Pass Benchmark: 70% (21/30) • Standard: USCG NMC / 46 CFR

USCG Marine Electrical Systems (Set 40)

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Question 1 of 30

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?

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30 MCQs

#1 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? #2 If a three-phase induction motor malfunctions and drops to a single-phase (one supply line open), what would be the result? #3 What would be the most likely fault if a single-phase permanent split capacitor induction motor fails to start? #4 In testing a three-phase delta-connected winding for an open circuit using a ohmmeter, what must be done? #5 As shown in figure "A" of the illustration, with a digital multimeter set up as an ohmmeter, what set of readings would be consistent with an open in phase "C" of the single circuit, wye- connected stator windings as shown? EL-0201 #6 As shown in the illustrated diagnostic setup checking for a reversed field pole on a ten- pole synchronous motor, if a rotor is being checked after reassembly and the steel bolts repel each other as shown in the illustration, what condition is indicated? Illustration EL-0205 #7 What would happen if the centrifugal switch or relay, for cutting out the starting winding of a split-phase induction motor, failed to open while the motor was in operation? #8 As shown in figure "B" of the illustration, when the DC motor in figure "A" is operating at base speed what are the armature and field characteristics? Illustration EL-0153 #9 How may temporary repairs to an open DC propulsion armature coil be made, allowing continued operation until permanent repairs can be made? #10 What can insufficient brush pressure on a DC motor cause? #11 Which of the listed colors properly describes a DC motor commutator when correct commutation is taking place? #12 If a short circuit in the armature of a DC motor occurs what would be the result? #13 Besides a condition of overload, what could be a cause of an open armature connection in a DC propulsion motor? #14 An open in the armature of a DC motor is suspected, but is not found by visual inspection of the commutator. What would be the next step in troubleshooting this problem? #15 How is a short in the shunt field of a DC motor best located? #16 Which of the listed conditions might contribute to very rapid wearing of a DC machine's commutator bars? #17 In the illustrated motor controller, what do the contacts across terminals "3" and "4" of the control circuit represent? EL-0017 #18 As shown in the illustration, what is the purpose of the main contacts of contactor "1S"? EL-0012 #19 By what means is the rotation of a three-phase induction motor reversed? #20 Which of the following statements is true concerning the motor controller circuit shown in the illustration? EL-0004 #21 As shown in the illustration, what type of motor and motor starter are featured? EL-0137 #22 A three-phase, induction-type motor experiences an open in one phase. Which of the listed automatic protective devices will prevent the motor from being damaged? #23 Referring to figure "B" of the illustrated control circuit schematic diagram, which of the following statements is true when the motor is running in the forward direction? EL-0011 #24 As shown in the two-speed single winding three phase motor connection diagrams illustrated in figures "B", "C", and "D", what type of motor is shown in the motor controller circuit illustrated in figure "A"? EL-0118 #25 As shown in the illustration, using the instructions provided and Chart "A" and Table "24", what size overload relay heater would be the proper selection for the motor associated with the motor nameplate data shown assuming the motor operates at sea level and that the motor and its starter share the same ambient temperature? EL-0171 #26 As shown in the illustration, by what means are all the 'MS' contacts are opened and closed? EL-0073 #27 With what kind of starting equipment are most three-phase induction motors of five horsepower or less started? #28 As shown in the illustration, what type of motor is controlled as depicted in both figure "A" and in figure "B"? EL-0144 #29 Which of the following illustrated circuit schematics provides phase failure protection for a three phase motor using load side current sensing technology? EL-0222 #30 Which of the following statements is true concerning the cleaning of electrical contacts?

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