Fault Current Analysis in Delta-Delta Connected Systems with Floating Alternator Ground

When facing a line-to-ground (LG) fault in a transmission line with delta-delta connected transformers and a floating alternator ground, the determination of fault current becomes crucial. This article delves into the necessary steps and factors to consider in such a scenario, providing a comprehensive guide for SEO and technical purposes.

Transformer Configuration

In a delta-delta (d-d) connection, the phase voltages are not directly referenced to the ground. This means that the fault current path is significantly influenced by the transformers' impedance. While the impedance of a d-d configuration can often be considered the phase impedance, the overall system impedance remains a critical component.

Alternator Grounding

With a floating alternator ground, there is no direct ground path for the fault current to flow through. As a result, the fault current primarily depends on the system's reactance and the impedance of the transformers. This factor, combined with the lack of a ground reference, adds a layer of complexity in calculating the fault current.

Fault Current Calculation

The fault current (Ifg) in such a scenario can be approximated using the formula:

Ifgu2002u2002Vph/Ztotal

Ifgu2002:u2002Fault current Vphu2002:u2002Phase voltage at the fault location Ztotalu2002:u2002Total impedance seen by the fault current

The total impedance (Ztotal) includes contributions from:

The impedance of the transmission line (considered line impedance) The impedance of the transformers, more specifically the phase impedance Any other system impedances, such as the alternator's internal impedance

Example Calculation

Let us consider an example to understand the practical application of these formulae:

Vphu2002u200211 kV Ztotalu2002u20025 u03A9

Plugging these values into the formula:

Ifgu2002u200211,000 u03A9/5 u03A9 u2002u20022,200 A

Key Points

Accurate fault current values heavily depend on specific system configurations and parameters such as voltage and impedance. Due to the floating alternator ground, the fault current may be limited compared to a grounded system. If detailed system parameters are available, a more precise calculation can be performed.

Summary

The fault current in a delta-delta system with a floating alternator ground can be determined using the phase voltage and the total system impedance. The accuracy of the calculated fault current depends on the specific characteristics of the system and the available detailed parameters.

Keywords: line-to-ground fault, delta-delta connection, floating alternator ground