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NCCER ELECTRICAL MODULE 2 LEVEL 2 MOTORS: THEORY AND APPLICATION EXAM | QUESTIONS & ANSWERS (VERIFIED) | LATEST UPDATE | GRADED At+ How DC motors operate? Correct Answer: Magnetic lines of force are continuous and always form closed loops; Magnetic lines of force do not cross. Armature: (Definition) Correct Answer: The rotating windings of a DC motor. The is a movable electromagnet located between the poles of another fixed permanent (field) magnet as shown. Correct Answer: Armature A twisting force called must be developed. is produced by mounting a loop in a fixed magnetic field and as long as the fields of the magnet and armature interact. Correct Answer: Torque Commentator: (Definition) Correct Answer: A device used on electric motors or generators to maintain a unidirectional current. In the neutral plane, no is produced and the rotation of the armature should stop Correct Answer: Torque A is produced by the fields poles, and a loop of wire in the armature turns and cuts this magnetic field, Correct Answer: Magnetic field CEMF Correct Answer: Counter electromotive force (CEMF) Horsepower: (Definition) Correct Answer: The rated output capacity of the motor. It is based on breakdown torque, which is the maximum torque a motor will develop without an abrupt drop in speed. Horsepower: (Equation) Correct Answer: Hp= Watts/746 Correct Answer: The speed of the revolving field of the stator, which is dependent on the supply frequency and number of poles in a stator winding. Field poles: (Definition) Correct Answer: The stationary portion of a DC motor that produces the magnetic field. The name of the motor part that rotates during operation is the 5 Correct Answer: Armature The principle reason for developing the brushless DC motor was to__. Correct Answer: eliminate commutator problems The electrical energy required to produce 1hp of mechanical energy is Correct Answer: 746W When there is a wide variation in both torque and speed requirements, such as a blower or hoist, use a Correct Answer: series DC motor The name of the stationary motor part that produces the magnetic field during operation is the 4 Correct Answer: stator The rpm of a 60Hz motor with two polesis___. Correct Answer: 3,600rpm In three-phase motors, the rotor most commonly used is the Correct Answer: squirrel cage rotor The starting torque characteristics of a wound-rotor motor are defined by Correct Answer: rotor resistance A three-phase synchronous motor is started with a(n) Correct Answer: amortisseur winding The speed of an induction motor depends on the power supply frequency andthe __. Correct Answer: numbers of poles The speed on a multiple-winding motor is normally changed by ; Correct Answer: switching contacts in the motor controller A consequent-pole motor has Correct Answer: two speeds Most industrial motors are NEMA Design : Correct Answer: B The multiplier to the nameplate horsepower rating is called the Correct Answer: service factor An insulation resistance test can be used to determine Correct Answer: whether a motor is damp The code requirements for motor disconnects are covered in : Correct Answer: 430.102 All motors must have a thermal protector if their voltage rating is greater than Correct Answer: 600V-1,000V To protect the motor from overloads and starting failures, use a : Correct Answer: thermal protector When studying the operation of electric motors, it is important to remember that magnetic lines of force__—. Correct Answer: do not cross Wh 48 A motor with the field coils connected in parallel with the rotor winding is a Correct Answer: shunt motor If a motor has 4 poles and is operating at a frequency of 60Hz, its synchronous speed is - 120(60Hz)/4= 1,800 rpm Correct Answer: 1,800 rpm| The type of motor most likely to be used in a location with flammable dust and torque fluctuations is a 4 Correct Answer: squirrel cage induction motor A type of motor used in precision applications that require constant speed with zero slip isa J Correct Answer: synchronous motor A heating system is most likely to use a Correct Answer: single-phase induction motor With a constant-torque load, the horsepower . Correct Answer: varies in direct proportion to the speed en variable-frequency speed control is used on a motor with a nameplate rating of \V at 6OHz, the voltage-to-frequency ratiois__. 480v/60hz=8 Per NEC Section 430.32, a motor with a service factor of 1.0 must trip at A Correct Answer: 115% of the full-load current The field coils of a series motor are connected in series with the : Correct Answer: armature A(n) is used to provide the switching action required for continuous DC motor rotation. Correct Answer: commutator The most common class of insulation used in manufacturing and rewinding is NEMA Correct Answer: class B Which type of motor requires brushes, slip rings, and an amortisseur winding? Correct Answer: Synchronous motor The difference between the synchronous speed and the rotor speed is known as Correct Answer: Slip What type of rotor is most commonly used in an induction motor? Correct Answer: Squirrel cage motor When a single motor is supplied from a branch circuit, the ampacity of the branch circuit must be of the motor full-load current as determined by NEC Section 430.6(A)(1) Correct Answer: no less than 12.5% How is the speed normally changed in a multiple-speed induction motor? Correct Answer: Change number of pole connections Name three conditions that can cause a synchronous motor to become out of step. Correct Answer: Excessive load applied to the shaft, Supply voltage reduced excessively, Motor excitation lost or too low ___ use dynamic braking. Correct Answer: Forklifts The most common service factor appearing on a motor nameplate is __. Correct Answer: 1.15 The four letters that designate insulation class are__,_, ___, and Correct Answer: A,B, F, andH A motor has three stator windings that are 120° apart. 
