JNE 314 Progress Check – Section # 2 AC Generators Sub-section 2.1 – General – Multiple choice questions. Choose the correct answer. 1. The principles behind the EMF generation are: a) Faraday’s Law and Flemings right hand rule on Electromagnetic Induction b) Fleming’s Law and Faraday’s right hand rule on Electromagnetic Induction c) Faraday’s Law and Lenz’s Law on Electromagnetic Induction d) Faraday’s Law, Flemings right hand rule and Lenz’s Law on Electromagnetic Induction 2. In a simple ‘one wire loop’ AC generator if you increase the rotational speed: a) The induced Voltage will increase b) The induced current will increase c) Both induced current and frequency will increase d) Both induced voltage and frequency will increase 3. The main difference between DC and AC generators is: a) In AC the magnet rotates while in DC it is stationary b) In AC the coil rotates while in DC it is stationary c) In DC the magnet rotates while in AC it is stationary d) None of the above 4. In a shunt DC generator: a) Excitation is through an electromagnet which is parallel to the armature b) Excitation is through a permanent magnet with residual magnetism c) Excitation is through an electromagnet which is in series to the armature d) Excitation is through an electromagnet which has residual magnetism 5. In a Compound DC generator: a) No load excitation is through the series winding and the on-load excitation is by the shunt winding b) No load excitation is through shunt winding and the on-load excitation is by the series winding c) No load excitation is through residual magnetism of shunt winding and the onload excitation is by the series d) No load excitation is through residual magnetism of series winding and the onload excitation is by the shunt6. Which statement describes Alternating Current and Voltage best? a) Alternating Current and Voltage can be represented by a Sine curve b) Alternating Current and Voltage is due to the sinusoidal wave pattern of electrons c) Alternating Current and Voltage can be represented by a rotating vector d) Alternating Current and Voltage is due to kinetic energy in electrons, resulting vibration like movement 7. In a 3-phase 440V, 60 Hz AC generator the maximum voltage developed is: a) 440V b) 622V c) 762V d) 691V 8. An AC generator is designed to develop 6.6 kV, 60 Hz. It is running at 1200 RPM. How many pole pairs are there in this machine? a) 6 b) 12 c) 3 d) 4 9. Which statement describes the geometrical degrees and electrical degrees accurately: a) There is no difference between electrical and geometrical degrees if the alternator has only 2 poles b) In one rotation geometrically there are 3600. Electrically, in one rotation of the rotor there are 7200 c) In an eight pole machine there are 7200 electrically in one rotation d) None of the above describes it accurately. 10. Generally the AC distribution on-board ships are: a) Pure resistive circuits with a lagging power factor b) Pure Inductive circuits with a lagging power factor c) Inductive + Resistive circuits with a leading power factor d) None of the aboveSub-section 2.2 – Generator Types, Operation and Protection 1. The excitation system of a Self-Excited Alternator is similar to that of a: a) DC Compounded generator. b) DC Shunt generator. c) DC Series generator. d) Brushless generator 2. In a self-excited Alternator, the excitation transformer: a) Primary 1 controls the on-load current b) Primary 1 controls the no-load voltage c) Primary 1 controls the no-load current d) Primary 1 controls the on-load voltage 3. The reactor coils of a self-excited alternator, a) Reacts to increase the inductance of the excitation system b) Split the phase of the generated EMF by 900 c) Counter act the capacitance created by the capacitors. d) Add magnetic flux necessary for excitation 4. The capacitors of a self-excited alternator, e) Compensate the temperature variations of the excitation system f) Split the phase of the generated EMF by 900 g) Counter act the inductance created by the reactor coils. h) Does all the above 5. In a brushless alternator, we have: a) Two rotating magnets and two stationary coils b) Two rotating coils and two stationary magnets c) One rotating coil and two stationary magnets d) None of the above 6. Which of the following statements is incorrect? a) A brushless alternator