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6 ACTUAL VALUES
The 745 can determine the harmonic components of every current that it measures. This allows it to calculate
total harmonic distortion (THD) as well as a harmonic derating factor that can be used to adjust phase time
overcurrent protection to account for additional internal energy dissipation that arises from the presence of har-
monic currents.
S HARMONIC CONTENT
S [ENTER] for more
a) HARMONIC SUB-COMPONENTS
The 745 is capable of measuring harmonic components up to a frequency of 21 times the nominal system fre-
quency. An actual value is calculated for each phase of each monitored winding.
The example below shows what is displayed in a typical case for harmonic components (in this case the sec-
ond harmonic). Similar displays exist for all harmonics up to the 21
S 2nd HARMONIC
S [ENTER] for more
W1 (% ƒo) H2a: 0.0
H2b: 0.0 H2c: 0.0
W2 (% ƒo) H2a: 0.0
H2b: 0.0 H2c: 0.0
W3 (% ƒo) H2a: 0.0
H2b: 0.0 H2c: 0.0
b) TOTAL HARMONIC DISTORTION (THD)
THD is calculated and displayed. Every THD value is calculated as the ratio of the RMS value of the sum of the
squared individual harmonic amplitudes to the rms value of the fundamental frequency. The calculations are
based on IEEE standard 519-1986
S THD
S [ENTER] for more
The following Actual Value messages are repeated for Windings 1, 2, and 3.
W1 THDa (2nd-21st):
0.0% fo
W1 THDb (2nd-21st):
0.0% fo
W1 THDc (2nd-21st):
0.0% fo
GE Power Management
This message indicates the start of the Harmonic Content actual values. To
view these actual values press
This message indicates the start of the Second Harmonic actual values. To
view these actual values press
sequential harmonic section.
The second harmonic magnitude for each phase current of Winding 1 is
displayed. Values are expressed as a percentage of the magnitude of the
corresponding fundamental frequency component.
The second harmonic magnitude for each phase current of Winding 2 is
displayed. Values are expressed as a percentage of the magnitude of the
corresponding fundamental frequency component.
The second harmonic magnitude for each phase current of Winding 3 is
displayed. Values are expressed as a percentage of the magnitude of the
corresponding fundamental frequency component.
This message indicates the start of the THD actual values. To view these
actual values press
E N TE R
This message displays the THD for Winding 1 phase A current, expressed
as a percentage of the fundamental frequency component. The numbers in
parentheses indicate the programmed frequency band (in terms of harmonic
number) over which THD is being calculated.
This message displays the THD for Winding 1 phase B current, expressed
as a percentage of the fundamental frequency component.
This message displays the THD for Winding 1 phase C current, expressed
as a percentage of the fundamental frequency component.
745 Transformer Management Relay
6.3.3 HARMONIC CONTENT
or press
E N TE R
M E SS AG E
st
.
or press
EN TE R
or press
for the next section.
M E SSA G E
6.3 A2 METERING
for the next section.
for the next
M E SSA G E
6
6-7
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