Satec Expertmeter EM720 Operation Manual page 207

Appendix E EN50160 Evaluation and Recording
Voltage Dips
Voltage Interruptions
EM720 Power Quality and Revenue Meter
A voltage dip is a sudden reduction of the RMS voltage
below 90% of the nominal value, followed by a return to a
value higher than 90% of the nominal in a time varying
from 10 ms to 60 s.
Method of Evaluation
A voltage dip is classified as one polyphase event
regardless of the shape and of the number of phases
affected (as per Eurelectric's Application guide to the
European Standard EN 50160, and IEC 61000-4-30). An
event can begin on one phase and end on another phase.
The fault magnitude is recorded separately for each phase
involved. The event duration is measured from the instant
at which the voltage falls below the start threshold on one
of the phases to that at which it becomes greater than the
end threshold on all affected phases including a threshold
hysteresis.
The basic voltage dip measurement is one-cycle RMS
voltage updated each half-cycle.
The voltage dip threshold can be changed in the meter via
the EN50160 PQ Recorder setup.
Statistical Results
The EM720 provides the statistical evaluation of voltage
dips using the classification established by UNIPEDE. Dips
are classified by residual voltage magnitude and duration
as shown in Appendix D.
Indicative Values
Under normal operating conditions the expected number
of voltage dips in a year may be from up to a few tens to
up to one thousand. The majority of voltage dips have a
duration less than 1 s and a depth less than 60%.
Voltage interruptions correspond to temporary loss of
supply voltage on all phases lasting less than or equal to 3
minutes in the event of short interruptions, and more than
3 minutes for long interruptions.
Method of Evaluation
The voltage interruption is detected when the voltages on
all phases fall below the interruption threshold (as per IEC
61000-4-30) specified by the EN50160 at a level of 1%Un.
The interruption threshold can be changed in the meter
via the EN50160 PQ Recorder setup.
The basic voltage measurement is one-cycle RMS voltage
updated each half-cycle.
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