There are several approaches to time travel in general.
1. Deterministic universe
Everything is set in stone. A time traveller not only is incapable of changing anything but every 'change' of history (from their point of view) is pre-determined.
2. Change-resistant universe
A time-traveller is capable of changing things, however, this produces minimal effects. For example, if Hitler parents are killed and he is never born someone else takes his place. WWII, Holocaust, and so on still happen, just the name of the leader changes. But as the time passes the changes become smaller and smaller until they fully disappear.
3. Forking universe (multiverse)
This is the concept of alternative universes which can be created either by changes introduced by a time traveller or in a more general case by different outcomes of the same events. Potentially, there is an infinite number of universes some of which are almost the same as our own.
4. Single, change-weak universe
In this universe, all changes are 'instant' and do not produce any forks. The effects can be unpredictable and vary in scale. This is the 'butterfly-effect' type of universe.
5. Single universe with time waves
Same as #4 this universe does not fork. However, the changes slowly propagate through time, e.g. time travellers from the 23rd century will be affected earlier than time travellers from the 29th century.
I am highly doubtful if it is even possible for time waves like this to exist, but a similar concept is used, for example, in Legends of Tomorrow.
6. Some other universe
I am sure I forgot about some other general type of time-travel enabled universe :) Please fit it here.
A time traveller does not need any protection in universes #1 (no change is possible) and #3 (the time traveller never belongs to a changed universe, hence does not experience any effects on themselves or their records).
A time traveller from universes #2 and #4 needs to find a way either to be outside of time (time-stasis field, tachyon field, before the time [before the Big Bang] or whatever handwavium is in fashion today) or not to introduce any changes to the history at all. It is especially critical in the universe #4 since the consequences can be catastrophic. However, if #2 (change-resistant) has time waves (as #5) protection can be delayed and there can be a chance to restore history. On the other hand, it is not that important since everything repairs itself anyways.
The #5 universe is probably the trickiest. Depending on a time travellers origination point and a history change point different degrees of protection are needed. It might even be possible to outrun the wave. However, being outside of time is, as usual, the best option.
In recent TV series, Travelers, this problem is somewhat solved by sending only consciousness (no physical matter) in a form of a matrix that gets imposed onto a host's brain. They do not get into many details, but the idea is that a brain of a human is rewired with personality and knowledge of a time traveller. When the timeline changes matrixes do not change because they are already in the past. It still creates some paradoxes, but it is an attempt...