PD measurement is a worldwide-accepted method for insulation diagnosis and a required part of the acceptance testing for many HV assets. To facilitate PD measurements different techniques/methods have been developed and they are in use for laboratory and on-site applications. All these methods can be divided into conventional and unconventional PD measuring methods. The latter are the subject of this guide.@en

In searching process for new, advanced technologies which could be applied for on-site diagnostics of machine insulation this paper discuses the application of damped AC voltages to detect and to analyze the PD processes. Based on laboratory investigation on a full scale stator insulation system, as well as during field inspections on large motors, a comparison of PD behavior: the PD inception conditions and PD levels at 50Hz AC stresses and damped AC stresses has been performed. The applicability of PD detection at damped AC voltage has been discussed.@en

Performing on-site non-destructive testing and diagnosis of HV power cables is becoming an important issue to determine the actual condition of the cable systems and to determine the future performances. Therefore in this contribution based on field application of on-site testing and available advanced diagnostics overview of experiences will be discussed with regard to on-site testing methods: energizing, diagnostic possibilities and to non-conventional PD diagnosis of new and service aged power cables.@en

Diagnostics of HV power cables are playing an important role in the meaning of two aspects: 1) on-site diagnostic of new installation, where a commissioning test has to prove the absence of any defects in the cable insulation and accessories, after transportation and installation. 2) On-site diagnostic of a serviced aged power cable where the condition after a period in service or information about workmanship of repairs has to be known. As it is known some installation defects can result in breakdown even after a successful after-laying test. Obtaining more diagnostic parameters like; Withstand Voltage, Partial Discharges (PD) and Dielectric Loss (tan ¿), providing a indication of insulation condition and accessory performance. In this paper several examples of on-site tests on new and serviced aged XLPE HV power cables will be discussed. Examples of: after-repair, after-laying, and condition assessment tests will be presented as performed with Damped AC diagnostics.@en

Partial discharges (PD) diagnostics play an important role in insulation diagnosis of HV power cables all over the world. By application of such diagnostic it is possible to asses the quality of final product (cable) during factory test, during after-laying test or during service life. In this way knowledge about the discharging defects in a particular cable insulation system including the accessories can be done. Using sensitive PD diagnostic parameters like: PD inception voltage, PD magnitude, PD fingerprint pattern characteristics, can help to recognize the symptoms of discharging insulation weak spots. In this contribution the application of two different PD detection methods will be discussed: conventional PD detection according to IEC 60270 and unconventional radio frequency (RF) PD detection. To investigate the sensitivity issues both methods have been applied to full size 150 kV cables system (length of 100 m). An example of insulation defect in a cable joint was used to investigate above mentioned PD detections methods as applied at different types of AC voltage energizing: continuous AC and damped AC voltages. Observed PD parameters have been analyzed and compared for both energizing methods (AC 50 Hz and DAC 60 Hz and 400 Hz) and PD detection methods.@en

This document describes application of statistical analysis to several diagnostic parameters obtained during on-site measurements on MV power cables. The goal of this analysis is to estimate statistical borders values for different diagnostic parameters related to PD phenomena for cable insulation as well as different cable accessories like joint and termination. Data input introduced to analysis consist of mass, XLPE and mixed (XLPE +PILC) insulated power cables. Investigated parameters were obtained with application of damped AC (DAC) diagnostic system during on-site non-destructive tests. For the purpose of clear distinction between cable components (joints, termination, insulation parts) categories, of different cable accessories were created). For proper interpretation of collected data related to cable insulation condition as well as different accessories condition, categorization based on such diagnostic parameters e.g. PDIV (Partial Discharge Inception Voltage), PD occurrence, and PD mappings was done. Additionally crated in this way measuring criteria based on calculated statistical norms by fitting data to several statistic distributions were employed for overall condition indexing. Later on condition indexing was used to indicate percentage ration how big population of insulation and components are in very good, good and moderate condition.@en

Water treeing is a phenomenon that is already known for more then 35 years and is one of the reasons for cable failures (polymeric cables) in the medium-voltage network. The final stage of water treeing is the formation of electrical trees on top of the water trees. Due to the fact that the moment of electrical tree initiation is crucial to determine the condition of the cable this paper will focus on the investigation of the moment of transition from water trees to electrical trees. The emphasis will be on the behaviour of the PDIV, PDEV and PD-level as function of time. It has been observed that after the moment of first initiation the PDIV decreased with 40% to 50% and the PD activity up to of hundreds of [pC] remained constant.@en

