Analysis of Three Phase Self Excited Induction Generator Using by smapdi62


									     Analysis of Three Phase Self Excited Induction
       Generator Using MATLAB/SIMULINK
                                Prerna Gaur, Avinash Kishore
                                        N.S.I.T., India

    SELF excited induction generator (SEIGs) are slowly replacing conventional synchronous
alternator in isolated power generation because of the former ruggedness lower unit cost, relative
ease of operation and maintenance easily availability in lower rating even under low speed
operation. Since a majority of loads even in isolated system are dynamic in nature, wider
applicability of the SEIGs would depend on its capacity to handle such loads satisfactorily.
Another bottleneck in the applicability of the SEIG is its inherent poor voltage regulation,
and the conquest requirement of a well designed voltage regulator. The cost complexity and
operational problems associated with the regulator often vitiate the advantage gained in using
an induction machine for isolated application.
    In an externally driven three phase induction motor, if a three phase capacitor bank is
connected across it’s stator terminals, an e.m.f. is induced in the machine windings due to self
excitation provided by the capacitor. The magnetizing requirement of the machine is supplied
by the capacitors.
    For self excitation to occur, the following two conditions must be satisfied:
   1. The rotor should have sufficient residual magnetism.
   2. The three phase capacitor bank should be sufficient value.
If the rotor has sufficient residual magnetism, a small e.m.f. is developed in the stator winding.
The e.m.f. if sufficient in magnitude would circulate leading current in the capacitors. The flux
produced due to these currents would assist the residual magnetism. This would increase the
machine’s flux .This process is thus cumulative and the induced voltage keeps on rising until
saturation is reached. As saturation occurs, the flux becomes constant and final steady state
value of the voltage is obtained. This voltage continues to exist till value of capacitance and
speed dare maintained favorably. Also, the value of the three capacitance bank should be of
sufficient magnitude in order to initiate self excitation and generate e.m.f of suitable value.
    To start with steady state analysis of the SEIG with the static load is critically analyzed. The
analytical technique used for the static load is found not directly applicable to dynamic load.
Consequently, a program is developed to predict the steady state performance of the SEIG.
Effect of capacitance on the performance of the SEIG is studied to enable selection of suitable
capacitor for a given operating condition. To start steady state analysis a equivalent circuit
is presented which represent the steady state model of SEIG. Using that circuit a equations
is developed to obtain the steady state behavior of the SEIG. In the steady state analysis
the magnetizing property of the machine is assumed to be linear. Following the circuit the
parameters are obtained.
    Following the steady state investigation response of the SEIGs for the different transient
conditions is studied to know it’s suitability to sudden switching of loads. The d-q axes model
which is widely used for the analysis of an induction motor is developed for the SEIGs system.
The condition which are considered for the studied include onset of self excitation, load per-
turbation, loss of excitation and short circuit. Starting of the induction motor by the SEIGs is
studied and methods for reliable starting of the motor are suggested. Based on the inferences
drawn from the steady state and transient performance of the system, guidelines are suggested
for the design and operation of a dedicated SEIG system for applications such as irrigation
pump sets.

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