Evaluation of a rotor angle measurement technique using synchrophasor methods
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Date
2016
Authors
Berry, Brian
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Abstract
All power systems are prone to electromechanical oscillations between generators which can
become unstable under certain conditions. This instability can have catastrophic consequences
such as plant damage or loss of power supply and it is therefore important to monitor these
oscillations and ensure that the risks are mitigated through corrective operational actions or
automatic control. Whilst this behaviour can be observed in a generators’ terminal voltage
phase and magnitude, the internal rotor angle (load angle) of a synchronous machine is useful
for understanding the true severity and interaction of electromechanical oscillations in a power
system. Both the Chinese and IEEE PMU standards mention a proposed method of measuring
the rotor angle directly using a phasor measurement unit (PMU) on the machine terminals and a
KeyPhasor measurement system [1,2]. KeyPhasors are usually installed on the turbine of large
synchronous machines as an aid to vibration monitoring. Whilst this measurement method is
mentioned in these standards, little is currently documented around its physical
implementation and accuracy. This research aims to evaluate the viability of such a method
within both simulation and laboratory environments. Laboratory tests using a miniature
synchronous generator and typical relay techniques were executed and the results proved
positive, but exposed challenges around the sampling resolution of the KeyPhasor signal. A
simulation environment was then used to improve these results and a sufficient method of
mitigating the resolution issue was proposed with accurate results to prove this method. The
rotor angle produced yields an error of around ±0.03°, which is well below the TVE requirement
of ±0.573° as per the IEEE C37.118.1-2011 standard.