If the utility short circuit current changes, what could possibly go wrong? It is quite an extensive list. However, I want to focus on how a change with the utility short circuit current and equivalent impedance can affect parallel resonance which is critical in a harmonic study.

I had a client with a power system that was operating with no issues. Then one day, the capacitors began to fail. Why? They had not made any changes. 

During the investigation it was discovered the utilities had changed their configuration and were using an alternate distribution line upstream. This changes the equivalent impedance which shifted the parallel resonance to a frequency almost identical to that created by their drives. 

Watch this video as I explain how changes to the utility system can make harmonic issues appear out of nowhere. What are the resonance trends when capacitor and utility data changes.

This video is from my live 32 hour Electrical Power System Engineering Class and also the on-demand class: Power Factor and Harmonic Analysis