PQA819 - PQA820
EN – 22
12. APPENDIX – THEORETICAL OUTLINE
12.1. VOLTAGE ANOMALIES
The instrument catalogs as voltage anomalies (sags, swells) all those RMS values,
calculated every 10ms (@ 50Hz), which are out of the thresholds set upon configuration by
1% to
30% of a set reference value with a 1% step.
To prevent recording events attributable to electric noise only, a hysteresis threshold of
1% is also present. These limits remain unchanged throughout the whole recording period.
The reference voltage value must be set as:
Rated voltage Phase-Neutral: for single-phase and three-phase 4-wire systems
Rated voltage Phase-Earth: for three-phase 3-wire systems
Example: Three-phase 4-wire system.
Vref = 230V, LIM(+) = 10%, LIM(-) = 10%, => Hysteresis 1%
Higher Lim = 230 + 23 = 253V, Lower Lim = 230 - 23 = 207V
Recording swells
The instrument starts recording an event if voltage exceeds 253V and stops recording if
voltage drops below 253 – 2.53 = 250.5V
Recording sags
The instrument starts recording an event if voltage is lower 207V and stops recording if
voltage rises over 207 + 2.07 = 209.1V
For each event, the instrument records the following data:
The number corresponding to the phase in which the anomaly occurred.
The “direction” of the anomaly: “UP” and “DN” respectively identify voltage swell and
sags
The date and time in which the event starts in a format day, month, year, hour, minutes,
seconds, hundredth of seconds.
The duration of the event, in seconds with a resolution equal to 10ms.
The minimum (or maximum) value of voltage during the event.
