Capacitance requirement for isolated self-exicted induction generator

Abstract

Advanced knowledge of the minimum capacitor value required for self-excitation of an induction generator is of practical interest. To find this capacitor value two nonlinear equations have to be solved. Different numerical methods for solving these equations are known from previous literature. However, these solutions involve some guessing in a trial-and-error procedure. In the paper a new simple and direct method is developed to find the capacitance requirement under R L load. Exact values are derived for the minimum capacitance required for self-excitation and the output frequencies under no-load, inductive and resistive loads. These calculated values can be used to predict theoretically the minimum value of the terminal capacitance required for selfexcitation. For stable operation C must be chosen to be slightly greater than Crnin. Furthermore, it is found that there is a speed threshold, below which no excitation is possible no matter what the capacitor value. This threshold is called the cutoff speed. Expressions for this speed under no-load and inductive load are also given. .ist of symbols RS, R , , R= p.u. per phase stator, rotor (referred to stator) and load resistance, respectively X h , Xb, X, X , = p.u. per phase stator leakage, rotor leakage (referred to stator), load and magnetising reactances (at base frequency), respectively = p.u. maximum saturated magnetising reactance = per phase terminal-excitation capacitance = p.u. per phase capacitive reactance (at base frequency) of the terminalexcitation capacitor = p.u. frequency and speed, respectively = base speed in rev/min = per phase base impedance = per phase airgap and output voltages,

Voltage and frequency control for island operated induction generators

“…This means that all the reactive power needed for magnetizing the generator at no load are produced by the capacitors. The values of the star connected capacitors are calculated from the generator parameters according to [3].…”

The Analysis and Modelling of a Self-excited Induction Generator Driven by a Variable Speed Wind Turbine

“…Loop impedance and nodal admittance methods used for the analysis of SEIG are both based on per-phase steady-state equivalent circuit of the induction machine (Figure 4), modified for the self-excitation case. They make use of the principle of conservation of active and reactive powers, by writing loop equations (Murthy et al, 1982], (Malik & Al-Bahrani, 1990), (Al-Jabri & Alolah, 1990) or nodal equations (Ouazene & Mcpherson, 1983), (Chan, 1993), for the equivalent circuit. These methods are very effective in calculating the minimum value of capacitance needed for guaranteeing self-excitation of the induction generator.…”

Steady State Modeling of Three Phase Self–Excited Induction Generator Under Unbalanced/Balanced Conditions

“…The first method is based on the generalized machine theory [5]. The second method is based on the analysis of the generalized per-phase equivalent circuit of the induction machine by applying either the loop impedance or the nodal admittance concept [6,7]. Furthermore, other studies have concentrated only on the singlephase self-excited induction generator and its voltage regulation improvement [8,9].…”