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INDUCTION GENERATOR Presentation Transcript
1.INDUCTION GENERATOR
2.Principle of operation
The stator is usually connected to the grid and, thus, the stator is magnetized
A rotating magnetic field with constant magnitude is produced, rotating with a speed
The stator is usually connected to the grid and, thus, the stator is magnetized
A rotating magnetic field with constant magnitude is produced, rotating with a speed
3.In order to generate power the rotor speed must be slightly above the synchronous speed
The harder the rotor is cranked, the more power will be fed into the electrical grid
The harder the rotor is cranked, the more power will be fed into the electrical grid
4.The Slip
Where s is the slip. Slip is one of the most important variables in the control and operation of induction machines.
Where s is the slip. Slip is one of the most important variables in the control and operation of induction machines.
5.Induction Generators
Same basic construction as squirrel-cage induction motors
Drive at a speed greater than the synchronous speed
Not started as a motor
Operated by wind turbines, steam turbines, etc.
Same basic construction as squirrel-cage induction motors
Drive at a speed greater than the synchronous speed
Not started as a motor
Operated by wind turbines, steam turbines, etc.
6.Motor – to – Generator Transition
7.Typical setup for induction-generator operation
8.When the speed approaches synchronous speed, the slip = 0, Rs/s becomes infinite, rotor current Ir = 0, and no motor torque is developed. (The motor is neither a motor or a generator – it is “floating” on the bus. The only stator current is the exciting current to supply the rotating magnetic field and the iron losses.
9.Air – gap Power vs. rotor speed
10.Developed torque and line current vs. rotor speed
11.The interaction of the magnetic flux of the stator and the magnetic flux of the rotor produce a “countertorque” that opposes the driving torque of the prime mover. Increasing the speed of the rotor increases the countertorque and the power delivered to the system by the generator. The maximum value of the countertorque is called the “pushover” torque.
12.Increasing the speed of the prime mover beyond the pushover point causes the power output to decrease. The countertorque decreases and the speed increases. This also occurs if the generator is loaded and the breaker is tripped. Motors used in these applications must be able to withstand overspeeds without mechanical injury. See Table 5.11, page 223.
13.Induction Motor Equivalent Circuit
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