# Electrical Machines I. Basics, Design, Function, Operation by Gerhard Henneberger

By Gerhard Henneberger

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Example: Z1KST = short-circuit on secondary side Z 1K ∆Z K ∆Z K (w − w )2 = Z 1K = Z1 K 2 2 1 Z 1K + ∆Z K Z2K w2 = Z1K (1 − ü ) 2 For ü close to 1, the short-circuit current rises high! 143) 4 Fundamentals of rotating electrical machines Rotating electrical machines are electromechanical energy converters: motor – generator The described energy conversion, expressed as forces on the mechanical side, whereas it appears as induced voltages on the electrical side. Basically electrical machines can be operated in both motor- and generator mode.

75) R 1K I X jX 1K I1N 1k U 1K 1N ϕ U 1K K R 1K I1N I1N Fig. 38: phasor diagram Fig. 37: short-circuit ecd For a reasonable comparison of transformers of different sizes and power ratings, a variable called “relative short circuit voltages” is introduced. These are short circuit voltage values normalized to the nominal voltage. 3 Load with nominal stress Due to relations applied in real transformers R : Xσ : Xh : RFe ≈ 1 : 2 : 1000 : 10000, sufficient accuracy is reached with usage of the simplified ecd (shown in Fig.

Generator P el stator air gap rotor n Stator and rotor are usually fitted with windings, with voltages to be induced, caused by spatiotemporal flux alteration. Forces either appear as Lorentz force in conductors or as interfacial forces on (iron) core surfaces. motor P mech P mech generator v Fig. 64: scheme of energy conversion Technical demands on energy converters: 1. time independent constant torque (motor) and according constant power output (generator) in steady state operation 2. quick adjustment of torque and speed (motor) and according voltage and current (generator) in transient operation Electrical machines are usually supplied by either DC or AC systems.

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