UtilX - CableWISE White Papers

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Condition Assessment of Electrical Equipment in Power Plants

Abstract Plant operations personnel can avoid a forced shutdown by applying a predictive maintenance program to power cable and equipment systems. However, the condition of an electrical power system, down to the individual component level, must be known before it can be scheduled for maintenance. A predictive maintenance program is beneficial for improving the reliability of medium voltage cable systems, transformers and motors. The CableWISE^® diagnostic tool developed by DTE Energy Technologies had been used to assess the condition of such equipment. CableWISE is an on-line, totally passive technique that utilizes radio frequency (RF) pulses, emitted by an operating cable system, to assess the remaining life of cable sections, splices, terminations, switchgear, transformers, and motors.

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Condition Assessment of Distribution and Transmission Class Voltage Cable Systems

Abstract System planners can avoid a forced shutdown by applying a predictive maintenance program to their transmission and distribution systems. However, the condition of the cable system must be known before it can be scheduled for maintenance. That is where the CableWISE condition assessment technique, developed by DTE Energy Technologies, can help. CableWISE is an on-line, totally passive technique that utilizes radio frequency (RF) pulses, emitted by a cable system while it is in service, to assess the remaining life of the cable, splices, terminations and other electrical equipment connected to the circuit. This paper describes the methodology, and the results obtained in the field.

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Condition Assessment of Power Cable Systems in the Energized State

Abstract CableWISE Technology is an excellent predictive maintenance tool that has been used to assess the condition of electrical equipment in the energized state while operating in electrical utility and industrial plant environments. It is an on-line totally passive technique which allows the measurement of signals at high frequencies emitted by the cable system while it is operating in service. The technique is particularly applicable for identifying the type of defects that cause aging and loss of life of cable system components. The analyses of the results are used to assess the severity of aging in cables, splices terminations and the electrical equipment connected to the system. This non-destructive, non-invasive approach assists the user in establishing a predictive maintenance program in a proactive manner. This paper describes the rationale for the studying signals prior to and after partial discharge inception.

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Effect of Shielded Distribution Cable on Very Fast Transients

Abstract Fast transients in power systems can be generated by switching of vacuum and SF6 insulated devices as well as by solid state devices such as those used in variable speed drives. Transients with nanosecond risetimes can be generated, which in a cable-connected system, propagate down the cable to inductive devices such as motors and transformers. In general, the amplitude of such surges is not out of the ordinary; however, the very short risetime can cause unacceptable voltages across the first turn of an inductive device. A cable with high frequency loss does not generally decrease the amplitude of such surges appreciably but can lengthen the risetime substantially by absorbing high frequency energy from the surge. This reduces the voltage across the first turn of inductive devices and thereby protects them from damage and failure caused by such surges. In the present contribution, we quantify the high frequency losses and effect thereof on very fast transients for four types of shielded, 15 kV distribution cable, three made from various EPR compounds and one made from TR–XLPE.

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On-Line Partial Discharge Detection in Cables

Abstract This paper describes an on-line partial discharge (PD) detection technique in power cables. The technique uses a digital spectrum analyzer with a high frequency preamplifier and several types of high frequency inductive sensors. In extruded and impregnated power cables, the PD detection is made in the VHF range. The suitability and the sensitivity of the VHF technique were checked against two other conventional PD detecting methods (Pulse Phase Analyzer and Fast Digital Scope) by performing PD measurements in an EPR-insulated cable under laboratory-controlled conditions. The suitability and senstivity of the VHF method were as good as the two conventional PD detection methods. The VHF method then was used to conduct on-site PD measurements in several power cables. These measurements were conducted while the cables were in service. Special care was given to distinguish between external electromagnetic noise and electromagnetic signals produced by the PD activities inside the cable insulation.

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On-Line Partial Discharge Detection in Transformers

Abstract This paper describes an on-line partial discharge (PD) detection technique applicable to distribution transformers. This technique uses a spectrum analyzer with a high frequency preamplifier and high frequency current probes. The PD measurements normally are made on each of the primary and secondary windings with a high frequency current transformer clamped around the cables below the bushing of each winding. This technique is capable of detecting PD activity in the range of lOOkHz to 200 MHz. The on-line PD detection technique was used alongside the Dissolved Gas Analysis (DGA) technique to check the insulation integrity of several transformers. This paper describes the results of these test methods applied on seven 300kVA transformers. These transformers show different levels of deterioration with the DGA concentrations in the range of 44 to 5,042 pprn and PD activity ranging from 15 to 1,800 pC.

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On-line versus Off-line Partial Discharge Testing in Power Cables

Abstract Two approaches are available to detect partial discharge (PD) from cables, namely on-line and off-line detection systems. The on-line system is based on detecting PD at the system operating voltage while elevated voltages are used to initiate PD in the off-line approach. This paper presents the fundamentals of partial discharge measurements. It also discusses the advantages and disadvantages of each approach.

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Partial Discharge Signals From TR-XLPE Insulated Cable

Abstract This work reports on signal measurements from an imaged TR-XLPE-insulated cable at constant voltage stress, prior to the onset of partial discharge, as conventionally measured in a time domain technique. Although physical events prior to partial discharge have been studied in the past, very few reports exist on signal measurements under prepartial discharge conditions. Signal intensity vs. (a) time at constant voltage, and (b) electrical tree length have been measured; signal intensity increases logarithmically with time, both prior to and after an electrical tree is observed. Tree retardant components in the insulation do not prevent such signals from appearing. Relevant reports have been summarized and relevance to aging phenomena are discussed.

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Partial Discharge Measurement in Transmission Class Cable Terminations

Abstract This paper describes on-line and off-line partial discharge (PD) measuring techniques applicable to transmission cable terminations. The on-line technique can be utilized for both extruded and pipe-type cable terminations. In pipe-type cable terminations, the on-line technique is only applicable to newly installed terminations, as it requires an internal inductive sensor. In the case of extruded cable terminations, on-line testing is made possible by using an external inductive coupler around the ground connection at the base of termination. Off-line PD measurements utilize high frequency capacitive couplers. The coupler is attached to the overhead line within 4-feet from the termination under test. The off-line testing is applicable to new and existing cable terminations.

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Partial Discharge Measurements in Distribution Class Extruded Cables

Abstract Several distribution class extruded cables subjected to laboratory-accelerated aging were examined for partial discharges (PD). The cables were subjected to different load cycling while fully immersed in water to obtain different aging conditions. PD initiated in these cables was measured at rated and at elevated voltages. Correlation between the PD-signature and the insulation-defects type was examined. This was achieved by comparing the PD frequency, magnitude and phase angles of different insulation defects. Correlation between the PD level and ac breakdown voltage of these cables also is presented in this paper. The same investigations also were repeated on several cables removed from service after 15-20 years of service. Correlation between the PD levels and the cable's remaining life also was investigated.

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Review of Space Charge Measurements in Dielectrics

Abstract In the last two decades, a significant effort has been directed to understand the internal charge distributions in dielectrics. This has resulted in the development of a number of methods which give detailed information about space charge distributions. This review presents the evolution of several experimental approaches for the determination of spatial charge and field distributions in dielectrics, including the non-destructive methods of direct probing such as the thermal-pulse methods and the methods using pressure waves that propagate through the charged sample. Detailed information is also provided on the principles used in each technique, typical resolution, limitations and advantages associated with each method. The applications of the methods to several insulating materials charged with various mechanisms are described. The paper concludes with a discussion on a number of quite interesting techniques which seem most promising.

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