Executive Summary

Switching loads on and off is a common occurrence in large scale power system distribution facilities. Under some circumstances, a switching event may generate a transient condition which may disturb system stability and exceed the insulation levels of the equipment and  degrading its insulation over time. This is particularly true for the most important and critical piece of electrical equipment – the power transformer.

A snubber circuit is a proven method to mitigate switching transients and maintaining power system reliability while keeping power system equipment operable for the long-term.

Objective

A Snubber Circuit Study seeks to improve the reliability of the system by minimizing the damaging effects of switching transients. Switching transients are caused by operating an isolation device (breaker) under load or fault conditions. A Snubber circuit study is a proven method for mitigating switching transients and maintain high reliability.

Brief Study Methodology

A Snubber Circuit Study is a three stage process comprising of.

• Quantization and parameterization of the transient caused by circuit breaker switching

  The concerned circuit breaker and equipment downstream of it is critically analyzed and modeled in an Electromagnetic Transients Program (EMTP), a ‘worst case scenario’ which gives rise to the highest Transient Recovery Voltage is simulated in the program. Key parameters of the Transient Recovery Voltage such as its magnitude, rate of rise, duration, frequency and energy are extracted from the simulation. Multiple simulations are done for scenarios other than the worst case scenario and possibility of damage and failure in downstream equipment is evaluated.

• Determination of the frequency response of the system downstream of the circuit breaker

  A sweep frequency response analysis of the downstream equipment is done to evaluate the possibility of resonance between the natural frequency of the system and the frequency of the occurring transient. Measures are taken at the proceeding design stage to avoid any possibility of occurrence of this resonance.

• Design of an optimum snubber circuit

  Design parameters of a snubber circuit are recommended that best reduce the switching transient to an optimum level. Due considerations are given to harmonize the frequency response of the added snubber with that of the system and any shifts in the frequency response of the system after addition of snubber are fully documented.

Expected Study Outcomes & Recommendations

The circuit breaker and downstream system under consideration is fully evaluated for its ‘worst case’ transient condition and made more robust in response to switching transients through corrective action recommended by a Snubber Circuit Study. It is therefore expected that:

• Switching transient is reduced to a safe level before it strikes the downstream equipment.
• Possibility of resonance between the transient and downstream system is avoided.
• Downstream equipment will have a prolonged life and will require less reactive maintenance due to being less prone to damages caused by transients.
• Overall reliability of the system will increase.

Study Deliverables

A comprehensive set of deliverable reports is provided presenting the findings and recommendations of the Snubber Circuit Study. The deliverable may be expected to include:

• Detail of the original system under consideration.
• Detail of the Electromagnetic Transient Stability Program simulation.
• Detail of the worst case transient encountered, its parameters and simulation results.
• Details of other simulated scenarios as per the operating conditions of equipment.
• Results of the sweep frequency response analysis of the downstream system.
• Simulation results in the Electromagnetic Transient Stability Program after the addition of a snubber circuit showing reduction in switching transient.
• Recommended design parameters and specifications of the snubber circuit.
• Recommended installation practice and location of the snubber circuit.
• Documentation of any shifts in the natural frequency of the system after the addition of the snubber.
• International standards and code compliance throughout the study process.

References

All studies conducted by AllumiaX, LLC are in full compliance of the set international standards of IEEE, NEC and NFPA.