Why Is Liquid Level Important In a Transformer?

Описание: Transformer fluids provide both dielectric strength and cooling. As the temperature of he transformer goes up, that fluid expands. As the temperature of the oil goes down, it contracts. We measure liquid levels with an installed level gauge. How you interpret the data from the gauge and how you cross reference that information with the oil temperature can tell you if you need to top up your transformer with oil. Bob Rasor explains in detail.

Transcription:

So the liquid in a transformer, whether it's oil or a different type of liquid, they do two things. They provide dielectric to keep the electricity where it belongs. And they also provide cooling. The transformer is not 100% efficient and that inefficiency shows up as heat. And in fact, as the temperature of the transformer goes up, due again to the losses in the transformer, the oil expands. And it's about 1% for every 10 degrees centigrade that the transformer temperature rises. So how is that measured? Well, what I have here is a liquid level gauge and you can see that this float follows the level gauge, the level in the transformer, and the gauge has this mark, when the level is sideways here lining up with the needle at 25 degrees centigrade. So a low level would be, of course, if it's resting on low, this arm would follow the liquid level.

And, however, at 25 degrees centigrade, which would be an ambient temperature and the transformer may not be loaded at that point. That's how they set a level to start off with. Now as the temperature goes up and that fluid expands, the float comes up and you can see, the needle shows as such. Now if the level gauge is reading 25 degrees centigrade and the temperature of the oil is 60 degrees centigrade, the level gauge really should be up here. So at 60 C, look at the, at the temperature gauge and you see this reading like this. This is a low level. It should be up here at 60 centigrade. And, conversely, if the transformer is 60 and you see, that the level gauge you know, is way down here, you have a chance at that point to be so low that when the transformer cools down, the radiator may not be flooded and there's where the real danger comes if you don't have the radiator, tube flooded with oil, that cooling effect of the transformers heat going into that radiator being exposed to the ambient air and the radio part, perhaps with a fan and the density changes, the oil sinks and that movement in this circular pattern is called thermal siphoning.

And that's how a transformer cools. Now, how can you confirm that this level gauge is reading correctly? Well you can for the most part, trust it. However, there's also a way to use a tube like this and connect to the bottom of the transformer and find a vent adequately at the top and the liquid level will follow this tube, we call it tygon tubing a transformer, and we can see them visually. The liquid will go up through this tube and you line it up where this gauge may be reading and you confirm it's reading properly, and a third way might be with an infrared camera. If the transformer is energized, you can shoot the side of the tank and you get some idea of where that level is. Anyway, the idea is to keep your transformer at the proper level a little bit low - let's get it topped off. Very low - It's dangerous. We need to do it right away.

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