This happens as Excel has an autocorrect feature which automatically changes some text.

Here is how to disable it:
Go to File --> Options. In the Excel Options dialogue box, select proofing and click on AutoCorrect Options.

In the Autocorrect Options dialogue box, there would be a scroll bar. Scroll down and you would find hsa within Replace. Select it and delete it.

Now whenever you type hsa, it will not get converted to has automatically.

Here is a snapshot: https://www.dropbox.com/s/zwjfdmqrxt...20has.png?dl=0