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Chapter 8—Waveform and Event Capture 63230-300-212
Types of Waveform Captures April 2001
© 2001 Schneider Electric All Rights Reserved
108
Using waveform captures you can monitor power sags and swells that may
be produced, for example, when an X-ray machine and an elevator are used
at the same time, or more commonly, when lightning strikes the distribution
system that feeds the facility. The system’s alarms can be programmed to
detect and record such fluctuations, enabling you to determine an
appropriate strategy for corrective action.
Circuit monitors use a sophisticated, high-speed sampling technique to
simultaneously sample up to 512 samples per cycle on all current and
voltage channels. From this sampling, the circuit monitor saves waveform
data into its memory. These waveform captures can be graphically displayed
using
SMS. The circuit monitor has one type of waveform capture that you
initiate manually; the other three event captures are associated with and
triggered by an event such as a digital input transition or over/under
condition. These event recordings help you understand what happened
during an electrical event. Using event captures you can analyze power
disturbances in detail, identify potential problems, and take corrective action.
See Chapter 9—Disturbance Monitoring on page 113 for more about
disturbance monitoring. The types of event captures are described in the
sections that follow.
The steady-state waveform capture can be initiated manually to analyze
steady-state harmonics. This waveform provides information about individual
harmonics, which
SMS calculates through the 255th harmonic. It also
calculates total harmonic distortion (THD) and other power quality
parameters. The waveform capture records one cycle at 512 samples per
cycle simultaneously on all metered channels.
Using
SMS from a remote PC, initiate a steady-state waveform capture
manually by selecting the circuit monitor and issuing the acquire command.
SMS will automatically retrieve the waveform capture from the circuit monitor.
You can display the waveform for all three phases, or zoom in on a single
waveform, which includes a data block with extensive harmonic data. See the
SMS online help for instructions.
Use the disturbance waveform capture to record events that may occur within
a short time span such as multiple sags or swells. The circuit monitor initiates
a disturbance waveform capture automatically when an alarm condition
occurs (if the alarm is set up to perform the waveform capture). The trigger
may be from an external device such as an protective relay trip contact
connected to a digital input or voltage sag alarm, or you can also initiate the
waveform capture manually from SMS at any time.
In
SMS, for the disturbance waveform capture, you select the sample rate and
how many cycles and pre-event cycles the circuit monitor will capture (see
Ta bl e 8–1):
See the
SMS online help for instructions on setting up disturbance waveform
captures.
Table 8–1: Available Resolutions for Disturbance Waveform Captures
Samples per Cycle (Resolution) Max Duration
16 915 cycles
32 457 cycles
64 228 cycles
128 114 cycles
256 57 cycles
512 28 cycles
TYPES OF WAVEFORM CAPTURES
Steady-state Waveform Capture
Initiating a Steady-state
Waveform
Disturbance Waveform Capture