HT instruments VEGA78 - Manual (Page 116)

VEGA78
EN - 114
10. APPENDIX – THEORETICAL OUTLINES
10.1. VOLTAGE ANOMALIES
The meter is capable of recording all those TRMS values as voltage anomalies, calculated
every 10ms, beyond the percentage thresholds of Voltage Reference (Vref) set during the
programming from ±1% to ±30% with steps of 1%. These limits remain unchanged
throughout the recording period.
The reference are set to:
Nominal Voltage Phase to Neutral:
For Single Phase and 4 wires three phase system.
Nominal Voltage Phase to Phase: For 3 wires three phase system.
Example1: Three Phase System 3 wires.
Vref = 400V, LIM+= 6%, LIM-=10% =>
High Lim = 400 x (1+6/100) = 424,0V
Low Lim = 400 x (1-10/100) = 360
Example2: Three Phase System 4 wires.
Vref = 230V, LIM+= 6%, LIM-=10% =>
High Lim = 230 x (1+6/100) = 243,08V
Low Lim = 230 x (1-10/100) = 207,0V
For each voltage anomaly the instrument records:
 The number corresponding to the phase where the anomaly occurred.
 The “direction” of the anomaly: “UP” and “DN” identify voltage drops (sag) and peaks
(swell) respectively.
 The date and time of the event beginning in the form day, month, year, hour, minutes,
seconds, hundredths of second.
 The duration of the event, in seconds with a resolution of 10ms.
 The minimum (or maximum) value of voltage during the event.
10.2. VOLTAGE AND CURRENT HARMONICS
10.2.1. Theory
Any periodical no-sine wave can be represented as a sum of sinusoidal waves having
each a frequency that corresponds to an entire multiple of the fundamental, according to
the relation:
) t sin( V V v(t)
k k
1 k
k 0
    



(1)
where:
V
0
= Average value of v(t).
V
1
= Amplitude of the fundamental of v(t).
V
k
= Amplitude of the k
th
harmonic of v(t).
In the mains voltage, the fundamental has a frequency of 50 Hz, the second harmonic has
a frequency of 100 Hz, the third harmonic has a frequency of 150 Hz and so on. Harmonic
distortion is a constant problem and should not be confused with short events such as
sags, swells or fluctuations.
It can be noted that in (1) the index of the sigma is from 1 to the infinite. What happens in
reality is that a signal does not have an unlimited number of harmonics: a number always
exists after which the harmonics value is negligible.