Schweitzer Engineering Laboratories SEL-167D, Instruction Manual

Page: 84 / 123

To construct a phasor diagram of voltages and currents, select a pair of adjacent rows in a
region of interest on the event report, e.g., prefault, fault, or postfault. On Cartesian
coordinates, plot the lower row (more recent data) as the X-components and the upper row
(older data) as the Y-components. Complete phasor diagrams may be rotated to the preferred
angle of reference. The effective value of any phasor equals the square root of the sum of the
squares of its components.
Note that moving forward one quarter cycle causes all phasors to rotate 90°, as can be seen
by plotting the phasor diagram using rows 1 and 2, then rows 2 and 3.
For example, refer to the first and second rows of cycle 6 of data in the full report:
Currents Voltages
IPOL IR IA IB IC VAB VBC VCA
0 217 294 -17 -58 57.2 -22.3 -34.5 (Y-component)
0 1219 1233 57 -63 -20.1 65.7 -45.8 (X-component)
These were taken near the
"
middle
"
of the fault, as can be judged from the action of residual-
overcurrent elements.
Convert these to polar form (magnitude and angle):
Currents Voltages
IPOL IR IA IB
IC VAB VBC VCA
0 1238 1268 60 86 60.6 69.4 57.3 (magnitude)
0 10 13 -17 -137 109 -19 -143 (angle)
0 -62 -59 -89 -209 37 -91 -215 (angle - 72)
In the third row, 72° are subtracted from all angles of the second row, so as to assign the
phase-A voltage phasor as the 0° reference. The magnitude and shifted angles can be
compared to the settings of the test set given earlier. The angle measurement errors are 1° or
less, and the magnitude errors are less than 1%.
The event report indicates a fault current of 1273.7 amperes primary, which agrees well with
the 1273-ampere test set current as referred to primary.
The indicated fault location is 9.02 miles The
"
actual
"
fault location is 9.00 miles. The
error is 9.02 - 9.00, or 0.02 mile, less than 1.0% of the actual fault location for this example.
4-4
Event Reporting
SEL-267D/167D Instruction Manual
Date Code 920326