9 Questions
What is the principal difference between synchronous machines and induction machines?
Synchronous machines require a dc field current to be supplied to their rotors, while induction machines have the field current induced in their rotors by transformer action.
What produces a uniform rotating magnetic field within the stator of a three-phase system of currents?
A system of three coils spaced 120 electrical degrees apart
How can the direction of rotation of the magnetic field be reversed in a three-phase system?
By simply swapping the connections to any two of the three phases
What types of losses occur in ac machines?
Electrical or copper losses (I2R losses), core losses, mechanical losses, and stray losses
How is the electrical angle of the voltages and currents related to the mechanical angle of the magnetic fields in a stator with more than two poles?
One mechanical rotation produces P/2 electrical cycles
What is the principal difference between synchronous machines and induction machines?
Synchronous machines require a dc field current, while induction machines have the field current induced by transformer action
What produces a uniform rotating magnetic field within the stator of a three-phase system of currents?
A system of three coils spaced 120 electrical degrees apart on a stator
How can the direction of rotation of the magnetic field be reversed in a three-phase system?
By simply swapping the connections to any two of the three phases
What types of losses occur in ac machines?
Electrical or copper losses (I2R losses), core losses, mechanical losses, and stray losses
Study Notes
Synchronous Machines vs. Induction Machines
- Principal difference: Synchronous machines rotate at a constant speed, whereas induction machines rotate at a speed dependent on the slip between the rotor and the rotating magnetic field.
Rotating Magnetic Field
- Uniform rotating magnetic field is produced by a three-phase system of currents in the stator.
- Reversing the direction of rotation of the magnetic field can be done by changing the phase sequence of the currents.
Losses in AC Machines
- Types of losses: Copper losses, Iron losses, Mechanical losses, and Stray losses.
Electrical Angle vs. Mechanical Angle
- In a stator with more than two poles, the electrical angle of the voltages and currents is related to the mechanical angle of the magnetic fields by a factor of pole pairs.
Explore the key differences between synchronous machines, which require a DC field current, and induction machines, which have the field current induced by transformer action. Learn about three-phase systems and stator coils in detail.
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