P.8.2
SEL-411L Relay Protection Manual Date Code 20151029
Oscillography, Events, and SER
Data Processing
Data Processing
The relay is a numeric, or microprocessor-based, relay that samples power
system conditions via the CT and PT inputs. The relay converts these analog
inputs to digital information for processing to determine relaying quantities
for protection and automation. Figure 8.1 shows a general overview of the
input processing diagram for the relay.
Raw and Filtered Data
The relay outputs three types of analytical data: high-resolution raw data
traveling wave data, and filtered data. Figure 8.1 shows the path a power
system signal takes through relay input processing. A CT or PT analog input
begins at hardware acquisition and sampling, continues through software
filtering, and progresses to protection and automation processing. The initial
hardware low-pass filter half-power or –3 dB point is 3.0 kHz. Next, the relay
samples the power system voltage or current with an 8000 samples/second
A/D (analog to digital) converter. This is the tap point for high-resolution raw
data captures. You can select 8000 samples/second, 4000 samples/second,
2000 samples/second, and 1000 samples/second effective sampling rates for
presentation and storage of the high-resolution raw data COMTRADE format.
The traveling wave data take a different path (see Figure 8.1). For these data,
the CT analog inputs are filtered through a hardware band-pass filter and then
sampled at 1.5625 MHz. The relay uses these data to calculate fault location
by means of the traveling wave method. These data are also available in
COMTRADE format. Traveling wave COMTRADE files are labeled with a
prefix of TW to differentiate traveling wave COMTRADE files from high-
resolution COMTRADE files, which have a prefix of HR).
The software portion of input signal processing receives the high-resolution
raw data sampled quantities and passes these to the Anti-Aliasing Digital
Filter. The half-power or –3 dB point of the anti-aliasing filter is 640 Hz.
Subsequent processing decimates the sampled data to eight samples per power
system cycle using additional digital filtering. This 8-samples/cycle
information is the filtered data for event reports and other relay functions. The
relay selects every other sample of 8-samples/cycle filtered data to present
4-samples/cycle event reports.
The relay samples the control inputs at a rate of 2 kHz.
The INT2, INT7, INTC, INTD, and INTE Interface boards have optoisolated
control inputs with fixed pickup voltages. Optoisolated inputs are ordered
with one of six available pickup voltage ratings. No analog voltage
information is available. The raw input digital status is available in high-
resolution (COMTRADE) data files. Contact bounce may be visible when the
raw data are viewed.
The relay filters the control inputs with settable debounce timers, and updates
the resulting Relay Word bits 8 times per cycle. Event reports can include the
filtered control input Relay Word bits.
Control input state changes will appear to occur faster in COMTRADE
oscillography files than in event reports (EVE command) or Sequential
Events Recorder reports (SER command) because of the control input
debounce time delays.
To Next Page
Loading...
