Datasheet

Theory of operation STPM01
48/60 Doc ID 10853 Rev 8
Equation 16
The reactive power will present then a ripple at twice the line frequency. Since the average
value of a sinusoid is 0, this ripple does not contribute to the reactive energy calculation over
time, moreover, in the STPM01 the reactive power is not used for meter calibration or to
generate the stepper pulses, then this ripple will not affect the overall system performances.
In case of Rogowsky coil, the same procedure is applied, but the current channel will be
proportional to the derived of the current and the differentiated is bypassed in the voltage
channel, so we have:
Equation 17
Equation 18
The reactive power is then calculated:
Equation 19
8.24.3 Apparent power and RMS values
The RMS values are calculated starting from the following formulas.
Shunt or current transformer
Equation 20
multiplying Equation 20 by
ω, the I
RMS
value is obtained:
()
)t2sin(sin
2
VI
)t(Q
2
1
)t(Q
13
ϕ+ω−ϕ⋅=ω⋅⋅=
()()
)t2sin(sin
2
VI
)tsin(I)tcos(
V
)t(i)t(Vdt)t(idt)t(v)t(Q
1
ϕ+ω+ϕ
ω
=ϕ+ω−⋅
⎟
⎠
⎞
⎜
⎝
⎛
ω
ω
−=⋅=
′
⋅=
∫∫
()()
)t2sin(sin
2
VI
)tcos(I)t(tsinV)t(i)t(v)t(Q
1
ϕ+ω−ϕ⋅ω⋅−=ϕ+ωω−⋅ω=
′
⋅=
()
)t2sin(sin
2
VI
)t(Q
2
1
)t(Q
13
ϕ+ω+ϕ⋅=ω⋅⋅=
2
I
dt)t(I
T
1
T
0
2
⋅ω
=
∫