Is the use of 4-wire Pt-100 thermometers necessary for motors and transformers in a power station or the use 2-wire or 3-wire is sufficient to achieve an accuracy of 0.5%?
The quick answer is (and most power station applications do this ), 3 wire is just right. The 0.5% accuracy is due mostly to the power supply and the RTD.
Suggestion: Check the paperwork requirements that are governing the power station. The specific thermometer type may be required by the power station rules.