Phasor Diagrams: Sequence Components vs Oscillating Reference by Doug Millner - Company: www.nerxpower.com - Email: douglas.millner@nerxpower.com - Blog: Doug Millner P.E. | LinkedIn Back to Main Menu

Phasor Diagrams: Sequence Components vs Oscillating Reference

Sequence Component Controls

0.5
1.0
0.3
180°
Phase A
Phase B
Phase C
Zero Sequence
Positive Sequence
Negative Sequence

Sequence Components

V₁₂ Components Around V₀

V₁₂ Around Real(V₀)

Phase-to-Ground Real Components

V₁₂ + V₀ Real Components

V₁₂ + Real(V₀) Components

Mathematical Explanation: Why All Three Representations Are Equivalent

Column 1: Traditional Sequence View

Mathematics:

Va = V₀ + V₁ + V₂

Vb = V₀ + a²V₁ + aV₂

Vc = V₀ + aV₁ + a²V₂

where a = e^(j2π/3) = 120° rotation operator

What it shows: All phasors originate from the origin. This is the standard textbook representation showing how sequence components combine to form phase voltages.

Key insight: Va + Vb + Vc = 3V₀ (zero sequence appears tripled in the sum)

Column 2: V₁₂ Around V₀

Mathematics:

V₁₂a = V₁ + V₂ (positive + negative sequence only)

V₁₂b = a²V₁ + aV₂

V₁₂c = aV₁ + a²V₂

Final: Va = V₀ + V₁₂a, Vb = V₀ + V₁₂b, Vc = V₀ + V₁₂c

What it shows: The V₁₂ components (containing only positive and negative sequence) rotate around the neutral shift V₀. This separates the "balanced" part (V₁₂) from the "unbalanced" part (V₀).

Key insight: V₀ represents the neutral-to-ground voltage shift that affects all phases equally.

Column 3: V₁₂ Around Real(V₀)

Mathematics:

Same V₁₂ components as Column 2, but:

Va = Real(V₀) + V₁₂a

Vb = Real(V₀) + V₁₂b

Vc = Real(V₀) + V₁₂c

Real(V₀) slides along x-axis as V₀ rotates

What it shows: The same V₁₂ components now oscillate horizontally as they follow only the real component of the neutral shift. This creates a "sliding" reference frame.

Key insight: Shows how the neutral shift's real component affects the horizontal positioning of all phase voltages.

Why All Three Are Mathematically Identical

All three columns show the same phase voltages Va, Vb, Vc - just with different reference points and visualization methods.

Mathematical Equivalence:

  • Column 1: Va = V₀ + V₁ + V₂
  • Column 2: Va = V₀ + (V₁ + V₂) = V₀ + V₁₂a
  • Column 3: Va = Real(V₀) + V₁₂a + j×Imag(V₀)

The final result Va is identical in all cases - only the visualization and reference frame differ.

Physical Interpretation:

  • V₀: Neutral-to-ground voltage (affects all phases equally)
  • V₁: Positive sequence (balanced, ABC rotation)
  • V₂: Negative sequence (balanced, ACB rotation)
  • V₁₂: Combined balanced components (V₁ + V₂)

Each representation emphasizes different aspects of the same underlying physics.