Obliquely Type Voltages and Currents - Agulhas Utilities Corporation

In this article, we dive into the concept of obliquely type voltages and currents, particularly how unbalanced voltages, negative phase sequencing, and harmonic disturbances shape voltage and current curves. This phenomenon can lead to a variety of operational issues, especially when utility companies don’t routinely monitor power quality.

What Are Obliquely Type Voltages and Currents?

Obliquely type voltages refer to the irregular shapes and sizes of voltage and current curves caused by unbalanced conditions in the electrical system. These conditions can be exacerbated by negative phase sequencing and harmonic disturbances, resulting in unpredictable and potentially damaging effects on industrial equipment.

The Gap in Utility Company Oversight

In a previous discussion, I raised a question about the oversight of unbalanced voltages, phase-shift variations, and harmonic disturbances by utility companies. The truth is: these utilities rarely inspect the power network for voltage magnitude or phase-shift variations. Harmonic disturbances go unchecked, which can lead to severe issues for industrial operations.

Real-World Example: Mysterious Plant Shutdowns

In January 2017, I was called to investigate an issue at a mid-sized factory in Gauteng, South Africa. The plant frequently shut down unexpectedly, even though the lights stayed on. The problem was traced to motor controllers—such as variable-frequency drives and soft-starters—malfunctioning due to poor power quality. These controllers were supplied from a single phase that was unstable, causing them to shut down when the voltage fluctuated outside acceptable limits.

This incident reminded me of a similar issue I faced years ago in the Western Cape. In both cases, the issue affected motor controllers, which rely on stable power to function. These disruptions are not limited to specific industries but affect various sectors, including mining.

The Cost of Power Disturbances

In the mid-1980s, I advised a customer to install a large motor-generator set with a flywheel to maintain momentum during power distortions. This was a costly solution, but it was necessary to prevent extensive downtime and financial losses caused by repeated plant shutdowns.

A Recent Incident: Investigating Power Quality Issues

In late August 2023, a consulting engineer approached me to measure and analyze the loading on a 6.6kV cable feeder. When reviewing the data, I noticed a significant imbalance between the feeders. One phase had near-zero voltage, which resulted in excessive current on the other two phases and a high current in the neutral conductor. The issue was traced to a faulty circuit breaker contact, which led to imbalanced power. Despite reporting this to the utility company, no action has been taken to resolve the issue, highlighting the lack of proactive monitoring of power quality.

A Call to Action for Utility Companies

I urge utility companies to recognize the widespread nature of these issues and take proactive steps to monitor power quality. Medium- to large-power users are particularly vulnerable to these disturbances. I encourage utility companies to contact me for Load Profiling exercises to assess whether similar problems are affecting their customers.

Visualizing Voltage and Harmonic Disturbances

On the Agulhas Utilities Corporation Negative Phase Sequencing webpage, I provide several images and videos that explain the concept of obliquely type voltages. One video demonstrates a three-phase voltage wave with a 6% voltage reduction in one phase and a 10% third harmonic disturbance on all phases. Pay close attention to the shifting phase crossing points, indicating phase shift and misalignment between the phases.

While some may consider this scenario extreme, I assure you, I’ve seen worse. The importance of monitoring and addressing power quality issues cannot be overstated.

Conclusion

Obliquely type voltages and currents are often overlooked but can cause significant disruptions in industrial operations. As seen in the examples above, these disturbances can lead to unexplained shutdowns, equipment failures, and financial losses. It’s crucial for utility companies and industrial users to be aware of these issues and take the necessary steps to prevent them.

Our newsletters aim to enlighten our audience about current trends and events. We strive to distribute a newsletter at most once a week, but the frequency may vary to avoid inundating our website visitors with irrelevant content.

The most recent newsletters will be dispatched via email to all individuals on our mailing list and will also be accessible under the Newsletter menu section.

General Disclaimer

The information provided on this page is for general informational purposes only. All opinions expressed here are my own and do not reflect the views of any organizations I am affiliated with. While I strive to ensure accuracy, I make no representations as to the completeness or validity of the information on this blog and will not be liable for any errors or omissions. Any actions taken based on the information provided are strictly at your own risk.

Legal Disclaimer

The information provided on this website is for general informational purposes only. All information on the site is provided in good faith, however, we make no representation or warranty of any kind, express or implied, regarding the accuracy, adequacy, validity, reliability, availability, or completeness of any information on the site.

Under no circumstance shall we have any liability to you for any loss or damage of any kind incurred because of the use of the site or reliance on any information provided on the site. Your use of the site and your reliance on any information on the site is solely at your own risk.

Key Points to Include:

Purpose: Mention that the information is for general informational purposes only.
Good Faith: State that the information is provided in good faith without any warranties.
Liability: Clearly state that there is no liability for any loss or damage.
Risk: Emphasize that the use of the site and reliance on information is at the user’s own risk.

Copyright Disclaimer

The content on this page, including text, images, graphics, and other material, is protected by copyright law. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to [Your Name or Your Blog’s Name] with appropriate and specific direction to the original content.