Effect of loading, voltage difference and phase angle on the synchronisation of a small alternator

Abstract

Synchronisation of small distributed generation, 30 kVA -2 MVA, employing salient-pole synchronous machines is normally performed within a narrow range of tolerances for voltage, frequency and phase angle. However, there are situations when the ability to synchronise with non-ideal conditions would be beneficial. Such applications include power system islanding and rapid generator start-up. The physical process and effect of out-of-phase synchronisation is investigated both through simulation and experimental tests on a salientpole alternator. There are many factors that affect synchronisation, but particular attention is given to synchronisation angle, voltage difference and, as generators will be loaded during islanding, the load angle. The results suggest that it would be acceptable for the maximum synchronisation angle of distributed generation to exceed that of current practice. Interesting observations on the nature of out-of-phase synchronisation are made, including some specific to small salient-pole synchronous machines. Furthermore, recommendations are made for synchronisation under different system conditions.reactance a angular acceleration u sync synchronisation angle d load angle t time constant F magnetic flux C flux linkage v angular speed Subscripts and superscripts a armature bus power system bus d direct axis (armature) e electrical f field k d direct-axis damper k q quadrature axis damper m mechanical m d direct-axis mutual m q quadrature-axis mutual

Loss‐of‐mains protection system by application of phasor measurement unit technology with experimentally assessed threshold settings

“…If the phase‐drift is less than the threshold ± θ a , then it is safe to reclose. The author's have previously shown an out‐of‐phase reclose of ±60° is within the transient torque and current limits for a synchronous machine [25, 26], but would not recommend such a large out‐of‐phase reclosure as common practice. A much smaller threshold is recommended in Section 5.…”

“…A much smaller threshold is recommended in Section 5. Detection time for out‐of‐phase reclosure is thus effectively zero seconds, since as the authors show in [25, 26], an embedded generator could be reclosed without damage even after the synchrophasor loss‐of‐mains has indicated an island has formed.…”

Current transients in the small salient-pole alternator during sudden short-circuit and synchronisation events

“…1(c), (d) and (e). The loaded short-circuit is a design constraint for larger synchronous machines [15], and out-of-phase synchronisations are of interest as they can be more severe for the machine than any other event [4,16,17]. Thus it is of benefit to understand the physical process during these events.…”

“…The worldwide installed capacity of distributed generation is increasing and an interest in islanding of distribution networks [1,2,3] has prompted the authors to review the out-of-phase synchronisation and fault characteristics of small alternators. Related work by the authors [4], concentrating on peak current and torque, has indicated that the synchronisation angle limits of salient-pole alternators could be increased 2 significantly beyond the current narrow range of tolerances stipulated in IEEE 1547 [5] and ETR 113 [6].…”

Techniques for Multiple-Set Synchronous Islanding Control

“…The results indicate that with a sophisticated governor and suitable communications structure, this is indeed feasible in the single-set case. Experimental work was also performed to determine suitable boundaries within which to control the phase angle [10]. A range of ±60° was proposed, this being no worse than a sudden three phase short-circuit, which the DG is designed to withstand, and is a significantly wider window than current synchronization schemes operate with [11,12].…”