Synchronous Machine Question & Answers October 8, 2026 By Dave Synchronous machines are an important part of electrical power systems and electrical engineering applications. They are widely used as alternators for electrical power generation and as synchronous motors for industrial drives and power-factor improvement. A thorough understanding of their construction, operating principles, characteristics, performance, and applications is essential for students of Electrical and Electronic Engineering. This article presents 150 multiple-choice questions (MCQs) on Synchronous Machines, covering major topics from the syllabus, including construction, salient-pole and cylindrical-rotor machines, working principles, generated EMF and its equation, pitch factor, distribution factor, armature reaction, synchronous impedance and reactance, voltage regulation and its methods, phasor diagrams, short-circuit ratio, parallel operation, synchronization, synchronizing power, power-angle characteristics, synchronous generators and motors, starting methods, V-curves, inverted V-curves, power-factor control, synchronous condensers, hunting, and damper windings. The questions are designed to strengthen conceptual understanding as well as provide practice for semester examinations, competitive examinations, viva-voce, and technical assessments. Each question contains four options, followed by the correct answer, allowing learners to test their knowledge and identify areas that require further study. The collection progresses across the major aspects of synchronous machines and provides a comprehensive revision resource for Electrical and Electronic Engineering students. 1). Which part of a synchronous machine carries the DC field winding? Stator Rotor Armature core Terminal box None Hint 2). In a conventional synchronous generator, the armature winding is generally placed on the: Rotor Stator Shaft Damper bars None Hint 3). The main purpose of laminating the stator core is to reduce? Copper loss Mechanical loss Eddy-current loss Field loss None Hint 4). The rotor of a synchronous machine is mechanically connected to the? Armature winding Prime mover or mechanical load Neutral conductor Excitation transformer only None Hint 5). The field winding of a synchronous machine is supplied with? AC DC Pulsating current only High-frequency current None Hint 6). Slip rings in a synchronous generator are primarily used to? Supply DC excitation to the rotor Reduce armature resistance Carry armature current Improve power factor automatically None Hint 7). Which component provides mechanical support for the rotating assembly? Rotor shaft Stator slot Armature conductor Pole shoe only None Hint 8). The air gap in a synchronous machine is provided between the? Field winding and damper winding Stator and rotor Shaft and bearings Pole shoe and pole coil None Hint 9). A salient-pole rotor is characterized by? Smooth cylindrical surface Projecting poles No field winding Permanent magnets only None Hint 10). Cylindrical-rotor synchronous machines are particularly suitable for? Low-speed hydroelectric plants High-speed turbo-generators Small DC motors Stepper motors None Hint 11). Salient-pole generators are commonly used in hydroelectric stations because hydro turbines generally operate at? Very high speed Low speed Zero speed Constantly varying speed None Hint 12). The rotor of a turbo-alternator is usually? Salient-pole type Cylindrical type Squirrel-cage type Reluctance type None Hint 13). A salient-pole rotor normally has a relatively? Small number of poles Large number of poles Zero number of poles Single pole None Hint 14). The cylindrical rotor generally has field conductors placed in? Rotor slots Stator teeth only Damper bars Bearings None Hint 15). In a salient-pole machine, the air gap is generally? Uniform Non-uniform Zero Infinite None Hint 16). The ratio of rotor diameter to axial length is generally larger in? Cylindrical-rotor machines Salient-pole machines Induction motors Transformers None Hint 17). A synchronous generator converts? Electrical energy into heat Mechanical energy into electrical energy Electrical energy into chemical energy Mechanical energy into magnetic energy only None Hint 18). The basic principle of operation of an alternator is based on? Faraday's law of electromagnetic induction Coulomb's law Ohm's law alone Kirchhoff's current law