PQube User Manual 2.1
Page 45 of 113
All PQubes can measure power systems with the following nominal voltages: 69V, 100V, 120V,
200V, 208V, 230V, 240V, 277V, 350V, 400V, 480V, 600V, and 690V (maximum 400V with respect to
Earth).
All PQubes can measure power systems with nominal frequencies of 50 Hz, 60 Hz, and 400 Hz.
Sampling and accuracy
RMS measurements are better than ±0,1% of nominal voltage, and sampled at 256 samples per
cycle to ensure full accuracy for all measurements.
Your PQube’s sampling rate is automatically locked to the frequency, and tracks the frequency as it
changes at a rate of up to ±3 Hz per second.
Frequency
Voltage frequency measurements are phase-locked to either L1-E or L2-E, depending on which
channel has the best signal. It measures frequency by timing the zero-crossings, with a 5-pole
analog low-pass filter and a 64-cycle digital low-pass filter.
Voltage Distortion (THD)
THD is a measurement of the amount of voltage harmonics present in the voltage waveform. Your
PQube uses a Discrete Fourier Transform of phase-locked 256-samples-per cycle to calculate total
harmonic distortion.
Voltage Unbalance
Voltage unbalance is a measurement of the difference in the magnitude voltages in a three-phase
system. This measurement is disabled if the power system being monitored is not three-phase.
Your PQube measures the unbalance of the voltage waveform using your choice of the following
definitions:
ANSI/IEEE Method
Widely used in the North America, the ANSI method only considers the RMS magnitudes on each
phase. Compared to the IEC method, the ANSI method is simpler, because it ignores harmonics
and phase angles. For small unbalance values, these two methods provide very similar results.
IEC Method
In the IEC unbalance method, only the fundamental voltage and/or current is considered. The IEC
method takes into account both the magnitude and angle of the fundamental, and produces two
different unbalance measures: zero-sequence unbalance, and negative-sequence unbalance.
GB Method
Used primarily in China, the GB method is a time-smoothed variation on the IEC method.
Voltage and Current – Harmonics and Interharmonics
Voltage harmonics are available in absolute volts or percent of fundamental. Use the
Voltage_Harmonics tag in the Measurement Setup section in your setup file. Total distortion for
voltage is reported as THD.
Current harmonics are available in absolute amps or percent of fundamental, using the
Current_Harmonics tag in your setup file. If you choose absolute amps, total distortion for current
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