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14.6 Fundamentals on the phasor diagram
The phasor diagram graphically describes the
phase shift or phase angle between the voltage
and the current. The phasors rotate at a constant
angular speed – proportional to the frequency of
the voltage and current – around an origin. The
phasor diagram thus shows the momentary state
of the variables in an AC circuit.
Representation of ohmic resistance:
·Voltage and current are in phase.
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Representation of inductance:
·The voltage is ahead of the current.
·The phase shift for an "ideal coil" is 90°.
Representation of capacitance:
·The current is ahead of the voltage.
·The phase shift of an "ideal capacitor" is 90°.
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With a combination of the states, the phase angle
"current to voltage" can assume values between
-90° and +90°.
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Current: Displayed with
short phasor
Voltage: Displayed with
long phasor
Example phasor diagram (3-phase)
UL1
IL1
IL2
UL2
UL3
IL3
Current and voltage are shifted against each other.
The current is ahead the voltage, i.e. the network is
capacitively loaded.