The HDPQ family of products have a number of trigger
mechanisms for capturing different types of power quality phenomena. Most users are familiar with settings for
sags and swells, but those typical limits usually don’t capture the “blinky
lights” problems. While the Pst
(perceptibility short term) parameter will indicate whether the voltage supply
is likely to produce light flicker when the Pst is close or above 1, it doesn’t
help determine where it comes from or what the source is since it is a
ten-minute journal value. The graph
below illustrates such.
The voltage and current plots show that it is an increase in
current over 100A that results in the voltage decreasing by 5-8V every 15
minutes. The rms variation limit for sags is set to 90% of the nominal 120V or
108V, so no sag was reported. In above
example, the red dotted line is that sag limit.
Yet the residents complained of “blinky lights” while the Pst does
increase to 0.8 each time, not over 1.
The rms deviation transient trigger is one method to capture
such as an event. However, there is a
parameter that is included in the IEC and IEEE standards that was defined just
for such disturbances. It is the RVC or
Rapid Voltage Change. It looks for a
sudden change in the voltage from one steady state value, waits for stability
in any continued variations until stable at another steady state voltage value
for 1 second or more. The delta change
limit is typically set to 2-3%. Since
the variation shown in the data above was 4-7%, this mechanism was ideal for
capturing and reporting each time that it happened. An example at 22:189:54 is shown below. The rms deviations and wave shape triggers
also captured the event, but they also triggered on other disturbances that
weren’t part of the investigation, which produced extra data to sort through
#39 10/03/2017 22:02:05.297 AV Misc at 0.8 Deg |
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#40 10/03/2017 22:02:05.297 BV
Misc at -179.1 Deg
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#41 10/03/2017 22:02:05.306 AVRmsDev Normal To High
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#42 10/03/2017 22:02:05.306 BVRmsDev Normal To High
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#44 10/03/2017 22:02:05.323 AVRmsDev High To Normal
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#45 10/03/2017 22:02:05.323 BVRmsDev High To Normal
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#48 10/03/2017 22:18:54.874 AV
Misc at 0.7 Deg
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#49 10/03/2017 22:18:54.874 BV
Misc at -179.0 Deg
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#50 10/03/2017 22:18:54.874 AVRmsDev Normal To High
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#51 10/03/2017 22:18:54.874 BVRmsDev Normal To High
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#52 10/03/2017 22:18:54.883 A Delta
V RVC Rapid Voltage Change 0.175 Sec.
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#53 10/03/2017 22:18:54.883 B Delta
V RVC Rapid Voltage Change 0.259 Sec.
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The right tool for the right job has always been a wise
adage. Setting the right tool up with
the right limits on the right parameters to help solve the customer’s problems
is an extension of that idea that can help get the answer quickly and
clearly. By the way, the answer here
was a common answer for such problems.
The HVAC unit was causing the blinky lights.
