YOKOGAWA WT500 User Manual page 339

AC RLC Circuits
IM 760201-01E
Appendix 3 Power Basics (Power, harmonics, and AC RLC circuits)
Resistance
The current i when an AC voltage whose instantaneous value u = U
to load resistance R [ ] is expressed by the equation below. I
Ω
current.
U
m
i sinωt I sinωt
= =
m
R
Expressed using rms values, the equation is I = U/R.
There is no phase difference between the current flowing through a resistive circuit and
the voltage.
R
I
U
Inductance
The current i when an AC voltage whose instantaneous value u = U
coil load of inductance L [H] is expressed by the equation below.
U
m
i sin t – I sin t –
= =
m
X 2
L
Expressed using rms values, the equation is I = U/X
and is defined as X = L. The unit of inductive reactance is
ω
L
Inductance works to counter current changes (increase or decrease), and causes the
current to lag the voltage.
L
I
U
Capacity
The current i when an AC voltage whose instantaneous value u = U
capacitive load C [F] is expressed by the equation below.
U
m
i sin t + I sin t +
= =
m
X 2
C
Expressed using rms values, the equation is I = U/X
and is defined as X = 1/ C. The unit of capacitive reactance is
ω
C
When the polarity of the voltage changes, the largest charging current with the same
polarity as the voltage flows through the capacitor. When the voltage decreases,
discharge current with the opposite polarity of the voltage flows. Thus, the current phase
leads the voltage.
C
I
U
U
I
2
. X is called inductive reactance
L L
U
2
I
2
. X is called capacitive reactance
C C
U
π
2
I
sin t is applied
ω
m
denotes the maximum
m
sin t is applied to a
ω
m
.
Ω
sin t is applied to a
ω
m
.
Ω
App-19
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App
Index