Endress+Hauser EngyVolt RV12, Руководство по эксплуатации

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Appendix EngyVolt RV12
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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.