Induction Generator Schemes for Wind Turbines.
Induction Generator Schemes for Wind Turbines.
1.) Cage Induction Generator.
Part A:
The classical ‘Danish Concept’ describes a wind turbine consisting of a stall-controlled rotor with three rotor blades, a gearbox, a pole-switched asynchronous generator with squirrel cage rotor and a direct mains grid coupling. In order to limit the inrush currents that are produced when the generator is coupled with the grid, soft-starters are used between the generator and the grid during the starting period.
Explain the operation of the above scheme with the aid of diagrams, equivalent circuits and equations.
(60 marks out of 100)
Part B:
A) Briefly explain what is meant by self-excited induction generator and outline its practical applications for wind turbines.
(5 marks out of 100)
B) A 400V, 3-phase cage induction machine has a rated current of 35A and a full-load power factor of 0.86 lagging. The machine is to be run as a self-excited generator.
Calculate the minimum capacitance required per-phase if the machine is connected in delta.
(10 marks out of 100)
2) Wound-Rotor Doubly-Fed Induction Generator (DFIG)
Figure 1 (provided in attachments) shows a typical DFIG scheme employing voltage source converters.
With the aid of power flow diagrams and appropriate equations, explain the generating mode of operation at (a) sub-synchronous and (b) super-synchronous speed.
(25 marks out of 100)
Assignment word count is 1400 not 1500 words as specified in the order box.
