Pass Benchmark: 70% (21/30) • Standard: USCG NMC / 46 CFR
USCG Marine Electrical Systems (Set 2)
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Question 1 of 30
What causes the rotor of a synchronous motor to operate in synchronism with the rotating field?
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30 MCQs #1 What causes the rotor of a synchronous motor to operate in synchronism with the rotating field? #2 What is the function of the squirrel cage windings installed on a synchronous motor rotor? #3 What is the most common source of excitation for the rotor of a synchronous motor? #4 What is the purpose of the squirrel-cage windings included as part of a synchronous motor? #5 For what purpose is the variable resistance placed in the rotor circuit of a wound-rotor induction motor provided? #6 As shown in the illustrated wound-rotor induction motor how is the direction of rotation of the motor reversed? Illustration EL-0148
Illustration EL-0148: the U.S. Coast Guard has not released this illustration. #7 What is the characteristic of a wound-rotor induction motor, with a high resistance inserted in series with the rotor winding at startup? #8 What is the characteristic of an wound rotor induction motor with maximum rheostat resistance inserted in the rotor circuit during starting? #9 9. When performing routine A.C. motor maintenance what should be included? #10 When performing routine A.C. motor maintenance what should be included? #11 What is a useful instrument for checking 3 phase A.C. motor performance by measuring possible unbalanced currents? #12 For what reason should engine room watch standers keep a constant check on the loads carried by electric motors? #13 Which of the following statements represents the FIRST step in seating new brushes on slip rings? #14 By periodically checking the stator-to-rotor air gap clearance in an induction motor with a feeler gauge, what is prevented? #15 A digital multimeter is set up as shown in the illustration to evaluate the single-circuit stator windings of a squirrel cage induction three-phase motor. The following readings are taken: From T1 to T2 reads "OL" ohms. From T2 to T3 reads "OL" ohms. From T3 to T1 as shown reads "1.6" ohms. What condition is indicated? Illustration EL-0219 #16 What would be the effect of carrying field excitation excessively high on a synchronous motor? #17 A single-phase capacitor-start induction motor starts, comes up to about 75% rated speed, slows down to a lower speed, and accelerates again. Where is the problem most likely to be? #18 If the centrifugal switch or relay used for cutting out the starting winding of a split-phase induction motor fails to open once the motor is in operation, what will be the result? #19 Which of the following methods should be used to test for an 'open' stator winding coil in a wye-connected AC squirrel cage induction motor? #20 If a three-phase induction motor is operated under a light load and it develops an open in one of its supply lines, what will be the result? #21 1. (1.1.1.As shown in figure "B" of the illustration, with a digital multimeter set up as an ohmmeter, what set of readings would be consistent with an open in a phase of the single circuit, delta-connected stator windings as shown? Illustration EL-0201 #22 The leads from a ohmmeter are attached to the leads of the opposite ends of an AC motor stator field coil. If a reading of infinity is obtained, what does this indicate? #23 If a single-phase capacitor start induction motor fails to start, but instead hums without starting, what is most likely to be the problem? #24 In testing a three-phase delta-connected winding for an open circuit using a ohmmeter, what must be done? #25 When testing the rotor of a synchronous motor for short circuits, a low voltage source is applied across the rotor coils through the collector rings. What would be the indication of a short- circuited coil? #26 In using a portable growler for the purpose of locating a shorted stator coil in an AC motor as shown in the illustration, what statement is true as the feeler is moved from slot to slot around the stator? Illustration EL-0200 #27 When troubleshooting AC motors, what can a portable growler be used to locate? #28 Which of the listed instruments can be best used to locate a grounded field coil in a synchronous motor onboard ship? #29 How does the resistance of a conductor vary? #30 In a three-phase circuit, how far apart are the phase voltages?
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