In three-phase electrical systems, it’s generally expected that each phase current will balance with the others. However, actual operating conditions often deviate from this ideal due to the presence of single-phase loads, even in facilities equipped with three-phase infrastructure.

For instance, in a shopping mall, lighting loads and localized air-conditioning systems typically operate in single-phase mode, completing their power flow via the neutral conductor. This setup can lead to variations in current distribution across the phases, contributing to unbalance.

The Main Causes of the Unbalanced Current

The primary cause of imbalance in three-phase systems is the unequal distribution of loads across the phases. This disparity results in different currents being drawn from each phase, leading to unbalanced currents flowing through the neutral conductor.

Calculation Approach

This guide provides a concise overview, focusing on the fundamental 50 Hz component in each of the three phases. It’s important to note that harmonic currents, particularly the 3rd harmonic at 150 Hz and its multiples, are not considered in this basic calculation. Future articles will delve into the effects of harmonic currents on neutral current, including a detailed Excel model.

What is Power Quality, Why is it Important?

Calculating Unbalance Current with Excel

To calculate unbalanced current:

1. Enter the currents and phase angles for each phase into the designated yellow-colored cells in our Excel sheet.
2. The neutral current is then determined by vectorially summing the three-phase currents according to their respective angles.

When the three-phase currents are equal and the phase-to-phase angles adhere to the standard 120°, the resulting neutral current is zero. However, discrepancies in phase currents or shifts in phase angles can still generate unbalanced currents on the neutral conductor.

Understanding the concepts of “phase” and “vector” is crucial for electrical engineers, as these principles form the basis of many calculations involving three-phase systems.

You can download the unbalanced current calculation Excel file by clicking on the image below or here.