Motors Book - Chapter 4

The stator is the fixed, unmoving part of a motor that consists of a core and windings. It is responsible for converting electrical energy into the energy of a magnetic field. The stator plays a crucial role in the operation of the motor by generating a magnetic field that interacts with the rotor to produce rotational motion.

A bearing is a motor component that is specifically designed to reduce friction and maintain clearance between the stationary parts and the moving shaft. It is an essential part of any motor system as it helps to support and guide the rotating shaft, allowing it to move smoothly and efficiently. Without a bearing, the friction between the stationary parts and the shaft would be significantly higher, leading to increased wear and tear and decreased overall performance of the motor.

The nameplate of a motor typically contains important information about its specifications, including the frequency at which it is rated to operate. This information is crucial for determining whether the motor is suitable for use with a 50 Hz power supply, a 60 Hz power supply, or both. Therefore, the nameplate is the correct answer in this case.

The correct answer is "wound-rotor". The question asks for the most common types of rotors used in squirrel-cage induction motors, ___ motors, and synchronous motors. Among the options provided, "wound-rotor" is the only type of rotor commonly used in these types of motors. Squirrel-cage induction motors, wound-rotor motors, and synchronous motors all typically use wound-rotor type rotors.

A single-voltage motor is a motor that is designed to operate at only one specific voltage level. This means that it cannot be used with different voltage levels and is limited to operating at a fixed voltage.

A 3-phase motor transfers energy from electric power to the load through the use of a rotating magnetic field. This type of motor is commonly used in industrial applications due to its efficiency and ability to provide high torque. The rotating magnetic field is created by the interaction of three separate phases of AC power, which allows for smooth and continuous operation of the motor.

The correct answer is "all of the above" because the question states that the common types of torque related to motors are locked-rotor torque and "___" torque. Since the options provided include full-load, pull-up, and breakdown, and the question does not specify any other types of torque, it can be inferred that all of these options are correct and related to motor torque.

In a delta-connected, 3-phase motor, each phase is wired end-to-end to form a completely closed circuit. This means that the starting point of one phase is connected to the finishing point of the previous phase, creating a continuous loop. This configuration allows for a balanced distribution of electrical current and provides higher efficiency and power output compared to other motor configurations.

The correct answer is "all of the above" because a typical dual-voltage, 3-phase motor rating can be either 230V or 460V, 240V or 480V, or 208-230V or 460V. These different voltage options allow the motor to be compatible with various power supply systems, providing flexibility in different locations or applications.

Flux-linkage loss refers to the loss of magnetic flux in the air gap of a magnetic circuit. This occurs because the air gap has a higher reluctance (opposition to the flow of magnetic flux) compared to the cores. As a result, the magnetic flux is reduced or lost in the air gap, leading to energy losses. This phenomenon is commonly observed in transformers, motors, and other electromagnetic devices where the magnetic circuit includes an air gap.

Motors for constant-torque loads are designed to provide the same maximum torque at all speeds. This means that regardless of the speed at which the motor is operating, it will be able to deliver the same level of torque. This is important for applications where a consistent level of torque is required, such as in conveyor systems or lifting equipment. Constant-torque motors are designed to maintain a steady level of torque output, ensuring reliable and consistent performance.

Apparent power is the product of the total current and voltage in a circuit. It represents the total power that is being supplied to a circuit, including both the real power (which is the actual power consumed by the circuit) and the reactive power (which is the power required to maintain the magnetic or electric fields in the circuit). Apparent power is measured in volt-amperes (VA) and is important in determining the sizing and capacity of electrical equipment.

In a wye connected, 3-phase motor, one end of each of the three phase windings is internally connected to the other phase windings. This means that the three windings are connected in a star or wye configuration, with one end of each winding connected together. This type of connection allows for a balanced distribution of voltage and current across the three phases, making it suitable for three-phase power systems.

The correct answer is "Core" because the statement mentions that the energy loss is specifically in the stator and rotor cores. This implies that the core itself is responsible for the loss due to circulating currents and the magnetic field escaping from it.

As the rotor begins to move, the frequency of the induced current in the rotor decreases because it is influenced by the relative speed between the rotating magnetic field of the stator and the rotor. As the rotor approaches synchronous speed, the relative speed decreases and the frequency of the induced current in the rotor approaches 0 Hz. This is because at synchronous speed, the rotor frequency matches the frequency of the rotating magnetic field, resulting in no relative motion and therefore no induced current.