The correct answer is C. Greater mechanical difficulties.
Direct water cooling of rotor winding presents greater mechanical difficulties than indirect water cooling. This is because direct water cooling requires the rotor to be made of a material that is compatible with water, such as stainless steel or titanium. Additionally, direct water cooling requires the use of special seals to prevent water from leaking into the rotor. These seals can be expensive and difficult to maintain.
Indirect water cooling, on the other hand, does not require the rotor to be made of a special material. Additionally, indirect water cooling does not require the use of special seals. This makes indirect water cooling a more cost-effective and reliable option than direct water cooling.
Here is a brief explanation of each option:
- Option A: No mechanical difficulties. This option is incorrect because direct water cooling of rotor winding presents greater mechanical difficulties than indirect water cooling.
- Option B: Lesser mechanical difficulties. This option is incorrect because direct water cooling of rotor winding presents greater mechanical difficulties than indirect water cooling.
- Option C: Greater mechanical difficulties. This option is correct because direct water cooling of rotor winding presents greater mechanical difficulties than indirect water cooling.
- Option D: None of the above. This option is incorrect because direct water cooling of rotor winding presents greater mechanical difficulties than indirect water cooling.