Key Lessons from a Transformer Installation: A Case Study
After installing a 1000kVA dry-type transformer, issues such as burnt smells, and a 60-amp neutral current arose. Investigation revealed the following root causes:
Root Causes Identified
Inadequate Earthing
Neutral earthing was not robust, using only one pit instead of two.
A GI conductor was used instead of copper, leading to higher resistance.
Improper spacing between pits compromised effectiveness.
Transformer and Load Issues
Testing revealed failed winding insulation.
Non-linear loads likely caused harmonics, leading to overheating.
Resolution
The transformer was replaced with a unit meeting Qpro, GTP and BIS standards. Post-installation, it passed Factory Acceptance Testing (FAT) and has operated smoothly.
To avoid recurrence:
Earthing Standards: Use two pits with copper conductors, spaced at least 3 m apart. Consider maintenance-free chemical earthing.
Transformer Selection: Choose units with appropriate K-factor ratings (e.g., K-4 to K-13) for non-linear loads.
Harmonic Control: Deploy harmonic filters to limit THD below 5% as per IEC 61000-3-2.
Surge Protection: Install SPDs per IEC 61643 to protect from over voltages.
Monitoring: Use advanced relays to track neutral current, THD, and temperature.
Maintenance: Regularly test earthing resistance and perform thermographic scans to identify issues early.
Key Takeaway: Effective earthing, proper equipment selection, harmonics management, and proactive monitoring are critical to ensuring safe and reliable operations.