Self-excitation Of Induction Generator Research Articles

Experimental determination of minimum capacitor for self-excitation of induction generators

This article addresses the issue related to determining the minimum capacitor required for the self-excitation of an induction generator. The determination of the minimum capacitance required for the self-excitation of a self-excited induction generator has already been the subject of several previous studies. It has been shown that the minimum capacitance depends on the rotation speed and the remanent magnetism. The study carried out in this paper shows that, in addition to the rotation speed and the remanent magnetism, there is a third parameter that has an influence on the self-excitation process, which is the acceleration or, in other words, the rotation speed ramp-up. In this paper, several experimental self-excitation tests for different values of the rotation speed ramp-up are carried out, leading to new characteristics of the minimum self-excitation capacitance as a function of the rotation speed. The results obtained from simulation and experimental studies prove the efficacy of the proposed approach.

Evaluation of the Capacitor Bank Design for Self-Excitation in Induction Generators

This paper presents an evaluation of the capacitor bank design for self-excited induction generators, which can be used in diesel groups. A methodology capacitor bank design is compared with the design from the magnetizing reactance of the three-phase induction generator. Assesses what types of capacitor bank design is ideal for self-excitation of the induction generator.

A study of the conditions of induction generator self-excitation

The results of studying in a classical way the self-excitation conditions of a two-phase induction generator with a phase-wound rotor and series-capacitor excitation are presented. The studies are performed with typical assumptions allowing the induction generator to be considered as a linear dynamic system with harmonic coefficients varying with the same frequency. An analytical solution is found for the system of linear homogeneous differential equations with harmonic coefficients describing an induction generator with capacitive self-excitation. The solution analysis made it possible to obtain strict conditions of its self-excitation. Correctness of the results is verified using mathematical simulation.

Influence of idling and short circuits on the self-excitation of a classical double-output induction generator

Experimental results for the capacitor self-excitation of an induction generator with a short-circuited phase rotor and a classical double-output induction generator are compared. The influence of the preceding conditions on the capacitor self-excitation of a classical double-output induction generator is the opposite of that for an induction generator with a short-circuited phase rotor. For the classical double-output induction generator, self-excitation is better after a three-phase short circuit than after idling.

The Complex Hurwitz Test for the Analysis of Spontaneous Self-Excitation in Induction Generators

Spontaneous self-excitation in induction generators is a fascinating phenomenon triggered by the instability of a zero equilibrium state. Prediction of this condition for various values of free parameters requires many computations of the eigenvalues of a 6 × 6 matrix over a large space. The technical note uses a novel approach to stability using a transformation of the state-space system and an extension of the Hurwitz test to polynomials with complex coefficients. The analytic formulas that are obtained give the values of the minimum load resistance, the range of capacitor values, and the range of speeds for which spontaneous self-excitation appears. The technical note concludes with an illustration of the results on an example.

Analysis of Triggered Self-Excitation in Induction Generators and Experimental Validation

In self-excited induction machines, a power generating mode of operation can often be attained only by precharging at least one of the capacitors connected to the windings. The paper shows how a carefully derived state-space model with nonlinear magnetic characteristics enables the assessment of all possible operating regimes including their stability properties. In particular, the analysis reveals the possible existence of an unstable operating regime, which creates a barrier that must be overcome through precharged capacitors. In such case, the analytical results of the paper yield a simple formula that predicts the voltage needed to trigger self-excitation. Close to the boundary, voltages can be generated for extended periods of time before growing to a stable operating regime, or collapsing to zero. Experimental results validate the results of the paper on the transient properties of self-excited induction generators.

Considerations of Islanding and Self-Excitation Problems of Induction Generators

Islanding of induction generators for wind power generation systems causes a variety of problems and must be prevented islanding in especial. In Japan, Ministry of International Trade and Industry (MITI) revised "technical requirements for distributed generators in the distribution systems" in 1998. The technical requirements do not require islanding detection systems for the wind power generation systems consist of the induction generators. However, if reactive power of the induction generators and capacitors of the distribution systems are closely matched, islanding detection by conventional relays become difficult because of self-excitation of induction generators. In this paper, islanding phenomenon of the induction generator, so called the self-excitation, is studied by analytical procedures. The analytical procedures and related simulation results, using Electro-Magnetic Transients Program (EMTP) and Transient NetworkSimulator (TNS), are described.

Impact of cross-saturation on accuracy of saturated induction machine models

Cross-saturation in smooth air-gap AC machines has been a subject of controversy in the 1980s. The discussions were based on the model of a saturated AC machine with d-q axis winding currents acting as state-space variables. The recently introduced concept of generalised flux and generalised inductance has enabled the derivation of a series of models of saturated smooth air-gap AC machines for various selections of state-space variables. All the models, except for the winding flux model, contain explicit terms that describe cross-saturation. The aim of this paper is to compare behaviour of various models when cross-saturation is neglected. Two transients of a single-cage induction machine are analysed: motor starting with increased voltage; and induction generator self-excitation. Some experimental results are included. It is shown that the impact of cross-saturation on accuracy depends on the type of the model. All the models that ask for a time derivative of the generalised inductance yield poor results if cross-saturation is neglected. However, the models that require a time derivative of the inverse of the generalised inductance are basically unaffected. Thus these models can be simplified without any loss of accuracy.

