Understanding Line-to-Ground Voltage in 33 kV Delta Configured Overhead Power Lines

Determining the line-to-ground voltage in a 33 kV delta-configured three-wire overhead power line is essential for ensuring the safety and operation of electrical systems. This article aims to explain the key concepts, calculations, and practical applications related to this topic.

Key Concepts

In a delta configuration, the line-to-line voltage (VLL) is equal to the voltage across each phase (VPh). Therefore, the line-to-ground voltage (VLG) in a delta system can be calculated using the following relationship:

V_{LG} frac{V_{LL}}{sqrt{3}}

Calculation and Explanation

Given a 33 kV delta-configured power line, we can calculate the line-to-ground voltage as follows:

V_{LL} 33 kV

Substituting this value into the formula, we get:

V_{LG} frac{33 kV}{sqrt{3}} approx frac{33 kV}{1.732} approx 19.05 kV

Conclusion: Your initial guess of approximately 19 kV is correct. In a balanced and symmetrical system, the line-to-ground voltage in a 33 kV delta-configured power line is approximately 19.05 kV.

Practical Considerations

It is important to recognize that this potential is not capable of sustaining a load current. This voltage arises due to capacitive coupling between each phase and ground, and the exact balance point is influenced by the phase loading. In a symmetrical system, the potential can be considered as 19 kV. However, in real-world applications, the actual voltage can vary due to impedance imbalances caused by single-phase or phase-to-phase loading.

In some systems, a delta ground point is intentionally used where one phase is grounded, resulting in one phase having zero volts to ground, while the other two phases are at the phase-to-phase voltage to ground, i.e., 33 kV to ground.

Practical Measurement Techniques

For obtaining a positive check of the phase-to-phase voltages and the power factor shift due to different loadings between two delta systems, a practical method involves:

Grounding the same phase from each system, e.g., both 'A' phases, and measuring the phase differential between the 'B' phases of both systems and then the 'C' phases of both systems. This method helps in identifying any phase-to-phase voltage differences resulting from different loadings.

Repeating the measurements by grounding the 'B' and 'C' phases to ensure a comprehensive comparison.

By following these steps, one can accurately measure and verify the phase-to-phase voltages and any power factor shifts due to different loadings in delta configured power systems.

Reference:

The Electrical4U and PowerLineIndia provide detailed information on delta configuration and phase-to-ground voltage calculations.