To extract important information about the nonlinear signals, this letter makes the utmost of the fitting advantages of Gaussian and polynomial functions, and proposes a nonlinear signal model with broader applications. Then we focus on the parameter estimation issues of the proposed models in the presence of noises. The stability factor recursive algorithm is devised based on the increasing noisy data, which makes full use of the information from the nonlinear signals. Applying the hierarchical identification principle, a two-stage recursive algorithm with higher computational efficiency is developed for the nonlinear signals. The simulation results test the effectiveness of the proposed algorithms from the aspects of estimation accuracy and prediction effect.

Fitting Nonlinear Signal Models Using the Increasing-Data Criterion

Design of Converter transformer insulation is a major challenge. The insulation of these transformers is stressed by both AC and DC voltages. Particle contamination is one of the major problems in insulation structures, as they generate partial discharges leading it to major failure of insulation. Similarly corona discharges occur in transformer insulation. This partial discharge due to particle movement / corona formation in insulation structure under different voltage wave shapes, are different. In the present study, UHF technique is adopted to understand the discharge activity and could be realized that the characteristics of UHF signal generated under low and high fields are different. In the case of corona generated signal, the frequency content of the UHF sensor output lies in the range 0.3-1.2 GHz and is not much varied except for its increase in magnitude of discharge with the increase in applied voltage. It is realized that the current signal injected due to partial discharges/corona is about 4ns duration measured for first one half cycle. Wavelet technique is adopted in the present study. It allows one to identify the frequency content present in the signal at different instant of time. The STD-MRA analysis helps one to identify the frequency band in which the energy content of the UHF signal is maximum. Keywords—Contamination, Insulation, Partial Discharges, Transformer oil, UHF sensors.

Understanding the Discharge Activities in Transformer Oil under AC and DC Voltage Adopting UHF Technique

This paper investigates model order reduction (MOR) methods of discrete-time systems via discrete orthogonal polynomials in the time domain. First, this system is expanded under discrete orthogonal polynomials, and the expansion coefficients are computed from a linear equation. Then the reduced-order system is produced by using the orthogonal projection matrix that is defined in terms of the expansion coefficients, which can match the first several expansion coefficients of the original output, and preserve the asymptotic stability and bounded-input/bounded-output (BIBO) stability. We also study the output error between the original system and its reduced-order system. Besides, the MOR method using discrete Walsh functions is proposed for discrete-time systems with inhomogeneous initial conditions. Finally, three numerical examples are given to illustrate the feasibility of the proposed methods.

Discrete orthogonal polynomials reduced models based on shift-transformation and discrete Walsh functions

ABSTRACT For open-loop stable processes, the internal model control (IMC) provides a simple and effective parameterisation of stabilising controllers. However, for unstable processes, it cannot be directly used for control system implementation. In this paper, a new unified approach for the IMC design is proposed for stable, unstable and integrating processes, using the modified IMC (m-IMC) structure in which an additional controller is introduced along with the basic IMC. Also, the partial IMC (PIMC) concept is utilised, wherein we write the plant as the summation of stable and unstable parts and consider only the stable part as the internal model. The combined approach is thereby referred to as modified partial IMC (m-PIMC). This paper presents a graphical method to obtain controller parameters for the proposed m-PIMC to satisfy the given gain margin ( ) and phase margin ( ) specifications. Further, stability boundary and robust boundary for the controller parameters are obtained which respectively give a set of all controller parameters stabilising the close loop and a set of all controller parameters ensuring robust stability. Seven different well-known standard stable, unstable and integrating process models are considered for the proposed m-PIMC design, and simulation examples are given for four selected plant models.

Robust modified partial internal model control for stable, unstable and integrating processes

Systematic learning-based system approximation using rank-exponent method exploiting GWO algorithm

Internal model control design based on approximation of linear discrete dynamical systems

There are several reasons of failure of power transformers in a system. One of the reasons of failure is attributed to the presence and movement of metal particles in oil. These induce partial discharge due to high electrical stresses, in the transformer. In order to theoretically determine the probability of occurrence of partial discharges in a high voltage 220/132 kV autotransformer only HV winding area is modeled. A metal particle of a given size and L/R ratio is introduced at the bottom of HV winding between inner surface of winding and pressboard barrier. Under the influence of oil flow the particle moves randomly within a predefined set of solid angles. During its upward movement the trajectory of the particle is calculated. The particles during their upward movement have demonstrated three different attributes, viz. (a) the particle escapes without striking a high voltage disc. (b) It strikes a disc, however the electric stress induced by the particle at the disc does not exceed threshold voltage for PD to occur and (c) The disc struck by particle provides adequate stress for PD to occur. The present paper deals with the occurrence of PD using probabilistic method for different sizes of wire like particle

Occurrence of partial discharge induced by metal particles in high voltage transformer

The paper deals with the partial discharge in a power transformer due to presence of metallic particle in a transformer oil or mineral oil. A conducting particle is assumed to be present in the oil, between High Voltage (HV) winding and pressboard inner cylinder gap. It is assumed that particle moves in random direction along with the transformer oil. Probabilities of Partial Discharge (PD) have been calculated by assuming various field intensification factor β and threshold voltages. Simulations have been carried out to find the probability of partial discharge at different oil velocities. Results of this paper show that the probability for the occurrence of partial discharge varies with respect to field intensification factor β, threshold voltage and velocity of the oil, as particle is also assumed to move with the same velocity of oil. It is observed that probability of PD increases with β for a given threshold voltage.

Probabilistic analysis of partial discharge in power transformer due to the presence of spherical particle

The paper deals with the movement of metallic particle contaminants in transformer oil and partial discharges due to its presence inside the power transformer. Transformer oil has several particle contaminations, which float and travel along with oil in the gap between transformer discs and inner pressboard cylinder. Activity of partial discharge (PD) is analyzed using Monte Carlo technique and Computational Fluid Dynamics. Probability of PD is calculated using Monte Carlo simulation, and particle movement is traced using Computational Fluid Dynamics. Using the above methods, point of contact between particle and transformer disc under different conditions is determined. Electric stress on the particle due to disc voltage is calculated theoretically. In the present simulation, impact of field multiplication factor is considered for initiation of PD. From the results, it is observed that particle movement and partial discharge are influenced by field multiplication factor, oil velocity, type of material and starting point of the particle.

M. Ramalinga Raju

Papers

Internal model control design based on approximation of linear discrete dynamical systems

Occurrence of partial discharge induced by metal particles in high voltage transformer

Probabilistic analysis of partial discharge in power transformer due to the presence of spherical particle

Investigation of Partial Discharge Due to Particle Movement in Power Transformer Using Computational Fluid Dynamics and Monte Carlo Technique