Dry-type distribution and power transformers—such as vacuum-pressure impregnated, cast coil, and vacuum-pressure encapsulated types—are widely used in industry. However, switching these transformers with vacuum circuit breakers (VCBs) causes a significant number of transformer failures worldwide, as documented in industry publications [1]–[3] and insurance reports [4]. When a VCB or SF6 circuit breaker exhibits virtual current chopping and multiple re-ignitions, it generates switching transients: Transient Recovery Voltage (TRV) and Temporary Overvoltages (TOV). Depending on the breaker characteristics and power system parameters, these transients reach magnitudes and frequencies that cause deterioration and insulation failure in the connected dry-type transformer and the circuit breaker itself (Fig. 1 and Fig. 2). RC snubber circuits are the only remedy for these failures. Fig. 3 and Fig. 4 show the effect of an RC snubber circuit during the switching of a dry-type transformer.
Hilkar provides RC snubber engineering services to protect dry-type transformers from switching-induced overvoltages. We develop detailed power system models to identify the worst-case circuit breaker (CB) switching conditions that produce the highest Transient Recovery Voltage (TRV) and Temporary Overvoltage (TOV) levels. Using electromagnetic transient simulation software such as EMTDC/PSCAD, we perform parameter sweep analyses to determine the optimum resistance (R) and capacitance (C) values for the RC snubber circuit. The acceptable TRV and TOV limits for the circuit breaker and transformer are established in accordance with IEEE C37.06-2009 and IEEE C37.06.1-2017. Following completion of the study, we provide a comprehensive engineering report containing the RC snubber design, simulation results, technical specifications, and component requirements for procurement from any qualified manufacturer.
Other Applications for RC Snubbers
In addition to dry-type transformers, Hilkar provides RC snubber design services for the following power system equipment:
- Shunt Reactors
- Medium-Voltage (MV) Motors
- Generators
- Arc and Ladle Furnace Transformers
- [1] D. D. Shipp et al., “Transformer Failure Due to Circuit Breaker-Induced Switching Transients,” IEEE Transactions on Industry Applications, vol. 47, no. 2, Mar./Apr. 2011.
- [2] C. S. Mardegan et al., “The Experience Acquired Sizing Snubbers to Mitigate Switching Transients in Industrial Power Systems,” IEEE Transactions on Industry Applications, vol. 52, no. 5, Sept./Oct. 2016.
- [3] Q. Yang et al., “Field Experiments on Overvoltage Caused by 12-kV Vacuum Circuit Breakers Switching Shunt Reactors,” IEEE Transactions on Power Delivery, vol. 31, no. 2, Apr. 2016.
- [4] Factory Mutual Insurance Company, “Arc Furnace Transformer Installations,” Property Loss Prevention Data Sheets, Jan. 2002.
