Power Quality Triggers
RMS Triggers
In accordance with IEC 61000-4-30 and other
standards, RMS measurements are computed over one
cycle, but incremented in ½ cycle steps. IEC standards
refer to this as
Urms(1/2
). It’s important to note that
the measurement window for PQ triggers is always 1
cycle, but the ½ cycle increment allows for more
detailed event detection. Any one cycle exceeding the
instrument’s limits will trigger an RMS type event,
regardless if it’s detected on a ½ cycle boundary.
If a trigger occurs, data is stored to memory in
accordance with the RMS Summary and Waveform (# of
cycles recorded) settings entered during setup. Like
other Dranetz products, Dranetz HDPQ detects and
records
current
RMS events in the same manner as
voltage. Please see the instrument user’s guide for
further details.
In addition to PQ triggers, the
Urms(1/2
) data is used
as the basis for all voltage and current min, max and
average measurements with a 1 cycle resolution with
½ cycle steps.
Transient Triggers
As per IEEE 1159, transients are divided into three
categories:
Low frequency (<5Khz)
Medium frequency (5 – 500Khz)
High frequency (500Khz – 5Mhz)
All Dranetz HDPQ instruments have extensive transient
capture capabilities. Each can capture low and
medium frequency transients, with the Dranetz HDPQ
Xplorer
and
Xplorer-400
having additional circuitry to
also capture high speed transients. It is important to
note that the Dranetz HDPQ goes well beyond the
requirements of IEC 61000-4-30 and EN 50160. In
addition, the Dranetz HDPQ family employs the
methods used for voltage transients to trigger on
current transients.
Transient trigger methods available are:
Instantaneous Peak – All Dranetz HDPQ
Cycle to Cycle Waveshape – All Dranetz HDPQ
RMS Difference Waveshape – All Dranetz HDPQ
High Speed Sampling – Xplorer, Xplorer-400
Instantaneous Peak
This trigger uses the RMS sampled data and looks for
any one of the 512 samples to exceed the
Instantaneous Peak limit. If at least one sample
exceeds the limit, data is recorded to memory based
upon the user’s pre/post waveform settings.
Applications for this trigger are events such as peak
over voltage (or current), lightning strikes, etc.
Waveshape Triggers
Waveshape triggers look for changes in each and every
waveform on a cycle-by-cycle basis. These are
important triggers, as many types of transients do not
affect the waveshape enough to change the RMS or
harmonics significantly. Therefore, traditional RMS
triggers will not detect these events.
There are two waveshape trigger methods available:
Cycle to cycle waveshape
RMS distortion (or difference) waveshape
Both methods look for changes in the waveshape by
comparing the present AC cycle to the previous AC
cycle. If the difference exceeds the user’s limits, an
event is recorded. Both methods have been available
in prior Dranetz products. Even though these are
similar trigger methods, both remain available since
some users prefer one over the other. Both methods
are available for voltage and current triggers.
Shop for Power Metering products online at:
1.800.561.8187
www.
PowerMeterStore
.ca
