Effects of Frozen Moisture in Oil Filled Equipment

Good Old, Quality H2O!

 

Recently, the temperatures have been rather cold in the Washington DC area. We hit a week of temperatures below 20°F. Yes, I know; not very cold when compared to our northern states or Canada. But it still brought up some very good talking points.

 

Do you test equipment below 0°C (32°F)?

 

In general, it is very hard to stop all work in the colder months due to temperature. Testing can continue to be done to all equipment, but we may have to make a trip back to the site to Power Factor or take oil samples in the warmer months. These two items in particular, can be done in the frigid temperatures, but we should keep in mind the temperature of the apparatus.

 

Why is temperature a concern?

 

Power Factor tests are used to measure dielectric losses, which relate to the wetness, dryness or deterioration of electrical insulation. If the temperature of the apparatus is below freezing (using Winding Temperature or Oil Temperature Gauge), any moisture present will be frozen.

 

Isn’t ice as conductive as water?

 

NO! Most liquids tend to shrink as they are cooled. The molecules are moving slower. They are less able to overcome the attractive intermolecular forces drawing them closer to each other. Once the freezing temperature is reached, and the substance solidifies, it contracts some more because crystalline solids are more tightly packed. Water is one of the few exceptions to this behavior.

 

Ice is 144 times more resistive than that of water. This is because of what happens on a molecular level with water. The molecules of water are packed much closer as a liquid, than as a solid. As water freezes, it freezes in a hexagonal pattern making them further apart from each other. A simple explanation is, if you place a half full cup of water into the freezer, when you inspect the cup after the water has been frozen, you will notice that the cup is more than half full. The liquid water has expanded into the solid ice. The molecules are further apart from when they were a liquid.

 

So what do we do about it?

 

We test on! We try to be smart about when Power Factor test and when oil samples are performed. If we are dealing with an outage, as soon as the equipment is de-energized, we should be thinking about Power factoring or oil samples while the temperature is above freezing. If this equipment will be de-energized for a longer duration over a frigid week, we definitely want to test before the moisture is frozen. Or plan to make a return trip when its not so frozen.

 

As Test Technicians, often times we are reminding our leaders (Project Managers, Bosses, etc.) of the best interest for the equipment. Testing just to test is a very close-minded way to be and it won’t help your reputation or your company’s. We want to be the experts that customers and business rely on! Where do you stand?

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