IEC TR 63042-303 pdf – UHV AC transmission systems – Part 303: Guideline for the measurement of UHV AC transmission line power frequency parameters
Parallel with the transmission line，connected equipment should be disconnected,such asshunt reactors and capacitive transformer.
Series reactors and capacitors used in the transmission line shall be bypassed.
lf 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 GlL,separately.
To eliminate the resistance of the connecting lines for test,two connecting lines，i.e. voltageand current connecting lines,can be applied. lf only one connecting line is applied, theobtained line resistance should be reduced by the connecting line resistance. Themeasurement system should be reliably connected to the substation earthing system.
4.4Measurement condition
Close attention should be paid to the weather condition along the line during themeasurement. The measurement should be stopped if the weather is not suitable formeasurement.
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 thisrule is followed. All local and international safety regulations shall be known and strictlyobserved.Safety precautions are given in Annex c.
5 Requirement of measuring instrument
5.1current transformer
Uncertainty of current transformer(CT) should be equal to or better than 0,5 %. lt is obtainedbased on the method of lEC Guide 115.
5.2Voltage transformer
Uncertainty of voltage transformer (VT) should be equal to or better than 0,5 %. lt is obtainedbased on the method of lEC Guide` 115.
5.3 Measuring instrument of DC resistance
The instrument to measure the DCresistance of a transmission line can be a specialinstrument or the combination of a DC power source, a DC voltmeter and a DC ammeter.
lf the DC resistance measurement meter is used, its uncertainty should be equal to or betterthan 0,5 %.
lf 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 than0.5%.
5.4Offset frequency power source
The offset frequency power source should be capable of supplying sinusoidal signals at asingle frequency that can be adjustable. Normally,the power source should generate asinusoidal signal at f-Af or f + Af , where Af is usually less than 10 Hz, such as 2,5 Hz,5 Hz
or 7,5 Hz.
NOTE±5 Hz are two typical values of frequency ofiset; the frequency of test power source can thus be 45 Hz or55 Hz for a 50 Hz system.
The total harmonic distortion for the voltage output of offset frequency power source shouldbe within 3 %. lt is recommended by lEC 61000-2-4:2002.
5.5Special measuring instrument of transmission line power frequency parameterThe instrument should meet the requirement as follows:
. The measuring instruments at the source and ending terminals should have the function of
synchronous phasor measurement and be capable of sampling single-phase and three-phase voltage and current phasors which include amplitude and phase angle of voltageand current.
For each measurement, all the measured voltage and current phasors take a GPS PPS as
a reference; phase angle of voltage or current is the difference between the measuredvoltage or current phasor and the reference. The magnitude of voltage or current isamplitude.
The synchronization error of sampling between the source terminal and ending terminalshould be less than 100 ns.
The measuring instrument should be capable of eliminating signal aliasing and leakage.
The measuring instrument should be capable of completing data analysis and calculationaccording to the prescribed method.
6 Conversion of offset frequency measurement results
lf there are no induced voltage and induced current on the measured line at power frequency,a power frequency test power source can be directly used.
lf there are induced voltage and induced current on the measured line at power frequency, an
offset frequency test power source should be used to eliminate the power frequencyinterference. The offset frequency measurement method is usually used to measure UHivtransmission line power frequency parameters. However，the parameters measured by usingoffset frequency method need to be converted to the parameters at power frequency.
Generally, the two frequencies f-Af and f +Af will be selected for the measurement.
The procedure of offset frequency measurement is as follows:
. Firstly，replace the frequency of power source f by f – Af， measure and calculate
parameters of the transmission lines at frequency j – Af according to the procedures andequations.
Secondly，replace the frequency of power source f by f + Af，measure and calculateparameters at frequencyf+ Af according to the procedures and equations.
Finally, calculate the impedance parameters at power frequency
f by