A Lock-in Technique for PD Measurement during Impulse Tests

Abstract

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.Index Terms -Impulse test, transformer, partial discharge, lock-in amplifier, virtual instrument.

Crosstalk suppression in networked resistive sensor arrays using virtual ground technique

“…The measurements setup uses a DSP lock-in-amplifier (SRS, model SR-830) (http:// www.thinksrs.com/products/SR810830.htm ;Gaspar 2004;Palani, Jayashankar, and Gopalakrishnan 2007) and an optical chopper, which is schematically shown in Figure 3(a). The setup also contains two light sources; one source (shown on the topside in the figure) keeps the LDR's base resistance at $4.7 k by constantly illuminating it as a background light and another one modulates the LDR resistance.…”

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

“…The transfer functions obtained using CLI and FW cannot be compared, and IEC 60076 (2000) standard portrays the limitations of the transfer function method. Hence, the reliable techniques for sensitive detection of internal defects in the insulation system of transformer during the impulse test are still an active area of research [7][8][9][10][11]. The transfer function method implicitly treats the device under test as linear, but faults are always not linear.…”

“…Thus, the transfer function method is not adequate for the case of faults that occur at different instant. Hence, the reliable techniques for sensitive detection of internal defects in the insulation system of transformer during the impulse test are still an active area of research [7][8][9][10][11]. Because, owing to the complex nature of the insulation structure of transformers and in the case of minor faults (like a breakdown between a winding turns and inter disk), the exact determination of the fault is a difficult task in many practical cases.…”