CET Electrical & Control Systems 1 — Questions and Answers
Question 1: What is the main function of a relay in elevator control systems?
- Measure electrical resistance
- Switch circuits using control signals (Correct answer)
- Regulate motor speed
- Store electrical energy
Correct answer: Switch circuits using control signals
Relays act as electrically operated switches that control circuits using low voltage signals.
Question 2: Which type of motor is commonly used in modern traction elevator systems?
- DC brushed motor
- AC induction motor
- AC gearless permanent magnet motor (Correct answer)
- Stepper motor
Correct answer: AC gearless permanent magnet motor
AC gearless permanent magnet motors are widely used for their energy efficiency and smooth operation.
Question 3: What is the purpose of a limit switch in elevator systems?
- Control car lighting
- Signal for door closing
- Prevent over-travel of the elevator car (Correct answer)
- Measure speed
Correct answer: Prevent over-travel of the elevator car
Limit switches prevent the elevator from moving beyond safe boundaries by cutting off power when limits are reached.
Question 4: Which component converts AC to DC for elevator control circuits?
- Transformer
- Capacitor
- Rectifier (Correct answer)
- Resistor
Correct answer: Rectifier
Rectifiers are used to convert alternating current (AC) to direct current (DC) for elevator control components.
Question 5: What safety component cuts off power during an elevator malfunction?
- Surge protector
- Voltage stabilizer
- Circuit breaker (Correct answer)
- Contactor
Correct answer: Circuit breaker
A circuit breaker or main disconnect switch is designed to interrupt power during overload or faults to protect the system.
Question 6: Which device is used in elevator systems for variable speed control of motors?
- Contactor
- Relay
- Variable Frequency Drive (VFD) (Correct answer)
- Thermostat
Correct answer: Variable Frequency Drive (VFD)
A variable frequency drive (VFD) regulates the speed and torque of elevator motors for efficient operation.
CET Electrical & Control Systems 1
What is the main function of a relay in elevator control systems?