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Fuels Vol. 1 Unit 5
Motors and Controls
| Question | Answer |
|---|---|
| what are the main parts of a DC motor | armature, frame, and endbells |
| what are the components of the armature in a DC motor | laminated iron core, windings, and commutator |
| the raised part of each commutator segment is called a | riser |
| the coil ends from the armature windings are __ to the riser | soldered |
| what serves as means of support for the motor, protects the windings, and completes the magnetic circuit that causes the armature to spin the shaft? | frame |
| what is located within the frame and consists of pole pieces and field coils? | field assembly |
| what is contained within the frame or directly outside of the frame in a separate housing and consists of the brushes, brush holders, and springs? | brush assembly |
| whats primary function are to keep the armature in position, house the bearings and complete the frame? | endbells |
| the armature's magnetic field is attracted by the magnetic field around the pole pieces which cause the armature to | rotate |
| all motors operate on the basic principle of attracting or repelling what? | magnetic fields |
| what motors are classified by the way that the armature and field windings are connected to power? | DC motors |
| what type of motor has the entire current flow through both the field and armature windings, and is characterized by speed changes due to load and is used when high starting torque is required? | series motor |
| what type of motor has the field coils and armature connected in parallel for high resistance, and is used when constant speed is desired | shunt motor |
| what type of motor has both the advantages of high starting torque and good speed regulation under load? | compound motor |
| what are 3-phase induction AC motors comprised of? | stator, rotor, and endbells |
| in a 3-phase induction AC motor, what serves to house the stationary windings and provides an attachment point for the supply voltage | stator |
| the coils inside of the stator of a 3-phase induction AC motor are insulated from the core with treated paper called | fish paper |
| in a 3-phase induction AC motor, what is the rotating part of the motor that provides a point to convert electrical energy to mechanical energy and to attach the motor to the load using a shaft? | rotor |
| what are the 2 types of rotors used in 3-phase induction AC motor? | wire-wound and squirrel-cage type (cheaper & need less maintenance) |
| in smaller motors w/ less than 1 hp that may have the rotor cast in one piece and rotor bars at an angle to the shaft, what is this called? | skew, and the effect increases the torque of the motor |
| what rotor is the best choice when you need variable speed control and low starting current | wire-wound |
| a 3-phase induction motor depends on what for operation? | rotating magnetic field |
| what type of motor is usually a fraction of a hp and are used to operate devices such as washing machines, small pumps, dryers, and blowers? | split-phase motors |
| what is the main difference between single-phase motors and 3-phase motors? | single-phase motors require some starting means |
| the start windings and run windings of a split-phase motor are connected to power until the motor reaches what percentage of it maximum rpm | 75% |
| what cuts the start winding from operation after the motor has been started? | centrifugal switch |
| what motor is similar to the split-phase motor but has an intermittent type of capacitor connected in series w/ the start winding, and is usually rated from 1/6 to 1 hp and are used on compressors, pumps, fans, and machine tools? | capacitor-start motor |
| the power stored in the capacitor of what type of motor gives a greater starting torque than a basic split-phase motor? | capacitor-start motor |
| what is used to enable the current in the start winding to reach its maximum value before the current in the run winding reaches its maximum | capacitor |
| centrifugal switch contacts will close by __ __ so that the motor can be started again | spring pressure |
| a device that transfers energy from one circuit to another by electromagnetic induction | transformer |
| a __ __ transformer received electrical energy at 1 voltage and delivers it at a higher voltage and a __ __ transformer receives energy at one voltage and delivers it at a lower voltage | step-up, step-down |
| the ratio between the number of turns in the primary and the number of turns in the secondary windings determines the voltage ratio for | a transformer |
| what is the term for when the circuit is closed and the connection is made, full voltage from the supply power is applied? | "across-the-line" |
| what term refers to a device that reacts to excess motor current? | overload protection |
| what device is designed to protect the motor windings by interrupting the current flow when an overload situation exists? | overload protection |
| what is used to turn a small motor on or off? | toggle switch |
| what type of controller usually has a green start button and red stop button | pushbutton controller |
| the most common type of motor control that is operated magnetically and connects the motor across the line using an electromagnet to close the main or load contacts and provides a safe, convenient, and economical means for controlling an electric motor? | magnetic motor control |
| the magnetic contactor of a magnetic motor control is made up of what 3 sections? | operating/holding coil & armature, main & auxiliary contacts, and 3 line (L1, L2, L3) & 3 load terminals (T1, T2, T3) |
| what are placed on the stationary core of a magnetic contactor to provide a split-second time delay, preventing contact chatter and wear in the moving parts of the AC magnetic controls? | shaded rings |
| what are the two basic types of overload relays? | thermal and magnetic |
| the two types of thermal relays are | bimetallic and melting-alloy types |
| what are the parts of a magnetic overload relay? | a coil, piston, dashpot, and set of contacts |
| what is determined by the full load current (FLC) rating of the motor it protects? | size of an overload relay |
| what action pulls the contacts apart in an across-the-line magnetic starter? | spring tension and gravity |
| what portion of the overload relay contains the main or load contacts, the line terminals, the load terminals, and the heater coil? | load circuit |
| the determining factor as to the size of the motor it controls | load circuit |
| what is the portion of the magnetic starter that performs the function of starting, stopping, controlling, and protecting power and contains the holding coil, the reset contacts of the overload relay, and the auxiliary contacts? | control circuit |
| what type of control circuit receives its power from the incoming leads to the starter? | two-wire control circuit |
