I recently received a rather new Lenovo Thinkpad Ultrabook for free because the machine running Windows would shut down after 30 minutes exactly. It was running Windows and I thought it was a problem with Windows, well…
Installing Linux, it would shut down after 30 minutes exactly.
On AC, Battery, or AC with no battery, it shut down after 30 minutes exactly.
In just the BIOS screen (no Operating System loaded), it shut down after 30 minutes exactly.
Updating the BIOS to the latest version, it still shut down after 30 minutes.
Verdict – Hardware
There are many forums discussing this topic across Lenovo and some will say “[SOLVED]”, but that is just because the post became stale. From what I can see, there is no solution to this and trying to fix it will be a waste of time. I believe this is only affecting older laptops so if you are reading this, you are probably out of warranty. But if you are in warranty, return the laptop. If you are out of warrant, get a new laptop.
References
Do a Google search for Lenovo shutting down after 30 minutes. I went through mostly all of the results.
Man and Keyboard 
This sounds like an Intel ME (Management Engine) related issue, since it has internal timeout for 30 minutes if it’s initialization failed.
Hope this information can help in your further investigation.
I deleted all partitions and installed windows 10. My laptop keeps on shutting down in exactly 30 minutes since then. I guess, stock partitions and settings should not be changed