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Loads on a distribution feeder
•
Loads on a distribution feeder can be modeled as• Wye connected
or
• Delta connected.
• The loads can be three phase, two phase, or single phase
wdegree of unbalanced.
• The ZIP models are:• Constant impedance (Z)
• Constant current (I)
• Constant real and reactive power (constant P)
• Any combination of the above
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Loads on a distribution feeder
•
The specified load will bethe “maximum
diversified demand.”
• This demand can be specified as kVA and power factor, kW and
pfactor, or kW and kVAr.
• The voltage specified will always be the voltage at the
low-voltagthe distribution substation.
• The load models developed are to be used in the iterative
proce
power flow program where the load voltages are initially assume•
The units of the complex power can be in volt-amperes and volts
unit volt-amperes and per-unit voltages.
• For all loads, the line currents entering the load are
required in operform the power-flow analysis.
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Wye Connected Loads
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Constant Real and Reactive Power Load
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Constant Impedance Loads
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Constant Current Loads
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Combination Loads
•
Combination loads can be modeled by assigning a percentagtotal
load to each of the three aforementioned load models
• The total line current entering the load is the sum of the
thrcomponents.
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Delta Connected Loads
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Constant Impedance Loads
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Constant Current Loads
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Combination Loads
•
Combination loads can be modeled by assigning a percentagtotal
load to each of the three aforementioned load models
• The total delta current for each load is the sum of the
threecomponents.
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Line Currents Serving a Delta-Connecte
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Two Phase and Single Phase Loads
•
In both the wye- and delta-connected loads, single-phase anphase
loads are modeled by setting the currents of the missphases to
zero.
• The currents in the phases present are computed using the
appropriate equations for constant complex power, constanimpedance,
and constant current.
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Shunt Capacitors
•
Shunt capacitor banks are commonly used in distribution syhelp
in voltage regulation and to provide reactive power sup
• The capacitor banks are modeled as constant susceptancesin
either wye or delta.
• Similar to the load model, all capacitor banks are modeled
a
phase banks with the currents of the missing phases set to
zsingle-phase and two-phase banks.
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Wye-Connected Capacitor Bank
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Delta-Connected Capacitor Bank
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Three Phase Induction Machine
• The analysis of an induction machine (motor or generator)
woperating under unbalanced voltage conditions has
traditioperformed using the method of symmetrical components.
• A method whereby all of the analysis can be performed in
tframe is presented.
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Three-Phase Induction Machine
h h d h
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Three-Phase Induction Machine
