The correct answer is: B. synchronous motor
A synchronous motor is a type of AC electric motor that runs at a constant speed synchronized with the AC power supply frequency. It has a stator winding that is supplied with AC power, and a rotor winding that is excited by a DC current. The stator winding creates a rotating magnetic field, which induces a current in the rotor winding. The interaction of the stator and rotor magnetic fields produces torque, which drives the motor.
A synchronous motor is not self-starting because the rotor must be brought up to speed by an external source of torque before it can start to rotate at synchronous speed. This can be done by using a starting motor, or by using a special type of synchronous motor that has a built-in starting winding.
The other options are self-starting motors.
- A DC series motor is a type of DC electric motor that has the field winding and the armature winding connected in series. This means that the same current flows through both windings. The magnetic field produced by the field winding interacts with the magnetic field produced by the armature winding to produce torque. DC series motors are very powerful and have a high starting torque. However, they are also inefficient and have a high speed regulation.
- A squirrel cage induction motor is a type of AC electric motor that has a squirrel cage rotor. The rotor consists of a series of bars that are short-circuited at each end. The stator winding is supplied with AC power, which creates a rotating magnetic field. The rotating magnetic field induces a current in the rotor bars, which creates a magnetic field of its own. The interaction of the stator and rotor magnetic fields produces torque, which drives the motor. Squirrel cage induction motors are very common and are used in a variety of applications. They are relatively inexpensive, efficient, and have good speed regulation.
- A wound round induction motor is a type of AC electric motor that has a wound rotor. The rotor consists of a series of coils that are wound around a laminated steel core. The stator winding is supplied with AC power, which creates a rotating magnetic field. The rotating magnetic field induces a current in the rotor coils, which creates a magnetic field of its own. The interaction of the stator and rotor magnetic fields produces torque, which drives the motor. Wound round induction motors are more expensive than squirrel cage induction motors, but they have better starting torque and speed regulation.