Assessment of the insulation serviceability of turbo-generator stators and of high-voltage bushings

SynopsisMethods of calibrating circuits for measuring partial discharges and radio-interference (r.i.) voltages are discussed. It is shown that discharge-measuring circuits, whether using a peak-measuring discharge detector or an r.i. meter, are best calibrated by applying a charge-quantity pulse calibrator of known repetition frequency in parallel with the test sample. The calibration of circuits for measuring r.i. voltages is more complex, and certain anomalies arise when a sine-wave signal generator is used to calibrate the circuit in terms of voltage input.It is established that, for a pulse-repetition rate of lOOpulse/s, it is possible to relate the results obtained from a conventional peak-reading discharge detector to those from a quasipeak r.i. meter; e.g. for a meter having 60 Q input impedance and a bandwidth of 9kHz, the relationship is: 1 JUV is equivalent to 2-6pC. At repetition rates other than lOOpulse/s, it is shown that theoretically the maximum error involved by using the above relationship is 6dB between 25-2000pulse/s. Practical measurements confirm that the error does not exceed ±6dB over a wide range of pulse sizes and repetition frequencies.Comparative measurements have shown that the conventional r.i. meter is approximately an order of magnitude less sensitive than a tuned-circuit discharge detector. Methods of improving the sensitivity of the former are described.It is concluded that for many applications either a discharge detector or an r.i. meter will enable both discharge magnitude and r.i. voltage to be determined with sufficient accuracy, considering the erratic behaviour of pulses in practice.

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“…According to CISPR publication 1,1961 repetition frequency n as shown in Fig. 3, which is reproduced from data in the CISPR specification.…”

Section: Fig 3 Variation Of Quasipeak Detector Factor With Pulse-repmentioning

confidence: 99%

Calibration and comparison of partial-discharge and radio-interference measuring circuits

Dembinski

Douglas

1968

Proc. Inst. Electr. Eng. UK

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“…The progressive deterioration of high voltage machine insulation is assessed through non destructive techniques like measurement of Insulation Resistance, Polarization Index , Dissipation factor , capacitance, Partial Discharge (PD) activity, etc. [1,2,3]. Methods based on Low frequency dielectric spectroscopy are also reported for stator insulation condition assessment [4,5].…”

Section: Introductionmentioning

confidence: 99%

Low frequency dielectric response of thermally degraded epoxy-mica insulation

Rao

Sudhindra

Ramachandra

2009

2009 IEEE 9th International Conference on the Properties and Applications of Dielectric Materials

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Dielectric spectroscopy measurement is essentially a dissipation factor measurement performed at multiple frequencies ranging from few mHz to kHz. Low frequency dielectric spectroscopy measurement has been performed on number of sound and thermally aged epoxy-mica representative laminates and on actual motor coils.Dielectric loss angle, Power Factor, capacitance was measured at frequencies ranging from I mHz to 1 kHz. The dielectric response exhibited by of thermally aged epoxy-mica insulation at lower frequencies shows the predominant influence of interfacial polarization on the total dielectric response of epoxy-mica layer.

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High-voltage stator insulation assessment by measurement of loss tangent and capacitance

Burnley

1989

IEE Proc. B Electr. Power Appl. UK

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Assessment of the insulation serviceability of turbo-generator stators and of high-voltage bushings

Cited by 6 publications

References 12 publications

Calibration and comparison of partial-discharge and radio-interference measuring circuits

Calibration and comparison of partial-discharge and radio-interference measuring circuits

Low frequency dielectric response of thermally degraded epoxy-mica insulation

High-voltage stator insulation assessment by measurement of loss tangent and capacitance

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