![]() ![]() Industrial turbines will normally operate at above synchronous speed and will drive an alternator via a reduction gearbox. The foundations of any turbogenerator installation play a significant part in the safe operation of the machine. I G Crow BEng, PhD, CEng, FIMechE, FIMarE, MemASME, K Shippen BSc, MBA, CEng, MIMechE, in Plant Engineer's Reference Book (Second Edition), 2002 22.6.3.2 Installation Where the system is strong enough, however, this is not too costly, and the total cost of the induction generator installation can be less than that of a synchronous unit. To maintain stability following system faults requires considerable reactive-power capacity beyond that needed for steady full-load operation. cable is required, for the cable capacitance will contribute to the reactive-power requirement, and at points in the system where substantial var support is installed anyway, the generator being run when active power is also required. The most suitable locations appear to be where transmission by h.v. By suitable design of the machine and the static compensator, efficiency and stability can be comparable to those of a synchronous machine. To reduce the current surge in large machines, the machine can be allowed to build up to normal voltage by first connecting a capacitor and then synchronising in the usual way. Speed control would then be essential to fix the frequency of the separate system.Ĭonnection to the power network can be made merely by closing the breaker when the machine is up to synchronous speed. Research in the USA has shown that, by using static var compensators to supply the reactive power, it should be practicable to run induction generators of a few hundred megawatts output either in parallel with synchronous generators or even as a separate supply system. The disadvantage is that it must draw from the power system magnetising power of 0.5–0.75 of its rated active power output, and this has limited the size to about 5 MW. for unattended hydrostations or wind-driven generators. This makes it cheaper than a synchronous machine and operationally more convenient, e.g. It has the advantage of simple construction, and needs no excitation, speed governing, or synchronising. If an induction motor is driven above synchronous speed it will deliver power to the system, with a slip of about −0.05 at full load. Torque is again established.į Parker MBA, PgD, BSc (Hons), CEng, MIEE, in Electrical Engineer's Reference Book (Sixteenth Edition), 2003 28.20 Induction generators 157–164 When the speed is reduced, magnetic flux lines produced by the stator windings again cut the rotor's windings, inducing a current and the resulting magnetic field. When this happens, there is no longer any torque on the rotor, and its speed drops below the synchronous speed. With no current flow in the armature, no magnetic field will be developed. ![]() Under this condition, no current would be induced to the rotor windings. The reason for this is if the armature turns exactly at synchronous speed, then the magnetic field of the stator windings no longer cuts the rotor windings. Some motors are designed to operate at synchronous speed.Īctual speed of the induction motor will be less than the synchronous speed. The RPM is calculated by multiplying the frequency times 60 and dividing by the number of pairs of poles. The synchronous speed of an AC motor is determined by the frequency of the source and the number of poles. George Patrick Shultz, in Transformers and Motors, 1989 Synchronous Speed
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