Measurement Computing WavePort 312P rev.1.0 - Manual (Page 58)

6-4 Detailed Harmonics PowerVista/312 User’s Manual
6.3.3 Maximized Spectra
The maximizing feature of Detailed Harmonics is clearly useful when measuring loads such as arc furnaces
where load if fluctuating wildly. Note however, that the maximized spectra is created through a routine that
repeatedly maximizes after a capture is processed as fast as the PC can process information and display it. Thus,
there will certainly be moments in time that are missed. Sampling theorems tell us that as we sample more
frequently and take more points, we generate a more accurate picture of what we desire. Thus, when measuring
loads such as an arc furnace it is recommended that data be taken through an entire load cycle, and that the
process be repeated several times.
Though the spectra will be maximized, generating a worst case and conservative measurement, note that
averaging (discussed above) is still occurring over a 10 cycle capture. Thus, we are generating a maximized
spectra with 10 cycle average harmonics. This has been found to be a good conservative starting point when
designing and properly rating harmonic mitigation equipment.
The maximizing is performed on spectral values in Volts and Amps. This is the only effective method for
determining a maximized spectrum. This insures that captures with severe distortion (as seen in percent) but
low total RMS value, do not impact the maximized spectrum falsely.
6.3.4 IEEE 519
The IEEE 519-1992 Standard discusses the Recommended Practices and Requirements for Harmonic Control in
Electrical Power Systems. It provides limits for both suppliers and consumers of electrical power. EasyPower
Measure automatically includes the tables of limits within the 519, for both voltage and current distortion.
Thus, the user only needs to connect the instrument, define the 519 data items in Configuration / Detailed
Harmonics, and capture data.
The Harmonics 519 Window is (under normal operation) minimized in the left hand bottom corner of the
harmonics view. To see the tabulated results for a data capture, simply restore the window by clicking on
.
To return the window to the corner, click on .
A lengthy discussion on the application of the 519 will not be supplied here. That topic would require several
pages as well as significant reference to the limit tables and text within the 519. We would recommend
acquiring a copy of the Standard and reading sections 10 to 13. One critical element of the standard however
should be made clear. The standard is not an equipment standard, but a system standard. Voltage distortion
limits are supplied for suppliers of electrical power (utilities, etc.), and current distortion limits are supplied for
consumers of electrical power. The standard however can be used as a guide within a facility, and users are
encouraged to apply the standard in this way to maintain safe and reliable load centers, substations, and feeders
within facilities.
For voltage distortion, the result table supplies THD and the worst case (highest) harmonic voltage measured.
Voltage limits are supplied in the row above the results.
For current distortion, the result table supplies THD and the worst case (highest) harmonic currents measured
within integer harmonic categories as specified in the 519. Current limits for even and odd harmonics are
supplied in the row above the results.
Note: The 519 tabulation only includes integer harmonic results.