Schweitzer Engineering Laboratories SEL-421-4, Instruction Manual

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18.5
Date Code 20171006 Instruction Manual SEL-400 Series Relays
Synchrophasors
Synchrophasor Measurement
PMU Data Block Status
In a PMU data frame, each data block is headed by a two-byte STAT field. This
field indicates the status of the PMU data block. Bit 15 of the STAT field indi-
cates the validity of data. SEL-400 series relays assert bit 15 of the STAT when
synchrophasor test mode indicator PMTEST asserts or SVBLK asserts in
SEL-400 series Sampled Values (SV)-subscriber relays.
For SV-subscribing relays, configure Global setting SVBLK to assert on errors
encountered in SV data acquisition. For example, set SVBLK := IAWBK OR
IBWBK OR ICWBK. In this example, if SV data for any Terminal W current is
lost, SVBLK asserts, which then asserts bit 15 in the STAT field, indicating cur-
rent data have errors and, therefore, synchrophasor data are invalid.
For an explanation of other bits in the STAT field, refer to the IEEE C37.118
standard.
Synchrophasor Frequency
The PMU calculates frequency deviation and rate-of-change of frequency from
the synchrophasor positive-sequence voltage angle (V1
n PMA where
n = PMFRQST) as follows.
First the PMU calculates the frequency deviation from nominal using the follow-
ing formula.
Equation 18.1
Where

k
is the V1 n PMA and

k -1
is V1 n PMA calculated 1 cycle previously.

t is the time difference between the angle calculations ( k increments once a
nominal power system cycle).
Next, the PMU averages the frequency deviation as shown in Equation 18.2 and
Equation 18.3 .
If the frequency application is smooth (PMFRQA = S)
Equation 18.2
If the frequency application is fast (PMFRQA = F)
Equation 18.3
f
k

k

k 1
–
–
 
t

360

----------------------------- =
favg
k
f
k
n
–
n 0
=
9

 
 
 
 
f
max1
–
f
max2
–
f
min1
–
f
min2
–
6
--------------------------------------------------------------------------------------------------------- =
favg
k
f
k
n
–
n 0
=
3

 
 
 
 
f
max
–
f
min
–
2
-------------------------------------------------------------- =