A3 Power Analysis; Power Quality; Thd - GE PQMII Instruction Manual

6.4

A3 Power Analysis

6.4.1

Power Quality

POWER QUALITY
VALUES
6.4.2

THD

TOTAL HARMONIC
DISTORTION
6–22
PATH: ACTUAL VALUES A3 POWER ANALYSIS
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• Ia/Ib/Ic CREST FACTOR: The crest factor describes how much the load current can
vary from a pure sine wave while maintaining the system's full rating. A completely
linear load (pure sine wave) has a crest factor of
peak value of sine wave to its RMS value. Typically, the crest factor can range from
to 2.5.
• Ia/Ib/Ic THDF: The Transformer Harmonic Derating Factor (THDF), also known as
CBEMA factor, is defined as the crest factor of a pure sine wave (
measured crest factor. This method is useful in cases where lower order harmonics are
dominant. In a case where higher order harmonics are present, it may be necessary
to use a more precise method (K-factor) of calculating the derating factor. This method
also does not take into consideration the losses associated with rated eddy current in
the transformer. The EnerVista PQMII Setup Software provides the K-factor method of
calculating the derating factor, which is defined on a per unit basis as follows:
where: = RMS current at harmonic
I
h
PATH: ACTUAL VALUES A3 POWER ANALYSIS
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POWER QUALITY VALUES
Ia CREST FACTOR =
1.233
Ib CREST FACTOR =
1.008
Ic CREST FACTOR =
1.000
Ia THDF = 0.944
Ib THDF = 0.999
Ic THDF = 0.988
h
max
2 2
∑
×
K = I h
h
h = 1
, in per unit of rated RMS load current
h
TOTAL HARMONIC DISTORTION
PHASE A CURRENT THD=
5.3%
PHASE B CURRENT THD=
7.8%
PQMII POWER QUALITY METER – INSTRUCTION MANUAL
CHAPTER 6: MONITORING
2 (1 /0.707), which is the ratio of the
2 ) divided by the
2
(EQ 6.3)