UMG 96-PA / UMG 96-PA-MID / UMG 96-PA-MID+
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13.5.1 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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u
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u
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Representation of inductance:
·The voltage is ahead of the current.
·The phase shift for an "ideal coil" is 90°.
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u
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u
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Representation of capacitance:
·The current is ahead of the voltage.
·The phase shift of an "ideal capacitor" is 90°.
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u
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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 phasors
Voltage:
Displayed with
long phasors
Example phasor diagram (3-phase)
UL1
IL1
IL2
UL2
UL2
IL3
Current and voltage are shifted against each other.
The current is ahead the voltage, i.e. the network
is capacitively loaded.
13.6 Checking of voltage and current inputs
by means of phasor diagram
