West African Power Industry Convention 2007, Abuja, NIGERIA
RELIABILITY OF TRANSMISSION BY MEANS OF LINE IMPEDANCE AND K-FACTOR MEASUREMENT
William KIBART, Ulrich KLAPPER, Michael KRÜGER, OMICRON electronics
Place your company logo here (i.e. replace the spintelligent logo with your logo)Your company logo is only permitted on the first slide!!!
West African Power Industry Convention 2007, Abuja, NIGERIA
Distance Protection
Distance relay Characteristics
West African Power Industry Convention 2007, Abuja, NIGERIA
Distance Protection – Ideal Behaviour
• k-factor is set properlyWrong k-factor settings in DIS 1 can lead to a zone overreach and a fault on Line 2 could trip DIS 1 leaving the customer without power
DIS 1Zone 1
DIS 2
Zone 1
DIS 3Zone 1
DIS 4Zone 1
Consumer
Line 1 Line 2
West African Power Industry Convention 2007, Abuja, NIGERIA
Settings of Distance Relays
• Positive Sequence Impedance
• Zero Sequence Impedance (sometimes)
• k-factor (Z0/Z1, ZE/ZL or XE/XL and RE/RL)
• All settings need to be correct within a few percent!
West African Power Industry Convention 2007, Abuja, NIGERIA
sagheight above
ground
horizontal distance
Calculation of Line Parameters
West African Power Industry Convention 2007, Abuja, NIGERIA
Calculation of Line Parameters
• Parameters depend on:
• Wire type of both ground wire or shield and phase conductor: geometry, spiraling, DC resistance...
• Construction: line length, tower geometry, average sag, average height of wires above ground, distance between ground wire(s) and phase conductors, cable data and cross bonding configuration on underground cables...
• Soil resistivity
• Calculation is possible but prone to error as too many parameters are needed
West African Power Industry Convention 2007, Abuja, NIGERIA
Conventional Measurement
West African Power Industry Convention 2007, Abuja, NIGERIA
Line Impedance and k-factor measurements
West African Power Industry Convention 2007, Abuja, NIGERIA
• Generated signal differs from mains frequency
• Measurement is frequency selective –measuring only the generated frequency – filtering out all other signals
• Suppressionof mainsdisturbances
Variable Frequency Principle
West African Power Industry Convention 2007, Abuja, NIGERIA
Positive Sequence for L-L faults
Example1Ω: Loop impedance0.8Ω: Fault inside protection zone 11.2 Ω: Fault outside protection zone 1
Distance protection relay
West African Power Industry Convention 2007, Abuja, NIGERIA
Zero Sequence for L-G Faults
• k-factor corrects the ground impedance to treat L-E faults like L-L faults
• A wrong k-factor could lead to a zone overreach – making a line accidentally dead
Distance protection relay
West African Power Industry Convention 2007, Abuja, NIGERIA
Case Study
West African Power Industry Convention 2007, Abuja, NIGERIA
Measurement Results
• The reason was found weeks after the measurement: DC Resistance of the earth wire was entered wrongly in the companies database…
West African Power Industry Convention 2007, Abuja, NIGERIA
Interferences at Mains Frequency
West African Power Industry Convention 2007, Abuja, NIGERIA
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