2 The measuring principle and method

It is necessary to wind search coils onto armature tooth tips of the tested generator to detect airgap flux. The d-axis pickup is also installed in the generator to detect the number of revolutions and to synchronize the execution of a program with the revolutions. The d-axis pickup generates one pulse per electric cycle, i.e. one pulse per half revolution.

The location of search coils at armature tooth tips and at various parts of the rotor and the location of the d-axis and the d-axis pickup in the tested generator are shawn in Fig. 1.

Fig. 1 Cross-section of synchronous generator and disposition of search coils and d-axis pickup.
(Fig. 1 is equivalent to the left part of Fig. 3.)

Fig. 3 Schematic diagram of instrument.

2.1 Airgap flux density distribution

2.2 Calculation of Fourier coefficients

2.3 Extraction of fundamental stationary components
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