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Symmetrical components of unbalanced voltages

Short answer

Using a = 1∠120°, V0 = (200∠0°+200∠245°+200∠105°)/3 = 21.61∠10.60° V, V1 = 197.81∠-3.32° V, V2 = 20.15∠158.24° V. The set is nearly balanced, so positive sequence dominates.

Determine the symmetrical components of three unbalanced voltage Va = 200∠0°, Vb = 200∠245°, Vc = 200∠105° V.

Using a=1∠120∘a = 1\angle120^\circ: V0=13(Va+Vb+Vc)V_0 = \frac13(V_a+V_b+V_c), V1=13(Va+aVb+a2Vc)V_1 = \frac13(V_a+aV_b+a^2V_c), V2=13(Va+a2Vb+aVc)V_2 = \frac13(V_a+a^2V_b+aV_c).

Rectangular form

Va=200∠0∘=200+j0Vb=200∠245∘=−84.52−j181.26Vc=200∠105∘=−51.76+j193.19\begin{aligned} V_a &= 200\angle0^\circ = 200 + j0 \\ V_b &= 200\angle245^\circ = -84.52 - j181.26 \\ V_c &= 200\angle105^\circ = -51.76 + j193.19 \end{aligned}

Zero sequence

V0=13(63.71+j11.92)=21.24+j3.97=21.61∠10.60∘ VV_0 = \tfrac13(63.71 + j11.92) = 21.24 + j3.97 = 21.61\angle10.60^\circ\ \text{V}

Positive sequence

aVb=200∠365∘=200∠5∘aV_b = 200\angle365^\circ = 200\angle5^\circ, a2Vc=200∠345∘=200∠−15∘a^2V_c = 200\angle345^\circ = 200\angle{-15^\circ}:

V1=13(200∠0∘+200∠5∘+200∠−15∘)=13(592.42−j34.33)=197.47−j11.44=197.81∠−3.32∘ V\begin{aligned} V_1 &= \tfrac13(200\angle0^\circ + 200\angle5^\circ + 200\angle{-15^\circ}) \\ &= \tfrac13(592.42 - j34.33) = 197.47 - j11.44 = 197.81\angle{-3.32^\circ}\ \text{V} \end{aligned}

Negative sequence

a2Vb=200∠485∘=200∠125∘a^2V_b = 200\angle485^\circ = 200\angle125^\circ, aVc=200∠225∘aV_c = 200\angle225^\circ:

V2=13(200∠0∘+200∠125∘+200∠225∘)=13(−56.14+j22.41)=−18.71+j7.47=20.15∠158.24∘ V\begin{aligned} V_2 &= \tfrac13(200\angle0^\circ + 200\angle125^\circ + 200\angle225^\circ) \\ &= \tfrac13(-56.14 + j22.41) = -18.71 + j7.47 = 20.15\angle158.24^\circ\ \text{V} \end{aligned}

Check: V0+V1+V2=200.0+j0=VaV_0 + V_1 + V_2 = 200.0 + j0 = V_a ✓

Answer: V0=21.61∠10.60∘V_0 = 21.61\angle10.60^\circ V, V1=197.81∠−3.32∘V_1 = 197.81\angle{-3.32^\circ} V, V2=20.15∠158.24∘V_2 = 20.15\angle158.24^\circ V. The positive sequence dominates because the set is nearly balanced (only the angles are unbalanced).

✓ Answer checked by Claude Sonnet 5.5

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