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.

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Paper presents generation system dedicated to small hydro power station. The conventional generation system uses cage induction generator which demand of reactive power is very high and then its power quality in transients and steady state is very poor. To improve the quality of power, a three level NPC power electronic parallel compensator is applied. The generation system reactive current and power is controlled using voltage oriented method. The rotating x-y frame responds space vector of the grid voltage. To prove such system a laboratory 7.5 kW generation stand was built and tested. The NPC three level converter operation was tested in transient condition during turn-on the generator to grid. As result of compensator operation the peak current was reduced. In steady state the compensator produces reactive power demanded by the generator and then the generation system reactive power demand is null.

Purpose The power electronic converter is used for the satisfaction of reactive power demand of induction generator, when grid-tied. This paper aims to present an application of STATCOM to reduce inrush transient caused by the connection of a squirrel-cage induction generator (SCIG) to the grid. Design/methodology/approach The power generation system consists of an uncontrolled prime mover, a SCIG and a power electronic converter connected to the grid. The three-phase Neutral Point Clamped (NPC) converter works as a STATCOM to satisfy a reactive power demand of the generator. A control scheme of STATCOM uses the x-y reference frame rotating synchronously with grid voltage vector and the p-q instantaneous power theory to calculate q component of grid power. Findings It is shown that the parallel converter, which works as a reactive power compensator allows decreasing transients during a grid connection of the induction generator. Research limitations/implications Transients during a grid connection of the induction generator are only partially decreased. Practical implications It is needed to compensate for the reactive power of a SCIG. The NPC converter works as a STATCOM. The converter partially reduces grid transients during generator connection. The laboratory tests are demonstrated by connection 7.5 kW induction generator to 8 kVA transformer. Originality/value The paper presents the mitigation of grid transients during connection of induction generator with the power electronic converter working as reactive power compensator.

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