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16.13. MEASURING METHOD: OUTLINES
The instrument is able to measure: voltages, currents, active powers, inductive and
capacitive reactive powers, apparent powers, inductive and capacitive power factors,
analogical or impulse parameters. All these parameters are analysed in a digital way: for
each phase (voltage and current), 6 x 128 samples are acquired on a module of 16 x
20ms, repeated for the three phases.
16.13.1.
Integration periods
The storage of all the data would require a huge memory capacity.
Therefore we've tried to find out a storage method which permits to compress the
information to be memorised, though providing significant data.
The chosen method is the integration one: after a certain period called "integration period",
which can be set from 5 seconds to 60 minutes (3600sec), the instrument extracts from
the sampled values the following values:
• Minimum value of the parameter during the integration period (harmonics excluded)
• Average value of the parameter (intended as arithmetic average of all the values
registered during the integration period)
• Maximum value of the parameter during the integration period (harmonics excluded)
Only this information (repeated for each parameter to be memorised) are saved in the
memory along with starting time and date of the integration period.
Once these data are memorised, the instrument restarts to take measurements for a new
period.
16.13.2.
Power factor calculations
According to the standards in force, the average power factor cannot be calculated as the
average of the instantaneous power factors. It must be obtained from the average values
of active and reactive power.
Each single average power factor (of phase or total) is therefore calculated, at the end of
each integration period, on the average value of the corresponding powers independently
on the fact that they must be registered or not.
Besides, for a better analysis of the type of load present on the line and in order to have
terms of comparison when studying the invoicing of the low cos ϕ , the values of inductive
and capacitive cos ϕ are treated as independent parameters.
Page 128 of 131
VR2250
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