Monday, July 23, 2012

What's New?


I haven't posted a blog entry for a long time.

I am busy working 50 hours a week (plus carpool time), so weekdays are tiring. My weekday evenings consist of eating supper, maybe seeing Robyn for a bit, watching an hour of TV then going to bed.

But work is interesting. Just last week we connected a 138,000 volt overhead line from SaskPower to a giant gas-insulated switchgear which feeds two brand-new transformers on our project site. The transformers transform the 138,000 volts into a more manageable 13,800 volts. After that, another pair of transformers step the voltage down to about 5,000 volts. For reference, your house outlets are 120 volts (your washer/dryer/dishwasher/oven might be 240 V).

This is our GIS.

What is a gas-insulated switchgear (GIS), though? The answer is interesting. Have you ever noticed a spark when you plug in an electrical appliance into a socket? You've just seen a tiny little electrical arc that bridges or "jumps" the air gap between two metal conductors. If you've been to a science centre and have seen a Jacob's Ladder or a Tesla coil, you've seen another kind of electrical arc. When you are playing with 138,000 volts, you don't get tiny fun arcs. You get humongous monster electrical arcs that can cause serious damage, injury or death due to burns or explosions. They can last for fractions of a second or several seconds.

Anytime you want to unplug from something that's providing 138,000 volts, you have to do it safely to minimize exposure to electrical arcs. One way to do this is to encapsulate the whole on/off switch (called a "disconnect") in an airtight, cast-aluminum enclosure and fill it with sulfur-hexaflouride (SF6) gas, a gas which is much heavier than air and naturally quenches electrical arcs. Arcs still form in GIS units, but are blasted with a jet of SF6 to disrupt and terminate them within milliseconds of them forming.

Fact: If you inhale SF6 gas, it has the opposite effect as helium gas - it lowers your voice! No, I haven't tried it.

Another fact: If the GIS leaks, it could fill the GIS building with colourless, odorless SF6 gas. This is an asphyxiation hazard (because it displaces oxygen), so we installed an SF6 detector that screams if the levels get too high, and automatically starts an exhaust fan to vent the building and bring fresh air in. So far, no leaks.