Omoigui, Michael. (1991). Precision Measurement of Rotor Angle of a Microsynchronous Alternator. Instrumentation and Measurement, IEEE Transactions on. 39. 1045 - 1047. 10.1109/19.65823. A precision instrument used for the measurement of rotor angles of
a laboratory microalternator is described. The measurement is performed
by integrating digital signals derived from a phase-locked loop (PLL)
reference (i.e. laboratory infinite busbar or the terminals of another
machine in a multimachine system) and an optical encoder mounted on the
shaft of the machine. The integration is executed by synchronous up-down
binary counters. A 12-b digital-analog converter enables both transient
and dynamic movement of the rotor to be displayed on an oscilloscope or
other suitable recorder. When used on a four-pole 3-MVA microalternator,
the resolution of the encoder is 0.2 electrical degrees. Relatively slow
and fractional movements of the rotor angle arising from dynamic power
imbalances as well as fast and large rotor excursions arising from
severe transient disturbances, which sometimes result in pole slipping,
are reliably and precisely recorded. It is possible to obtain constant
information on the stability or lack thereof for the machine under every
operating condition. With appropriate transducers, the principle may
easily be applied to continuously monitor changes in the rotor angle of
large alternators in interconnected power systems