Grid connection transients of small hydropower generator

Abstract

This paper presents a transients of an cage induction generator connected to the power grid as it is in small hydropower station. In such power station, there is no control of prime mover speed. The no load speed of water turbine and then induction generator depends on reservoir water level and water pipe diameter. The transient state during connection of the cage induction generator to the power grid is discussed in dependence on generator initial slip. The negative impact of connected cage induction generator on the line is described. The transient current to grid connected generator is very high and produces transient overload of the supply system. The reduction of that negative influence is proposed by using a power electronics converter which works as reactive power compensator. The power electronic compensator is used in steady state to reduce demand of the grid reactive power needed by induction generator and in transients to reduce surge current. The computer model of the generation system, made form induction generator and power electronic compensator, has been designed and used to preliminary verification. Moreover a laboratory generation system has been built and tested.

Power quality improvement of small hydro station

“…The analysis of initial slip impact on generator peak current was previously done and presented [11]. …”

Asynchronous Grid Connection of a Cage Induction Generator Excited by a Power Electronic Converter

“…The most frequently used ways of cage induction generators grid connection are direct connection of an unexcited generator or application of thyristor soft-starters. The first method leads to an inrush current and a voltage drop in the local grid [3], and the second method limits the inrush current, but introduces higher harmonics to the grid [4]- [7]. However, in both systems the induction generator demand on the reactive power is covered by the grid, so the capacitor bank is used to partially compensate for reactive power demand [8], [9].…”

“…The parallel-connected electronic converter, which usually satisfies the reactive power demand of an induction generator, may decrease an inrush current of the generator during grid connection transient [3]- [16]. When the power converter is permanently connected to the grid and the induction generator is connected separately as an unexcited machine, an inrush current is reduced to only about a few percent [3]. Another way of generator connection is possible, when the parallel power converter is connected to the generator terminals and the grid connection process is related to the whole set -induction machine and power converter.…”

Pengaruh Penutupan-Balik Tak-Sinkron terhadap Generator Induksi 3-Fase dalam Skema Pembangkitan Tersebar

“…Beberapa peneliti telah mengkaji unjuk kerja dan karakteristik generator induksi yang terhubung ke saluran distribusi, baik kajian melalui simulasi maupun eksperimen. Pengaruh buruk arus transien menuju generator saat proses koneksi dapat dikurangi dengan pemasangan konverter elektronik yang bekerja sebagai konpensator daya [4]. Peningkatan faktor daya dan efisiensi dapat dilakukan dengan mengatur tegangan terminal generator [5].…”

“…Titik operasi optimum diperoleh dengan memperhitungkan perbandingan daya reaktif dan daya nyata, baik pada keadaan stand-alone maupun connected to grid [8]. Pada penelitian-penelitian tersebut tidak dibahas keadaan saat terjadi putus-sambung generator ke grid [4]-- [8]. Makalah ini mendiskusikan karakteristik tegangan, arus, dan daya di terminal generator induksi berkaitan dengan PBTS karena operasi PBO.…”