With the promotion of the national double carbon goal, the acceleration of urbanization, and the continuous improvement of urban construction standards, the requirements for a new power system for cable network are higher and higher, and power cables are more and more widely used in urban construction. However, there are still various problems in the current cable network construction, such as uneven construction technology, a wide variety of cable pipes, poor product quality, large consumption of raw materials, and so on, resulting in the high cost of cable network construction, transformation, operation, and maintenance. Based on the above background, it is urgent to explore the application of new materials, new processes, and new technologies in the construction of the cable pipe network.

Online partial discharge (PD) monitoring system for high voltage power cable lines is different from that for other power equipment like GIS or transformer. For cable lines, the PD can be detected at cable joint and termination. Since the PD signal must decay when it propagates along the cable, distributed PD detection can increase the detection sensitivity. PD sensors and local signal processing units must be installed at each cable joint and termination, spreading over the whole cable line of several kilometers or more than ten kilometers. Therefore, all detected signals from each sensor point must be collected to the centric signal processing stage for displaying, analysis, judgment, and alarming via fiber network or wireless communication. The PD online system to operate effectively and reliability for years also required some necessary automatic-measurement functions such as auto-change of different noise filters, synchronous PRPD pattern comparison, PD identification, PD localization, and periodic system self-checking. This paper gives an example to illustrate the practical application of online PD monitoring technology for a large-scale online PD monitoring system installed on a pair of 16km-500kV XLPE cable transmission lines.

Partial discharge (PD) synchronous detection is an effective means to improve the quality of the handover test when the withstand voltage test is carried out on the high-voltage cable line, because it is easier to find the hidden defects when the voltage is higher than the operating voltage. However, PD detection of cable lines requires that PD sensors and signal processing devices must be installed at each cable junction or termination. The detection signals distributed in each joint of the cable must be transmitted and collected to the central processing unit for centralized analysis and display. For those several kilometers to more than ten kilometers of buried cable line, if there is no pre-wired communication network, the only way to rely on wireless communication. Due to the complex conditions of the test site, the speed and the stability of the wireless communication network are difficult to guarantee the data transmission of more than 3M bytes/s required by PD measurement. A new distributed PD detection system with wireless communication has been successfully developed and used in recent voltage tests of several 110 kV and 220 kV cable lines. A hybrid wireless communication system was used at the trial site, utilizing 4G/5G communication between the local distributed signal processors and Wi-Fi communication between the central signal processing unit. This communication method can not only meet the data needs of PRPD and PRPS graphs for displaying PD detection signals distributed in the whole line synchronously, but also realize the display of point-to-point signal waveform, and ensure the trend observation effect of each distributed signal and the synchronous comparison function of multi-point signal actograms. This paper attempts to briefly describe the composition and technical parameters of the PD detection system, the form of field application and the system method through a 110kV cable circuit withstand voltage test case.

The modules mismatch loss and strings mismatch loss in PV module is theoretically and universally recognized in the PV industry [1]. But for specific projects, how to calculate these losses as well as how to reduce the impact of these losses through external rational wiring was rarely studied. In this paper, the engineering calculation method will be summed up and the relevant formulae suitable for engineering calculation or equipment configuration principles such as cables can finally be obtained by constructing the DC side equivalent circuit model of the photovoltaic power station, and also calculating of modules and strings mismatch loss data based on circuit analysis, which can in turn provide the essential theoretical basis for the accurate efficiency calculation of the photovoltaic power plant system and provide certain theoretical support for engineering drawing optimization design as well.

