DC XLPE Cables Research Articles

Application of multi‐source information fusion based on D‐S evidence theory in insulation defect identification of DC XLPE cable

During the installation and laying process of cross-linked polyethylene (XLPE) cable, it is difficult to avoid the influence of external harsh environment, which leads to insulation deterioration and failure. The partial discharge and leakage current play an important role in formation mechanism, characteristic law and identification technology of DC XLPE cable defect. However, the defect identification accuracy of single source data is limited. The correlation between partial discharge and leakage current of typical defect is analysed here. Based on the shape characteristic parameters of typical DC partial discharge spectrum and the energy characteristic parameters of leakage current wavelet decomposition node, a weighted Dempster–Shafer (D-S) evidence theory is used to fuse and identify different information sources. The results show that the classification rate of the proposed method can reach 88%, which can effectively identify insulation defects.

Evaluation of insulation condition detection methods applied to DC XLPE cable

At present, with the construction and operation of new energy grid-connected and offshore wind power projects in China, DC XLPE cables have been widely used. Under the operating conditions, there are mainly two feasible technical means of DC cable insulation state detection, partial discharge (PD) and leakage current. However, it is still a blank in the world to apply it to the validity and condition of DC cable operation detection. Based on the semi-conductive layer residual defect model of XLPE cable, the characteristics of PD and leakage current under different voltage values and polarities are studied by setting up an experimental platform for detecting PD and leakage current of DC XLPE cable. The results show that both PD and leakage current can detect cable defects, among which PD is easier to detect cable defects under negative polar voltage and higher voltage. Leakage current characteristics change obviously under positive polar voltage. When applied voltage is lower than rated voltage, obvious changes can also be measured. In this paper, the feasibility of live detection of leakage current of DC cables under operating conditions is proposed, which is of great value to improve the detection capability of DC XLPE cables.

Improvement of insulation defect identification for DC XLPE cable by considering PD aging

Crosslinked polyethylene (XLPE) insulated power cable has a wide application in flexible DC transmission areas. PD measurement is considered as an effective tool to detect and even identify insulation defects for XLPE cable. In this paper, four kinds of insulation defects were constructed, i.e. inner semi-conductive layer breakage, internal air cavity defect, insulation surface scratch defect and outer semi-conductive layer creepage, and PD aging experiments for each type of defect were conducted at DC voltage. It was found that PD characters significantly varied with different aging phases, leading to the fluctuation of PD fingerprint parameters. Without taking the time-sequence feature of PD data into consideration, the recognition rate was only 72.93% in the usage of fingerprint parameters. For the aim to improve recognition effect, a model based on bidirectional recurrent neural networks (BRNN) algorithm was proposed. By dividing the PD process into several stages, the model takes both the fingerprint parameter and the stage information as input, in which the output of each stage is not only related to itself, but also influenced by the preceding and subsequent inputs. Therefore, the model can reflect the time-sequence characteristic of PD. With the dataset acquired by four insulation defects testing, the recognition rate of the BRNN model is 93.71%. It is proved that the BRNN-based recognition model effectively eliminate the influence of insulation aging on the PD fingerprint of XLPE cable, and improve the identification efficiency to a certain extent.

Classification of partial discharge images within DC XLPE cables in contourlet domain

This paper presents a new method to improve the insulation defect classification rate of DC cross linked polyethylene (XLPE) cables. A partial discharge (PD) test platform is built in the laboratory and four DC cable defect models are designed. The PD signal is collected by a high frequency current transducer (HFCT) and the q-At-n image is constructed. The contourlet transform is performed on the PD image, and the Tsallis entropy feature of each subband coefficient is calculated. The error-correcting output codes (ECOC) classifier is optimized by the adaptive cuckoo search (ACS) algorithm optimization sparse random (SR) coding matrix to realize the defect classification. The experimental data show that the ACS-SR-ECOC classifier in this paper has shown promising performance in the classification of each defect and the Gaussian noise model. Compared with to four kinds of traditional ECOC classifiers, the proposed method has higher overall classification accuracy, which provides a new approach for the defect type identification of PD image in the DC cable.

Practical Application of +/-250kV DC-XLPE Cable for Hokkaido-Honshu HVDC Link

Long term DC properties of DC-XLPE insulation material, which have been developed for DC use, were investigated. It was found that the life time of DC-XLPE under DC voltage application becomes longer by addition of nano-sized filler. The time dependence of space charge distribution at 50kV/mm was observed for 7 days. As a result, there is almost no accumulation of space charge in DC-XLPE. The 250kV DC-XLPE cables and accessories were manufactured and subjected to a type test and PQ test for the use in the Hokkaido-Honshu DC link facility owned by the Electric Power Development Co., Ltd. These tests were done under the conditions that include a polarity reversal test for line commutated converter (LCC) systems as recommended in CIGRE TB 219. The test temperature was set at 90°C. The type test and PQ test were successfully completed. The DC-XLPE cable and accessories were installed in summer 2012 for the Hokkaido-Honshu DC link. After the installation of the DC extruded cable system, a DC high voltage test at 362.5kV (=1.45PU) for 15 minutes was successfully completed in accordance with CIGRE TB 219. This DC extruded cable system was put into operation in December 2012 as the world's highest voltage extruded DC cable in service and the world's first DC extruded cable for a LCC system including polarity reversal operation.

