Transmission System Unbalanced Three-Phase Power Flow


Use of DEW/ISM to perform three phase unbalanced power flow to evaluate the impact of EHV/HV transmission system voltage imbalances on distribution systems. Project work included:

  • Build three-phase, unbalanced model of a portion of the TVA power system.
  • Perform quasi-steady state power flow analysis and compare calculated results of unbalanced voltages of unbalanced voltages against field measurements of the unbalanced voltages.


  • Demonstrated that calculated unbalanced voltages as a function of time matched well against TVA unbalanced measurements on 500 kV/161 kV transformers.
  • Demonstrated that phase rotations within substations could be used to improve the imbalance.

Comparison of Measured Values with DEW Calculated Results

Variable Measured Value DEW Calculated Value
Max Spread in % of VRMS for phases A, B, and C 3.2% 3.2%
Negative Sequence Voltage / Positive Sequence Voltage 1.75% 1.84%
ANSI C84.1 Standard Imbalance 1.84% 1.85%

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