Power distribution feeder response to the asymmetric saturation of substation transformers caused by significant high-side DC currents.

High-altitude electromagnetic-pulse and geomagnetic disturbances can lead to asymmetric saturation of utility transformer cores by causing significant DC current to flow through the transformer windings. Transformer secondary voltage and current waveforms are distorted by core saturation and this distortion can be amplified at points on power distribution feeders where circuit topologies create series or parallel resonances. The performance of distribution feeders during asymmetric core saturation is explored in this work using harmonic powerflow simulation. A harmonic voltage source model is developed to represent steady-state transformer secondary terminal response during DC current flow in the primary windings. The model performance is compared to field test measurement data and then used to simulate the energization of realistic electric power distribution feeder models. The response of the feeder models is compared to industry standards of power quality.