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DISTRIBUTION LINE LOSS COMPUTATION THROUGH POWER-FLOW ANALYSIS

DISTRIBUTION LINE LOSS COMPUTATION THROUGH POWER-FLOW ANALYSIS
How power-flow analysis is computed in a distribution system?

The analysis of a distribution feeder line will typically consist of a study of the feeder under normal steady-state conditions (power-flow analysis) and a study of the feeder under short-circuit conditions (short-circuit analysis). Model of all of the components of a distribution feeder must first be developed before the analysis can be done. These models will be applied for the analysis under steady-state and short-circuit conditions.

The power –flow analysis of a distribution feeder is similar to that of an interconnected transmission system. Typically what will be know prior to the analysis will be the three-phase voltages at the substation and the complex power of all of the loads and the load model (constant complex power, constant impedance, constant current, or a combination). Sometimes, the input complex power supplied to the feeder from the substation is also known.

In conducting power-flow analysis, the development of a reliable system model must first be established. Electrical components that are significant to the analysis like capacitors, avrs and other shunt components of the distribution feeder must be included. These models are used in the “power-flow” analysis of a distribution feeder.

A power-flow analysis of a distribution feeder can determine the following by phase and total three-phase:

1. Voltage magnitudes and angles at all nodes of the feeder.
2. Line flow in each line section specified in kW and kVAr, amps, and degrees, or amps and power factor.
3. Power loss in each line section.
4. Total feeder input kW and kVAr
5. Total feeder power loss
6. Load kW and kVAr based upon the specified model for the load

LADDER ITERATIVE TECHNIQUE.  Iterative techniques are used to determine the power-flow analysis results. Because a distribution feeder is radial, iterative techniques commonly used in transmission network power-flow studies are not used because of poor convergence characteristics. Instead, an iterative technique specifically designed for a radial system is used.

LINEAR NETWORK. A distribution feeder is nonlinear because most loads are assumed to be constant kW and kVAr. However, the approach taken for the linear system can be modified to take into account the nonlinear characteristics of the distribution feeder.

NONLINEAR NETWORK. A linear network is modified to a nonlinear network by replacing all of the constant impedances by constant complex power loads.

Manual power-flow analysis can be practically applied in simple electrical system like the transmission network. Unfortunately, the study of a large feeder with many laterals and sublaterals cannot be performed without the aid of a computer program.

source: Distribution System Modeling and Analysis by William H. Kersting 2nd edition
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