In general, the same transition should not be used more than once in a paragraph. There are two main reasons for this. Firstly, it can become repetitive when a word or term is repeated in a paragraph. Secondly, transitions link ideas in specific ways. If the same transition is used repeatedly in a paragraph, it can become confusing. Consider the following poorly written example:
The new centrifuge is more effective than the old design. However, the old design is more durable and less expensive. However, the benefit of the improved results obtained from the new design outweighs these drawbacks.
In the above paragraph, the author seems to present one contrasting argument (sentence 2) followed by another one (sentence 3), each one introduced with “however”. The use of the same transition implies that each of these sentences presents a new argument, even though sentence 3 actually sums up the first two sentences. It could also leave the reader confused as to which argument contrasts with which, and which argument carries the most weight. Here is an improved version:
The new centrifuge is more effective than the old design. However, the old design is more durable and less expensive. Nevertheless, the benefit of the improved results obtained from the new design outweighs these drawbacks.
Here, the transition “nevertheless”, makes it clear that the final sentence does not present a new argument, but rather sums up the two arguments already presented, and states which one (the first) carries more weight.
Here is another example of repeated transition use (which reads poorly):
In this study, we aimed to test which of the two centrifuge designs was most efficient. In addition, we compared other attributes of the centrifuges, namely cost and durability. In addition, we conducted a literature review and compared our findings with previously published results.
In this paragraph, the repeated use of “in addition” sounds clumsy, and gives the impression that the authors had not thought through what they wanted to write before they wrote it. It sounds like the authors were having trouble remembering what they did, and kept remembering additional details, which they had forgotten to mention earlier, as they went along. Here is an improved version:
In this study, we aimed to test which of the two centrifuge designs was most efficient. In addition, we compared other attributes of the centrifuges, namely cost and durability. Finally, we conducted a literature review and compared our findings with previously published results.
In the improved version, the use of “finally” makes it clear that there was an order to what they did, and that the literature review and comparison of results was the last thing they did. It is much clearer that the authors had a clearly thought-out and well-reasoned plan, and that they still had this plan in mind when they wrote this paragraph.
It might occasionally be acceptable to use the same transition more than once in a paragraph, especially if the paragraph is much longer than the examples above, and the repeated transitions are far apart (one near the beginning of the paragraph and the other near the end). Look out for transitions in the next few well written papers you read and make note of how frequently the same one is repeated within one paragraph. When you find examples of repeated transitions in a paragraph, check whether they are confusing or clumsy, and if not, try and work out why.