"In-zone" - Influence of Magnetic
SaturationThe SIEMENS RSTM was developed on large, hydrogen
cooled generators with direct cooled field windings. Hundreds of
waveforms were captured to file on units with known shorted turns. From
analysis of these waveforms it was possible to determine how well the
analysis algorithm coped with the effects of magnetic saturation of the
rotor teeth. The analysis method removes the effects of saturation
by:
- including a bias towards the search coil voltage waveform corresponding
to rotor winding slots/teeth on the leading (in the direction of rotation) sides
of the poles, the regions where the airgap flux is least.
- scaling of calculated voltage waveforms by comparison with actual
(measured) waveforms.
over a range of angles which are related to the 'flux angle' -
the angle that the airgap flux makes with the pole axis. The range of
angles differs for each coil. When the generator is on a low load so that the
flux angle is small, the larger pitch coils fall within this range of
angles; we refer to these coils are being "in-zone". On higher loads the flux angle
is larger and the shorter pitch coils are "in-zone". If the airgap flux
angle is outside the favourable range of values ("out-of-zone") for a
particular coil, a reduced level in shorted turns is not
reported, to avoid (probably) false reports that a previously existing
short has a reduced magnitude.(back to introduction) |
