Influence of Series Choke on Damping of Switching Transients in Distribution Transformers

Distribution transformers operating in modern system grids or in industrial networks are subjected to many switching transients,which may occur due to routine operations,network reconfigurations or as reaction on protection signals.Depending on the network configuration and parameters,such events may lead to external overvoltages and result in additional stresses on the insulation system.This paper presents the influence of a series choke on damping of switching transients in distribution transformers.The impact of the choke is assessed by both amplitude and rise time reduction.The suppression of the transient rise time is shown for a test configuration involving distribution transformers connected to low loss cable lines and a medium voltage breaker.Such phenomena are especially typical for industrial networks where switching operations are very frequent.Both simulation and experiment results are given.Simulation results as well as measurement results confirmed that switching events can lead to high dU/dt and in consequence,can have adverse impacts on insulation system.Voltage escalation during switching event is strongly related with system conditions.The results obtained for presented mitigation method are promising and indicate significant dU/dt reduction as well as number of ignitions and voltage peak value.The protection of distribution transformers with a series choke is a new approach dedicated to environments prone to the occurrence of transients with high steepness.Experimental results show that the application of serial choke with suitable parameters realizes the reduction of dU/dt at the machines terminal from 24 kV/μs to 5 kV/μs,as well as the reduction of voltage peak value from 10 kV to 5 kV.The number of ignitions is also reduced.

Distribution transformers operating in modem system grids or in industrial networks are subjected to many switching transients, which may occur due to routine operations, network reconfigurations or as reaction on protection signals. Depending on the network confi- guration and parameters, such events may lead to external overvoltages and result in additional stresses on the insulation system. This paper presents the influence of a series choke on damping of switching transients in distribution transformers. The impact of the choke is assessed by both amplitude and rise time reduction. The suppression of the transient rise time is shown for a test configuration involving distribution transformers connected to low loss cable lines and a medium voltage breaker. Such phenomena are especially typical for industrial networks where switching operations are very frequent. Both simulation and experiment results are given. Simulation results as well as measurement results confirmed that switching events can lead to high dU/dt and in consequence, can have adverse impacts on insulation system. Voltage escalation during switching event is strongly related with system conditions. The results obtained for presented mitigation method are prom- ising and indicate significant dU/dt reduction as well as number of ignitions and voltage peak value. The protection of distribution transformers with a series choke is a new approach dedicated to environments prone to the occurrence of transients with high steepness. Ex- perimental results show that the application of serial choke with suitable parameters realizes the reduction of dU/dt at the machines terminal from 24 kV/μs to 5 kV/μs, as well as the reduction of voltage peak value from 10 kV So 5 kV. The number of ignitions is also reduced.