Siemens 9410DC, Руководство пользователя, Страница: 151 / 172

Power quality 9410 series
Harmonic content calculations
Harmonic content (H
C
) is equal to the RMS value of all the non-fundamental harmonic
components in one phase of the power system.
The meter uses the following equation to calculate H
C
:
HC = (H
2
)
2
+ (H
3
)
2
+ (H
4
)
2
...
TDD calculations
TDD (total demand distortion) evaluates the harmonic currents between an end user
and a power source.
The harmonic values are based on a point of common coupling (PCC), which is a
common point where each user receives power from the power source.
The meter uses the following equation to calculate TDD:
TDD = ( (HCIA)
2
+ (HCIB)
2
+ (HCIC)
2
) / (ILoad) x 100
Where
ILoad
is equal to the maximum demand load on the power system.
thd and TDD
Your meter can be configured to provide thd (total harmonic distortion using the total
RMS value for the content rather than the fundamental content) and TDD (total
demand distortion, the harmonic current distortion against the maximum demand of
the electrical system.
thd = H
C
/ RMS *100%
TDD = H
C
/ Demand
Max
*100%
This is an advanced procedure that should only be performed by users with an
advanced knowledge of power quality, ION architecture, and the power system being
monitored.
See the ION Reference, available from www.usa.siemens.com/pds, for details about
the Harmonics Measurement module.
Phasors
Phasors are used to represent the voltage and current relative magnitude and angles.
The length of the lines in the phasor diagram represent the relative magnitude of the
voltages with respect to the other phase voltages, and the currents with respect to the
other phase currents. All angles are measured with respect to the Va/V1 phase. The
Va/V1 phasor is fixed to the right-hand horizontal axis (positive x-axis). Positive angles
are measured counterclockwise.
Numeric values are provided for the magnitude and relative angle for each voltage and
current phase.
Phasor information can be used to troubleshoot incorrect connections on the meter’s
voltage and current inputs (for example, switched phase wiring or polarity errors), if
you know how the phasors should be oriented for your power system.
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