H.3
Date Code 20170814
Instruction Manual
SEL-700G Relay
Synchrophasors
Synchrophasor Measurement
Figure H.2
Waveform at Relay Terminals May Have a Phase Shift
Equation H.1
If the time shift on the PT measurement path
t
pt
= 0.784 ms and the nominal
frequency, freq
nominal
= 60Hz, use Equation H.2 to obtain the correction
angle:
Equation H.2
Figure H.3
Correction of Measured Phase Angle
The phasors are rms values scaled in primary units, as determined by Group
settings PTRX, PTRY, PTRS (for synchronism-check input), CTRX, CTRY,
and CTRN.
Because the sampling reference is based on the GPS clock (IRIG-B signal)
and not synchronized to the power system, an examination of successive
synchrophasor data sets almost always shows some angular change between
samples of the same signal. This is not a malfunction of the relay or the power
system, but is merely a result of viewing data from one system with an
instrument with an independent time base. In other words, a power system has
a nominal frequency of either 50 or 60 Hz, but on closer examination, it is
usually running a little faster or slower than nominal.
94.851
–94.851
Δ
t
pt
0
t
V
A
(t)
Actual
Waveform
Measured
Waveform
Compensation Angle
t
p t
1
freq
n ominal
----------------------------
----------------------------------
360
•
=
t
p t
freq
no min al
360
• •
=
0.784
10
3
–
s
60s
1
–
360
• • •
16.934
=
Imaginary
Real
M
M
V
A measured
V
A corrected
Compensation Angle
Summary of Contents for SEL-700G Series
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