniques have better detection <br />Intelligent relays<br /> - Intelligent relays can detect HIFs at very high degree of accuracy<br />
Regardless the method used, not all HIFs are detectable. For example, the case where a conductor near the end of a feeder breaks and falls to the ground. <br />