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10.1 Introduction
10.1 Introduction
The main characteristic of synchronous machines is that they rotate at a constant speed. Synchronous speed (n) is the name we give to this constant speed. The machine's number of poles (2p) and network frequency (f) determines this speed. We can express it as:
Synchronous speed = n rpm 60 · f p (10.1)
Depending on the direction of energy conversion -from mechanical to electrical or electrical to mechanical- these devices can be motors or generators. The most important application is the electrical generator. Large power plants with synchronous generators are responsible for maintaining the electrical grid. In synchronous machines, alternating current powers the stator winding while direct current powers the rotor winding.
练习题
A synchronous machine is connected to a 50 Hz electrical network and has 4 poles (2p = 4). What is the synchronous speed of this machine?
A. 1500 rpm
B. 3000 rpm
C. 1000 rpm
D. 750 rpm
Which parameters determine the synchronous speed of a synchronous machine?
A. Number of poles and network frequency
B. Rotor resistance and stator voltage
C. Mechanical load and power factor
D. Winding inductance and capacitance
What is the most important application of synchronous machines?
A. Electric motor drives in industrial applications
B. Electrical power generation
C. Electric vehicle propulsion
D. Household appliance motors
Which of the following statements about synchronous machines are correct?
A. They rotate at a constant speed called synchronous speed
B. Alternating current powers the stator winding
C. Direct current powers the rotor winding
D. They can only function as generators, not motors
E. Synchronous speed depends on the mechanical load
The main characteristic of synchronous machines is that they rotate at a variable speed that depends on the mechanical load applied to the shaft.
Large power plants use synchronous generators to maintain the electrical grid.
In synchronous machines, direct current powers the stator winding while alternating current powers the rotor winding.
The synchronous speed formula is , where is the speed in rpm, is the network ___ in Hz, and is the number of pole pairs.
Explain how synchronous machines differ from asynchronous (induction) machines in terms of their operating speed characteristics.
Describe the two possible operating modes of synchronous machines and explain what determines which mode the machine operates in.
A 4-pole machine is connected to a 50 Hz network. Which statement correctly describes the relationship between synchronous speed and actual rotor speed for synchronous versus asynchronous (induction) machines?
A. Both synchronous and asynchronous machines operate at exactly 1500 rpm
B. Synchronous machines operate at 1500 rpm, while asynchronous machines operate slightly below 1500 rpm under load
C. Asynchronous machines operate at 1500 rpm, while synchronous machines operate slightly below 1500 rpm
D. Both machines operate below 1500 rpm due to mechanical losses
Both synchronous machines and asynchronous (induction) machines can operate as motors or generators, but synchronous machines are primarily used as generators in power plants while asynchronous machines are primarily used as motors in industrial applications.
Which of the following statements correctly describe the relationship between synchronous speed and machine operation? Select all that apply.
A. Synchronous speed depends on the number of poles and the network frequency
B. Synchronous machines rotate at exactly synchronous speed during normal operation
C. Asynchronous motors rotate at exactly synchronous speed during no-load operation
D. The rotor speed of an asynchronous motor under load is always less than synchronous speed
While synchronous machines rotate at exactly synchronous speed, the rotor speed of an asynchronous motor is reduced by the factor of ___ relative to the rotating magnetic field.
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