None Hint 19). When the rotor magnetic field rotates relative to the stator conductors, it produces? Mechanical torque only Induced EMF Resistance Capacitance None Hint 20). For a synchronous generator operating normally, the rotor speed is? Less than synchronous speed Greater than synchronous speed Equal to synchronous speed Random None Hint 21). The frequency of generated EMF depends on rotor speed and? Armature resistance Number of poles Power factor only Air-gap length only None Hint 22). A synchronous motor operates because the rotating stator field? Repels the rotor permanently Locks with the rotor magnetic field Eliminates the rotor field Stops the rotor field None Hint 23). The generated EMF in an alternator is approximately: DC Sinusoidal AC Purely pulsating DC Constant DC None Hint 24). The generated EMF of a three-phase alternator has phase displacement of? 60° 90° 120° 180° None Hint 25). The RMS value of a sinusoidal voltage having maximum value Em is? Em/2 Em Em/√2 2Em None Hint Synchronous Machine MCQs for Exams 26). The frequency of generated EMF in an alternator increases when? Rotor speed increases Rotor speed decreases Number of poles becomes zero Resistance increases None Hint 27). The phase sequence of a three-phase alternator is determined by the? Direction of rotation and winding arrangement Armature resistance only Bearing size Rotor weight only None Hint 28). The EMF equation of an alternator is E=? 4.44KpKdfΦT 2.22KpKdfΦT KpKdΦ/T 4.44fT/Φ None Hint 29). In the alternator EMF equation, T represents? Number of turns per phase Torque Temperature Time period None Hint 30). In the EMF equation, Φ represents? Flux per pole Flux density only Resistance Reactance None Hint 31). If the flux per pole is doubled while other parameters remain constant, generated EMF becomes? Half Unchanged Double Four times None Hint 32). If frequency is increased by 20%, generated EMF, with all other quantities constant, becomes? 20% lower 20% higher 40% higher Unchanged None Hint 33). The winding factor of an alternator is given by? Kw=Kp+Kd Kw=KpKd Kw=Kp/Kd Kw=Kp−Kd None Hint 34). Pitch factor is also known as? Distribution factor Chording factor Leakage factor Utilization factor None Hint 35). For a full-pitch coil, the pitch factor is? 0 0.5 1 2 None Hint 36). The pitch factor of a short-pitched coil is generally? Greater than unity Equal to zero Less than unity Infinite None Hint 37). Short-pitching an alternator winding is useful mainly for reducing? Fundamental EMF Harmonic EMF Rotor speed Field current to zero None Hint 38). The pitch factor for the fundamental component can be expressed as? cos(ϵ/2) sin(ϵ/2) tan(ϵ/2) sec(ϵ/2) None Hint 39). The distribution factor accounts for the fact that coils belonging to one phase are? Concentrated in one slot Distributed over several slots Placed on the rotor only Connected in parallel mechanically None Hint 40). For a concentrated winding, the distribution factor is? 0 0.5 1 Greater than 2 None Hint 41). The distribution factor of a practical distributed winding is generally? Greater than unity Equal to unity always Less than unity Negative None Hint 42). Distribution of winding coils mainly helps to reduce? Harmonic components Rotor inertia Bearing friction Shaft torque None Hint 43). The distribution factor is influenced by the? Number of slots per pole per phase Shaft diameter only Bearing type only Rotor material only None Hint 44). If coil sides are distributed over several slots, their individual EMFs are: Exactly in phase Phase displaced from one another Always 180° apart Zero None Hint 45). Armature reaction refers to the effect of? Rotor resistance on speed Armature MMF on the main field Bearing friction on voltage Load torque on shaft diameter None Hint 46). At unity power factor, the armature reaction of an alternator is approximately? Cross-magnetizing Demagnetizing only Magnetizing only Zero in every case None Hint 47). At zero power factor lagging load, armature reaction is predominantly? Magnetizing Demagnetizing Cross-magnetizing only Mechanical None Hint 48). At zero power factor leading load, armature reaction is predominantly? Demagnetizing Magnetizing Zero Mechanical None Hint 49). Armature reaction causes a change in the? Main flux distribution Shaft length Number of poles Rotor mass None Hint 50). The effect of armature reaction depends strongly on the