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OES-4015 - Test 3 - AC Generators – HM
questions with answers
________ law summarizes the way voltage can be generated a) lenz' b) faraday's c) ohm's d) kirchoff's - .... 🔰 VERIFIED ANSWERS.... ✔✔ b) in an A/C generator, a ____ source is supplied to the rotating field coils - .... 🔰 VERIFIED ANSWERS.... ✔✔ DC In an AC generator, what is moved by the prime mover? a) rotor b) stator c) field coil magnets d) non of the above - .... 🔰 VERIFIED ANSWERS.... ✔✔ a) Ordinary household current in most of the world is ____v with __ cycles per second - .... 🔰 VERIFIED ANSWERS.... ✔✔ 230v, 50Hz Number of cycles per second is also called
a) peak b) cycle c) period d) frequency - .... 🔰 VERIFIED ANSWERS.... ✔✔ d) In the USA, household current is ___v with __ cycles per second
- .... 🔰 VERIFIED ANSWERS.... ✔✔ 130v, 60Hz The principles of a three phase generator vary drastically from single phase. T or F - .... 🔰 VERIFIED ANSWERS.... ✔✔ F they are the same basically Three phase generators contain how many windings? Placed at what angle out of phase with each other? a) 6, 60 b) 3, 60 c) 6, 120 d) 3, 120 - .... 🔰 VERIFIED ANSWERS.... ✔✔ d) Three phase generators can be connected in both Star and Wye connections
d) non of the above are classifications - .... 🔰 VERIFIED ANSWERS.... ✔✔ c) The revolving field type of A/C generator has a _________ armature/stator. - .... 🔰 VERIFIED ANSWERS.... ✔✔ Stationary High output voltages are available to A/C generators (11 800v - 13 800v) T or F - .... 🔰 VERIFIED ANSWERS.... ✔✔ T High output currents can be generated in the AC generator because a) speed of rotation is much faster b) sustained high frequency resonance c) many turns of ligh guage wire are used in the field poles d) heavy copper wire can be used in the stator - .... 🔰 VERIFIED ANSWERS.... ✔✔ d) In the standard synchronous design, the _______ carries the field windings and the _______ carries a set of three phase windings which form the armature. - .... 🔰 VERIFIED ANSWERS.... ✔✔ rotor, stator List 3 advantages of an A/C Generator (3) - .... 🔰 VERIFIED ANSWERS.... ✔✔ Simpler constructions
3 phase generators can be made A/C voltage is more easily distributed with transformers List 2 disadvantages of A/C generators (2) - .... 🔰 VERIFIED ANSWERS.... ✔✔ The electricity grid needs fine co-ordination to ensure that all generators are in phase with each other A/C current is significantly more dangerous than the equivalent D/C current in an electric shock List 2 advantages of D/C generators (2) - .... 🔰 VERIFIED ANSWERS.... ✔✔ A lot of devices rely on D/C currents for their operation At a given voltage a D/C current can be more powerful than the equivaleny A/C current List 3 disadvantages of D/C generators (3) - .... 🔰 VERIFIED ANSWERS.... ✔✔ More complex construction with split-ring commutator Sparking occurs in the gap of the commutator, wasting energy. D/C is more difficult to distribute efficiently.
a) AC b) DC - .... 🔰 VERIFIED ANSWERS.... ✔✔ b) The output is always induced in the rotor a) AC b) DC - .... 🔰 VERIFIED ANSWERS.... ✔✔ b) The output is induced in rotor or stator a) AC b) DC - .... 🔰 VERIFIED ANSWERS.... ✔✔ a) Brushes always remain in contact with smooth slip ring, leading to less wear with little to no chance of a short developing a) AC b) DC - .... 🔰 VERIFIED ANSWERS.... ✔✔ a) brush and commutator will wear out quickly and short circuits/arcing is likely after prolonged use a) AC b) DC - .... 🔰 VERIFIED ANSWERS.... ✔✔ b)
Requires more maintenance a) AC b) DC - .... 🔰 VERIFIED ANSWERS.... ✔✔ b) Requires less maintenance and is more reliable a) AC b) DC - .... 🔰 VERIFIED ANSWERS.... ✔✔ a) Current is generated in a rotor, if large current is needed rotor coils must be used a) AC b) DC - .... 🔰 VERIFIED ANSWERS.... ✔✔ b) rotor used to create magnetic field that induces current in the stator. Current is drawn using a fixed connection that is more reliable a) AC b) DC - .... 🔰 VERIFIED ANSWERS.... ✔✔ a) Can be made using many coils in a regular pattern around the armature resulting in a smooth output with a small "ripple" Advantage for equipment that requires steady voltage
Which of the following is not a type of rotor a) Non-salient pole b) Salient pole c) Guided pole d) Non-guided pole e) None of the above - .... 🔰 VERIFIED ANSWERS.... ✔✔ c) What type of rotor is used for rotation at high speed? a) Non-salient pole b) Salient pole c) Guided pole d) Non-guided pole e) None of the above - .... 🔰 VERIFIED ANSWERS.... ✔✔ a) What type of rotor is used for rotation at low speed? a) Non-salient pole b) Salient pole c) Guided pole d) Non-guided pole e) None of the above - .... 🔰 VERIFIED ANSWERS.... ✔✔ b)
non-salient rotor is also called a ________ rotor a) polar b) cubic c) cylindrical d) test - .... 🔰 VERIFIED ANSWERS.... ✔✔ c) Which rotor should be used for rotational speed under 1800 rpm a) cylindrical pole b) salient pole c) non-salient pole d) test pole - .... 🔰 VERIFIED ANSWERS.... ✔✔ b) Water turbines have low speed, so a _________ pole should be used - .... 🔰 VERIFIED ANSWERS.... ✔✔ salient Steam turbines have high speed, so a ________ pole should be used - .... 🔰 VERIFIED ANSWERS.... ✔✔ cylindrical / non-salient Label the Salient Pole Generator - .... 🔰 VERIFIED ANSWERS.... ✔✔ A) Stator Frame B) Rotor Field Winding C) Distributed Stator Winding D) Salient Pole E) Basement
