Allen-Bradley 1404-M4, User Manual

Page: 31 / 356

Publication 1404-UM001D-EN-E - October 2004
Powermonitor 3000 Operations 3-5
•
Frequency Averaging – like the RMS result averaging, the default
setting provides for a smoother response by averaging the
frequency of each of the last 8 cycles. You may select “no
averaging” to return the frequency of only the last cycle
Refer to Advanced Device Configuration on page 3-23 for more
information.
Symmetrical Component Analysis Results
The Powermonitor 3000 calculates sequence voltages and currents for
use in symmetrical component analysis, a method of mathematically
transforming a set of unbalanced three-phase vectors into three sets of
balanced vectors. The positive sequence components are a set of
vectors that rotate the same direction as the original power vectors,
and represent that portion of the applied voltage or current capable of
doing work. Negative sequence components rotate opposite to the
original vectors, and represent the portion of the applied power that
results in losses due to unbalance. The percent Unbalance value is the
ratio between the negative and positive current sequence in a 3-phase
system and is the most accurate measurement of current unbalance
because it takes into account the magnitude of the individual currents
and the relative phase displacement. The zero sequence component is
a single vector that does not rotate, and represents ground or neutral
current or voltage. The component analysis results returned include:
•
Positive Sequence Current
•
Negative Sequence Current
•
% Current Unbalance
•
Positive Sequence Voltage
•
Negative Sequence Voltage
•
% Voltage Unbalance
•
L4 current , which is the zero-sequence current on a wye system
when neutral current is connected to the I4 current input or in
delta systems when an external zero sequence transformer is
connected to the I4 input
Table 3.3 summarizes the voltage and current metering information
provided by the Powermonitor 3000.
Allen-Bradley HMIs