General method of magnetising flux saturation modelling in d–q axis models of double-cage induction machines

Two models of induction machines with two rotor windings, that include magnetising flux saturation, are available at present: the first one is the current state-space model, where state-space variables are selected as d-q axis components of stator and both rotor currents; while in the second model state-space variables are d-q axis components of stator and both rotor flux linkages. The paper presents a general procedure for inclusion of magnetising flux saturation in a d-q axis model of induction machines with two rotor windings. Using the procedure, it becomes possible to derive a model of a saturated induction machine with two rotor windings for any selected set of state-space variables. The approach to magnetising flux saturation modelling relies on the concept of 'generalised flux space vector', which has recently been introduced for single-cage induction machines. Several characteristic models of a saturated induction machine, derived by applying the concept of the generalised flux space vector, are presented in detail. In order to verify the models, an extensive simulation study of the double-cage induction generator self-excitation process is performed, accompanied by the corresponding experimental investigation. The main results of the study are included. Finally, advantages of some of the novel models over the existing ones and possible applications are addressed.

Case study on the integration of a non-utility induction generator to the Hydro-Quebec distribution network

This paper investigates the influence of different factors (such as load and capacitive compensation levels, load and turbine dynamic behaviors, machine parameters) on induction generator self-excitation phenomena and related overvoltages, resulting from a fault and/or an unwanted network disconnection. Simulations are performed on a 25 kV distribution network related to an actual project of integration of a nonutility induction generator to the Hydro-Quebec power system. The paper presents the analysis of the results, as well as the derived guidelines for the determination of new relay settings and integration criteria for the Hydro-Quebec distribution network. >

A unified approach to main flux saturation modelling in D-Q axis models of induction machines

Main flux saturation is most frequently modelled by selecting either stator and rotor d-q axis currents or stator and rotor d-q axis flux linkages as state-space variables. This paper attempts to unify main flux saturation modelling in d-q axis models of induction machines by presenting a general method of saturation modelling. Selection of state-space variables in the saturated machine model is arbitrary and appropriate models in terms of different state-space variables result by application of the method. A couple of models, obtainable with different selection of state-space variables, are presented. The cross-saturation effect is explicitly present in all the models, except for the one with stator and rotor flux linkage d-q axis components as state-space variables. The models are verified by simulation and experimental investigation of induction generator self-excitation. >

Modelling of deep-bar and double-cage self-excited induction generators for wind-electricity generation studies

The paper presents the derivation of a current state-space model of saturated deep-bar and double-cage induction machines. The approach adopted in the paper closely parallels that utilized in the derivation of the current state-space model of a saturated single-cage induction machine. The developed model is then adapted to the terminal conditions met in the self-excitation of induction generators. Simulation of voltage and current build-up during self-excitation is performed. Simulation results are confirmed by experimental investigation, thus providing verification of the derived saturated double-cage induction machine model. It is believed that the model could be very useful in transient studies concerning unconventional energy sources, especially wind-electricity generation.

Shunt capacitor failures due to windfarm induction generator self-excitation phenomenon

In this paper, a capacitor failure at a wind energy electric generation facility is investigated. The probable cause of the capacitor failures is identified to be overvoltage resulting from self-excitation of the induction generators. Relationships between the voltage escalation and the characteristics of the wind turbines is evaluated. Results of time domain digital simulation are presented along with a comprehensive explanation for this particular type of self-excitation phenomenon. The nature of the problem indicates that similar events could occur in any windfarm which uses capacitor compensation for the reactive power demand of induction generators. Methods for avoiding occurrences similar to that described in this paper are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Factors influencing the protection of small-to-medium size induction generators

The performance and unique characteristics of induction generators as they relate to the protection of the units are discussed. Machines in the range of several kW up to 1500 kW are considered. Contrasts are provided to demonstrate the differences in protection suggested for traditional synchronous generators and induction units. The need for overvoltage protection due to self-excitation of induction generators under load rejection is addressed. Recommendations are provided for the minimum amount of protection on these units in several electrical system configurations as they might apply to single or multiple-unit installations. >

Ferroresonance and Loading Relationships for DSG Installations

Self-excitation of induction generators or small synchronous generators connected to distribution feeders is analyzed during the transient period following the islanding of a generator on the feeder. The relationship of feeder load after separation and the occurrence of ferro-resonance with an isolated induction, synchronous or single-phase generator are developed. The results indicate that an isolated distribution system generator (DSG) can theoretically support as much as three times the generator's rated power output in a ferroresonant mode provided the prime mover has the needed inertia or torque available at the abnormal isolated speed. The abnormal voltage and frequency operation during separation modifies load, generator, and prime mover characteristics and may result in an energy balance, although such balance is not obvious before separation.

The process of self excitation in induction generators

The phenomenon of self excitation in induction machines is examined and a physical interpretation of how self excitation occurs is presented. The important parameters are shown to be the shaft speed, the residual magnetism, the reduced permeability at low magnetisation, and the size of the capacitor connected to the machine. The results are important in applications where induction machines are used as stand-alone generators for a power system, as the reliability of self excitation in such cases must be very high.