Partial Discharges In Gas Insulated Substations Research Articles

Analysis of the intrinsic characteristics of the partial discharge induced by typical defects in GIS

Partial discharge (PD) monitoring plays an important role in the maintenance of the high voltage (HV) apparatus, such as transformer and gas-insulated substation (GIS). In recent years, the ultra high frequency (UHF) method for PD detection arouses great interest of many researchers because of its high sensitivity and anti-interference capability. The coupling of UHF signal and process of the signal constitute the UHF detection method. There are three key components for the coupling of UHF signal in GIS, including the frequency spectrum characteristics of the PD source, the propagation characteristics in GIS, the coupling style and the capability of the UHF coupler. Many researchers are interested in the recognition algorithm and the analysis procedure of the PD data. But the intrinsic attributes of the partial discharges should attract more attentions because they are the foundation of the UHF detection method. This paper focuses on the intrinsic characteristics of the typical defects in GIS, such as the amplitude of the time-domain signal and frequency spectrum characteristics. Four types of typical partial discharge sources are designed and fabricated, including floating metal, protrusions, particle on the spacer, and void in solid insulation. Several different structure sizes of each defect are applied to ensure the consistency of the results and discover the factors that affect the frequency spectrum characteristics. The results of the study present the essential characteristics of the partial discharge. It can be applied to the design of the coupler and amplifier circuit. In addition, the sensitivity and anti-interference capability of the UHF method are promoted effectively, and it is valuable for calibrating the intensity of PD in GIS.

Partial discharge measurement in the ultra high frequency (UHF) range

The paper provides essentially a summary of PD measurements applying the UHF range in order to increase the detection threshold, to improve the localization accuracy and to perform on-line measurements of Partial Discharge (PD) in noisy environments. The electromagnetic UHF technique offers good signal to noise ratios, because external PD signals and disturbances can be shielded effectively. A new developed method allows the localization of PD in gas-insulated substations (GIS) by frequency domain measurements. The basic idea is the displacement law of Fourier transformation. The interference phenomena of superposed signals from two sensors give information about the time delay of the sensor signals. On-site PD measurements are made at cable connectors by means of monopole antennas housed in a barrel sleave, while the cable is in service. Thus a sensitive PD measurement even in noisy environment is possible. PD measurements on several 72 kV cable connectors were performed in an unshielded laboratory. On-site measurements during operation showed the great potential for condition assessment. For decoupling sensitive UHF PD signals from the inner of a power transformer tank UHF sensors applied through drain/oil valves are used. Experimental studies indicate that all relevant types of PD possibly occurring within a transformer emit high frequency spectra to be detected with UHF sensors. Furthermore in laboratory experiments and on-site measurements very moderate UHF signal attenuations have been observed.

Separation of Corona Using Wavelet Packet Transform and Neural Network for Detection of Partial Discharge in Gas-Insulated Substations

It is essential to detect partial discharge (PD) as a symptom of insulation breakdown in gas-insulated substations (GIS). However, the accuracy of such measurement is often degraded due to the existence of noise in the signal. In this paper, a method using wavelet packet transform and neural network is proposed to separate the PD pulses from corona in air, which enables more accurate detection of insulation breakdown of GIS.

Resonance characteristics and identification of modes of electromagnetic waves excited by partial discharges in GIS

Electromagnetic waves are used for detection of partial discharges (PD) in GIS (gas-insulated substations). A very wide frequency band up to 1.5 GHz is utilized for detection. There are three categories of electromagnetic wave which can be excited and propagate in coaxial cylindrical structures like GIS, namely, TEM, TE, and TM modes. The characterization and identification of each mode is indispensable to understanding the partial discharge phenomena in GIS. In this paper, peaks in the frequency spectrum excited by PD are identified in each mode and the resonant characteristics of each mode are studied. The following are the major results: (1) The resonance peaks appear at the frequencies defined by the spacer distance. (2) The intensity of each mode depends on the position of discharge source along the radial direction. The lower-order modes including TEM are excited when a discharge source is located near the center conductor. On the other hand, higher-order modes are excited when the discharge source is at the enclosure surface. (3) The experimental profile of each mode excited by PD along the radial direction approximately agrees with the general theory of electromagnetic wave propagation in coaxial cylindrical cavity. © 2000 Scripta Technica, Electr Eng Jpn, 131(2): 1–11, 2000

The excitation of UHF signals by partial discharges in GIS

The fundamental theory of the UHF method for detecting partial discharge (PD) in gas insulated substations (GIS) is presented. The effects of position, size, current amplitude and pulse shape of the PD source on the UHF signal can be predicted using this theory. Excitation of propagating electromagnetic waves by a PD current pulse within the coaxial waveguides formed by GIS components is explained by making use of dyadic Green's functions for the electric fields of propagating modes. Experiments with a coaxial test chamber are used to verify the theoretical predictions, and comparisons are made between measured and simulated UHF signals. Some implications for the UHF measurement of PD are discussed, together with positioning and sensitivity requirements for UHF couplers. A scheme is proposed for standardizing PD measurements made using the UHF technique.

Broadband couplers for UHF detection of partial discharge in gas-insulated substations

The paper describes investigations of the UHF performance of a disc coupler designed for continuous monitoring of partial discharge in gas-insulated substations and indicates how the UHF sensitivity can be improved. Resonant frequencies of the disc are calculated, and the coupler is shown to be most sensitive at these frequencies. The bandwidth of the coupler can be extended by coupling the UHF signal from the edge of the disc, allowing detection of a greater number of the possible resonant modes of the disc, including the dominant, lowest frequency mode. Sensitivity to the UHF signals generated by partial discharge can be further improved by various means. The disc can be earthed at certain points while still retaining the coupling function. A novel nonresonant experimental coupler design is also presented, based on the design techniques used for broadband log-spiral antennas. The frequency response of the spiral coupler is much flatter than that of a comparable disc coupler.

Development of detection and diagnostic techniques for partial discharges in GIS

This paper describes detection and diagnostic techniques for partial discharges in gas insulated substations (GIS). Partial-discharge current waveforms of SF/sub 6/ gas and external noise characteristics of actual substations were investigated, and a measuring system having sensors in GIS and employing frequency range of VHF band was developed. By this system, detecting very small partial discharges of several 10 pC level has become possible. Also, a neural network system, focusing attention as a method for recognizing patterns, was applied for determining causes for partial discharge in GIS, and its applicability has been proved. >

Partial discharge. X. PD in gas-insulated substations-measurement and practical considerations

For pt.IX see ibid., vol.7, no.6, p.5 et seq. (1991). An overview of engineering practice related to partial discharge (PD) measurements in gas-insulated substations (GISs) is provided. The following questions are addressed: why measure PD in GIS?; in which phases of the life cycle should PD be measured?; what PD measurements are presently available?; and, what results can be expected under various measurement conditions?.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Partial discharge. IX. PD in gas-insulated substations-fundamental considerations

For pt.VIII see ibid., vol.7, no.5, p.9 et seq. (1991). The physical aspects of partial discharge (PD) in SF/sub 6/ gas-insulated substations (GIS) are reviewed. The orientation is toward present and developing techniques for evaluating defects in solid and gaseous insulation systems on the basis of PD measurement. Standard evaluation methods provide an indication of PD in GIS, but cannot quantitatively determine the type and size of defect. Statistical analysis of PD activity, together with physical models for the various types of discharge and defects, provides the basis for more advanced interpretation. Measurements of PD activity that do not require an absolute calibration are of greatest utility. >