| what circuit uses the same components as the two-wire control circuit, except that the auxiliary contacts and stop-start station are introduced? | three wire control circuit |
| what action returns the buttons of a stop-start station to their original position? | spring |
| type of across-the-line magnetic starter that is used to control a 3-phase motor | 3-phase across-the-line magnetic starter |
| common types of automatic control devices are | float switches, pressure switches, thermostats, and photocells |
| 3 basic solid-state components are | diodes, transistor, and integrated circuits |
| a network of interconnected semi-conductors that condenses the circuitry into a single small unit to control and route electricity to any number of small and large components performing fuctions | integrated circuits |
| what provides a highly accurate method of motor starting and speed control? | solid-state starters |
| what factors such as physical location, ambient temp, duty, bearings, voltage, mechanical connection to load, and motor data plate info do you consider when deciding upon | motor selection |
| motor enclosure that has ventilation opening in the frame that permits the passage of outside air to cool over and around the windings | open |
| motor enclosure that is an open motor in which the vent slots are made to prevent liquids or solids from entering them except at indirect angles | splash-proof |
| motor enclosure that is built to prevent free passage of outside air; not airtight therefore it cannot be used in an explosive area | totally enclosed |
| open motor enclosure in which the ventilating openings are constructed so that drops of liquids or solid particles falling on the machine will not enter the motor | drip-proof |
| totally enclosed motor constructed so that it prevents water from entering even if applied in the form of a stream from a hose | waterproof |
| motor enclosure designed to withstand an internal explosion of the vapors or dust from the area in which they are used and is used in fuel systems | explosion-proof |
| maximum amount of ambient temp is | 40*C or 104*C |
| what motor component depends on its application to a load or its mounting plane, horizontal or vertical | bearings |
| whats objective is to increase the operating life span of rotating machinery | shaft alignment |
| what occurs when the centerlines of the motor and the driven equipment shafts are not in line w/ each other and is characterized by excessive vibration, noise, coupling and bearing temp increases, and premature bearing or coupling failure? | shaft misalignment |
| 3 types of motor misalignment | angular, parallel, and combination |
| kind of misalignment that occurs when the motor is set at an angle to the driven equipment | angular misalignment |
| kind of misalignment that occurs when the two shaft centerlines are parallel, but not in the same line | parallel misalignment |
| kind of misalignment that occurs when the motor shaft suffers from angular misalignment in addition to parallel misalignment | combination misalignment |
| machines that are aligned at what pre-operating condition are almost always out of alignment when operating temps are attained | "cold" |
| most common methods of attaching the motor shaft to the load are | pulleys, couplings, and gears |
| the first step in disconnecting a motor in a fuels area is to ensure that it is electrically isolated using your | lock-out/tag-out procedures and area well ventilated |
| what can be determined by multiplying the normal hp by the service factor | amount of overload a motor can safely carry without damage to the unit |
| air pressure for cleaning motors should not exceed | 25 psi nozzle pressure |
| never use what type of solvents for cleaning motors | flammable or toxic solvents |
| first thing to check when diagnosing an overhead motor is | restricted ventilation |
| what causes motor bearings to overheat and eventually causes bearing failure? | improper lubrication |
| what part of the movable core in a starter produces the most prominent noise and is embedded in part of the laminated magnetic structure? | shaded pole |
| 5 common malfunctions for motors are | will not start, run hot, stop running, operate w/ excessive noise, run slowly |
| what malfunction troubleshooting includes check for power failure, check for temporary overload failure, check for a faulty relay or other overload device, check for frozen bearings | motor stops running |
| what malfunction troubleshooting includes check for load blockage, check for overload, check rating of overload relay, check for deficient voltage, proper ventilation and lubrication and duty | motor runs hot |
| what malfunction troubleshooting includes check switches are on, check for blown fuses, check line voltage for failure, check for bad conductor | motor will not start |
| what malfunction troubleshooting includes check for dry/worn motor bearings, check rotor shaft for movement, check for rotor endplay,securely mounted on solid surface | motor operates w/ excessive noise |
| rotor endplay should not exceed | 1/32 to 1/16 of an inch |
| what motor malfunction troubleshooting includes check for deficient voltage supply, binding of bearings, faulty driven load, excessive motor slippage | motor operates slowly |
| when there is an open circuit, you must disconnect the power and use what to make point-to-point checks for continuity | multimeter |
| with the main disconnect of a ground circuit open, check with a what across each power phase to ground | an ammeter |
| if continuity exists across two conductors when the circuit is purposely open, the circuit is | shorted |
| what are designed to protect an electrical circuit from causing fire or irreparable damage to motors and their components? | fuses |
| if the heat generated by current flow reaches a predetermined temperature, the fuse's metal alloy will __ and __ the circiuit | melt, open |
| fuses are rated in both __ and __ | voltage and amerage |
| what are the two basic types of fuses? | plug and cartridge fuses |
| type of fuse used in low-capacity branch circuits only | plug fuse |
| two types of cartridge fuses | knife-blade and ferrule |
| cartridge fuse type that is used for high-capacity circuit protection | knife-blade fuses |
| since the purpose of the fuse is to protect the circuit, it must be the __ point of the circuit | weakest |
| fuses should be rated no higher than the __ rated component to be protected | lowest |
| what indicates that something in the circuit system went wrong and the problem must be corrected | blown fuse |
| to replace cartridge fuses, use a | fuse puller |
| what overload protection device trips when an overload condition exists | circuit breaker |
Created by:
Scottydick
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