05 - Unbalanced Load Flow

Unbalanced Load Flow

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Real Unbalanced Power Systems •

Distribution System –

–

•

3-phase, 2-phase, and single-phase network components Unbalanced loads

Transmission System –

Untransposed long transmission line









Harmful Effects of System Unbalance •

Overheating of generators

•

Nuisance tripping of protective relays

•

Increased real power losses

•

Transformer failure









Unbalance Factors/Indexes •

•

•

•

System unbalance is considered by power quality standards as a disturbance Voltage/Current Voltage/Current unbalance factors Ratio of zero/negative sequence to positive sequence Voltage/Current unbalance indexes









Unbalanced Load Flow Analysis •

Current Injection (CI) method

•

The most robust algorithm ever developed

•

Converge in less iterations than other methods, especially for heavily loaded systems









Sequence Models of 3-Phase Machines











Unique Concepts of 3-Phase Machines •

Swing Machine –

The specified magnitude and the phase angle of the









Concepts of Load Connections •

Single-Phase Loads

•

Connected in the phase connection types of









Modeling Capabilities •

A mixture of 3-phase, 2-phase and and singlesinglephase network components 3-phase machines with internal impedance









Modeling Capabilities •

2-winding and 3-winding transformers of various winding connections Lumped loads consisting of constant power,









Study Case •

Same pretense as Balanced Load Flow with more detailed modeling, calculations, and results











Output Results









Reporting









Example 1









Example 2























05 - Unbalanced Load Flow

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