Separated damper windings is provided Describe Cylindrical Type Rotor (8) - .... 🔰 VERIFIED ANSWERS.... ✔✔ Unslotted portion of the cylinder acts as poles hence poles as non projecting Air gap is uniform due to smooth cylindrical periphery Small diameter and large axial length is the feature Mechanically robust Preferred for high speed alternators Prime moved used are steam turbines, electric motors For same size, rating is higher than salient pole type Separate damper winding is not necessary What are the two main classifications to provide the rotor with DC voltage a) Rotary and Static b) Rotary and Brush c) Brush and Brushless
d) Shunt and Static - .... 🔰 VERIFIED ANSWERS.... ✔✔ a) What rotary method of DC supply to the rotor requires slip rings, commutator and brushes and requires periodic maintenance a) brush b) brushless c) shunt d) series - .... 🔰 VERIFIED ANSWERS.... ✔✔ a) What rotary method of DC supply to the rotor do not require slip- rings or brushes and are practically maintenance free a) brush b) brushless c) shunt d) series - .... 🔰 VERIFIED ANSWERS.... ✔✔ b) What static method of DC supply to the rotor requires operating field power from generator output voltage a) brush b) brushless c) shunt d) series - .... 🔰 VERIFIED ANSWERS.... ✔✔ c)
d) None of the above - .... 🔰 VERIFIED ANSWERS.... ✔✔ a) The magnitude of the AC voltage generated is controlled by the amount of __ __________ _________ creating the field. - .... 🔰 VERIFIED ANSWERS.... ✔✔ DC Exciting Current ____________ voltage regulators or static exciters are commonly used to control the field current and thereby accurately control generator terminal voltage. - .... 🔰 VERIFIED ANSWERS.... ✔✔ solid state The exciter is therefore is the "__________" of the generator control system. It is the power source that supplies the dc magnetizing current to the field windings of a synchronous generator thereby ultimately inducing ac voltage and current in the generator armature. - .... 🔰 VERIFIED ANSWERS.... ✔✔ Backbone You cannot hook up an A/C generator unless it is in __________ with the grid a) tolerance b) resonance c) phase d) all of the above - .... 🔰 VERIFIED ANSWERS.... ✔✔ c) What will happen if the generator is not in phase with the grid when you hook it up? - .... 🔰 VERIFIED ANSWERS.... ✔✔ huge
power surge which will result in huge sparks, and ultimately damage to the circuit breaker (the switch), and/or the generator. ______________ refers to the voltage stability, frequency stability and the absence of various forms of electrical noise a) power factor b) power quality c) power surge d) power stability - .... 🔰 VERIFIED ANSWERS.... ✔✔ b) Power companies are looking for AC current with what? a) high voltage peak b) low frequency oscilation c) high phase tolerance d) good sinusoidal shape - .... 🔰 VERIFIED ANSWERS.... ✔✔ d) DC generators and alternators have nearly the same losses!!!! T or F - .... 🔰 VERIFIED ANSWERS.... ✔✔ T Fixed or Stray power losses include: a) bearing losses
the dc field current and voltage and the maximum temperature rise When is an emf NOT generated a) when there is relative motion between the armature conductors and the field. b) in armature conductors when rotating in a magnetic field with stationary field poles. c) when a galvanic cell is created and electrons travel from cathode to anode d) in stationary armature conductors when the field poles rotate past the conductors. - .... 🔰 VERIFIED ANSWERS.... ✔✔ c) A/C generators do NOT use commutators to change voltage direction T or F - .... 🔰 VERIFIED ANSWERS.... ✔✔ T The kilovolt-ampere capacity and the low-voltage rating of Revolving Armature Alternator machines are usually rather small. T or F - .... 🔰 VERIFIED ANSWERS.... ✔✔ T
Which of the following is a characteristic of the revolving field alternator with stationary armature a) The field poles rotate inside the stator b) Higher voltages can be generated without insulation failure. c) Higher current values can be obtained without arcing or heat production at the brushes and slip rings. d) all of the above - .... 🔰 VERIFIED ANSWERS.... ✔✔ d) Name the two types rotors of revolving field generators (2) - .... 🔰 VERIFIED ANSWERS.... ✔✔ 1. The salient field rotor (used with slow-speed alternators up to 1800 r/min).
- The cylindrical field rotor (used for speeds from 1800 to 3600 r/min; most steam turbine-driven alternators have cylindrical rotors). How does the AC generator obtain it's field current a) External DC power supply b) External AC power supply c) Self Exictation d) None of the Above - .... 🔰 VERIFIED ANSWERS.... ✔✔ a) A commutator and brushes are used to take the excitation current from the external source to the field windings in an A/C generator.
