Evaluation of a Unique Transient Hardened Transformer Designed to Withstand Primary Switching Transients: Simulation, Lab Tests and Analysis

Many modern electrical distribution systems, such as those used in data centers, demand high power densities, small electrical footprints, high efficiency transformers, redundant systems and frequent testing requiring switching at primary voltages. These various parameters that ensure the highest reliability and availability to mission-critical loads also place the facility in the highest risk category for distribution transformer failures due to primary switching transients. Over the last decade, this phenomenon has been attributed to a significant number of failures of certain types of transformers involving primary circuit breaker switching in data centers and other facilities exhibiting similar characteristics. Although the RC snubber has been proven to safely mitigate the transient overvoltage imposed on the primary winding of the transformer, manufacturers have continued to look for other solutions to the primary switching transients problem resulting in an alternative solution: a unique transient hardened transformer designed to withstand switching transients. The authors conducted an evaluation to prove analytically, through a combination of simulations and field tests, that the transient hardened transformer design will withstand switching transients without the need for transient mitigation using RC snubbers, relying only on conventionally applied surge arresters. This paper focuses specifically on data center transformers, however, the lessons learned here may be applied to numerous applications.