Padmounted Transformer Tank Fault Withstand Capabilities

An important function of DSTAR investigations is determining the ability of typical equipment to withstand real-world duties not addressed by the existing standards. A prime example is the fault-energy withstand of padmount transformers, which has become an important issue for utilities confronted with high short-circuit current levels on their feeders. Although the standards specify poletop transformer lid retention requirements, there are no standards which specify the mechanical integrity of padmount transformers for internal faults.

Based on DSTAR testing, the fault withstand capabilities of typical designs have been identified. Definitive maximum current and time-current withstand capabilities have been determined which are being implemented by DSTAR members in their transformer protection strategies. An example is shown below. The results have provided the members a great opportunity for cost reduction through the elimination of unnecessary current-limiting fuse application.

A more recent project, P12-7, has also developed guidelines for current-limiting fuse application on transformers and capacitors from an industry survey and review of best practices.

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This study was conducted in: P3-4