Partial Discharge Pulse Sequence Research Articles

Development and Discharge Characteristics of Surface Tracking on the Interface Between the PD Suppression Coatings Outside of Stator Winding Slots

During the operation of high voltage (HV) motors, the end-winding surface can be contaminated by oil or dust, resulting in a type of intense discharge: surface tracking, which gradually develops into phase-to-phase or phase-to-ground faults. To improve our understanding of the development process and characteristics of surface tracking on the end-winding, an accelerated aging test was performed on 10-kV stator coils to induce surface tracking under electrical and oil contamination stresses. To understand the evolution of surface tracking, the partial discharge (PD) was collected and the characteristics of the corresponding phase-resolved PD (PRPD) patterns and pulse sequence analysis (PSA) patterns were analyzed. Combined with finite element analysis (FEA) simulations, the development process of surface tracking was interpreted. It is established that the electrical field of a dry band with high resistivity on the contamination is much higher than other contaminated areas via FEA simulation, causing the electrical breakdown of the adjacent air and discharge. Such continuous and intense discharges finally leave on the end-winding surface a carbonized channel, forming a tree-like structure. This article presents the results of changes in PRPD patterns and PSA patterns during different stages, together with the surface potential distribution after tracking generation. The research of this article is devoted to providing a reference for PD monitoring and fault diagnosis of HV motors.

Partial Discharge Diagnosis in GIS based on Pulse Sequence Features and Optimized Machine Learning Classification Techniques

Partial discharge (PD) diagnostics in Gas Insulated Switchgear (GIS) is important for reliable and secure operation of electrical utilities. Different techniques were used for PD diagnosis in GIS. In this work, PD diagnosis in GIS is proposed based on PD pulse sequence. PD pulse sequence only requires the measurement of PD phase appearance and its corresponding instantaneous voltage. The PD diagnosis of various defect types is implemented using five optimized machine learning classification techniques: decision tree classification, ensemble methods, k-nearest neighbouring, Discriminant analysis, and Naïve Bayes classification. The features used for PD pulse sequence are the voltage change and phase angle change between successive PD pulses. Three scenarios are proposed for predicting the defect types in GIS. The first scenario is built based on the extracted features for two successive PD pulses, the second scenario is built based on the extracted features for three successive PD pulses, while the last scenario is built based on the extracted features for four successive PD pulses. The results illustrate the superior detecting accuracy of the second scenario with the proposed five ML classification techniques. The optimized ML classification techniques are implemented and carried out based on MATLAB software package. The ensemble classification method exhibited the highest accuracy for PD-based diagnosis in GIS with an overall accuracy of 97.1%.

De-noising of partial discharge signal using wavelet transform for GIS under HVDC

Abstract Detection and analysis of partial discharge (PD) have been regard as the most effective method for condition monitoring and asset management of gas-insulated structures (GIS) in the power system. However, PD detection sensitivity and accuracy are greatly influenced by on-site noise and interference, resulting in failures in PD severity assessment, defect identification or localization. Although de-noising of PD signal under AC was well studied, related investigations under DC have not been carried out. With the rapid development of HVDC technology, it is a new challenge to eliminate noise from PD signal under DC for diagnosis of related power facilities. Therefore, this paper dealt with the discrimination of PD signal based on wavelet transform (WT) techniques for HVDC GIS, aiming to improve the sensitivity and accuracy of insulation diagnosis. Experimental setup was configured to generate PD signal under DC and four types of artificial defects were fabricated to simulate typical insulation defects in GIS. The WT techniques were used to discriminate PD pulse sequences from background noise, amplitude modulation radio interference, non-sinusoidal noise, and switching impulse and the effectiveness was compared with a high-pass filter.

Performance evaluation system for partial discharge detector based on Tesla coil structure

Partial Discharge (PD) detection aiming at finding the insulation defects make great effort for ensuring the reliability of the electrical equipment. Thus the performances, such as sensitivity and classification and recognition of PD pattern of PD detector need verified. This paper offers an effective tool to evaluate these performances of PD detectors. Design of the system consists of three modules, including PD pattern simulation module, PD pulse sequence generating module, and high voltage simulation module. Example of realization is also given in detail, which takes advantage of Tesla coil structure to generate programmable pulse sequence under the control of embedded system according to PD pattern. After that, the performance analysis of this proposed evaluation system is discussed, the performance evaluation system can simulate PD pulse sequence with controllability of pulse position distribution and randomness of amplitude in a range referring to PRPD pattern from database.

