Elex Module 5

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ELECTRONIC S MODULE 6

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Transcript of Elex Module 5

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electronics module 6AC In electrical machines, what type of voltage is generated at the armature winding?To reduce eddy currents What is the purpose of laminating the field poles and armature of a dc machine?Greater than An alternator with a lagging power factor of 0.8 will have a __________ voltage regulation at unity power factor.Changing the rpm of the prime movers With alternators connected in parallel, the frequency of the system can be changed by _________.Changing the field excitation With alternators connected in parallel, the voltage of the system can be changed by __________.Series Among the DC motors, which produces the highest torque?Shunt DC motors that has the most stable speed?Becomes maximum When a DC motor has no load, what will happen to the back emf?load The running speed of a dc series motor is greatly affected by what factor?The motor will over speed What will happen to a dc series motor when its load is removed?DC shunt In applications where an almost constant speed is required, a _______ motor is a good choice.Copper loss In dc motors, power loss is contributed greatly by _________.Theres still a low back emf Why do motors take large current during starting?Copper loss With transformer, what is measured when performing open-circuit test?Low - voltage Open-circuit test with transformers is always done on what winding?High - voltage Short-circuit test with transformers is always done on what winding?constant loss For transformers, maximum efficiency happens when copper loss is equal to ____________.Almost equal as that of secondary In transformers, the amount of copper used in the primary is _________.To decrease eddy current loss What is the purpose of laminating the core of a transformer?Eddy-current damping What damping method is most commonly used in induction type ammeters?Dc and ac Where can we use dynamometer?Maxwell bridgeThis refers to a four-arm ac bridge used for measuring inductance against a standard capacitance.underdamped When the meter is insufficiently damped, it is considered as ________.High, low Lap windings are used in high _______, and low ________ applications.speed What motor characteristic is affected by counter emf?Faradays first law Whenever the flux linking a coil or current changes , an emf is induced in itspeed What motor characteristic is affected by counter emf?Electromagnetic induction Voltage produced in a coil due to the relative motion between the coil & magnetic lines of force.By reversing either field or armature connections In a dc motor that must be able to rotate in both directions, how is the direction changed? Motor will slow down What is the effect on motor speed if the field current is increased?Opposite the rotation Armature reaction in a dc motor causes a shift of the neutral plane in which direction? By varying the voltage applied to the field windings How is output voltage controlled in practical alternators?They operate on either ac or dc Why are series motors sometimes called universal motors?Reciprocating Pump Which of the following is best driven by DC compound motors?Cranes and Hoists0.5 ohms The typical armature resistance is _________.Electrodynamometer Measuring instrument uses the interaction of the magnetic fields of two coils to measure current or voltage or powerIncomplete ChargingTrickle charging is result of ________.Wein bridge What has series RC combination in one arm and a parallel RC combination in the adjoining arm and used as a notch filter in harmonic distortion analyzer Lead-AntimonySediments that will be suspended below the lead-acid battery due to sulphation is _______.Two conductors separated by a dielectricCapacitors are __________.Float chargingWhat refers to a method in which the charger and the battery are always connected to each other for applying current to a loadSwinburnes testThe most economical test for efficiency in motors is __________.90 degreesIn electric machines, j refers to how many electrical degrees.Band RejectA filter that rejects the band of frequencies between cut-off points and either passes the signals outside the band. 270 electrical degreesIn 6-phase electrical machines, 90 mechanical degrees is ________.The field/armature windingsIn DC shunt motor, if the rotation is reversed, you will interchanged eitherIt will not build-upIf critical armature resistance is surpassed, the motor ________.CumulativeVoltage build-up in motors is ________.ScottIt is a power transformer that is used for transformation from 3 to 2 phase.Semi-convertorIf a converter contains some semiconductor elements aside from mechanical....Core lossOpen circuit test is used to measure ________.More and highSeries winding has _____turns and _______ resitance than ..Fields Test Traction induction motors efficiency is measured through ______.Bench 45 degrees RMS voltages are measured in what electrical degrees ________.Dependent to frequency Speed of dc motors is _________.zero Ideal voltage regulator has voltage regulation of ________.Hysteresis motor What type of motor efficiently used a phenomenon which is undesirable to them?Inductors and capacitors Transients usually occur due to _______.Resistance, inductance, and capacitance Double transients occurs in what type of circuit?Electrical input The efficiency of electrical machines is due to ______.An open armature coil Intermittent sparking at the brushes of dc motor may be caused due to _______.kelvin It is often necessary to make rapid measurements of low resistances. What basic bridge circuit is suited for this type of measurent?Zero percent _________ load regulation is considered ideal for a power supply.Armature winding The real working part of a dc machine is the _________.Ward-leonard system Combination of ac motor, dc generator, and exciter to provide adjustable voltage dc power to a dc motor.860 kcal 1 kWh is equivalent to ________.Nine times When current through the operating coil of a moving-iron instruments is tripled the operating power increases.Primary may burn out When the primary of a transformer is connected to a dc supply....Squared Moving-iron instruments has what scale?4 A 4-pole dc machine has _____ magnetic circuits?series For 20% increase in current, the motor that will give the greatest increase in torque is _______ motor.Terminal voltage drop considerably with load The main drawback of a dc shunt generators is that _____.interpoles What is used to counteract armature reactions?Hay bridge What bridge is used to measure high-Q inductors?Inductance with large phase angle What does heaviside-campbell bridge measure?There is a relative motion between conducting wires and magnetic lines of force Generation of voltage in a generator can only happen when...Alternating current In electrical machines, what type of voltage is generated at the armature winding.It prevents hunting In alternators, what is the purpose of damper windings?Armature winding To minimize arcing during starting of dc motors, a resistance should be added to limit the current in the _______.Friction loss One of the causes why the shaft torque is less than the developed armature torque of a dc motor.The number of watts being used at the time A utility meters motor speed depends directly on...It is because losses are rated in kVA Why is it that the motors are rated in kVa?Draws less current from the circuit under test The main advantage of a FETVM over a conventional voltmeter is the fact that the FETVM A small change in the resistance to be measured Which of the following will not normally cause a large error in an ohmmeter reading?The electromagnet meter is more rugged An important advantage of an electromagnet-type meter over a permanent-magnet meter is the fact that ______.energy A utility meters readout indicates _____.Is a quick-break type Suppose you see a fuse with nothing but a straight wire inside. You can assume that the fuse ______.Connecting multiple diodes in parallel, with low-value resistors in series with each diode In order to minimize the risk of diode destruction as a result of surge current, which of the following can be useful?Leave it alone and have a professional work on it To repair a damaged power supply with which you are not completely familiar, you should ______.Armature winding The real working part of a dc machine is the ________.Controlling force A moving system force in analog instruments which ensures that the deflection of the pointer for a given value of measured quantity has the same value.A closed one The main requirements for the armature winding of a dc machine is, it should be ________.cranes A dc series motor is most suitable forIt is economical What is the advantage of Swinburne's test?Inversely proportional to the supply frequencyThe maximum flux produced in the core of a transformer is...Back emf is high A motor takes a large current at starting because _______.keep it fresh and fully charged Trickle charging of a storage battery helps toleading A transformer has a negative voltage regulation when its load power factor is ________.Because it has almost the same potential Why is it that earth ground is usually used as an electrical ground.Closed one It is a requirement for DC motors that they should be a __________.0.707 Cut-off response in RC filter attenuates voltage level by ________.45 degrees Half-power bandwidth in RC filters describes phase shift of ________.-40 dB / decade In RC filter, -12 db/octave attenuation is equal to ________.Armature current multiplied to back emf Efficiency in DC motors is ________.They operate in different power factor When Induction motors uses AC machines having different impedance triangle.0 to 1 Power factor in AC machines ranges from ________.negative The power factor for over-compounded motors is always _______.Keep it fresh and fully charged Trickle charging is used for lead acid battery to ________.Commutation What limits the induced emf in dc motors.Induced emf What parameter stays the same every time we have to reverse the supply in motors.Reverse power supply sequence When we found out that a self induced motor does not work at the first attempt, what should we do.TT provides true 3-phase, 4 wire system What is the advantage of T-T system over the V-V connection.Sinusoidal Induced emf in the coil in generators is _______.Different waveforms Non-periodic signal is composed of ________.It provides smooth, quieter operation What is the advantage of using Ward-Leonard sytem.stable The purpose of using equalizers in dc motors is to make the output waveform _______.undamped The type of dc motor that does not need an equalizer is ________.Low at light loads only Power factor characteristic of an induction motors is _________.Cut-off What refers to the point where RC filter does not respond at all to incoming signals.De - sauty An AC bridge that is used to compare dielectric strength in two or more capacitances.Maxwelll - wein Anderson Bridge is modification of ______.recording kWh meter is what type of an instrument.Worn bearings Low induced emf in motors is due to ________.sparking Interpole winding in dc motors is used to prevent _______ between the coils.Rate of discharge The capacity of the cell depends on the following EXCEPT one.Full pitch What classification of winding pitch in the armature of dc generator where the coil span is exactly 180 degrees?Speed-torque What characteristic is considered in choosing a motor for a particular application?Differentially compounded What motor whose speed increases as the load is increased?load What determines the running speed of a DC series motor?Flat - compounded A DC compound generator having full-load terminal voltage equal to the no-load voltage is called ________ generator.To decrease the total flux What is the effect of armature reaction?By the use of interpoles How to compensate the distortion of the main field by interaction with the armature field?Speed of rotation and number of poles What are the two factors