A Quick Overview of Short Circuit
Problems and Solutions
Ron Chu, Ph.D., PE, Fellow IEEE
Exelon Corporation
Presented at the August 8, 2013
PJM Planning Committee Meeting
Objectives
• Present
a simple example showing a Short Circuit Problem
• Review the general approaches to mitigating the problem including:
–Replace Circuit Breakers with CBs with higher interrupting capability (may
replace substation equipment to complement the higher CB duty)
–Reduce short circuit current contributions to Circuit Breakers (i.e. install
series reactors, increase generator step-up transformer impedance, install
fault current limiters, etc.)
–Isolate the sources of short circuit currents (i.e. install Back-to-Back High
Voltage Direct Current system, reconfigure the transmission system (by
opening bus ties, etc.), relocate generators, etc.)
–Rebuild the system
• Discuss a commercially available Fault Current Limiter as a potential solution
alternative
• (Main Objective) Bring to the attention of a robust and cost
effective alternative for considerations to mitigate current and
future Short Circuit problems
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An example of a Saturated AC Transformer based FCL
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Concept of Saturated AC Transformer based FCL
• The concept is to make use of the non-linear magnetic characteristic of a ferromagnetic core of a
regular AC transformer.
• The AC transformer is driven into deep saturation by a superimposed DC current during steady
state operation when there is no fault (the FCL transformer represents a lower impedance path).
• The AC transformer is driven out of saturation by the fault AC current during a fault (the FCL
transformer represents a high impedance path).
(Voltage)
Low Slope = Low
Impedance
High (V/I) Slope =
High Impedance
(Current)
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Key Takeaways of this Presentation
• Saturated
AC Transformer based Fault Current Limiters are regular AC
transformers.
• The FCL impedance can increase, during fault condition, up to 15 times.
• The Short Circuit current can significantly be reduced.
• The changes in SC impedance are instantaneous.
• They use available proven technologies (standard materials and processes)
• They are manufactured using available production lines.
• They are subjected to existing testing standards and techniques.
• The existing operation, maintenance and testing practices apply.
• The lead time is similar to the lead time of regular AC transformers.
•We may want to consider them as an alternative solution to short circuit
problems if they are found to be more cost effective and practical now and in
the near future.
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