Wednesday, June 24, 2009


A behind the scenes explanation of some of the repairs we were dealing with last week...

The power transformers found in our substations are the key principle element in our electrical system. Each transformer has a specific software and relay protection scheme that does its best to shield the transformer from a daily onslaught of power surges caused by lightning, system switching, and breaker cycling opening and closing due to tree limbs and debris.

A transformer is in effect a huge electromagnet. When it sees a huge current spike, it transforms this into a massive magnetic pulse that causes its interior coils to repel each other with unbelievable force. Each power transformer has its own dedicated breaker that serves as its last line of defense. After years of constant diligence even the best equipment may be pushed past it limit.

This was the case for a power transformer at substation 67 shortly after the storm on June 13th. A power transformer and its related breaker and buswork were destroyed when they could no longer keep its 161,000 volts under control. You can see from the pictures that the failure was catastrophic. The event took place in about a minute and a half.

The most surprising damage was found atop the breaker where the high voltage porcelain bushings were reduced to cinders. This would take a blast of ~3500 F.

The overall system typically has a backup for every element. When one part is damaged beyond repair, MLGW replaces it quickly. In this case no one lost power and the repair and restoration of this substation began almost immediately. A spare transformer and breaker were brought in within a couple of days, and the buswork has been rebuilt.

In a few weeks this substation will be even more robust than before and ready for the future storms to come.

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