The Unexpected I

The scenary:

A 1500 KVA, 6/0.48 Kv, 3 ph, 60 Hz step-down transformer used to feed an ammonia process plant ( part of a fertilizer complex), Suddenly the transformer respective CB trip shuting down the ammonia process plant, therefore the whole complex. Let me say that for this kind of chemical process plant a total power black-out may result extremely catastrophic if the programmable Emenrgency Shutdown (ESD) do not operate as preseted, because at that moment begin to develope a series of adverse and dangerous chemical and process chain reaction that include explosives gas-vapor likages, high pressure fluids, set of valve operation etc jeopardizing the whole chemical complex.

Afterward, once the plant undercontrol, the engineer found as follow: The only protective device operated was the earthlikage relay connected through a set of CT configurated as differential protection by HT - LT sides of the transformer.

This event took place at the midnight so no evidence were found, late on at daylight, and small piece of "Frog" ( the alleged guilty) were found two metes far from the transf. Evidently the frog tried to jump from one of the phese bushing into the neutral bushing and cause the UNESPECTED costly short ccircuit.

Good lesson: Be careful with so simple detail that cost this time 120 000 USD

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