IEC TR 63042-303-2021 pdf UHV AC transmission systems – Part 303: Guideline for the measurement of UHV AC transmission line power frequency parameters

4.3 Main circuit configuration Disconnectors at the two terminals of the transmission line should be open during measurement. Parallel with the transmission line, connected equipment should be disconnected, such as shunt reactors and capacitive transformer. Series reactors and capacitors used in the transmission line shall be bypassed. If the transmission line to be measured is composed of overhead lines, cables or gas- insulated lines (GIL), it is recommended to measure the parameters of the overhead lines, cables or GIL, separately. To eliminate the resistance of the connecting lines for test, two connecting lines, i.e. voltage and current connecting lines, can be applied. If only one connecting line is applied, the obtained line resistance should be reduced by the connecting line resistance. The measurement system should be reliably connected to the substation earthing system. 4.4 Measurement condition Close attention should be paid to the weather condition along the line during the measurement. The measurement should be stopped if the weather is not suitable for measurement. Ambient temperature of measuring instrument: −10 °C to +40 °C, relative humidity: ≤ 85 %. Before starting the measurements, check that all temporary grounding connections have been removed. No work may be done on the lines during the measurements. Make sure that this rule is followed. All local and international safety regulations shall be known and strictly observed. Safety precautions are given in Annex C. 5 Requirement of measuring instrument Current transformer 5.1 Uncertainty of current transformer (CT) should be equal to or better than 0,5 %. It is obtained based on the method of IEC Guide 115. 5.2 Voltage transformer Uncertainty of voltage transformer (VT) should be equal to or better than 0,5 %. It is obtained based on the method of IEC Guide 115.
5.3 Measuring instrument of DC resistance The instrument to measure the DC resistance of a transmission line can be a special instrument or the combination of a DC power source, a DC voltmeter and a DC ammeter. If the DC resistance measurement meter is used, its uncertainty should be equal to or better than 0,5 %. If the combination of a DC resistance, a DC power source, a DC voltmeter and a DC ammeter is used, the uncertainty of the DC voltmeter and ammeter should be equal to or better than 0,5 %.