35kV bus line voltage and phase voltage

For a 35 kV three-phase bus, the line-to-line voltage is 35 kV, and the corresponding phase (line-to-neutral) voltage is approximately 20.2 kV.

Voltage Relationship in a Three-Phase System

In a three-phase system, the line-to-line voltage (V_L) and line-to-neutral voltage (V_Ph) are related by the square root of three: V_Ph = V_L / √3 For a 35 kV bus:

• Line-to-line voltage (V_L) = 35 kV
• Phase voltage (V_Ph) = 35 kV / √3 ≈ 20.2 kV This means each phase of the bus has a voltage of about 20.2 kV relative to neutral or ground, while the voltage between any two phases is 35 kV .

Practical Considerations

• Equipment Ratings: Transformers, switchgear, and bushings are rated according to the line-to-line voltage of the bus, which in this case is 35 kV .
• Fault Conditions: During single-phase-to-ground faults, the voltage of the faulted phase drops, while the other two phase-to-ground voltages can rise to √3 times the normal phase voltage, but the line-to-line voltage remains largely unchanged .
• Distribution Standards: Utilities often refer to the voltage class (35 kV) rather than the exact operating voltage. The actual line-to-line voltage may vary slightly depending on system design, load, and regulation .

Summary

For a 35 kV bus:

• Line-to-line voltage: 35 kV
• Phase (line-to-neutral) voltage: 20.2 kV This relationship is fundamental for designing and operating medium-voltage distribution systems, ensuring proper insulation, equipment selection, and fault analysis.