What does kansui do to dough in noodle making? I'm trying to understand how to properly prepare hand pulled noodles. I've read about Kansui and Lye water and in some instances I've read that they serve a similar purpose. However, after some reading, it seems that kansui could potentially affect the dough differently than lye water. Some expert insight into this would be appreciated very much.
Kansui is a mixture of sodium carbonate and potassium carbonate, both alkaline. Since lye is also alkaline, it could serve a similar function in the dough but it would depend on the relative strengths of their alkalinity.

Specifically, alkaline water interfere with enzymes in the flour and thus inhibit the development of gluten, allowing for the dough to be stretched more readily. That being said, you need some gluten development or else the dough won't form.

Alkaline water also will change the color yellow and make the noodles slippery on your tongue. This reaction is the same one that would take when you combine soap with water.

Harold McGee wrote an article in The New York Times about the effects of alkalines. 

All this being said, I've only made ramen style noodles, not the hand pulled ones. Your best bet would be to try both and see whether there truly is a difference or not... but I imagine the most traditional method would be to use kansui or jian.