Measurement Computing WavePort 312P rev.1.0 - Manual (Page 57)

PowerVista/312 User’s Manual Detailed Harmonics 6-3
⇒ Continuous Refresh: In this mode, as quick as a capture is processed and displayed, another capture will
begin. This will continue indefinitely. This gives a spectrum analyzer feel to the output and allows the user
to observe fluctuations in spectral content as they occur.
⇒ Single Trigger: In this mode, a single capture is processed and displayed.
• IEEE 519 Settings: are used to map harmonic currents and voltages onto demand base for display in the
Harmonics 519 Window. Refer to IEEE Standard 519-1992 for additional description of the following items.
⇒ Voltage Base: is the base line-to-line voltage at the PCC (point of common coupling).
⇒ Short Circuit Ratio: is the short circuit ratio at the PCC. This is defined as maximum symmetrical short
circuit current divided by the Max Demand current.
⇒ Max Demand: is the maximum facility demand current at the PCC. This represents maximum demand of a
facility based on measurements or billing records.
6.3 Detailed Harmonics Application
Detailed Harmonics should be used when desiring harmonic measurements that include both integer and non-
integer frequencies. This function works similar to a spectrum analyzer in that it allows the user to take
snapshots of a given capture as well as to update the display continuously. However, a major difference is that it
centers its attention and sampling rates around the defined base frequency, while capturing and analyzing data
for all signals input. A spectrum analyzer is typically a one or two channel device. To spectrum analyze a
single signal at a much higher sampling rate, refer to the Spectrum Analyzer acquisition feature. Several topics
are discussed below to aid the user in the application of Detailed Harmonic measurements.
6.3.1 Average Harmonics
Since this harmonic analysis uses 10 cycles for each input signal, an average spectrum over 10 cycles is
determined. For measurements on widely fluctuating loads, this is a significantly more realistic measurement
than single cycle harmonics. For a single cycle with severe waveform distortion, integer harmonics will show
severe harmonic distortion levels. If a single cycle with severe distortion resides within a waveshape of 10
cycles where all other cycles are of a much more moderate distortion level, then harmonics will tend toward the
moderate level. Average levels of harmonic current will also give a better measure of spectra that can be used to
determine harmonic heating.
6.3.2 Non-Integer Frequencies
Of equal significance to average harmonics, is the ability to see non-integer frequencies. For example, if there is
a resonance occurring at a mill at a non-integer frequency, an integer harmonic decomposition will falsely note
increased levels of integer harmonic distortion as the energy of the non-integer frequency is spread over nearby
integer frequencies. EasyPower Measure supplies results in steps of 0.1 per unit Hz of the Base Frequency.
That means there are 9 frequency steps between each integer harmonic. For 60 Hz and its 120 Hz 2
nd harmonic,
this would correspond to additional frequency information at 66, 72, 78, 84, 90, 96, 102, 108 and 114 Hz. This
will allow the user to either verify that frequencies captured are truly integer, or measure distortion problems
that might have earlier been attributed to integer harmonics, and thus analyzed incorrectly.