Knowledge rules for paper/oil insulated high voltage (HV) power cables are necessary to support asset management decision processes. For development of these knowledge rules investigation has been done into a diagnostic method, for integral condition assessment of paper/oil insulation to DC voltage charging. This method is called the recovery voltage measurement and is based on the dielectric response of cable insulation. In the recovery voltage (RV), parameters have been investigated on possibility to indicate insulation degradation. In this paper single and periodic measurements with different temperatures have been performed. These measurements result in the conclusion that an increase in insulation degradation can be observed by selected recovery voltage parameters as well as dielectric losses behavior in function of test voltage. Measurement results of HV power cables performed at two temperatures can be used in line with dielectric losses measurements to support condition assessment.@en

Failure data together with the length and the ages of mass-insulated power cables the still in service of a Dutch utility are used as input for the statistical analysis. The choice of the appropriate distribution depends on the goodness of fit to the data. The fitted statistical distribution gives the relation of the number of expected failures per kilometer together with the age of the cable. To see what can be expected in the future the population in service together with the obtained failure rate curve is used. This gives statistical information regarding expected failures and critical connections. The analysis can help the asset manager to determine if immediate action has to be taken to meet the business policy e.g. condition assessment, maintenance or replacement, or if the current policy fulfils the conditions.@en

In this paper measuring results of partial discharges in power cable accessories are described. For the purpose of measuring simultaneously partial discharge activity in three or more accessories during an acceptance test, a wireless partial discharge detection system was developed. Therefore, each power cable accessory is equipped with either an internal or external sensor to decouple the partial discharge signals. The system uses narrow-band detection and is described in this paper. The computers controlling the measuring units are connected via a wireless network which allows communication between the different units and the main computer situated at the voltage source site. Moreover, effective real time noise-suppression is possible by tuning the system to a noise-free frequency band. Practical examples of this system are shown based on several measurements performed in the field.@en

For advanced, non-destructive on-site condition monitoring of HV power cables up to 150kV by partial discharge detection and dielectric losses measurement it is necessary to energize the disconnected cable system. One of the methods available for this purpose is based on applying damped AC voltages up to 150kV. In this paper, the use of modern technological solutions in power electronics and signal processing as well as in technical design and production methods will be discussed on the basis of the ultra light system (300kg) which is able to test cables up to 20km lengths.@en

The practical interest of power utilities regarding the maintenance and replacement policy of insulating systems such as cables, switchgear and transformers is often based on experiences knowledge and data from the past. The ages of components in the network are increasing and this can result in an increase of the number of failures in coming years. To be able to monitor the components powerful tools are diagnostic measurements performed on the network components and analysis of life time data obtained from the exploitation of the components. In this contribution the analysis procedure is applied to life time data of 50 kV mass-insulated cables of a Dutch utility.To see what can be expected in the future the population in service together with the obtained failure rate curve is used. This gives statistical information regarding expected failures and critical connections. The analysis can help the asset manager to determine if immediate action has to be taken to meet the business policy e.g. condition assessment, maintenance or replacement, or if the current policy fulfils the conditions.@en

It is known that many failures of power transformers are related to aging effects of the on-load tap changer contacts. This paper discusses the recently developed analysis method for service aged power transformers. In particular, the effect of several aging stages of the tap changer change-over selector contacts on dynamic resistance have been considered. As a result, to assess on-site the condition of a power transformer, the following approaches are combined: - The dynamic resistance measurement, to detect deviant contact resistances inside an on-load tap changer; - The velocity measurement to the driving axis of the tap changer drive mechanism and the motor power measurement on the drive motor of the tap changer, to detect mechanical wear or damage inside the drive mechanism; - Transformer turns ratio measurement and DC winding resistance measurement, to diagnose the transformer windings. This paper also presents decision support rules for dynamic resistance measurements to make an unambiguous decision about the status of the tap changer contacts.@en

