SMY133-SMY134-SMP133 Operating Manual
The data for the longer measurements are aggregated from these measurement cycles. Long time
interval starts after the RTC tick occurrence at the beginning of the next measurement cycle time
interval. This principle enables to configure other intervals up to 2 hours for datalogging purposes.
Measured phase voltages U
1
to U
3
correspond to the potential of terminals
VOLTAGE / U1
to
U3
towards the terminal
VOLTAGE / N
.
Measuring voltage inputs impedance is in range of units of MΩ. If no signal connected (for
example when protection fuse is blown), due to parasite impedance of power supply input a
parasite voltage of up to tens of volts can appear on the measuring voltage inputs. In such
case the instrument can show non-zero voltages !
At the star (wye, 3Y) connection, three current signals - I
1
, I
2
, I
3
- are measured. Another current is
calculated from samples of directly measured ones as negative vector sum of current vectors I
1
, I
2
, I
3
( Kirchhoff rule ). The calculated current is referenced as
I
NC
.
If an instrument is equipped with four current inputs, the fourth current I
4
is measured too. Then
another current, referenced as
I
PEC
, is calculated as negative vector sum of current vectors I
1
, I
2
, I
3
, I
4
.
At the Aron (3A) connection, the current I
2
is not measured, but it is calculated as negative vector sum
of current vectors I
1
and I
3
.
4.3.1.3 Harmonics and THD Evaluation Method
Entire spectrum of harmonic components and THD is evaluated discontinuously - periodically every
second from 10 / 12 mains cycles long signal according to IEC 61000-4-7 ed.2 as harmonic sub-
groups (H
sg
).
Following quantities are evaluated :
Harmonic components of voltage and current up to 50
th
order :
Uih
1
, Iih
1
( i …. order of harmonic component )
Absolute angle of voltage harmonic component phasor :
φUih
1
Current harmonic component phasor angle relative to phasor Ufh
1
:
φIih
1
Relative angle between correspondent voltage and current phasors :
Δφi
1
Total harmonic distortion of voltage :
THD
U
1
=
1
U
1
h
1
√
∑
i
=
2
40
Uih
1
2
∗
100 %
Total harmonic distortion of current :
THD
I
1
=
1
I
1
h
1
√
∑
i
=
2
40
Iih
1
2
∗
100 %
4.3.1.4 Power, Power Factor and Unbalance Evaluation Method
Power and power factor values are calculated continuously from the sampled signals according to
formulas mentioned below. The formulas apply to basic type of connection – wye (star).
Active power :
P
1
=
∑
k
=
1
40
U
k
,1
∗
I
k
,1
∗
cosΔφ
k
,1
Reactive power :
Q
1
=
∑
k
=
1
40
U
k
,1
∗
I
k
,1
∗
sinΔφ
k
,1
where : k … harmonic order index, odd components only
U
k,1
, I
k,1
… the k
th
harmonic components of voltage and current ( of phase 1 )
Δφ
k,1
... angle between the k
th
harmonic components U
k,1
, I
k,1
( of phase 1 )
( these harmonic components of U and I are evaluated from each measurement cycle )
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