The standard way to tell the time when it’s X:30 is “half past X”. For example, 5:30 is “half past five”, 7:30 is “half past seven”, and so on (or, if precision is required, there’s nothing wrong with saying “five thirty”, “seven thirty”, etc.).
Brits, however, sometimes use expressions like “half five” or “half seven”. These can be quite confusing for speakers of Slavic and Germanic languages, who would expect the expression “half X” to mean “half before X”. For instance, halb sieben (literally “half seven”) means “half past six” (6:30) in German.
The expression is thought of in a different way in British English. “Half five” is just a colloquial way of saying “half past five”, with the word “past” being implied, i.e. an hour more than speakers of other languages would assume. To make the concept completely clear, take a look at the following examples:
half seven = half past seven = 7:30
half ten = half past ten = 10:30