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motors
lesson 3 AC Alternators
| Question | Answer |
|---|---|
| An AC alternator is a synchronous machine that produces ? . | alternating current (AC) |
| A(n) ? is an alternator in which a fixed magnetic field is created in the stator, with the rotor turning within the stator, and AC power is supplied through the rotor slip rings and brushes. | revolving-rotor alternator |
| It is common for utilities that generate high-voltage power to use ? . | revolving-field alternators |
| A rectifier assembly mounted on the main rotor shaft along with the exciter generator is referred to as a(n) ? . | brushless exciter |
| what factor will not control the output voltage of an alternator? | The number of poles |
| The speed of a 6-pole AC generator operating on 60 hertz is ? . | 1,200 rpm s=(120xf)/poles |
| Though not the common practice today, 3-phase AC power can be generated by rotating three coils through the ? . | magnetic field |
| A(n) ? is the power source used to turn the rotor that creates the relative motion between the coil and the magnetic field. | prime mover |
| true/false Large alternators are often powered by steam turbines, which use natural gas, nuclear energy, coal, or oil as fuel to generate steam. | true |
| true/false Alternators are rated according to the maximum load they can withstand. | false alternators are rated according to the load they can maintain on a continuous basis. |
| Alternators are rated in kilowatts at a standard power factor of ? . | 80% |
| ? is often used to cool small AC alternators. | Air |
| If there is a(n) ? mismatch, a slowly turning alternator is a load to other alternators. | frequency |
| A ? can be used to match two alternators, or to help match the frequency and phase of an alternator to a busbar. | synchroscope |
| true/false In the 3-lights-out method of manual alternator synchronization, the phase connection is incorrect if the lights do not all turn on and off at the same time. | true |
| true/false With automatic synchronization, a controller monitors the frequency, phase angle, current of the incoming source, and current of the busbar. | false a controller monitors the frequency, phase angle, and Voltage of the incoming source and the busbar. |
| true/false In manual synchronization, it is easier for the alternator rotor to slow down than to speed up. | true |
| What is the first step in determining the correct size of a generator for an application? | List the electrical loads that must be operated by the generator. |
| Portable generators are rated by their maximum power output, surge power output, and ? output(s). | voltage |
| The ? output from an alternator or generator must be between +5%/−10% of the requirements for the load(s). | voltage |
| AC power is ? in the United States and Canada, and ? in Europe and other parts of the world. | 60 Hz / 50 Hz |
| At position ? of the sine wave, the rotor voltage has changed to its maximum negative value. | D |
| A portable generator is being specified for a job site where a one-horsepower compressor and a 200-ampere electric welder are to be operated. The recommended minimum-size generator (based on 25% additional power) for operating power should be ? . | 15,000 W |
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Yusosweet1