load? Resistance temperature Power factor Mechanical size Bearing clearance None Hint 51). Armature reaction in a synchronous machine is produced by? Field current alone Armature current Bearing current Exciter speed only None Hint 52). Synchronous impedance of an alternator is the combination of? Resistance and synchronous reactance Capacitance and resistance Inductance and capacitance only Mechanical resistance and inertia None Hint 53). The synchronous impedance is commonly represented by? Zs=Ra+jXs Zs=Ra−jXs only Zs=RaXs Zs=Ra/Xs None Hint 54). The magnitude of synchronous impedance is? Ra+Xs √(Ra²+Xs²) RaXs Ra−Xs None Hint 55). The synchronous impedance method is also called the? MMF method EMF method ZPF method ASA method None Hint 56). The synchronous impedance method generally gives voltage regulation values that are? Usually optimistic Usually pessimistic Always zero Independent of power factor None Hint 57). Synchronous reactance includes the effects of? Leakage reactance and armature reaction Resistance only Bearing friction Rotor inertia None Hint 58). Synchronous reactance is usually denoted by? Xl Xs Xc Xm only None Hint 59). The unit of synchronous reactance is? Henry Ohm Weber Tesla None Hint 60). If armature resistance is negligible, synchronous impedance is approximately equal to? Ra Xs 1/Xs Zero None Hint 61). A high synchronous reactance tends to cause? Better voltage regulation Larger voltage drop under load Zero voltage drop Higher mechanical speed None Hint 62). Voltage regulation of an alternator indicates the change in terminal voltage when? Load changes from zero to rated at constant excitation and speed Speed becomes zero Poles are removed Rotor is disconnected None Hint 63). Voltage regulation is normally expressed as a? Percentage Weber Henry Newton None Hint 64). The approximate percentage voltage regulation is calculated using? (E0−V)/V×100 V/E0×100 only I/V×100 R/X×100 None Hint 65). For an alternator supplying a lagging power-factor load, voltage regulation is generally? Positive Negative always Zero always Infinite None Hint 66). Under certain leading power-factor conditions, an alternator may have? Negative voltage regulation Infinite voltage regulation No induced EMF Zero frequency None Hint 67). Voltage regulation is ideally zero when the terminal voltage? Changes greatly with load Remains unchanged from no-load to full-load Becomes zero Doubles at full load None Hint 68). Which method uses synchronous impedance to determine regulation? EMF method Potier method MMF method Zero-power-factor method None Hint 69). The MMF method of voltage regulation is also called the? Synchronous impedance method Ampere-turn method Two-reaction method only Slip method None Hint 70). The Potier method separates? Armature resistance and speed Leakage reactance and armature reaction Rotor copper loss and friction Field copper loss and windage None Hint 71). The zero-power-factor method requires the? ZPF characteristic Speed-torque characteristic only V-curve only Slip characteristic None Hint 72). Compared with the EMF method, the MMF method generally gives? More pessimistic regulation More optimistic regulation Identical results under all conditions Zero regulation None Hint 73). The Potier triangle is used to determine? Leakage reactance and armature-reaction MMF Rotor speed and torque Bearing friction Pole pitch only None Hint 74). In an alternator phasor diagram, E generally represents? Generated EMF Mechanical energy Rotor speed Field resistance None Hint 75). For a synchronous generator, the generated EMF is related to terminal voltage by? E=V+I(Ra+jXs) E=V−I(Ra+jXs) E=VI E=V/I None Hint 76). In a lagging power-factor load, armature current lags terminal voltage by? Power-factor angle 180° 90° exactly in every case Zero None Hint 77). In a leading power-factor load, armature current? Lags voltage Leads voltage Is always zero Is always in phase opposition None Hint 78). The synchronous reactance voltage drop is represented by? IR IXs C) V/I I2R None Hint 79). The angle between the generated EMF and terminal voltage of an alternator is called the? Load angle or power angle Pitch angle Slot angle D) Bearing angle None Hint 80). Short-circuit ratio (SCR) is associated with the? Open-circuit and short-circuit characteristics V-curves only Speed-torque curve only Rotor resistance characteristic None Hint Synchronous