Alstom iSTAT M355, Руководство пользователя, Страница: 46 / 154

M3x5/EN M/B User Manual
Page 44
iSTAT M3x5
10.4.17 Starting voltage for SYNC (V)
The device needs to synchronize its sampling with the measuring signals period to
accurately determine its frequency. For that purpose, the input signal has to be large enough
to be distinguished from the noise.
If all phase voltages are smaller than this (noise limit) setting, the device uses the current
inputs for synchronization. If all of the phase currents are also smaller than the Starting
current for PF and PA setting, synchronization is not possible and frequency displayed is 0.
The value for starting voltage should be set according to conditions in the system (level of
noise, random voltage fluctuation…)
10.4.18 Calculation of Harmonics
The selection of the reference for the calculation of harmonics is important for the calculation
of the absolute values. It is possible to select harmonics

As a percentage of the RMS signal value where a value is calculated for all harmonics

Or relative to the fundamental (first harmonic) where all other harmonics are
calculated relative to the 1
st
harmonic.
10.4.19 Reactive power and energy calculation
Two different principles of reactive power and energy calculation can be used:
Standard method:
With this method a reactive power and energy are calculated based on assumption that all
power (energy) that is not active is reactive.
Q
2
= S
2
– P
2
This means also that all higher harmonics will be measured as reactive power (energy).
Displacement method:
With this method, reactive power (energy) is calculated by multiplication of voltage samples
and delayed current samples.
Q = U × I|
+90°
With this method, reactive power (energy) represents only true reactive component of
apparent power (energy).