Design and development of a portable partial discharge generator

Intensive study of Partial Discharge (PD) phenomenon is of great importance for detecting and distinguishing different types of partial discharge. A portable device for partial discharge generation is designed and developed in this paper, which possesses advantage of miniaturization, dependability and flexibility. Such device is composed of power supply module, PD generating module and PD output interface. An implementing example of the partial discharge generator is given here in detail. Simulated high voltage signal is generated by a waveform generator and applied on physical PD generating model after being amplified by power amplifier and being boosted by a high voltage transformer with high transformation ratio. The generated PD pulse sequence are acquired and further analysed by MATLAB. Point to plane discharge is used as an example and verifies the performances of this device.

Application of a Programmable Partial Discharge Calibrator

This paper presents the application of a programmable partial discharge calibrator, which used to test the performance of four partial discharge measuring systems by injecting a program controlled known charge sequence into the device under test. Performance of linearity, response to opposite polarity pulses, pulse resolution time and response to random pulse sequence are compared and the results obtained show that the tests prescribed by the standards do not fully characterize the partial discharge measuring system behavior. A random partial discharge pulse sequence generated by this calibrator can help to evaluate those systems.

PD pulse sequence analysis and its relevance for on-site PD defect identification and evaluation

Digital partial discharge (PD) diagnosis has become a state of the art, but computer aided procedures based on pattern recognition principles are negatively effected by on-site disturbances. The benefits and limits of expert diagnosis compared to machine intelligent systems are discussed. It is pointed out that a sufficient noise resistivity and test voltage independency of the diagnosis concept is a must for a successful on-site PD defect identification and evaluation. Experimental results are presented, taken into account especially novel evaluation procedures, which are more independent from the applied PD sensors. It is shown that PD defect identification on site at operating voltages and respectively disturbed data is still a challenge. A method of resolution with an intelligent noise resistant diagnosis concept is discussed. A hierarchical and redundant approach is presented, which improves the on site PD source identification as well as on-site risk assessment.

Characteristics of partial discharges in artificial simulated tree channels during tree propagation

In order to clarify partial discharge (PD) mechanism in an electrical tree, we investigated PD pulse sequence and light emission from a single PD in an artificially-simulated tree channel during the tree propagation in low-density polyethylene (LDPE). For positive PD, the light emission was observed near the needle-tip and there was a positive correlation between the PD magnitude and the length of luminous region. The pulse-sequence analysis showed that PD took place at constant voltage increments. These results suggest that PD starts at the needle-tip and the PD magnitude is determined by the PD length. On the other hand, for negative PD, there was no correlation between the PD magnitude and the length of luminous region. The PD pulse sequence can be explained by a simple PD model, since the voltage increment is related to the magnitude of preceding PD. These results suggest that there is a difference between positive and negative PD characteristics and their mechanisms in an artificial channel during tree propagation.

Partial discharge characteristics and tree inception in artificial simulated tree channels

In attempt to clarify the mechanism of electrical treeing degradation and tree propagation, partial discharge (PD) characteristics in an artificially-simulated tree channel in a low-density polyethylene (LDPE) were investigated. The PD pattern and PD pulse sequence showed that the PD in artificial channel with diameter of 10 /spl mu/m was useful for clarification of PD in actual tree. The PD formed a PD pulse train whose magnitude changed with time. In the samples where tree propagation was seen at the tip of the artificial channel, pulse trains with large PD magnitude sometimes occurred and the region of light emission reached the vicinity of the channel tip before tree propagation. In the samples where tree propagation was not seen, the region of light emission due to PD did not reach the channel tip. These results suggest that tree propagation takes place when the PD with large magnitude and long luminous region occur in an artificial channel and damage the channel tip.

New partial discharge detection method for live UHV/EHV cable joints

Partial discharge (PD) detection for live UHV/EHV power cables and accessories is the most important test on cable systems, to prevent problems caused by minor mistakes in jointing the cable. A new PD detecting method is proposed. A REDI (resonance type partial discharge) sensor was developed for detecting PD occurring inside the joints of live XLPE insulated cables. This sensor picks up the high frequency components of a PD pulse in the noiseless range (for example, for 10 to 50 MHz). This new method was employed to observe the initial AC breakdown tests applied to three different types of joints used in UHV/EHV power cables. PD pulse sequences were observed just before the breakdown in all cases. A PD pulse sequence against the phase of applied voltage (A gamma -q characteristic) changed with time or degree of deterioration of the sample. Results of these experiments show that a REDI sensor can be used for insulation diagnosis of live power cable joints. >