it has a 180w psu but the i3 7100 draws 51w

That's a really low power PSU.
It's proprietary too. With all of that it has 15A on the 12V rail which means that it has a max power output of 180W.

Since the tdp of the CPU is only 51W and the TDP of the GT 1030 is 30W, you're looking at a total system power consumption of under 100W. That PSU has a 80+ bronze rated efficiency(means it's not that crappy), so the GT 1030 will work.

Just make sure that you're buying a low profile version of the GT 1030, since the height of the case is low.