YOKOGAWA wt3000, User Manual, Page: 354 / 384

App-22
IM 760301-01E
RLC of AC Circuits
• Resistance
Current i when AC voltage of instantaneous value u = U
m
sin
ω
t is applied to load
resistance R [ Ω ] is expressed by the equation below. I
m
denotes the maximum
current.
i =
U
m
R
sin ω t = I
m
sin
ω
t
If expressed using rms values, the equation is I = U/R.
There is no phase difference between a current flowing through a resistive circuit and
the voltage.
R
I
U
U
I
• Inductance
Current i when AC voltage of instantaneous value u = U
m
sin ω t is applied to a coil load
of inductance L [H] is expressed by the equation below.
i =
U
m
X
L
sin ω t – sin ω t –
p
2
= I
m
p
2
If expressed using rms values, the equation is I = U/X
L
. X
L
is called inductive
reactance and is defined as X
L
= ω L. The unit is Ω .
Inductance works to counter current changes (increase or decrease), and causes the
current phase to lag the voltage.
L
I
U
U
I
π
2
• Capacity
Current i when AC voltage of instantaneous value u = U
m
sin ω t is applied to a
capacitive load C [F] is expressed by the equation below.
i =
U
m
X
C
sin ω t + sin ω t +
π
2
= I
m
π
2
If expressed using rms values, the equation is I = U/X
C
. X
C
is called capacitive
reactance and is defined as X
C
= 1/ ω C. The unit is Ω .
When the polarity of the voltage changes, the largest charging current of the same
polarity as the voltage flows through the capacitor. When the voltage decreases,
discharge current of opposite polarity as the voltage flows. Thus, the current phase
leads the voltage.
C
I
U
U
I
π
2
Appendix 4 Power Basics (Power, Harmonics, and RLC of AC Circuits)