4.20
SEL-734 Meter Instruction Manual Date Code 20090730
Metering
Harmonic Metering
Each Magnitude value has an associated analog quantity (see Appendix H:
Analog Quantities) that uses the following format:
HRMxx_yyM
These analog values are available for use in SEL
OGIC control equations.
K-Factor Calculation Another use for harmonic metering is to prevent transformer overheating due
to the harmonics. The meter calculates K-factor on a per-phase and
three-phase basis for use in the detection and monitoring of the harmonics.
The K-factor is calculated for each phase current channel by the following
equation.
Equation 4.3
Distortion Power Distortion power is calculated as the ratio of average power to fundamental
power and is reported in a percentage. It is calculated on a per-phase or
three-phase basis as follows.
Equation 4.4
Total Harmonic
Distortion (THD)
Total Harmonic Distortion (THD) per phase is calculated as follows.
Equation 4.5
where:
xx = the harmonic number (2–50 or 2–15)
yy = the specific current or voltage phase (IA, IB, IC, IN, VA,
VB, or VC)
where:
x = the channel (A, B, C)
h = the harmonic number (1 to 25)
KFACTOR_x
I
xh
2
h
2
h 1=
25
∑
I
2
1
∑
------------------------=
where:
Dx = the distortion power ratio for the respective phase
Px_avg = the average power for the respective phase
Px = the fundamental power for the respective phase
Dx
Px_avg
Px
------------------1–
⎝⎠
⎛⎞
100=
where:
XX = the channel I
A
, I
B
, etc.
THDXX = the per-phase THD in percent
XX
DISTORTION =
the channel DISTORTION
XX
MAG =
the channel fundamental magnitude
THDXX
XX
DISTORTION
XX
MAG
----------------------------------------
⎝⎠
⎛⎞
100=
Courtesy of NationalSwitchgear.com
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