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Date Code 20011026
Event Reporting
4-5
SEL-321/321-1 Instruction Manual
Analog data are filtered by an analog low-pass filter with a cutoff frequency of 540 Hz. A digital
filter processes the sampled data and removes dc and ramp components. The digital filter is a
full cycle long, cosine filter centered on the sensed frequency.
Successive lines of the event report occur every 90
°
. With respect to the present value, the
previous value was taken one quarter-cycle earlier and appears to be leading the present value by
90
°
.
Quarter-cycle event report values can be used to represent the signals as phasors:
The previous value of the output is the Y-component.
The present value of the output is the X-component.
It may seem confusing to refer to the older data as the leading component of the phasor. The
following example may help.
Consider a sine wave having zero phase shift with respect to t = 0 and a peak amplitude of 1.
Now consider two samples, one taken at t = 0, the other taken 90
°
later. They have values 0 and
1, respectively. By the above rules, the phasor components are (X,Y) = (1,0).
Now consider a cosine function. Its samples taken at t = 0 and t+90
°
are 1 and 0; its phasor
representation is (0,1). The phasor (0,1) leads the phasor (1,0) by 90
°
. This coincides with a 90
°
lead of the cosine function over the sine function.
To construct a phasor diagram of voltages and currents, select a pair of adjacent rows from an
area of interest in the quarter-cycle event report. On Cartesian coordinates, plot the lower row
(newer data) as the X-components and the upper row (older data) as the Y-components. Rotate
the completed diagram to any angle of reference. The magnitude of any phasor equals the square
root of the sum of its squares.
Note that moving forward one quarter-cycle rotates all phasors 90
°
. You can verify this by
plotting the phasor diagram with rows 1 and 2, then rows 2 and 3 of an event report. Example
Event 1 shows the process of converting the rectangular format voltages and currents displayed
in the event report to polar format.
R
ELAY
E
LEMENT
C
OLUMNS
D
ATA
The states of all relay elements are indicated in the columns headed "Relay Elements." Active
states of the various relay elements are indicated by designator symbols which correspond with
the relay element names. The contents of the columns for active relay elements appear as
follows.
Column Value Description
ZAB
.
If no AB phase-phase distance element set
1
If Zone 1 AB phase-phase distance element (
MAB1
) set
2
If Zone 2 AB phase-phase distance element (
MAB2
) set, not ZAB1
3
If Zone 3 AB phase-phase distance element (
MAB3
) set, not
ZAB1
│
ZAB2
4
If Zone 4 AB phase-phase distance element (
MAB4
) set, not
ZAB1
│
ZAB2
│
ZAB3
Содержание SEL-321
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