Flicker; Interruptions; Voltage Fluctuations; System Time Deviation - Arbiter Systems Power Sentinel 1133A Operation Manual

11.15 Flicker

11.15 Flicker
Flicker is measured in accordance with IEC 61000-4-15, the successor standard to IEC 868. Unlike
the other measurements described above, flicker measurement is a continuous process. This process
is performed using a sample rate of 640 samples per second (sps). Anti-alias (decimation) filtering is
performed on the 10240–sps data stream, and the resulting samples are further processed following
the block diagram suggested in IEC 61000-4-15. The resulting measurements of flicker perceptibility
are classified using a 256-level logarithmic classifier at the full 640–sps rate. Pst is then determined
every ten minutes (or as specified), as described by the standards.
Although no standards currently require it, the 1133A also measures flicker on the current
inputs. This information can be useful in determining whether a customer's load is causing flicker
on the power system, or whether the customer is being subjected to flicker from other sources. It
is unrealistic to penalize a utility for poor power quality at a customer's load when the cause of
the problem is the load itself.
11.16

Interruptions

Interruptions are monitored on the voltage inputs by comparing the 20-per-second voltage
measurements with a user-supplied threshold. Events are triggered when the voltage dips below
the preset threshold. These can cause the logging of pre-fault and post-fault data, contact closure,
or any of the other actions described under "Event Logging."
11.17

Voltage Fluctuations

Voltage fluctuations are monitored by classifying the 20-per-second voltage data, per phase, with a
256-step linear classifier covering a range of
summarized as a cumulative probability table over a specified interval
addition, the minimum, maximum, mean and standard deviation are calculated. The data may be
recorded in flash memory either continuously or on demand. Voltage fluctuations corresponding to
system stability events may also be monitored and a trigger generated using Schulz-Laios filtering
of the voltages.
11.18

System Time Deviation

System time deviation, which is the accumulated error of a clock using the system frequency as its
reference, compared to an absolute reference such as UTC, is determined from the 20-per-second
phase data described earlier. System time deviation is accumulated as integer cycles of error plus
fractional phase, and is converted to seconds as needed. The positive-sequence voltage phase angle
is used for this measurement. Since this is an integrated value, the constant of integration (initial
time offset value) must be specified by the user.
11.19

Phasor Measurements

Phasor data are formatted and output in accordance with IEEE Synchrophasor Standard C37.118.
Phasors consist of the real and imaginary component of magnitude for the voltages and currents
20 percent of nominal voltage. These data are then
typically 15 minutes. In
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