Trident TRIDENT 1U1I, User Manual

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5.4 MEASUREMENT PRINCIPLES OF TRIDENT
TRIDENT analyses the measurements in 4 stages:

Input signals are sampled every 1millisecond,

Then the RMS values of voltages are calculated over 20ms, rolling every 2ms, for the detection of
voltage faults,

Then the instantaneous RMS values are calculated (averaged over one second) of voltages, currents
and active power,

Then the Slow Variations are calculated (RMS values averaged over 1 to 60mn) of voltages,
currents and active power for sequential recording.
5.4.1 Sampling
Every millisecond TRIDENT measures all the a.c. inputs (V1 to V3, I1 to I3, Vearth).
TRIDENT calculates instantaneously :

the 3 differences between V1, V2 and V3 in order to obtain the 3 samples of true line
voltages

the sum of the 3 currents to obtain the samples of the neutral current

the 3 products of V x I to obtain the samples of the 3 active powers.
5.4.2 Calculation of the 20ms RMS values and fault detection
Every 2ms, TRIDENT calculates the rolling RMS value over 20ms of the 4 phases of voltage V1,
V2, V3 and Earth or line voltage U12, U23, U31 and Earth depending on whether it is measuring
phase-to-neutral or line voltages.
This value is used for the detection of voltage faults that is carried out simultaneously and
independently on the 4 phases.
The detection of faults is made every 2 ms, using these rolling 20ms values.
As soon as one voltage passes one of the 3 thresholds (rise, fall or interruption), a fault is
registered :

the date is memorized,

a fault duration counter is initialised at 2ms,

the sum of voltages of the phase or phases in fault is initialised with the current voltage
value (rolling 20 ms average), and is used for the calculation of the mean value,

the rolling 20 ms average establishes the value of the peak of the fault,

TRIDENT 3U3I archives the mean values over 1sec of the 3 voltages and the 3 currents at
the instant of the beginning of the fault. These values will be memorized as the values
preceding the fault, when the fault is finished and recorded.
The end of a fault is provoked by another passage of the threshold of the voltage, this threshold
being corrected by a hysteresis of 1% of the nominal value, to avoid the proliferation of faults
should the threshold barely be passed.