Elevator hoisting mechanisms typically utilize which type of electric motor ?
Show answer Hide answer
Answer: A. Induction motor
Explanation
Induction motors deliver dependable starting torque and maintain stable rotational speeds under fluctuating mechanical loads. Their robust squirrel-cage construction eliminates brushes and commutators, ensuring minimal mechanical wear during daily lifting cycles. Smooth acceleration and deceleration characteristics make induction drives ideal for passenger comfort in modern elevator systems. Elevator hoisting machinery requires precise control to lift and lower heavy passenger cars safely between building floors. Three-phase induction motors operate reliably on standard industrial AC power supplies without complex synchronization controls. Electromechanical brakes work in tandem with the motor drive to hold the elevator car stationary at floor landings.
Synchronous motors require complex starting mechanisms and precise excitation control, making them impractical for frequent elevator stops. Capacitor start single-phase motors lack the high power ratings and continuous duty capabilities required for heavy commercial elevators. Saying any of the above applies is incorrect because single-phase and synchronous motors are rarely used for heavy hoisting.
- Subject
- Engineering
- Category
- Electrical Engineering
- Topic
- —
- Difficulty
- medium
Related questions
Q1. A rheostat differs from a potentiometer in the sense that it_____________?
Show answer Hide answer
Answer: B. has higher wattage rating
A rheostat is typically designed with a higher wattage rating than a potentiometer because it controls current directly. Handling large electrical currents requires thicker resistive elements capable of dissipating subst...
Q2. Which type of machinery experiences heavy load fluctuations ?
Show answer Hide answer
Answer: A. Printing machine
Printing machines experience continuous and heavy load fluctuations during high speed paper feeding and printing. Variable torque demands require printing presses to utilize robust mechanical drives and motor controls. S...
Q3. Which of the following can serve as an indicator of electric intensity ?
Show answer Hide answer
Answer: B. V/A
Electric intensity, or electric field strength, measures potential difference distributed across a specific distance interval. Potential measured in volts divided by distance represented dimensionally matches the intensi...
Q4. When selecting an electric motor to drive a flour mill, which electrical specification is of minimal relevance ?
Show answer Hide answer
Answer: D. Braking
Flour mills require constant running and high starting torque for heavy milling machinery. Electric braking is generally unnecessary for their standard continuous grinding operation. Motors operate steadily without needi...
Q5. Given a 21 V source applied to a circuit where R1 = 5 ohms, R2 = 35 ohms, and R3 = 14 ohms, with R1 in series with the parallel pair R2 and R3, what is the current through R2?
Show answer Hide answer
Answer: B. 400 mA
Calculating the parallel resistance of thirty-five and fourteen ohms yields exactly ten ohms of equivalent resistance. Adding the series resistor of five ohms gives a total circuit resistance of fifteen ohms altogether....
Q6. Which device operates on the principle of magnetic torque exerted on a current-carrying conductor in a magnetic field ?
Show answer Hide answer
Answer: D. all of the above
Galvanometers, ammeters, and voltmeters all operate based on magnetic torque exerted on current-carrying conductors inside a magnetic field. When electric current flows through a movable coil positioned within a permanen...