Mega MEg40+ - Page 38

Měřící Energetické Aparáty
38
As well, powers are evaluated in each of the measuring time intervals T
m
. e following
formula is applied to compute the active power:
(3)
where K = 320. From the values u
1
(k) and i
1
(k), the active power P
1
in phase 1 is obtained,
from the values u
2
(k) and i
2
(k) the active power P
2
in phase 2 is obtained, from the values
u
3
(k) and i
3
(k), the active power P
3
in phase 3 is obtained.
From the RMS phase voltage value U and from the RMS current value I in the same
phase and the same measuring time interval T
m
, the apparent power is evaluated.
S = U I (4)
Particularly S
1
= U
1
I
1
, S
2
= U
2
I
2
, S
3
= U
3
I
3
.
e reactive power (including the deformation one) in each phase and in the same
measuring time interval T
m
is determined according to the formula
(5)
So Q
1
is obtained from S
1
and P
1
, Q
2
from S
2
and P
2
, Q
3
from S
3
and P
3
.
To assess the electrical power eciency in each phase, the coecient of performance (true
power factor) is used:
(6)
particularly η
1
, η
2
, η
3
.
e total outlet powers result from the powers in the individual phases.
In case of long-term measurements, a high number of data is obtained in the follow-
up measuring time intervals T
m
for each voltage and current. Recording of all of these
data would be demanding on the monitor memory and would not provide any general
overview of measurement results. erefore, time aggregation of the mentioned data is
used. e recording interval T
z
is selected, containing L measuring time intervals T
m
,
i.e. T
z
= L T
m,
where L is a natural number. From data measured in the measuring time
intervals T
m
for the individual voltages, currents and powers, simple data are derived
characterizing voltage, current and power values in the individual recording intervals T
z
.
If for the given voltage, the RMS values U(l) were obtained in the measuring intervals T
m
and with the serial numbers l = 1, 2, … L, the following total RMS value is corresponding
in the recording intervals T
z
.
22
PSQ −=
SP /= η
( ) ( )
kiku
K
P
K
k
∑
−
=
=
1
0
1