3 WMU – WAVEFORM MEASUREMENT UNIT
The WMU transmits Ethernet messages that are analogue signals calculated and sent within a PMU frame
with a transmission rate equal to 4 times the system nominal frequency.
The analog signal sent is a representation of a three-phase signal that is used to evaluate wide-area
subcyclic oscillations. The WMU uses the analogue field (No 10) of the frame below to send its data.
The WMU uses the commanded logic through the port number 4723.
The table below exemplifies a frame of PMU described as per IEEE C37.118.2-2011.
Sync byte followed by frame type and version number
Stream source ID number, 16-bit integer
SOC timestamp, for all measurements in frame.
Fraction of Second and Time Quality, for all measurements in frame.
Phasor estimates. May be single phase or 3-phase positive,
negative, or zero sequence. 4 or 8 bytes each depending on
the fixed 16-bit or floating point format used, as indicated
by the FORMAT field in configuration the frame. The
number of values is determined by the PHNMR field in
configuration 1, 2, and 3 frames.
Frequency (fixed or floating point).
Rate of change of frequency (fixed or floating point).
Analog data, 2 or 4 bytes per value depending on fixed or
floating point format used, as indicated by the FORMAT
field in configuration 1,2, and 3 frames. The number of
values is determined by the ANNMR field in configuration 1,
2, and 3 frames.
Digital data, usually representing 16 digital status points
(channels). The number of values is determined by the
DGNMR field in configuration 1, 2, and 3 frames
Fields 6 - 11 are repeated for as many PMUs as in NUM_PMU field in
configuration frame.
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