500 kV直流XLPEケーブルおよび同径接続部の開発

We have worked on developing 500 kV DC XLPE cable. The first time, the space charge profile was measured using model cables insulated with the improved inorganic filler-added XLPE (SXL-A). Results showed that SXL-A could sufficiently suppress space chargeunder DC voltage. So, full-size 500 kV DC SXL-A cables with an insulation thickness of 23mm and associated factory joints were manufactured and initial electrical performance test were carried out. It was confirmed that they had sufficient initial electrical performance to satisfy the requirements for 500 kV DC XLPE cable.

Space change behavior in full scale �250 kV dc XLPE cables

Space change behavior in full scale �250 kV dc XLPE cables

Space charge behavior in full-size 250 kV DC XLPE cables

The space charge in full size 250 kV HVDC power cables was measured using the pulse-electroacoustic method. Measurements of two types of newly developed DC XLPE cables with 20 mm insulation were taken under a DC voltage of 500 kV with the conductor temperature at room temperature and at 85/spl deg/C. A qualitative analysis of the space-charge distribution and a quantitative analysis of the electric fields in the vicinity of semicon interfaces were conducted. It was shown that the field in the vicinity of the inner semicon tends to increase by 10-40% when the polarity of the applied voltage was reversed, in the case when the conductor was kept at 85/spl deg/C. However, the distortion of the electric field was significantly less than that expected in conventional XLPE cables. As the result, the subjected DC cables are considered to have stable DC characteristics from the viewpoint of space charge-behavior.

Research and development of ±250 kV DC XLPE cables

This paper describes the development of /spl plusmn/250 kV DC XLPE cables. Through a series of material investigations and the evaluation of model cables using two kinds of XLPE compound containing inorganic filler to suppress the accumulation of space charge within XLPE insulation, /spl plusmn/250 kV DC XLPE cables and factory joints were designed and manufactured. To check the DC electrical performance and reliability of /spl plusmn/250 kV DC submarine cable, electrical tests, mechanical test and long-term aging tests were performed. The test results showed that they had sufficient properties and reliability for practical use.

Decreasing space charge accumulation in polyethylene with an inorganic filler

The applicability of polyethylene polymerized using a metallocene catalyst as an insulation material for DC XLPE cables has been investigated. The space charge distribution was examined using the pulsed electroacoustic technique over a temperature range from room temperature to 90°C. Hetero-charge was observed near the surface of the sample at higher temperatures. Hetero-space charge, produced by ionization derived from activation of an antioxidant added to the sample, either increased or decreased with increasing temperature of the sample. A hetero-charge absorber was added to control the hetero-space charge. As a result, hetero-charge was not observed in the sample under a high electric field for temperatures extending from room temperature to high temperatures and the DC breakdown strength at 90°C was increased. It was confirmed that the volume resistivity of the sample increased at high temperature.

Development of XLPE insulated DC cable

AbstractThis paper describes the development of dc XLPE cable. Through a series of material investigations, an XLPE compound containing highly purified special filler was developed.To check the dc insulation performance of the cable insulated with this new material, a prototype cable with 9 mm insulation thickness was manufactured. It was confirmed that the performance of the prototype cable was excellent. Based on the study of the prototype cable, a 250‐kV dc cable with 20 mm insulation thickness was designed and manufactured. Through a series of voltage tests, excellent dc insulation performance of the developed cable was verified.

Study on the dielectric characteristics of DC XLPE cables

The DC characteristics of XLPE (crosslinked polyethylene) power cables were investigated. Cables with an insulation thickness of 2.5 mm, 9 mm, and 13 mm using either XLPE or conductive-inorganic-filled XLPE (XL-A) were manufactured, and four kinds of breakdown tests (DC, polarity reversal, impulse, and superposing opposite polarity impulse on DC prestress) were performed. A 250 kV, XL-A cable (20 mm thickness) was designed and manufactured using the results. The test results show that the XL-A cable possesses much better DC breakdown characteristics than the XLPE cable and is adequate for use in DC cables.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Investigation on Test Method of DC XLPE Cable

There is no standard specification for type test on dc cables except one recommended by CIGRE SC-21 for oil impregnated paper insulated cables up to 600kV. In Japan 250kV class XLPE dc cables were manufactured and subjected to a long term test program including the type test mentioned above. As a result it seems that this type test is not suitable for XLPE cables. This paper presents a new consideration in voltage withstand test for XLPE dc cable based on dc insulation characteristics of XLPE.

Investigation on Test Method of DC XLPE Cable

Investigation on Test Method of DC XLPE Cable

Insulation Properties of 250 kV DC XLPE Cables

The difficulty of obtaining the electric power generation sites close to the city forces us to install long transmission lines and to adopt dc transmission. During the execution of the Hokkaido-Honshu dc submarine cable project, 250 kV class XLPE dc cable was developed in parallel with self-contained oil-filled cables. While XLPE dc cable samples were subjected to a modified CIGRE Recommendation type test for a long term, insulation breakdown occurred frequently.

Experimental Investigation of Space Charge in XLPE Cable Using Dust Figure

In order to use XLPE in dc cable insulation, it isnecessary to solve various problems about space chargein XLPE insulation. The cross-section dust figure (CDF)is introduced as a new method to study a space chargedistribution in solid insulations and new results arepresented. The XLPE insulation layer is mostly occupiedby positive and negative hetero-charges rather than byhomo-charges, and these hetero-charges cause the dcinsulation characteristics to differ from those of oilfilled cables. The space charge distribution varies ina complicated way as a function of temperature, voltageand voltage application time. We further found thatalthough charges injected from an electrode form a homocharge layer, most of them spread toward the oppositeelectrode and form a hetero-charge layer. The distributionobtained by the CDF is consistent with otherexperimental results on dc XLPE cable.