Machine MCQs for Interviews 81). SCR is approximately the reciprocal of? Per-unit synchronous reactance Armature resistance Power factor Frequency None Hint 82). A higher SCR generally indicates? Higher synchronous reactance Lower synchronous reactance Zero excitation Lower number of poles None Hint 83). A synchronous generator with a high SCR generally has? Better voltage regulation Poorer voltage regulation No generated voltage No armature reaction None Hint 84). SCR is particularly useful for comparing? Alternator electrical characteristics Bearing materials Rotor mechanical strength only Insulation color None Hint 85). Alternators are operated in parallel mainly to? Increase system flexibility and capacity Eliminate all losses Reduce frequency to zero Prevent power transfer None Hint 86). Before connecting an alternator to live busbars, its phase sequence must be? Opposite Identical Random Zero None Hint 87). One essential condition for paralleling alternators is equality of? Frequency Rotor diameter Shaft length Bearing temperature None Hint 88). For proper synchronization, the incoming alternator and busbar should have approximately equal? Voltage magnitude Rotor weight Armature resistance only Number of slots only None Hint 89). If two alternators connected in parallel have different frequencies, they will experience? Synchronizing power oscillations Zero current Zero torque No interaction None Hint 90). In parallel operation, active power sharing is mainly controlled by? Prime-mover input Field excitation alone Bearing lubrication Stator resistance None Hint 91). Reactive power sharing between parallel alternators is mainly influenced by? Excitation Shaft diameter Mechanical friction Rotor material None Hint 92). Synchronization means connecting an incoming alternator to a busbar when their? Electrical conditions are compatible Mechanical speeds are always zero Frequencies are intentionally different Phase sequences are opposite None Hint 93). The three-lamp synchronization method uses lamps to detect? Phase relationship Rotor temperature Armature resistance Bearing friction None Hint 94). In the dark-lamp method, the alternator is ideally connected when the lamps are? Brightest Dark Flickering randomly Permanently disconnected None Hint 95). A synchroscope indicates the? Phase and frequency difference between incoming alternator and busbar Rotor resistance only Field winding temperature Armature copper loss None Hint 96). If the synchroscope pointer rotates rapidly, it indicates a relatively large? Frequency difference Rotor diameter Resistance Number of poles None Hint 97). Synchronizing an alternator at an incorrect phase angle can produce? Large transient currents and torque Zero current Permanent zero excitation Zero magnetic field None Hint 98). Synchronizing power is the power that tends to? Restore synchronism after a small displacement Stop all generators Reduce field current to zero Increase mechanical friction None Hint 99). The synchronizing torque is associated with the change in? Electromagnetic power with load angle Resistance with temperature only Rotor mass with speed Frequency with voltage only None Hint 100). For a cylindrical-rotor machine, the power-angle relation is proportional to? sinδ cosδ only tanδ δ2 only None Hint 101). Synchronizing power per electrical radian is related to? dP/dδ Pδ P/δ2 V/I None Hint 102). Synchronizing torque is important because it provides? Stability between synchronous machines Rotor insulation Armature cooling Mechanical braking only None Hint 103). For a cylindrical-rotor synchronous generator neglecting resistance, power output is? 3EV/Xs · sinδ 3EVXssinδ EV/Xs2 3I2R None Hint 104). The maximum power in the cylindrical-rotor power-angle equation occurs when? δ=0∘ δ=30∘ δ=90∘ δ=180∘ None Hint 105). The power-angle curve of a cylindrical-rotor machine is approximately? Sinusoidal Linear under all conditions Exponential Parabolic only None Hint 106). In a salient-pole machine, the power-angle equation contains an additional term involving? Xd−Xq Ra+Rf Xl+Ra only Frequency squared only None Hint 107). The load angle δ generally increases when the mechanical load on a synchronous motor? Increases Decreases to zero Is disconnected Becomes negative only None Hint 108). The open-circuit characteristic of an alternator is a graph of? Generated EMF versus field current Torque