Pass Benchmark: 70% (21/30) • Standard: USCG NMC / 46 CFR
USCG Marine Electrical Systems (Set 22)
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Question 1 of 30
In testing a hand cranked megger prior to use, what statement is true?
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30 MCQs #1 In testing a hand cranked megger prior to use, what statement is true? #2 When a megohmmeter is being used to test insulation resistance, current leakage along the surface of the insulation is indicated by a very specific megohmmeter pointer movement. What would be the characteristic of the pointer movement under these conditions? #3 When a megohmmeter is used to test insulation, what condition causes the gradual rise of the pointer reading as a result of continued cranking? #4 In which of the situations listed will a megohmmeter give the most accurate readings? #5 What is the resistance reading at "1" on the megger scale illustrated in figure "A"? EL-0044 #6 What condition associated with a lead-acid battery cell can cause the plates to partially short-out and cause the cell to fail to hold a charge. #7 When troubleshooting a lead-acid storage battery, what is the best method for detecting a weak or dead cell? #8 As the electrolyte level in the cells of a lead-acid battery evaporates over time, what will tend to happen to the specific gravity of the electrolyte in the cells as the level drops due to evaporation? #9 What could prevent a lead-acid battery from accepting a full charge? #10 To determine the state of charge of a nickel-cadmium wet-cell storage battery during charging and discharging, what is the most reliable method? #11 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? #12 A split-phase induction squirrel-cage motor will not start and come up to speed, even though the rated voltage, rated frequency, and rated load are applied. Which of the following troubles would be suspected? #13 As shown in the illustrated diagnostic setup for locating a shorted field coil of a ten- pole synchronous motor, if 240 VAC 60-Hz is applied across the brushes, what would be the individual voltage drops measured across each field coil assuming that none of the field coils are shorted? EL-0202 #14 Grounds occurring in electrical machinery as a result of insulation failure may result from deterioration over time and excessive heat. What could be another contributing cause? #15 A lightly loaded three-phase squirrel-cage induction motor, while running, begins to vibrate excessively but continues to run. After shutting down the motor, the motor will not restart, but makes growling noises, overheats, and smokes. What caused this? #16 What would excessive sparking at the brushes of a running DC motor be an indication of? #17 If a D.C. motor hums, but does not run when energized, which of the listed conditions could exist? #18 Besides checking for grounds, for what other purpose can a megohmmeter be used on a DC motor? #19 What is the most effective method of locating a loose commutator bar in a D.C. motor? #20 How may temporary repairs to an open DC propulsion armature coil be made, allowing continued operation until permanent repairs can be made? #21 When using a megohmmeter to determine which shunt field coil is grounded in a DC machine, what must you do? #22 What can be the cause of excessive heat or burning contacts in an operating motor controller? #23 The motor fails to start on an attempted startup. With the start button depressed, a voltmeter reading between 1 and 5, as in figure "A" shown in the illustration, indicates line voltage available to the control circuit, what should be your next step in the troubleshooting process? Illustration EL-0007 #24 If the motor shown in the illustration will not start when the "off-run" switch is placed in the run position, which of the listed components should be checked FIRST? EL-0017 #25 As shown in figure "B" of the typical ground fault relay shown in the illustration, what statement concerning the leakage current setting adjustment is true? Illustration EL-0223 #26 In order to properly set up programmable motor protection, it is necessary to know the locked rotor current of a motor. Given the chart of code letters for locked-rotor kVA/HP and the necessary instructions shown in the illustration, calculate the estimated locked rotor current for the motor represented by the illustrated motor nameplate using a mid-range value for the code letter, assuming the motor is to run at 440 VAC. EL-0175
Illustration EL-0175: the U.S. Coast Guard has not released this illustration. #27 If the cooling water system is isolated for repairs, but it is still desirable to run the alternator pictured in figure "A" of the illustration, what must be done? Illustration EL-0037 #28 If a shipboard AC generator experiences a failure to produce a voltage, what may be the cause? #29 How can the loss of residual magnetism in an alternator or generator be corrected? #30 #1 SSDG was operating in parallel with #2 SSDG in supplying the 480 VAC main bus while sharing the electrical load evenly. As a result of a problem, if #1 SSDG begins to motorize, but the generator has not yet tripped out by the action of the reverse power relay, what would be the indication of this?
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