There are regulations that cover every viva at your university: strong ideas of what needs to happen at a viva.
There are viva expectations that filter out into common understanding: patterns, trends and descriptions that guide future candidates (and examiners) in their anticipation and preparation.
There are viva norms for your department or discipline: common ideas of practice for the viva and for what you need to have as a candidate, both on the day and in your past experience.
All of these aspects combine with you and your thesis to create a different viva every single time – and still you might expect your viva to be even more different from other vivas because of your personal circumstances, your specific thesis, your personal needs and more.
Get a sense of what might happen from regulations, expectations and norms. Get a sense of what you, your work and your situation might do to make changes from past experiences. Get a sense of what you might need to do or ask for to be ready.
A different viva doesn’t mean a difficult viva or anything worse.
PS: checking regulations is a good use of your time when you get to submission. There’s a lot you can do then to get ready and work towards viva prep. If you’re looking for more pre-viva support then take a look at The Submission Issue, the latest Viva Survivors Select collection, out this week, and featuring twenty posts from the archive and two original pages of help for £3.