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16 bits.
It has a higher resolution than other WT series instruments (the
WT2000, WT1600, and other models have 12-bit resolution). |
When the selected data update cycle of the fundamental wave is shorter
than the width of the analysis window determined by the fundamental
frequency (cycle of the fundamental wave), measurement is not performed
and no data is displayed. Change the currently selected data update
rate to something longer.
- For harmonic measurement of a 50 Hz distorted wave signal, the
fundamental frequency is 50 Hz and the width of the analysis window
is ten waves, so the data measurement interval is 200 ms. Since
(data measurement interval + data computation interval) = approximately
300 ms or more, select a data update rate of 500 ms or more.
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Selecting formulas for calculating apparent power and reactive power
There are several types of power—active power, reactive power, and
apparent power. Generally, the following equations are satisfied:
Active power P = UIcosθ (1)
Reactive power Q = UIsinθ (2)
Apparent power S = UI (3)
In addition, these power values are related to each other as follows:
(Apparent power S)2 = (Active power P)2 +
(Reactive power Q)2 (4)
U: Voltage RMS
I: Current RMS
θ: Phase between current and voltage
Three-phase power is the sum of the power values
in the individual phases.
These defining equations are only valid for sinewaves. In recent years,
there has been an increase in measurements of distorted waveforms,
and users are measuring sinewave signals less frequently. Distorted
waveform measurements provide different measurement values for
apparent power and reactive power depending on which of the above
defining equations is selected. In addition, because there is no
defining equation for power in a distorted wave, it is not necessarily
clear which equation is correct. Therefore, three different formulas
for calculating apparent power and reactive power are provided with
the WT3000.
TYPE 1 (method used in normal mode with older WT Series models)
With this method, the apparent power for each phase is calculated
from equation (3), and reactive power for each phase is calculated
from equation (2). Next, the results are added to calculate the power.
Active power for three-phase four-wire connection: PΣ=P1+P2+P3
Apparent power for three-phase four-wire connection:
SΣ=S1+S2+S3(=U1×I1+U2×I2+U3×I3)
Reactive power for three-phase four-wire connection: QΣ=Q1+Q2+Q3
TYPE 2
The apparent power for each phase is calculated from equation (3),
and the results are added together to calculate the three-phase apparent
power (same as in TYPE1). Three-phase reactive power is calculated
from three-phase apparent power and three-phase active power using
equation (4).
Active power for three-phase four-wire connection: PΣ=P1+P2+P3
Apparent power for three-phase four-wire connection:
SΣ=S1+S2+S3(=U1×I1+U2×I2+U3×I3)
Reactive power for three-phase four-wire connection:
TYPE 3 (method used in harmonic measurement mode with WT1600
and PZ4000)
This is the only method in which the reactive power for each phase
is directly calculated using equation (2). Three-phase apparent power
is calculated from equation (4).
Active power for three-phase four-wire connection: PΣ=P1+P2+P3
Apparent power for three-phase four-wire connection:
Reactive power for three-phase four-wire connection: QΣ=Q1+Q2+Q3
Also, the power factor is calculated as P/S. By selecting the formula
TYPE for apparent power and reactive power, the value of the three-phase
total power factor λΣ also changes.
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Supplement:
<TYPE 1>
This is equivalent to the normal mode formula used by the conventional
WT series instruments (WT1600, WT2000, etc.).
QΣ=Q1+Q2+Q3
 * s1, s2, and s3 express
the polarity of Q1, Q2, and Q3 of the reactive power of each phase.
When current leads or lags the voltage, it is accompanied by a “-“
sign (reactive power is a negative value), or a “+” sign (reactive
power is a positive value), respectively.
QΣ is calculated from the reactive power of each phase Q1, Q2,
and Q3 with the signs.
With TYPE1 there can be cases where, if the waveform is distorted,
polarity determination (lead/lag is detection) may not be successful,
and as a result the QΣ value may not be calculated correctly.
For polarity determination, specifications such as the following are
listed in the catalog.
Lead/Lag Detection in WT3000 specifications:
The phase lead and lag are detected correctly when the voltage and
current signals are both sine waves, the lead/lag is 50% of the range
rating (or 100% for crest factor 6), the frequency is between 20
Hz and 10 kHz, and the phase angle is ±(5°to 175°)
or more.
<TYPE 2> (New mode not dependent on leading phase/lagging
phase detection error)
For Type 2 the method is changed and QΣ is calculated from SΣ
and PΣ, so this problem does not occur.
For example,
In order to improve the power factor as a measure against harmonic
current in the switching power supply, to confirm the effect of the
power factor on the current distortion waveform → TYPE1 and
TYPE2 are applied.
<TYPE 3>
A mode for direct measurement of reactive power through harmonic
measurement (same as WT1600 and PZ4000).
Since this mode involves harmonic measurements, measurements can be
taken for each harmonic component. Since the results reflect each
frequency component, the reactive power Q for each order is correct.
Also, the QΣ is a simple summation so the sum of each order
QΣ is also correct. The active power and reactive power of the
harmonic components are computed, so the mode allows for more accurate
calculation of phase information by order.
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Precision Power Anlyzer |
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