Endress+Hauser EngyVolt RV15, Руководство по эксплуатации

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Appendix EngyVolt RV15
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11 Appendix
11.1 Basis of measurement and calculations
11.1.1 Phase to Phase voltages for 3 phase 4 wire devices
Phase to Phase voltages are measured directly and calculated as RMS values. Situations where the
phases are not spaced 120 degrees apart (e.g. 4 wire open delta) are indicated correctly.
11.1.2 Reactive and Apparent Power
Active powers are calculated directly by multiplication of voltage and current samples. Reactive
powers are calculated using the frequency corrected quarter phase time delay method. Apparent
power is calculated as the square root of the sum of the squares of active and reactive powers.
11.1.3 Energy resolution
Cumulative energy counts are reported using the standard IEEE floating point format. Reported
energy values in excess of 1
000 000 one million may show a small non cumulative error in the
integer digits due to the limitations of the number format. Internally the count is maintained with
greater precision. The reporting error is less than 1 part per 1
000 000 and is automatically corrected
when the count increases.
11.1.4 Power factor
The magnitude of Per Phase Power Factor is derived from the per phase active power and per phase
reactive power. The power factor value sign is set to negative for an inductive load and positive for
a capacitive load. The magnitude of the System Power Factor is derived from the sum of the per
phase active power and per phase reactive power. Individual phases whose apparent power is less
than 2 % of nominal are not included in power factor determinations. The system power factor value
sign is set to negative for an inductive load and positive for a capacitive load. The load type, capacitive
or inductive, is determined from the signs of the sums of the relevant active powers and reactive
powers. If both signs are the same, then the load is inductive, if the signs are different then the load
is capacitive. The magnitude of the phase angle is the ArcCos of the power factor. Its sign is taken
as the opposite of the VAr's sign.
11.1.5 Maximum demand (drag indicator)
The maximum power consumption of an installation is provided as power utilities often levy related
charges. Many utilities use a thermal maximum demand indicator (MDI) to measure this peak power
consumption. An MDI averages the power consumed over a number of minutes, reflecting the
thermal load that the demand places on the supply system. The Integra Ci3 digital meter uses a
sliding window algorithm to simulate the characteristics of a thermal MDI instrument, with the
demand period being updated every minute.
Demand Integration Times can be set to various values. Maximum Demand is the maximum power
or current demand that has occurred since the unit was last reset. This is maintained as a continuous
record of the highest demand value that has been reached. Note: During the initial period when the
“sliding window” does not yet contain a full set of readings (e.g. during initial commissioning). Then
maximum demands may not be true due to the absence of immediate historical data.
11.1.6 Total harmonic distortion – THD
The calculation used for Total Harmonic Distortion is: THD = ((RMS of total waveform – RMS of
fundamental) / RMS of total waveform) x 100. This is often referred to as THD–R, and lies in the
range 0 to 100 %. THD measurement is subject to the 'range of use' limits. The device may give
erratic or incorrect readings where the THD is very high and the fundamental is essentially absent.