essentially requires an AVR b) A brushless alternator does generate voltage when one diode fails c) A self-excited generator essentially requires an AVRd) A self-excited alternator does generate voltage when one diode fails 7. Self-excited alternator is still preferred for certain marine installation because: a) It has a simple construction and is inexpensive than a brushless generator b) It can function without an AVR c) It has a rotary exciter d) None of the above 8. When a healthy brushless alternator is starting: a) The voltage initially builds up due to the gradual speed increase of the prime mover and then it is controlled by the AVR unit b) The voltage initially builds up due to the residual magnetism and then it is controlled by the AVR unit c) The voltage initially builds up by the AVR unit d) All above can happen 9. We have a situation that an incoming alternator cannot be switched on to the bus bars after proper synchronising. What can be the most likely reason? a) Incomer ACB is faulty b) Incomer AVR is faulty c) The synchroscope is faulty d) Incomer Governor is faulty 10. Two alternators with similar governor droop are running parallel sharing load equally. They are not on auto power management. What happens if you increase fuel to No. 1 alternator? a) The frequency of No. 1 alternator will increase b) The frequency of No. 2 alternator will decrease c) The system frequency will increase. d) The system frequency will remain same. 11. An Alternator is feeding a bus bar. When an Induction motor is connected to this bus bar a) The prime mover slows down due to kW load and the voltage dips due to kVAr load b) The governor responds to increase the frequency and the voltagec) The prime mover slows down due to kVAr load and the voltage dips due to kW load. d) The governor responds to increases the voltage and current 12. A Chief Engineer /ETO can test the reverse power (RP) protection of an alternator by: a) Injecting a reverse current to the RP relay b) Increasing the load to the alternator gradually by switching on various loads c) Reducing the load of the alternator below zero load d) Chief Engineer / ETO cannot test the RP relay as it must be done by an authorised technician. 13. The synchronous compensator of a shaft generator: a) Regulates the frequency and voltage b) Corrects the power factor and provides the reactive power for the loads c) Provides the load kW’s at unity power factor d) All of the above 14. On starting a brushless alternator it was observed that the voltage was only 435V instead of the rated 440V. What cannot be a reason for this: a) The excitation adjustment is turned down b) The volt meter is faulty c) AVR is faulty d) Prime mover RPM is 895 instead of 900 15. A 440V 60 Hz brushless alternator has to be IR tested. Assuming that all windings of the exciter and the main alternator can be separated, how many IR readings need to be recorded? a) 8 b) 12 c) 14 d) 16Sub-section 1.3 – Alternator Maintenance 1. What would be IR tester setting for a 440V stator of an alternator? a) 250V b) 500V c) 1000V d) 2000V. 2. What would be the over current instantaneous setting for an ACB fitted to ac 440V 1000A alternator: a) 1000A for 20 seconds b) 1000A for 1 second c) 1500A for 15 seconds d) 1500A for 1 second 3. An electric propulsion cruise ship’s alternator is driven by a gas turbine. The Reverse Power setting for this must be: a) 2 – 3 % for 3 seconds. b) 5 – 15 % for 3 seconds c) 2 – 3 % for 5 seconds d) 5 – 15 % for 3 seconds 4. When inspecting an ACB for maintenance, if everything else is healthy: a) Arcing contacts must be replaced as necessary and main contacts must be polished b) Arcing contacts and arc chutes must be replaced as necessary and main contacts must be polished c) Arcing contacts, arc chutes and main contacts must be inspected and replaced as necessary d) Only the arcing contacts are inspected and replaced as necessary. 5. When you rack out and draw the ACB to test position: a) There is no power in the ACB as both the alternator side and the Busbar side are disconnected b) There is power in ACB although both the alternator side and the Busbar side are disconnected c) You need to keep the generator running if you need to test the reverse power protection d) It is safe to touch the interior of the ACB, as there is no supply to it.