In this paper, we present a method that simplifies the interconnect complexity of N × M resistive sensor arrays from N × M to N + M. In this method, we propose to use two sets of interconnection lines in row–column fashion with all the sensor elements having one of their ends connected to a row line and other end to a column line. This interconnection overloading results in crosstalk among all the elements. This crosstalk causes the spreading of information over the whole array. The proposed circuit in this method takes care of this effect by minimizing the crosstalk. The circuit makes use of the concept of virtual same potential at the inputs of an operational amplifier in negative feedback to obtain a sufficient isolation among various elements. We theoretically present the suitability of the method for small/moderate sized sensor arrays and experimentally verify the predicted behavior by lock-in-amplifier based measurements on a light dependent resistor (LDR) in a 4 × 4 resistor array. Finally, we present a successful implementation of this method on a 16 × 16 imaging array of LDR.

A new discrete circuit for readout of resistive sensor arrays

The coherent phase detection technique is used for location of partial discharge (PD) in transformer windings. The experimental studies are performed on a 22-kV interleaved winding to prove the feasibility of the method.

Coherent Phase Detection Technique for Location of Partial Discharge in Transformer Windings

In 2D resistive sensor arrays, the interconnections are reduced considerably by sharing rows and columns among various sensor elements in such a way that one end of each sensor is connected to a row node and other end connected to a column node. This scheme results in total N + M interconnections for N × M array of sensors. Thus, it simplifies the interconnect complexity but suffers from the crosstalk problem among its elements. We experimentally demonstrate that this problem can be overcome by putting all the row nodes at virtually equal potential using virtual ground of high gain operational amplifiers in negative feedback. Although it requires large number of opamps, it solves the crosstalk problem to a large extent. Additionally, we get the response of all the sensors lying in a column simultaneously, resulting in a faster scanning capability. By performing lock-in-amplifier based measurements on a light dependent resistor at a randomly selected location in a 4 × 4 array of otherwise fixed valued resi...

Crosstalk suppression in networked resistive sensor arrays using virtual ground technique

Summary

One of the important research areas in transient phenomena is sensitive recognition of fault in the complicated insulation system of transformer to make a decision about either go (acceptance) or no-go criterion after impulse test at factory. The existing methods are, in principle, able to indicate the delay in coupling between the signals, but inferring causality from the time delay is not always straightforward. In this paper, the time delay between simultaneously measured signals is calculated and further extended to identify the impulse fault in transformers using Granger causality analysis. The principle of Bayesian information criterion is used in Granger causality analysis to estimate the minimum number of lags. Granger causality analysis enables the calculation of neutral current signal for any input excitation of full wave and chopped wave impulse for typical power transformers. The experimental studies are performed on 60/90 MVA (132/33 kV) and 150/200/250 MVA (500/275/33 kV) transformers to prove the feasibility of the analysis. Copyright © 2015 John Wiley & Sons, Ltd.

Prediction of winding faults between non-stationary signals: Granger causality analysis for lightning impulse testing of transformers

Changes in resonant frequencies of a winding can identify the location of breakdown during impulse tests. This is difficult with a uniform winding. We propose the use of concurrent UHF antenna and winding currents in order to locate breakdown. The work can be extended to identify partial discharge events in dry type transformers.

Location of breakdown in windings using concurrent UHF antenna and current responses

A method is proposed for recognizing PD events within a winding during impulse tests using a lock-in amplifier technique. The resonant frequencies of the winding serve as the basis of selection of the lock-in amplifier reference frequencies. It is implemented with a virtual instrument and validated with an independent stand-alone lock-in amplifier. A physical model of a winding with discrete elements is used to demonstrate the results. A theoretical basis for the instrument is established using an 'abc' model of PD along with a linear discrete winding model. The influence of location of PD is also addressed. The method will provide online recognition of PD during the impulse test and can be adapted for onsite measurements.

M. Gopalakrishnan

Papers

A Lock-in Technique for PD Measurement during Impulse Tests