A 62.5 kVA 3-Phase Ferroresonant Transformer Cures Equipment Failures Caused by Severe Utility Interface Conditions

Unusual failure rates in satellite communications earth stations purchased by the Algerian government and steps taken to reduce fault occurrences are reviewed. Discussed in this case study are problems resulting from operation of tele-communications equipment in remote areas where 220/380 volt utility power experienced swings of 100 volts, transients ranged to 2000 volts, noise levels exceeded 60 volts, and harmonic distortion was sometimes greater than 20%. The primary causes of these power problems were electrical utility systems with marginal capability to meet demand, due to continuing industrialization programs. Environmental conditions also were a factor. Ambient temperatures to 60° C, and brief but violent electrical storms also contributed to equipment failures. This combination of hostile environment and unstable power resulted in excessive earth station downtime; Mean Time Between Failure (MTBF) was measured in days. After study of power conditions, and investigation of a variety of isolation devices, the project team decided on ferroresonance as the primary power conditioning technology. Custom transformers, based on an Uninterruptible Power Supply (UPS) three-phase ferro were designed and installed. This approach reduced voltage swings to acceptable levels, provided the necessary transient suppression and produced distortion-free sine-wave power. These power conditioning systems have been operating satisfactorily for some seven years. This design proved to be the forerunner of one of today's most successful versions of power conditioning equipment. Since installation of the original systems, the concept has evolved into an even higher reliability, higher performance product.