Khaled el naggar high impedance faults detection in electrical power systemsPresentation Transcript
High impedance faults detection in electrical power systems Dr. Khaled M. EL-Naggar College of Technological Studies, Kuwait
High impedance faults Definition Why it is a problem Different techniques for detection Comparison & Evaluation ANN-GA Technique Conclusions
High Impedance Faults (HIFs)
HIFs result when an energized primary conductor comes in contact with a semi-insulated object such as a tree, structure or earth ...
HIFs, generally, are associated with arcing at the point of contact.
Little threat of damage to power system equipment, but potential safety and fire hazard
Hi-Z faults produce primary current levels of 0 to 100 Amps
Therefore, conventional phase or ground overcurrent protection are unable to distinguish between the high-impedance faults and normal load currents
Causes The main causes of HIFs are tree branches touching a phase conductor, Broken line on ground (Downed Conductor)Almost all HIFs involve the ground directly orindirectly.
Fault currents on various surfaces Surface Fault current (A)Dry Asphalt 0Dry Sand 0Wet Asphalt 1Wet Sand 5 Dry grass 25Concrete(non-reinforced) 10 Wet grass 50Concrete (reinforced) 70
Why should be detected
Hi-Z faults often arc and can be a significant fire hazard
Detect partially failing insulation before complete failure which can lead to power outages and loss of production
If not detected and isolated, live Downed Conductors can be fatal to public
Little effect on voltage
Small fault current (10 – 100 Amps)
Current values will continue to fluctuate
Significant harmonic currents
The majority occurs at 15 Kv and lower
Different Methods Mechanical detection methods, Comprise devices that provide a low impedance ground path by catching the falling conductor . This causes the conventional relaying to operate. The main drawbacks of these methods are the high installation and maintenance costs.
Electrical Detection Methods Open Conductor Detection This electrical HIF detection method detects loss of voltage to determine a broken conductor. The system measures the phase voltage at each end of a single phase lateral. 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.
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
Phase current rate of change The phase current rate of change is high (quick ) at the moment of fault, while the current changes progressively with load variation. This algorithm monitors the sample difference at the corresponding sampling point of two subsequent cycles
Harmonic Based Detection Second harmonic detection
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.
Third harmonic detection 1-The variations in amplitude of the third-order harmonic current and the variations of ratio of third–order harmonic to fundamental are monitored 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
3rd ,5th and 7th harmonic detection The variations in amplitudes and phase angles of the third, fifth and seventh order harmonic currents are monitored
High frequency harmonics
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
Digital based techniques used for extracting signal signature
Fast Fourier Transform
Conventional static estimation
Dynamic state estimation
Recursive LES Iterative LAV KF
Ii(actual) − Ii(calculated ) = errori Fitness Function to be minimized based on the error (absolute or square)
High Impedance Fault Detection and Relaying Scheme Data Collection, CT& PT Sampling Waveforms Genetic Algorithm Signal Analysis (GA) ANN Based Detection
Input Data Fundamental Component Lower Harmonics Higher Harmonics GR Current before the highest transient value Current after the highest transient value Current Rate of change cycle to cycle
Study System 11 KV Radial system 19 11 KV feeders 11/0.4 KV Transformers Loads Capacitors
Simulated Cases & Results 200 different cases
Different fault location
Different inception angle
Different loading conditions
Different capacitor switching conditions
98% HIFs detection
HIFs result in:
Poor customer service
HIFs Detection techniques classified as
Mechanical techniques can not protect the whole distribution system Electrical techniques use digitized samples of the Current and voltage signals. These techniques have better detection Intelligent relays - Intelligent relays can detect HIFs at very high degree of accuracy
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.