6-49. A high-speed, turbine-driven alternator is prevented from overheating  by  which  of  the following  safety  provisions? 1. An  alternator  used  with  other alternators that automatically goes off when it becomes warm 2. A forced air ventilation system that  circulates  air  through  the stator  and  rotor 3. A heat-limiting governor that controls  the  temperature 4. A metal structure surrounded by cold  water  that  encases  the alternator  parts 6-50. Turbines  that  drive  the  ships service  generators  receive  their energy  from  what  source? 1. Batteries 2. Diesel engines 3. Saturated steam 4. Superheated steam 6-51. Ships generators supply electricity at a constant voltage and frequency. For this to happen, what  condition  must  be  met? 1. A high-frequency output 2. A low-frequency output 3. The turbines must operate at a variable speed to meet demands of  variable  loads 4. The turbines must operate at a constant  speed  under  variable loads 6-52. Emergency generators are driven by diesel power rather than steam turbine  power  because  diesel engines  have  what  advantage? 1. They generate more power than turbines 2. They start faster than turbines 3. They are easier to operate than turbines 4. They are less of a fire hazard than  turbines 6-53. Special, closely regulated electrical  power  used  for  specific loads is furnished by which of the following  power  suppliers? 1. Turbine generator 2. Diesel generator 3. Motor generator 4. Ship’s  service  switchboard 6-54. Ship’s  service-generating  units  and 6-55. 6-56. 6-57. 6-58. their  associated  distribution switchboards  are  interconnected  to other distribution switchboards by what  circuit? 1. Short 2. Bypass 3. Bus  tie 4. Alternator During  load  changes,  the  automatic voltage  regulator  maintains  a constant  voltage  by  varying  the 1. armature   resistance 2. field  excitation 3. generator speed 4. governor  speed What device is used to isolate a faulty  circuit? 1. A resistor 2. A rectifier 3. A circuit breaker 4. A voltage regulator What device maintains the generator voltage  to  within  specified  limits? 1. A voltmeter 2. A voltage regulator 3. A circuit generator 4. A resistor regulator An ac motor has which of the following  advantages  over  a  dc motor? 1. It is larger 2. It  is  smaller 3. It  requires  less  power 4. It rotates at a faster speed 37