Compressed air can be used to clean generator and motor windings provided the air is:

Using dry compressed air to clean generator and motor windings is essential to avoid damaging the electrical insulation and components. Moisture in the air can lead to corrosion, electrical short circuits, and reduced effectiveness in cleaning because it can cause dust and debris to clump together rather than being effectively removed. This is especially important in electrical equipment where moisture can adversely affect performance and reliability.

Moreover, dry air helps in dissipating static electricity that can build up during the cleaning process, thus ensuring that sensitive components are not harmed. Therefore, ensuring that the compressed air used is dry is fundamental to maintaining the integrity and functionality of generator and motor windings when performing cleaning operations. The other options may not provide the necessary conditions for effective and safe cleaning.