This contribution is focused on the application of laboratory dielectric losses measurements to the insulation of service aged oil-impregnated HV power cables. The goal is to investigate the dependence between the electrical and temperature stresses to impregnated paper insulation at different aging stages. By means of laboratory tests with differential transformer testing circuit on aged paper samples the following has been investigated: ldr The influence of voltage stress on tan delta measured on samples taken from different parts of cable insulation: close to conductor, middle part and outer part. ldrThe behaviour of dielectric losses as a function of test voltage and temperature for paper samples in different age condition.@en

This paper introduces a new advanced partial discharge detection system for detecting partial discharge activity in the accessories of power cables during the acceptance test. The system consists of three autonomous PD measuring systems which communicate via a wireless communication network with one main computer. As a result, the measured data of each measuring unit can be displayed and analyzed at one single point near e.g. the voltage source which makes easy communication between the measuring technician and test engineer possible. Based on several field measurements performed in Europe on different 380kV and 150kV cables systems aspects of measurement and data processing are discussed.@en

Resistance measurements on power transformers are offline diagnostic methods that are performed without opening the transformer main tank. In case the power transformer is equipped with an on-load tap changer (OLTC), this resistance measurement can be used to find degradation and defects inside the OLTC. Many OLTC defects as well as contact degradation can be measured by means of dynamic resistance measurements, which is a resistance test during OLTC operation. A low (DC) test current through the on-load tap changer is used during dynamic resistance measurements. This method is in particular sensitive to maintenance errors, contact degradation and contact timing problems. In general, distinction can be made between defects that interrupt the current through the OLTC, defects that affect the timing of the OLTC contacts and contact degradation resulting in abnormal contact resistance.@en

Already existing knowledge about aging phenomenon in type insulated power cables as well as measuring criteria has been continuously improved during last 20-30 years. Nowadays many HV power circuit with paper insulation reach their end of service life time due to extensive deterioration of insulation under high operational temperatures and electrical, mechanical overstressing. Growing demand of energy market for new sources of energy and increment of current loads on existing serviced HV power transmission cables change aging rates and lead to often unexpected failures. Accelerate in this way insulation deterioration processes in many cases need new interpretation of diagnostic parameters related to aging of cable insulation to support condition assessment decision and foreseen failure development. Additionally when costs of repairs, cable replacement and customer claims due to breakdown and blackouts are taken into consideration, finance balance for the repair of a single failure in a 150 kV link can costs around 75 kC. For this reason reliable judgment of actual cable condition with available on market diagnostic methods is in great of importance from utility point of view. In this contribution effort was put to estimate actual service condition of four sections of external gas pressure 110 kV-150 kV power cables with two integral diagnostic methods. Interpretation of diagnostic data has been done with aspect to several diagnostic parameters. All relevant diagnostic parameters were obtained during on-site tests in with low-voltage method based on recovery voltage phenomena and high voltage method based in DAC voltages to estimated dielectric losses.@en

Condition assessment of HV assets is one of the issues of asset management in power utility business. In particular, due to there importance in the transmission network is the knowledge about the starting conditions during after-laying as well as the actual condition of HV power cable sections during operation after several years of service very important. With regard to partial discharge (PD) processes in transmission power cables there is a need for advanced, sensitive and economical attractive tools suitable for non-destructive PD diagnosis on-site: the after-laying testing as well as the service diagnosis. In an international co-operation, based on utility experiences and laboratory investigations as obtained for PD diagnosis of distribution power cables using damped AC voltages, a complete new method of PD detection and localization for transmission power cables up to 250kV has been developed in 2003 and in field use for already three years. In this contribution based on field experiences on power cable system up to 220kV the test procedure and the data interpretation are discussed.@en

For advanced, non-destructive on-site condition monitoring of HV power cables up to 150 kV by partial discharge detection and dielectric losses measurement it is necessary to energize the disconnected cable system. One of the methods available for this purpose is based on applying damped AC voltages up to 150 kV. In this contribution, the use of modern technological solutions in power electronics and signal processing as well as in technical design and production methods will be discussed on the basis of ultra light system which is able to on-site service aged HV cables.@en

This paper describes important aspects of 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 PILC and XLPE cables 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 determing threshold levels and relevant condition indexes for the asset management.@en