PPA5xx/15xx user manual
12-2
TIF is defined by IEEE standard 115 and the weighting
factors are given in ANSI standard C50-13. The harmonic
factors for TIF are specified for harmonics of 60Hz.
THF (Telephone Harmonic Factor) is a similar computation
to TIF but uses different weighting factors and is
expressed as a percentage.
i = n
THF = 1/rms √
(h
i
x t
i
)²
i = 1
where h
i
is the i
th
harmonic
and t
i
is the i
th
weighting factor
The THF computation and weighting factors have been
implemented according to IEC standard 60034 part 1
(1996) with amendments A1 (1997) and A2 (1999). The
harmonic factors are specified for harmonics of 50Hz.
TRD (Total Rated Distortion) uses a different reference to
scale the harmonic percentages instead of the
fundamental. The voltage harmonics are scaled by the rms
voltage, and the current harmonics are scale by the larger
of the rms current or the rated current entered by the
HARM menu. The rms is computed from the series of
harmonics.
i = n
TRD = 1/ref √
h
i
²
i = 2
where h
i
is the i
th
harmonic
and ref is rms or rated current
Similarly, TDD (Total Demand Distortion) scales the
computed harmonic distortion by the measured rms. For
voltage, TDD is the same as TRD; for current, TRD is less
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