Multichannel Printing Voltmeter Using Intel Sdk - 85 Kit

ABSTRACT

The design of a data logger to print voltages from eight channels at a programmed time interval is described. Software interfacing of the numeric printer is done With minimum hardware to print voltages, time interval and the number of measurement-cycle.     

Relaxation studies on power equipment

This paper describes a method of studying and modeling the dielectric relaxation for stationary power apparatus in an interconnected network to get the necessary aging indicators. The polarization phenomenon was studied using Recovery Voltage (RVM) and Polarization Current (PCM) Measurements on individual power apparatus and on network with other connected apparatus. Because of dielectric absorption in composite insulation, all RVM responses showed a single peak response and the response was linear with charging voltage. PCM decreased monotonically with a sudden drop in the initial period and after 100 s, it decreased very slowly and the response was linear with charging voltage. The responses were analyzed by modeling the dielectric function as an exponential function and as two-time dependent fractional power law function to determine suitable aging parameters. Exponential function model was found to fit both responses to get an equivalent electrical circuit of the system. Interrelation of RVM and PCM was established in most of the cases. Predicted dielectric response function for generator was more linear with time than for transformers and cable. In the frequency plane, it was found to have distinct regions of relaxation spectrum. Studies indicated that the parameters of fit for RVM response with each charging period differed from all RVM responses.     

Programmable Integrator

ABSTRACT

The programmable integrator is a digital instrument used for estimating the area or coulombs rapidly and accurately in any portion of I-t curve (current-time). There are two ways by which programming can be done. In the first method, the scanning potential limits have to be set, The instrument measures the coulombs directly irrespective of scan rate. Integration can be carried out on any I-t curve which is got by varying sweep signal in a programmed mode. In the second method, starting potential and period of integration have to be set. Integration will be carried out from the instant the sweep reaches the starting potential for the programmed time period.     

The study of PD propagation phenomenon in power network

This paper presents the measured and analyzed responses of the partial discharge (PD) when it propagates in a power network from its origin to the measuring nodes. On and offline measurements are done in a power network consisting of a 16.5-kV/250-MVA-rated power generator, busbar, and step-up transformer. The simultaneously measured PD at two ends of the busbar indicated that the intensity of PD decreased as it traveled a longer distance and the time interval of its occurrence had a finite delay indicating the dominant mode of PD propagation as a transmission line. Frequency-domain analysis indicated the presence of characteristic resonance frequencies and the number increased as the measuring node moved away from the PD origin. The offline measurement by injecting an exponential PD signal at the neutral indicated that the signal will be absorbed in the generator, and the signal at the measuring node will be attenuated by 50 times and will be distorted. Pspice simulation is used to develop the network model for the propagation path. The Pspice analysis indicated that the distributed models of generator, busbar, and lumped parameter models of a transformer can be used to match the offline measurement. The model showed that each model can have the characteristic resonant peaks depending on the selected parameters and it can distort the simultaneously observed PD at two different nodes.     

A parameter identification technique for metal-oxide surge arrester models

A simple numerical technique to identify the parameters of metal-oxide arrester models is described. Using measured arrester voltage obtained under impulse test conditions the arrester parameters are determined using an optimization technique. The validity and the accuracy of the model are then assessed by comparing the predicted against the measured values of arrester energy, initial slope, residual voltage, and the overall deviation. Application of the arrester model on network system studies is illustrated.     

Frequency response characteristics of gas sensors

This paper presents the novel experimental observations and analysis of the frequency response of a sensed gas surface. The main objectives of this study were: (i) to characterise the gas sensors with additional A.C. parameters apart from reported D.C. conductance response, and (ii) to understand the A.C. conduction mechanism. The outcome of this study was that the gas sensors from Motorola, Capteur and Figaro behaved similarly with an A.C. frequency sweep. Essentially their behaviour can be characterised into three distinct frequency bands. For the Motorola micro gas sensor, the flat response from 10 Hz to around 100 kHz range was like a simple R_PC_P (a zero in admittance function) parallel circuit. From 100 kHz to around 1 MHz, the real part of admittance decreases indicating the presence of an inductive pole in admittance function. Beyond 1 MHz and up to 13 MHz, both real and imaginary parts of admittance increase significantly revealing the presence of higher order zeros. The frequency band differs for Figaro and Capteur sensors. The lumped circuit representation may be a form of representing the distributed reacting layers on the surface. Best fitting of the entire frequency range response using MATLAB indicated the presence of two poles and two zeroes or more. Cleaning by finite triangular or pulse waves restored the surface for sensing. R_P, C_P, f_C, the frequency at which reactive impedance was maximum, the measured negative peak of reactive impedance (Z_i), the slope of estimated capacitance with frequency (C_P/f) and pole/zero locations can be used as additional parameters to improve the sensitivity and selectivity of gas and other contaminating environments. The A.C. conduction mechanism indicates that the ohmic conduction (1/R_P) in the intergranular region follows the barrier theory. The majority charge carriers in the semiconductor increases with sensing temperature (T). The barrier potential decreases at high absolute humidity and longer cyclic heating duration (PW). The capacitance (C_P) may be due to the geometry of the semiconducting intergranular separation between grains. It increases with T due to the closeness at high T. The variation of C_P with f may be due to the polarisation contribution of adsorbed gas molecules.     

Possible indicators of aging in oil-filled transformers part 1: measurements

Degradation model development using basic research, and remaining life estimation, are essential for modern electrical engineering aging-asset management programs [1]. A CIGRE report [2] presents in detail the different aging factors and models, mechanisms of failure, condition-assessment and diagnostic techniques, and life assessment and extension methods.     

Off/on-line FRA condition monitoring technique for powertransformer

This letter presents a novel and sensitive frequency response analysis (FRA) technique for off/on-line condition monitoring of expensive power apparatus. The main objective is to investigate the applicability of this predictive maintenance technique to diagnosing power transformer failures, to characterize the transformer in a frequency plane for safe operation, and to develop on-line monitoring technique. The effectiveness of this technique is demonstrated on a 2.5 MVA transformer housed at the High Voltage Laboratory of Pacific Power International (PPI) and then tested on three field transformers. The on-line technique is verified on a single-phase high voltage transformer. This study shows that FRA results are very sensitive to faults. The configuration of the measurement set up, frequency range and terminations play a greater role in getting reproducible, fault-indicating results. The interpretation of the voluminous data and analysis relevant to the faults opens a gateway to develop smart power apparatus