STANDARD. Third edition. High-voltage test techniques –. Partial discharge measurements. This English-language version is derived from the. voltage testing techniques, was submitted to the IEC-CENELEC parallel vote and was The text of the International Standard IEC was approved by. between conductors and which can or can not occur adjacent to a conductor. - IEC High-voltage test techniques – Partial discharge measurements.
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A general correlation between the measurement according to IEC standard and measurements in the UHF range is not possible. By the use of a. 3 days ago PDF | Defect classification using partial discharge (PD) measurement has Around RF and IEC PD pulses have been recorded. Partial Discharge IEC - Download as PDF File .pdf), Text File .txt) or read online.
IEC From a physical point of view self-sustaining elec- [High-voltage test techniques — Partial discharge mea- tron avalanches may happen only in gaseous dielectrics. Moreover, also happen in gaseous inclusions due to imperfections the maintaining of specific characteristics of PD mea- in solid and liquid dielectrics.
The pulse charge of glow suring systems by the user in a record of performance discharges is in the order of few pC. Streamer discharges is recommended. A transition from streamer to tap coupling mode which is generally utilized for induced WG leader discharges may occur if the pulse charge exceeds voltage tests of liquid-immersed power transformers.
Here the high voltage bushing capacitance C1 represents in principle the coupling capacitor Ck. The measuring Original PD current pulses are characterized by a dura- impedance Zm is connected to the tap of a capacitive tion as short as few ns, as exemplarily shown in Fig. Con- graded bushing, usually intended for loss factor mea- sequently, the frequency spectrum covers the VHF and surements. UHF range. The shape of such pulses, however, is strongly distorted if traveling from the PD site to the terminals of External electromagnetic noises disturbing sensitive the test object.
Different to this behavior the current-time PD measurements can be eliminated at certain extend if integral is more or less invariant. As a consequence, not the a balanced bridge is employed. Here both, the measur- peak value of the PD current pulses but the current-time ing and the reference branch, consist of a coupling unit integral, i.
The most common cir- measurement of the apparent charge an evaluation of cuit employed in practice is shown in Fig. An and extinction voltage, as well as the pulse repetition rate, option of the PD coupling unit is the so-called bushing the pulse repetition frequency, the phase angle, the aver- age discharge current, the discharge power and the quadratic rate.
All these quantities, however, are either derived from or related to the appar- ent charge, which can thus be considered as the most important PD quantity to be evaluated.
For measuring the apparent charge conven- tional analogue PD instruments are equipped with a band-pass filter amplifier followed by a peak level indicator. As long as the band-pass filter extracts the measuring frequency in a range where the spectral density of the PD Fig.
Another option for measuring the apparent charge The main feature of a digital PD measuring system is a very wide-band pre-amplification of the PD signal is the ability to store the following characteristic param- captured from the test object followed by an electronic eters of each PD event: integration.
This principle offers several advantages not only for the reduction of electromagnetic interferences, ti — instant time of PD occurrence but also for the location of PD faults in long power cables. A bloc diagram for a computerized PD visualization of phase-resolved PD patterns.
This ensures measuring system is shown in Fig. Here the digitaliza- the evaluation of all PD quantities recommended in IEC as well as an in-depth statistical anal- ysis of the very complex PD occurrence. More- over, a PD pulse waveform analysis can be per- formed capable for the location of the PD site in power cables as well as for the recognition of different PD sources and also for the de- noising of PD signals.
The quantitative assessment of the appar- Fig. Therefore, knowledge rules for PD diagnosis have been established in the past which are based on practical experiences gained from comprehensive PD studies in laboratory and on-site.
That means the response at the output of the PD instrument and thus the reading of the peak level indicator is proportional to the apparent charge. Another option for measuring the apparent charge is a very wide-band pre-amplification of the PD signal captured from the test object followed by an electronic integration.
This principle offers several advantages not only for the reduction of electromagnetic interferences, but also for the location of PD faults in long power cables. The performance of such an electronic integrator is shown in Fig. Nowadays the conventional analogue PD pulse processing is more and more substituted by the advanced digital technique.
A bloc diagram for a computerized PD measuring system is shown in Fig. Here the digitalization of the PD pulses captured from the test object is done in the real-time mode, i. The main feature of a digital PD measuring system is the ability to store the following characteristic parameters of each PD event: ti instant time of PD occurrence qi apparent charge at ti ui test voltage magnitude at ti i phase angle at ti The vector [qi ui ti i] stored in the computer memory is utilized for further processing as well as for a visualization of phase-resolved PD patterns.
This ensures the evaluation of all PD quantities recommended in IEC as well as an in-depth statistical analysis of the very complex PD occurrence. Moreover, a PD pulse waveform analysis can be performed capable for the location of the PD site in power cables as well as for the recognition of different PD sources and also for the denoising of PD signals.
Consequently, the PD severity of HV apparatus cannot be estimated on the basis of the apparent charge alone, because the No. Therefore, knowledge rules for PD diagnosis have been established in the past which are based on practical experiences gained from comprehensive PD studies in laboratory and on-site.
To measure this quantity in terms of pico Coulomb pC the Standard IEC specifies a calibration method which is based on the simulation of the internal charge transfer between the PD source and the terminals of the HV apparatus by means of an external adapted calibrator, as evident from Fig.
Based on this calibration procedure the apparent charge of a PD pulse is defined in IEC as: that charge which, if injected within a very short time between the terminals of the test object in a specified test circuit, would give the same reading on the measuring instrument as the PD current pulse itself. The PD calibrator is generally equipped with a pulse generator connected in series with a calibrating capacitor. In order to simulate the transient voltage across the PD defect the pulse generator creates equidistant voltage steps of known magnitudes U0.
If the value of the calibrating capacitor C0 is substantially lower than the value of the virtual test object capacitance Ca, the calibrating charge injected in the test object terminals, see Fig. This should be performed prior each PD test.
Determination of the specified characteristics of the complete PD measuring system.