CHAPTER 5: MONITORING A3 POWER ANALYSIS
PQM POWER QUALITY METER – INSTRUCTION MANUAL 5–25
5.4 A3 Power Analysis
5.4.1 Power Quality
FIGURE 5–17: Actual Values Page 3 – Power Quality Values
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 ( ), which is the ratio of the peak value of
sine wave to its rms value. Typically, the crest factor can range from to 2.5.
Ia/Ib/Ic THDF: Transformer Harmonic Derating Factor (THDF), also known as CBEMA factor,
is defined as the crest factor of a pure sine wave ( ) divided by the 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 PQM Setup software provides the K-factor method of calculating the derating
factor, which is defined on a per unit basis as follows:
where: I
h
= rms current at harmonic h, in per unit of rated rms load current
]] ACTUAL VALUES
]] A3 POWER ANALYSIS
] POWER QUALITY
] VALUES
Ia CREST FACTOR =
1.233
Ib CREST FACTOR =
1.008
Ic CREST FACTOR =
1.000
Ia THDF = 0.944
]] ACTUAL VALUES
]] A4 PRODUCT INFO
ACTUAL
Ib THDF = 0.999
Ic THDF = 0.988
MESSAGE
MESSAGE
MESSAGE
2 1 0.707⁄
2
2
KI
h
2
h
2
×
h 1=
h
max
∑
=
Courtesy of NationalSwitchgear.com
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