NHP Terasaki TemBreak PRO P SE Series, User Manual

Page: 61 / 122

Measurements and settings
61
TemBreak PRO
P_SE-UM-001-EN
– V1.2.0
Total Harmonic Distortion (THD)
The P_SE OCR calculates the total harmonic distortion levels from the real-time current and voltage measurements (every second).
These calculations are performed up to the 31st harmonic. The total harmonic distortion levels may be used to indicate load or power supply quality
according to the purity of the current and/or voltage waveform, where low level of wave distortion is ideal.
Harmonic content of the respective waveform (THD) is normally attributed to non-linear load and equipment (as is typical in rectifiers, switch-mode power
supplies, variable speed drives, and modern electric lighting), which produces non-sinusoidal current waveforms.
A low level THD is generally acceptable, whereas a high level of unwanted THD may have detrimental effects on equipment connected to the same circuit
or supply and may result in increases to current and temperature in neutral conductors and distribution transformers, and core losses and overheating of
motors. If not mitigated, high THD levels may result in serious degradation, dangerous overheating and/or risk of malfunction of connected equipment.
Acceptable THD levels are dependent on the application and relative standards for the installation.
THD
I
is used to determine the current wave harmonic distortion level. THD
U
or THD
V
is used to determine the voltage wave harmonic distortion level for Ph-
Ph and Ph-N voltages respectively.
Total Harmonic Distortion Symbol 3Ph 3Ph+N
THD phase current THD
I1
,THD
I2
, THD
I3
✓ ✓
THD voltage Ph-N THD
V1N
, THD
V2N
, THD
V3N
─
✓
THD Voltage Ph-Ph THD
U12
, THD
U23
, THD
U31
✓ ✓
For heavily distorted waveforms, it is possible for the THD
percentage to exceed 100%, as this indicates that a majority of the total RMS current or voltage is
produced by harmonic content. The maximum values indicated by the P_SE OCR are provided in the Range and accuracy section.
Current (THD
I)
The current THD is measured as the percentage of the RMS current of each harmonic above the fundamental frequency (harmonic order > 1) of the current
waveform as compared to the RMS current of the fundamental frequency (harmonic order = 1):
THD
I
p
=
√
I
ph2
2
+ I
ph3
2
+ … + I
ph31
2
I
ph1
× 100
Where I
ph
n
= effective harmonic component of order n for phase p.
E.g. I
1h
1
is the RMS phase 1 current of the fundamental frequency, I
1h
2
is the RMS phase 1 current of the 2 nd harmonic, and so on.
Voltage (THD, THD
U
, THD
V
)
The voltage THD is measured as the percentage of the RMS voltage of each harmonic above the fundamental frequency (harmonic order > 1) of the voltage
waveform as compared to the RMS voltage of the fundamental frequency (harmonic order = 1):
THD
U
pg
=
√
U
pgh2
2
+ U
pgh3
2
+ … + U
pgh31
2
U
pgh1
× 100
Where U
pgh
n
= effective harmonic component of order n for the voltage between phases p and g.
E.g. U
12h
1
is the RMS Ph1-Ph2 voltage of the fundamental frequency, U
12h
2
is the RMS Ph1-Ph2 voltage of the 2 nd harmonic, and so on.