determine the frequency of the output voltage of an alternator?load What determines the amount of slip in an induction motor?Armature current What current flows in the interpole windings?Intermittent sparking _________ is the effect when an armature in DC motor opens.Synchronous motor Refers to a DC motor generator with common field coils for both motor and generator.There is still a low back emf Why do motors take large current during starting?Cumulatively compounded motor What motor is best choice in applications where sudden heavy loads happen for short duration?twice How many times should induction motors. For stable voltage outputSemi-converter If a converter contains some diodes and switching devices, it is called as ______.Lower the dc level of the output Thyristors in DC machines is used to _______.decibels Power level in usually expressed in _______.anderson _________ bridge is used to measure inductance in terms of known capacitance and inductance.1/4 If a heater rated 220 V used 110 V ac mains, the power dissipated will be ______.2nd, 4th, 3rd, etc. In a Fourier series, waveforms having the same phase are the ff:parallel To have a maximum power, equipments should be connected in _______.1333 kW It is noted that 25% of the power in device was dissipated resulting to useful energy of only 1000 kW, what was the original power?Rotor cu loss / rotor input The efficiency of the motor is the ratio of ________.Electrical input power The true source of mechanical power in dc motors is the _________.Load current in the armature The true working parameter in a motor is the _______.Series Which is WRONG? A schrage motor function as a _______.compound A motor which characterize with having large starting torque and constant speed which is useful to crushers.Constant speed operation Ward Leonard system is not applicable for _______.Synchronous motor It a motor where the stator and rotor windings is in synchronism.Ampere -hour The capacity of battery is usually expressed in _______.Mutual flux Which is not considered as basic component for transformers.inductance Hay bridge is used to measure ______. zero Ideal voltage regulator has ______ voltage regulation.Magnetic induction Generators convert mechanical motion to electrical energy using what principle?The left hand rule for generators What rule should you use to determine the direction of induced emf in a coil?Parallel operation What term applies to the use of two or more generators to supply a common load?No flux lines are cut Why is no emf induced in a rotating coil when it passes through the neutral plane?Direction of armature current, and direction of magnetic flux in field What factors determine the direction of rotation in a dc motor?four How many commutator segments are required in a two-coil generator? by varying the input voltage to the field coils How can field strength be varied in a practical dc generator?Improper commutation What causes sparking between the brushes and the commutator?Distortion of the main field due to the effects of armature currents What is armature reaction?Speed What motor characteristics is affected by counter emf?It must have a load connected to avoid damage from excess speed What is the main disadvantage of a series motor?Rotating armature and rotating field What are the two basic types of alternators?To provide dc current for the rotating field Most large alternators have a small dc generator built into them. What is its purpose?slip The speed of the rotor is always somewhat less than the speed of the rotating field. What is the difference called? load What determines the amount of slip in an induction motorSingle phase induction motor What type of ac motor is most widely used?Series, synchronous, induction What are the three basic types of ac motors?To power small appliances Series motors are generally used to operate what type of equipment?They operate on either ac or dc Why are series motors sometimes called universal motors?Armature current What current flows in the interpole windings?Intermittent sparking _________ is the effect when an armature in DC motor opens.Synchronous motor Refers to a DC motor generator with common field coils for both motor and generator.There is still a low back emf Why do motors take large current during starting?Cumulatively compounded motor What motor is best choice in applications where sudden heavy loads happen for short duration?twice How many times should induction motors. For stable voltage output45 degrees RMS voltages are measured in what electrical degrees ________.Dependent to frequency Speed of dc motors is _________.zero Ideal voltage regulator has voltage regulation of ________.Hysteresis motor What type of motor efficiently used a phenomenon which is undesirable to them?Inductors and capacitors Transients usually occur due to _______.Resistance, inductance, and capacitance Double transients occurs in what type of circuit?Electrical input The efficiency of electrical machines is due to ______.An open armature coil Intermittent sparking at the brushes of dc motor may be caused due to _______.Only outside of coils cut flux (inefficient) Why is the gramme-ring armature not more widely used?Resistance in the armature coils, which increases with temperature What causes copper losses?By laminating the core material How can eddy current be reduced?Motor will slow down What is the effect on motor speed if the field current is increased?Higher load currents are possibleLap winding are used in generators designed for what type of application?constant loss For transformers, maximum efficiency happens when copper loss is equal to ____________.Almost equal as that of secondary In transformers, the amount of copper used in the primary is _________.To decrease eddy current loss What is the purpose of laminating the core of a transformer?Eddy-current damping What damping method is most commonly used in induction type ammeters?Dc and ac Where can we use dynamometer?Maxwell bridgeThis refers to a four-arm ac bridge used for measuring inductance against a standard capacitance.