PQM-700 Operating Manual
68
Reactive power
Reactive energy
2% I
nom
≤ I
RMS
< 5% I
nom
sin
= 1
depending on
U
nom
and I
nom
√4.0
2
+ 𝛥
𝑝ℎ
2
%
5% I
nom
≤ I
RMS
< I
nom
sin
= 1
√3.0
2
+ 𝛥
𝑝ℎ
2
%
5% I
nom
≤ I
RMS
< 10% I
nom
sin
= 0.5
√4.0
2
+ 𝛥
𝑝ℎ
2
%
10% I
nom
≤ I
RMS
< I
nom
sin
= 0.5
√3.0
2
+ 𝛥
𝑝ℎ
2
%
10% I
nom
≤ I
RMS
< I
nom
sin
= 0.25
√4.0
2
+ 𝛥
𝑝ℎ
2
%
Apparent power
Apparent energy
2% I
nom
≤ I
RMS
< 5% I
nom
depending on
U
nom
and I
nom
2.5%
5% I
nom
≤ I
RMS
≤ I
nom
2.0%
Power factor (PF)
0…1
50% U
nom
≤ U
RMS
< 150% U
nom
10% I
nom
≤ I
RMS
< I
nom
0.01
0.03
Displacement power
factor (cosφ/ DPF)
0…1
50% U
nom
≤ U
RMS
< 150% U
nom
10% I
nom
≤ I
RMS
< I
nom
0.01
0.03
(1) See sec. 7.3.7.
7.3.7 Estimating the uncertainty of power and energy measurements
The total uncertainty of active and reactive power and energy measurements and the harmonics
power is based on the following relationship (additional time measurement uncertainty is omitted in
case of energy as much smaller than other uncertainty types):
𝛥
𝑃,𝑄
≅ √𝛥
𝑈ℎ
2
+ 𝛥
𝐼ℎ
2
+ 𝛥
𝑝ℎ
2
where:
P,Q
– uncertainty of active or reactive power measurement,
Uh
– total uncertainty of voltage harmonic amplitude measurement (analyzer, transducers),
Ih
– total uncertainty of current amplitude measurement (analyzer, transducers, clamps),
ph
– additional uncertainty caused by the error of phase measurement between the voltage
and current harmonics.
The
ph
uncertainty can be determined if we know the phase shift angle for a given frequency
ranges. Tab. 6 presents the phase difference error between the voltage and current harmonics for
the PQM-700 analyzer (without clamps and transducers).
Tab. 6. Phase error in the PQM-700 analyzer depending on the frequency
Phase difference error
Frequency range
0..200 Hz
200..500 Hz
500 Hz..1 kHz
1..2 kHz
2..2.4 kHz
Error
≤1
≤2.5
≤5
≤10
≤15
The phase error caused by used transducers and clamps can be usually found in their technical
documentation. Such being the case, we need to estimate the resultant phase error between the
voltage and the current for a given frequency caused by all elements of the measuring circuit: cur-
rent and voltage transducers, clamps, and the analyzer.
The phase uncertainty of the harmonics active power measurements can be calculated according
to the following formula:
Δ
ph
= 100 (1-
cos(φ+Δφ)
cosφ
) [%]
,
cos φ ≠ 0
On the other hand, the phase uncertainty of the harmonics reactive power measurements can be
calculated according to the following formula:
Summary of Contents for PQM-700
Page 85: ...85 Notes...
