Ferrorresonace

Up until the other day when I decided to go through some of my APE books to refresh myself; I've known of Ferro in Wye-Delta banks and with underground when the length of the cable exceeds the KVA of the transformer.

One that slipped my mind was the DELTA-WYE bank, probably because you hardly ever see them out here.

Here's what it says;

FOR DELTA-WYE TRANSFORMATION-THREE SINGLE PHASE TRANSFORMERS

In order to prevent possible ferroresonance during the opening or closing operation of fuse cutouts, any gang operated air break switch, 3 phase circuit recloser or circuit breaker available should be used to de-energize the line to the above described transformer if feasible before opening or closing the fuse cutouts. Installation of a gang operated air break switch on the line side of this type transformer connection may be justified in some instances.

Had some switching to do in Cali on a big pad mount trans. Task was to isolate the feed to the next transformer. I lifted the first Elbow and the whole thing sounded like it was going to launch it self. The CA yelled '"CLOSE IT!!!!!". I did.

Then I cleaned my shorts.