Wapcos Service Engineer Interview Questions and Answers

Blocked rotor test is performed on a 3-phase induction motor to determine its impedance and calculate its locked rotor current.

• The motor is connected to a 3-phase supply with the rotor blocked.

• The voltage and current are measured and used to calculate the motor's impedance.

• The locked rotor current can be determined from the impedance.

• The test helps in assessing the motor's performance and identifying any faults or issu

Single phase induction motor is not self-starting due to the absence of rotating magnetic field. Different methods of starting include capacitor start, split-phase, shaded pole, and reluctance start.

• Single phase induction motor lacks rotating magnetic field

• Capacitor start uses a capacitor to create a phase shift and start the motor

• Split-phase uses a starting winding to create a phase shift

• Shaded pole uses a shading coi...read more

Different methods of resistance measurement and their ranges

• Low resistance measurement: 4-wire Kelvin method, range 0.1 μΩ to 1 Ω

• Medium resistance measurement: 2-wire method, range 1 Ω to 1 MΩ

• High resistance measurement: Megohmmeter method, range 1 MΩ to 10 TΩ

• Other methods include 3-wire method and 4-wire guarded method

• Measurement accuracy depends on the method used and the quality of the equipment

Lightning arresters are used in transmission lines to protect the equipment and infrastructure from damage caused by lightning strikes.

• Lightning arresters divert the high voltage surge caused by lightning strikes to the ground, preventing it from damaging the transmission lines.

• They provide a low-resistance path for the lightning current to flow, reducing the risk of electrical breakdown and flashovers.

• Lightning arrest...read more