This paper presents a theoretical study relating to partial discharge (PD) source localization in high voltage power transformers using UHF technique. It also includes a brief review of typical PD sources, continuous UHF-based monitoring system, and some suitable UHF sensor types. Using MATLAB calculations and some basic assumptions, the differences in potential accuracy of PD source location are shown for different numbers of sensors, including the influence of sensor position. In addition, in the case of four UHF sensors, other effects were taken into accounts such as background noise sources, signal attenuation, multivariate wavelet denoising and the first peak detection method. By using the programs, at first, it is shown how to find the corresponding loci on which a PD source can be expected to lie by means of two and three UHF sensors in power transformers. Furthermore, using four sensors, it is presented on two different examples how simulated UHF signals, which travel from the partial discharge source to individual UHF sensors, can be used to find a partial discharge source position with sufficient accuracy. Multivariate wavelet transform was applied to the simulated signals in order to remove noise from the signals, and thus to reduce a localization error. The first peak detection method was applied to two various presumed shapes of UHF signal, in order to find time differences of arrival between related signals at the sensors. The corresponding results of partial discharge source location were analyzed and compared.

Application of UHF method for partial discharge source location in power transformers

Power transformer is one of the most important high voltage apparatus in any power system network. The life span of such apparatus commonly relies upon its insulation condition. The primary reason for an insulation breakdown is partial discharge. Partial discharges (PDs) are electrical discharges that happen in the insulation system of the transformers. Occurrence of PDs results in deterioration of the transformer insulation system. Hence, measuring and detecting the PD at an initial stage is necessary to avoid complete breakdown of the transformer. Currently, various PD detection and measurement methods, such as, electrical, chemical, acoustic, UHF and optical methods are being used for PD monitoring in power transformers. The conventional PD monitoring techniques like electrical or chemical have some limitations. The optical Fiber Bragg Grating (FBG) Sensor has been used as a PD sensor for PD monitoring in the power transformer to overcome these issues. This paper presents a review of FBG sensors’ application as a sensor for PD monitoring in an oil-filled power transformer. The challenges and future prospects in this area are also discussed.

Partial Discharge Detection in an Oil-Filled Power Transformer Using Fiber Bragg Grating Sensors: A Review

Partial discharge (PD) field tests are widely used for cable assessment or cable commissioning. Usually, these tests are carried out by means of off-line tests where PD pulses are measured with capacitively coupled PD sensors. In off-line single-sided cable measurements, time-domain reflectometry (TDR) is used to locate the source of the PD along the cable. However, when the PD pulses are originated at the cable ends, the TDR technique cannot, by itself, properly distinguish between PD pulses produced at the cable near-end or at the far-end. This paper describes three different methods that produce an unambiguous localization of PDs produced at the cable ends, complementing the TDR.

Localization techniques of partial discharges at cable ends in off-line single-sided partial discharge cable measurements

There is no doubt that the electrical and thermal stress conditions in modern electrical networks are becoming much more challenging than in the past. The presence of voltage transients and power electronics, especially in grids involving renewables, is stressing insulation systems in a not-conventional and often not-predictable way. This paper is looking at the potential effect on insulation aging of repetitive voltage transients, in the presence or absence of partial discharges, raising the point that such transients can cause significant aging acceleration, thus reduce life considerably with respect to the design life. This is why condition monitoring becomes a must: the health of an insulation system has to be evaluated dynamically as a function of time, in order to approach in the most convenient way the matter of maintenance and asset reliability. A general approach to aging under non-sinusoidal waveforms is presented here, referring to both phenomenological and probabilistic algorithms, and examples are reported for speed-controlled rotating machines and train transmission lines. It is emphasized that the aging processes in a transformer will require a more complex modeling approach.

Why residual life estimation and maintenance strategies for electrical insulation systems have to rely upon condition monitoring

More and more transmission power cable circuits with lengths up to several tens of kilometers will be installed and put into operation. This contribution discusses basic aspects of selecting an on-site test voltage and the partial discharge measurement under on-site testing conditions of power cable lines with long length. On the one side, the generation of suitable test voltages for high capacitive loads, especially long cables, is evaluated and experiences of on-site measurements are described. On the other hand, the challenges for sensitive partial discharge measurement on long length power cables are discussed. Under this scope, partial discharge measurement by dual-sided measurement technique is described and examples are shown.

Basic aspects of partial discharge on-site testing of long length transmission power cables

Guidelines for partial discharge detection using conventional (IEC 60270) and unconventional methods

This paper describes important aspects of partial discharge (PD) diagnostics of distribution power cables. PD parameter were discussed under consideration of attenuation and dispersive effects of cable characteristics. Field experiences with PD diagnosis on paper insulated cables (PILC) and cables with cross linked polyethylen insulation (XLPE) by energizing with damped AC voltage demonstrate relevant demands and the effective outcome for asset management decision support. The main difficulty is to evaluate the risc of PD occurrences on the reliability of the cable system. If an sufficient amount of PD diagnostic data for the cable components is available statistical methods can be used for determining threshold levels and relevant condition indexes for the asset management.

Advanced solution for on-site diagnosis of distribution power cables

PD testing is an important tool for the asset management in terms of reliability of medium voltage cable networks and maintenance decisions The quality control of cable installations by PD measurements will become increasingly important in the future, because the increasing cost pressure upon the network operators to reduce installation cost For the evaluation of PD occurrences, the PD inception and extinction voltages and the local concentration of PD have to be considered as the most important parameters besides the trend or preset levels of PD Statements regarding the remaining life time of a cable are generally not possible via the PD diagnosis nor are they with any other diagnostic method However, an evaluation based on practical experience permits to perform a risk assessment regarding the condition and reliability The PD diagnosis provides valuable information for required maintenance activities and helps to spend available budgets prudently

On Site PD-Diagnosis of Power Cables using the Oscillating Voltage Method

This paper describes important aspects of partial discharge (PD) diagnostics of distribution power cables. PD parameter were discussed under consideration of attenuation and dispersive effects of cable characteristics. Field experiences with PD diagnosis on paper insulated cables (PILC) and cables with cross linked polyethylen insulation (XLPE) by energizing with Damped AC Voltage demonstrate relevant demands and the effective outcome for asset management decision support. The main difficulty is to evaluate the risc of PD occurrences on the reliability of the cable system.

F. Petzold

Papers

Guidelines for partial discharge detection using conventional (IEC 60270) and unconventional methods

Advanced solution for on-site diagnosis of distribution power cables

On Site PD-Diagnosis of Power Cables using the Oscillating Voltage Method

Advanced solution for on-site diagnosis of distribution power cables