Interactive Transformer Fault Current Visualization Toolkit

Explanation of Transformer Behavior

This visualization demonstrates how the delta winding blocks zero-sequence current. For single line-to-ground faults, the zero-sequence component gets blocked by the delta winding, resulting in different current patterns on the high-voltage side.

Key observations:

• In SLG faults, the LV side contains all three sequence components in equal amounts
• The delta winding blocks zero-sequence currents from flowing on the HV side
• Positive sequence components are shifted by the vector group number × 30° in the positive direction
• Negative sequence components are shifted by the vector group number × 30° in the negative direction
• Different transformer vector groups produce different HV current patterns for the same fault type
• For three-phase balanced faults, only positive sequence currents exist
• For phase-to-phase faults, equal positive and negative sequence components appear, but no zero sequence

Phasor Rotation Convention in Power Engineering

In power engineering, phasors are represented as rotating vectors in the complex plane. By convention:

• Counterclockwise rotation is the standard direction of phasor rotation
• Positive phase shifts are always in the counterclockwise direction
• Negative phase shifts are in the clockwise direction
• A phase shift of +30° means the phasor is rotated 30° counterclockwise from the reference
• In transformer vector groups, the number indicates the phase shift in multiples of 30° (e.g., Dy11 means 330° or -30°)
• Positive sequence components rotate counterclockwise at the system frequency
• Negative sequence components rotate clockwise at the system frequency

This convention is consistent throughout power systems analysis, including transformer connections, symmetrical components, and fault calculations. In this visualization, you can observe how the phasors rotate counterclockwise when their angle increases.

ABC Phase Sequence in Power Engineering

The standard phase sequence in power engineering is ABC, with counterclockwise rotation:

• Phase A is typically used as the reference at 0°
• Phase B is at -120° relative to Phase A (or equivalently 240°)
• Phase C is at +120° relative to Phase A
• In the counterclockwise direction: A leads B by 120°
• In the counterclockwise direction: C leads A by 120°
• In the counterclockwise direction: C leads B by 240°
• The full 360° rotation represents one complete cycle of the AC waveform

This standard convention in power engineering represents the physical reality of three-phase systems. With counterclockwise rotation, the phases pass a fixed point in the sequence A-B-C, with each phase separated by 120 electrical degrees. The "Demonstrate CCW Rotation" button shows this standard rotation, with all three phases maintaining their proper angular relationships while rotating counterclockwise together.