reliability of transmission by means of line impedance …

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