versus speed Current versus resistance Power versus frequency only None Hint 109). The short-circuit characteristic of an alternator is generally a plot of? Short-circuit armature current versus field current Voltage versus speed Torque versus voltage Frequency versus rotor diameter None Hint 110). The open-circuit characteristic becomes nonlinear at higher excitation mainly because of: Magnetic saturation Bearing friction Copper expansion Rotor imbalance None Hint Synchronous Machine MCQs for Quiz 111). The short-circuit characteristic is approximately linear because the machine operates at? Very high saturation Low flux density Zero current Infinite speed None Hint 112). The external characteristic of an alternator represents terminal voltage as a function of? Load current Rotor mass Pole pitch Shaft length None Hint 113). At a constant excitation, increasing lagging load generally causes alternator terminal voltage to? Increase greatly Decrease Remain exactly constant Become negative immediately None Hint 114). A synchronous motor converts? Electrical energy into mechanical energy Mechanical energy into electrical energy Heat into mechanical energy Chemical energy into electrical energy None Hint 115). A synchronous motor normally operates at? Synchronous speed Zero speed Slip speed Half synchronous speed None Hint 116). The steady-state speed of a synchronous motor is primarily determined by? Supply frequency and number of poles Armature resistance only Load resistance Field winding resistance only None Hint 117). A synchronous motor is inherently? Self-starting Not self-starting Always variable-speed A DC motor None Hint 118). The rotor of a conventional synchronous motor receives? DC excitation High-frequency AC only No excitation under all conditions Three-phase armature voltage None Hint 119). Once synchronized, a synchronous motor runs with? Constant average speed Large continuous slip Zero rotor field Random speed None Hint 120). A synchronous motor can be operated at a leading power factor by? Over-excitation Under-excitation Removing field excitation Increasing mechanical friction None Hint 121). The most common traditional starting method for a synchronous motor uses? Damper winding Slip rings only Capacitor-start winding only Transformer action alone None Hint 122). A synchronous motor with damper bars initially starts as a? DC motor Squirrel-cage induction motor Universal motor Stepper motor None Hint 123). During starting using damper bars, DC field excitation is usually? Applied immediately at standstill in all cases Applied after the rotor approaches synchronous speed Permanently disconnected Replaced by capacitor current None Hint 124). Another method of starting a synchronous motor is to use? An external auxiliary motor A resistor connected to the shaft A transformer core A capacitor across the bearings None Hint 125). Variable-frequency starting of a synchronous motor allows the motor to? Gradually accelerate while maintaining synchronism Operate only at zero speed Eliminate excitation completely Operate only as an induction generator None Hint 126). The V-curve of a synchronous motor represents armature current versus? Field current Rotor speed Mechanical torque only Supply resistance None Hint 127). The minimum armature current on a V-curve occurs approximately at? Unity power factor Zero power factor Maximum leading power factor only Zero field current None Hint 128). When a synchronous motor is under-excited, it generally draws? Leading current Lagging current Zero current DC current only None Hint 129). When the field current of a synchronous motor is increased beyond the unity-power-factor point, armature current? Increases and becomes leading Becomes zero Remains unchanged Becomes DC None Hint 130). The V-curve is useful for studying the relationship between? Excitation and armature current Rotor diameter and speed Bearing friction and voltage Pole count and resistance None Hint 131). At a particular load, the V-curve has a minimum corresponding approximately to? Unity power factor Zero torque Maximum slip Zero excitation Answer: A) Unity power factor None Hint 132). An inverted V-curve of a synchronous motor is a plot of power factor versus? Field current Rotor resistance Load speed Armature resistance None Hint 133). The maximum value of power factor in an inverted V-curve occurs near? Unity power