How can I prevent Windows OS from entering Sleep mode - .Net [duplicate]

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• Disabling Screen Saver and Power Options in C# 1 answer

Using C#, how can I prevent Windows OS from entering Sleep mode?

I know, that I can turn Sleep Mode off, that is what I do now. This question is about preventing the OS from Sleeing while a program is in a long running operation. Afterwards, entering Sleep mode shall be reenabled again.