IEEE 644:2019 pdf free download – IEEE Standard for Measurement of Power Frequency Electric and Magnetic Fields from ACPower Lines
The free-body meter is suitable for survey-type measurements because it is portable, allows measurementsabove the ground plane,and does not require a known ground reference. Therefore, this type of meter isrecommended for outdoor measurements near power lines.
This standard presents measurement techniques for only the free-body type meter.Flat ground-reference-type meters can be used only under special conditions described in 5.2.Electric field strength metersintended for characterization of radio-frequency electric fields should not be used to measure the power-frequency electric field strength from ac power lines.
An electric field strength meter consists of two primary parts,the probe and the detector. For commerciallyavailable free-body meters，the detector is usually contained in, or is an integral part of, the probe. Theprobe and detector are introduced into an electric field on an insulating handle. The detector measures thestcady-state induced current or charge oscillating between the conducting halves (electrodes) of the probe.The observer is sufficiently removed from the probe to avoid significant perturbation of the electric field atthe probe (see 4.1). The size of the probe should be such that charge distributions on the boundary surfacesgenerating the electric field (energized and ground surfaces) are, at most,weakly perturbed when the probeis introduced for measurement. The electric field should be approximately uniform in the region where theprobe will be introduced. Probes can be of any shape; however,meters commercially available in the U.S.are generally in the shape of rectangular boxes，with side dimensions ranging from approximately 7 cmto 20 cm. The meters are calibrated to read the rms value of the power frequency electric field componentalong the electrical axis (the axis of greatest electric field strength sensitivity).
Free-body meters designed for remote display of the electric field strength also are available. In this case, aportion of the signal processing circuit is contained in the probe and the remainder of the detector is in aseparate enclosure with an analog or digital display. A fiber-optic link connects the probe to the display unit.This type of probe is also introduced into an electric field on an insulating handle.
When performing measurements, it is necessary to understand the instrumentation to be able to account forfactors such as a dependence on temperature or if the electrical axis of the field strength meter is notcoincident with the geometric axis. Other relevant information, is indicated in Figure 1, section C.
lf the ratio I/E for a given electric field strength meter is known, a current injecting circuit can be used forcalibrating the electric field strength meter. The above ratio, however, is normally determined by using aparallel plate structure or ground plate under a high-voltage line. Thus,the current injection procedureserves as a convenient calibration check.
lf current injection is used，adequate shielding should be employed to eliminate signal contributionsfrom such ambient sources as interior lighting， power cords，or nearby power supplies. If sufficientshielding cannot readily be achieved because of field meter design,an indication of the magnitude ofinterfering ambient fields may be obtained by changing the phase relationship between the calibrating andinterfering signals. This magnitude may be determined by interchanging the lead connections to the sensingplates of the meter being calibrated, or by reversing connections to the power supply. If the calibratingvoltage required for a given meter reading is the same for the two configurations，the interfering signal maybe regarded as negligibly small. If a small difference exists, the average of the two voltages is that whichwould be required for the same meter reading in the absence of interference(Kotter [B19]).