Question Detail
No-load speed of which of the following motor is highest?
Options
- Option A: Differentially compound motor
- Option B: Cumulative compound motor
- Option C: Series Motor
- Option D: Shunt Motor
Correct Answer
Series Motor
Solution & Explanation
{"type":"technical","methodBadge":"Concept & Principle","explanation":"The DC series motor exhibits the highest no-load speed because its flux is inversely proportional to the armature current, which approaches zero at no-load. Consequently, the speed, being inversely proportional to the flux, tends toward infinity, creating a dangerous 'runaway' condition.","workingPrinciple":"In a DC series motor, the armature and field windings are connected in series. The speed equation is given by $N \\propto \\frac{E_b}{\\Phi}$, where $E_b$ is the back EMF and $\\Phi$ is the magnetic flux. Since $\\Phi \\propto I_a$ (armature current), at no-load, $I_a$ is extremely small, making $\\Phi$ nearly zero, resulting in a theoretically infinite speed.","diagramSvg":"Speed-Torque CharacteristicsTorque (T)Speed (N)DC Series Motor Curve0","keyFormulas":["$N \\propto \\frac{V - I_a R_a}{\\Phi}$ тАФ Fundamental speed equation for DC motors","$\\Phi \\propto I_a$ тАФ Flux dependence in series motors"],"keyPoints":["A DC series motor should never be started at no-load due to the risk of mechanical destruction.","The torque in a series motor is proportional to the square of the armature current ($T \\propto I_a^2$) at light loads.","Mechanical coupling (belt drive) must never be used with DC series motors as the sudden loss of load leads to runaway speeds."],"advantages":["High starting torque","Excellent for traction and heavy lifting applications"],"disadvantages":["Unstable at no-load conditions","Requires mechanical load at all times"],"applications":["Electric Locomotives","Hoists and Cranes","Conveyor systems"],"comparisonTable":[],"additionalInfo":["Differentially compound motors also have speed instability concerns, but the series motor is defined by the absolute lack of current at no-load to maintain flux.","Shunt motors are considered 'constant speed' motors because flux $\\Phi$ is independent of load."],"answer":"C is correct тАФ The DC series motor has no field current at no-load, causing flux to drop to near-zero levels and forcing the motor speed to reach dangerously high levels.","correctedOptions":["Differentially compound motor","Cumulative compound motor","Series Motor","Shunt Motor"],"coreConcepts":["Back EMF","Magnetic Flux","Runaway Speed","Series Excitation"],"crossTopicTip":"Always remember: Series motors are for high starting torque, Shunt motors are for constant speed, and Compound motors offer a balance based on configuration."}
Question (Hindi)
рдирд┐рдореНрдирд▓рд┐рдЦрд┐рдд рдореЗрдВ рд╕реЗ рдХрд┐рд╕ рдореЛрдЯрд░ рдХреА рдиреЛ-рд▓реЛрдб рдЧрддрд┐ (no-load speed) рд╕рдмрд╕реЗ рдЕрдзрд┐рдХ рд╣реЛрддреА рд╣реИ?
Options (Hindi)