MTR-3
Installation Instructions
DEIF A/S
Page 49 of 51
8. Appendix B: Calculations and equations
Calculations
Definitions of symbols
No.
Symbol
Definition
1
M
v
Sample factor
2
M
P
Average interval
3
U
f
Phase voltage (U
1
, U
2
or U
3
)
4
U
ff
Phase-to-phase voltage (U
12
, U
23
or U
31
)
5
N
Total number of samples in a period
6
n
Sample number (0 ≤ n ≤ N)
7
x, y
Phase number (1, 2 or 3)
8
i
n
Current sample n
9
u
fn
Phase voltage sample n
10
u
fFn
Phase-to-phase voltage sample n
11
φ
f
Power angle between current and phase voltage f (φ
1
, φ
2
or φ
3
)
12
U
c
Agreed supply voltage
Equations
Voltage
N
u
=
U
2
n
N
1
=
n
f
∑
Phase voltage
N − 128 samples in
one period (up to 65 Hz)
N − 128 samples in M
v
periods (above 65 Hz)
Example: 400 Hz → N = 7
(
)
N
2
yn
xn
N
1
=
n
xy
u
u
=
U
−
∑
Phase-to-phase voltage
u
x
, u
y
− phase voltages (U
f
)
N − a number of samples in a period
Current
N
=
i
I
2
n
N
1
=
n
RMS
∑
Phase current
N
−
128 samples in a period (up to 65 Hz)
N − 128 samples in more periods (above 65
Hz)
(
)
N
i
i
i
=
2
n
3
n
2
n
1
N
1
=
n
n
I
+
+
∑
Neutral current
i − n sample of phase current (1, 2 or 3)
N = 128 samples in a period (up to 65 Hz)
