DC Partial Discharge Research Articles

Diagnostic Methods in Revealing Internal Moisture in Polymer Housed Metal Oxide Surge Arresters

Diagnostic measurements performed for surge arresters are normally studied by evaluating their suitability to detect ageing and degradation of metal oxide material. The suitability of different methods for revealing intemal moisture in arresters has not been studied much. This aspect is considered in the paper based on measurement results obtained during a 1.5 year laboratory test series conducted for six different types of polymer housed distribution class arresters. AC power losses, third harmonic content of resistive leakage current, DC leakage current and partial discharge measurement results over the test period are given and discussed. Details of the measurement procedures suitable for measuring polymeric arresters with intemal moisture are also studied. AC power loss and DC leakage current measurements were found to be good methods, while the other two can only be used as additional methods when diagnosing intemal moisture in polymer housed arresters.

Space charge behaviour and corona stabilization effect in SF6 gasviewed from sequential generation of a dc partial discharge

We investigated the sequential generation characteristics of partialdischarge (PD) pulses in SF6 gas under the application of a positive dcvoltage, in order to discuss the PD mechanism based on space charge behaviourand corona stabilization effect. Highly time-resolved measurement of PDcurrent pulses enabled us to discuss the relationship between the PD chargeq and the time interval Δt of sequential PD pulses. Experimentalresults revealed that q-Δt characteristics exhibited negative andpositive correlation at small and large Δt regions, respectively.Numerical calculations of ion diffusion and ion drift verified thetime-dependent characteristics of the space charge behaviour and the resultantcorona stabilization effect.

On the influence of measuring circuit on a DC partial-discharge repetition rate

A simple model of DC partial discharges running in cable and capacitor dielectrics is described in order to investigate the influence of the measuring circuit on the DC partial-discharge repetition rate. This model shows that the measuring circuit can only influence the discharge repetition rate temporarily. On reaching the stationary state the DC partial discharges are governed by the electric qualities of the dielectric used.

Ramp Technique for DC Partial Discharge Testing

A stepwise ramp technique has been used successfully in direct current (dc) partial discharge (PD) testing on high voltage components and on resin-packaged HV devices such as the Faint Object Camera for the Space Telescope. PD data is acquired separately on part-way ramps to rated voltage and on the intermediate voltage plateaus. For test specimen intended for dc service, this ramp method gives more information about insulation integrity than purely quiescent dc measurements. This is especially true for specimens of high resistivity which causes the discharge frequency to be deceptively low at constant dc voltage. By contrast, during ramping upwards the voltage distribution is capacitive, and the PD behavior resembles that of an ac test. This gives many more pulses in the voids, and without the undesirable heat produced if 60 Hz ac were applied. PD histograms are presented on various materials, with and without intentional defects. Influence of test parameters such as ramping speed are discussed. Experience with a variety of samples and commercial HV capacitors, as well as their life test performance, can lead to approximate acceptance/rejection criteria.

Partial Discharge Testing under Direct Voltage Conditions

DC partial discharge (PD) (corona) testing is performed using a multichannel analyzer for pulse storing, and data is collected during increase of voltage and at quiescent voltage levels. Thus high voltage ceramic disk capacitors were evaluated by obtaining PD data interspersed during an accelarated life test. Increased PD activity was found early in samples that later failed catastrophically. By this technique, trends of insulation behavior are revealed sensitively and nondestructively in high voltage dc components.

Screening Method and Accelerating Test of DC Partial Discharges in Molded Polyethylene Components

A method for measuring simultaneously the dc partial discharge of many samples, a screening method by soft X-rays and a voltage and/or temperature accelerating test are proposed in order to save time for measuring the dc partial discharge. Theoretically, it is possible to distinguish a sample where the dc partial discharge has occurred from many other samples by using the band pass filters having different central frequencies at both sides of the samples and the detector parts.It is also clarified that soft X-rays are useful in detecting the cavities in polyethylene. From the voltage and temperature dependence of the repetition rate of the dc partial discharge, the following acceleration coefficient is obtained: α=(\\frac{V_{2}}{V_{1}})n\\frac{\\sum\\limits_{j{=1}}^{N_{2}}\\cfrac{1}{E_{ij}}}{\\sum\\limits_{j{=1}}^{N_{1}}\\cfrac{1}{E_{ij}}}exp {\\frac{W}{k}(\\frac{1}{T_{1}}-\\frac{1}{T_{2}})} where the voltage, the temperature and the number of discharge sites are changed from V1, T1 and N1 to V2, T2 and N2, respectively; Eij is the discharge inception stress of the jth discharge site; and W is the thermal activation energy of polyethylene.