SATEC EM920 Operation Manual - Manual (Page 217)

Appendix F EN50160 Evaluation and Recording
EM920 Power Quality and Revenue Meter 217
Supply Voltage Variations
This characteristic defines slow variations of steady state
supply voltage magnitude.
Method of Evaluation
The basic supply voltage magnitude measurement is the RMS
value of the steady state voltage over a period of 10 minutes
under normal operating conditions.
A voltage variation is not evaluated if the supply voltage
crosses a voltage tolerance limit (±15% Un).
Target Values
The range of voltage variations given in the EN50160 is:
±10% Un for 95% of a week
The supply voltage compliance limit can be changed in the
meter via the EN50160 PQ Recorder setup.
Rapid Voltage Changes
Rapid voltage changes are sudden but relatively weak voltage
variations between two steady state voltage levels.
Method of Evaluation
Evaluation of rapid voltage changes is made on an hourly
basis. The RMS voltage is evaluated over 1-second time
integration intervals. The meter establishes the maximum
difference of the RMS voltage between two intervals selected
from three 1-second consecutive intervals and compares it
with the target compliance limit.
A rapid voltage change is not classified if it crosses a voltage
tolerance limit (±10% Un), as it would be considered a
voltage dip or a temporary overvoltage.
Target Values
The maximum rate of rapid voltage changes in normally once
per hour or less. For voltage variations repeating more than
once an hour, amplitude is limited by the flicker index. The
maximum rate of rapid voltage changes in variations per hour
can be changed in the meter via the EN50160 Advanced
Setup. The target magnitude limit of rapid voltage changes
can be programmed in the meter via the EN50160 PQ
Recorder setup.
Under usual operating conditions the magnitude of rapid
voltage changes (once per hour or less) should generally not
exceed 5% of nominal voltage in LV networks, and 4% in MV
networks. In some circumstances, like in systems where
equipment switching must be carried out to meet supply
system or load requirements, it can reach 10%Un in LV
networks, and 6%Un in MV networks.
Flicker
Flicker expresses the visual discomfort caused by repetitive
changes of brightness in lightning subjected to fluctuations of