factor condition Zero excitation Maximum lagging current Standstill None Hint 134). On the under-excited side of an inverted V-curve, the motor operates at? Lagging power factor Leading power factor Zero power factor always Negative power factor None Hint 135). On the over-excited side of an inverted V-curve, the motor operates at? Leading power factor Lagging power factor Zero power factor Unity current None Hint 136). Inverted V-curves are especially useful for observing the effect of excitation on? Power factor Rotor speed only Mechanical losses Number of poles Answer: A) Power factor None Hint 137). The power factor of a synchronous motor can be controlled by changing its? Field excitation Shaft diameter Number of bearings Stator core length only None Hint 138). An under-excited synchronous motor draws? Reactive power from the supply Reactive power into the supply No active power Only DC power None Hint 139). An over-excited synchronous motor can supply? Reactive power to the AC system Mechanical power to the grid DC voltage to the transformer Frequency to the grid None Hint 140). For unity power factor operation, the field excitation is adjusted so that armature current is? In phase with terminal voltage 90° behind voltage 180° from voltage Always zero None Hint 141). Power factor improvement using a synchronous motor is achieved by operating it? Over-excited when supplying leading reactive power Under-excited at zero load only Without a rotor field At standstill None Hint 142). A synchronous condenser is essentially a synchronous motor operating? Without significant mechanical load At standstill As a DC generator With its rotor removed None Hint 143). A synchronous condenser is primarily used for? Reactive power compensation Mechanical power generation Frequency measurement Increasing shaft friction None Hint 144). To supply reactive power to an AC system, a synchronous condenser is generally? Over-excited Under-excited Unexcited Short-circuited None Hint 145). A major advantage of a synchronous condenser is that its reactive power can be controlled by? Varying field excitation Changing shaft length Changing pole count during operation Changing bearing pressure None Hint 146). Synchronous condensers can be installed in power systems to improve? Voltage profile and power factor Mechanical friction Transformer oil temperature only Rotor weight None Hint 147). Hunting in a synchronous machine refers to? Oscillation of the rotor about its equilibrium position Permanent loss of excitation Increase in stator resistance Mechanical failure of bearings None Hint 148). Hunting may be caused by? Sudden changes in load Constant zero load only Absence of magnetic field Perfectly constant operating conditions only None Hint 149). Excessive hunting can cause? Loss of synchronism Elimination of all losses Zero armature current Permanent increase in frequency None Hint 150). The principal purpose of damper winding in a synchronous machine is to? Reduce hunting and assist in starting Increase armature resistance Eliminate the main field winding Produce DC output voltage None Hint Synchronous machines play a vital role in modern electrical power generation, transmission, and industrial applications. Understanding their construction, operating principles, EMF generation, armature reaction, synchronous impedance, voltage regulation, synchronization, power-angle characteristics, and motor performance is fundamental to the study of electrical engineering.The 150 MCQs presented in this article provide comprehensive coverage of the important syllabus topics related to synchronous machines. They help students revise theoretical concepts, understand machine characteristics, distinguish between different operating conditions, and prepare for questions involving both fundamental principles and practical applications. Topics such as V-curves, power-factor control, synchronous condensers, hunting, and damper windingsalso provide insight into the practical operation and control of synchronous motors and generators.Regular practice with these questions can improve conceptual clarity, examination performance, and confidence in solving objective-type questions. Students are encouraged to use this MCQ set alongside their textbooks, classroom notes, numerical problems, and laboratory studies for a more complete understanding of synchronous machines. Time's up