Partial discharge (PD) detection in withstand voltage test is different from that under operation voltage for after-laying cable circuit. For large-scale XLPE cable circuit of 15km, a special distributed PD detection in-sync testing system was created for the withstand voltage test of 500kV (1.7Uo/1Hr), HFCT PD sensors were distributed and installed at every cable joint and cable termination. To localize a PD where and when it is just detected between any two neighboring PD sensors on a cable, all local signal process units are made to work synchronously, and the communication system is constructed by optical fiber cable. To ensure the high quality examination, measurement of PD propagation velocity of cable, frequency characteristics, and calibration with injection by PD simulated pulse generator were conducted onsite before test. This paper also shows some print-screen photos from the practical test to tell how the corona and the other background noise signals can be distinguished by the detected original signal waveform, selecting detection frequency filters, and the time differential identification unit. It should be a valuable reference case.

It is introduced that a new type of portable PD measurement system has been developed especially for the periodic inspection tour of power cable circuit in operation. Based on the causes of PD produced in cable and its accessories various PD sensors such as HFCT, UHF, AE and TEV have also been developed for site PD detection application. Therefore, this new type PDM equipment is designed and made to be matched with eight kinds of PD sensors, so it can perform multiple measurement functions in which signals from four same PD sensors or four different PD sensors can be detected. The signals can be analyzed at frequency domain with PC program like a spectrum analyzer and the signal waveforms can be recorded and be shown on the PC screen as analyzed at time domain like an oscilloscope, with which four-channel signals can be used for localization synchronously. This paper also gives two successful on-site PD measurement examples to show that how this kind of high-end PDM equipment can provide PD measurement and localization with high efficient and safety during operation.

It is discussed firstly the correct way to install PD sensor HFCT to pick up PD current from cable joint based on a equivalent high frequency circuit of cable joint with a PD in it. PD measurement system for cable circuit under withstand high voltage test is different from that for regular PD periodical inspection on cable without outage to some extent. Especially for those long length circuit with many joints, it is required that the power supply system should be PD free and anti-corona, and the local signal processing unit distributed on each joint bay should obtain variable voltage frequency different from the 50/60Hz operating frequency, for PD recognition and judgment based on phase resolved partial discharge analysis. For PD detection and location it is also required that each signal processing unit should be in synchronization. It is shown that with on-site examples of the cable circuit of more than twenty joint bays passed through withstand test, how the PD sensor like HFCT was installed in the link box for cable sheath cross-bonding or grounding connection, how the test voltage was raised up step by step to cooperate with PD detection, and how to determine the configuration and specification of the multi-sites distributed PD measuring system.

为了将升压谐振电抗器、测压电容分压器及其均压环通过优化设计布置在750 k V开关设备现场交流耐压车载试验平台有限的空间里,对电抗器与分压器共用均压环一体化设计进行了研究,包括具体实现方式、电抗器与分压器之间电位差、电场分布仿真计算和测量系统校准试验等,目前已在现场得到了成功应用。

For the partial discharge (PD) measurement of cable circuit only detecting a PD signal is insufficiency, determining the PD location is the real goal, since the purpose of PD measurement is to evaluate the PD correctly and support the maintenance of the cable reasonably. For cable circuit the PD location, the distance between PD sensor and PD source is a very important factor directly affecting the PD evaluation. In this paper, through two examples of successful PD localization at cable circuits it is shown that the analysis and judgment of the PD signals detected on-site should be better based on the comparison of a serial measurement results from PD measurement at multiple positions, joints or their link boxes, and terminations.

It was reported previously that partial discharge (PD) existing in GIS can be localized with a PD localization method based on the time difference of PD detection, in which more than one pulse current sensors are installed at the GIS sealing end or cable termination. However, the localization accuracy is not satisfactory since the PD propagation speed is too high and not average inside GIS. To increase the accuracy combined PD sensors to detect pulse current and to catch the acoustic signal were applied for the on-site PD localization. The result shows that higher location accuracy can be obtained.

Partial discharge measurement is a kind of effective condition check method for high power transformer. Normally, when a high power transformer needs to be checked by partial discharge measurement periodically, outage is required. Here, a newly developed measurement method for transformer is introduced in which a new kind of capacitive coupling sensor is applied. The sensor consists of a pair of metal plates and a high frequency CT, which can be installed at the flange of the high voltage bushing of the transformer during the transformer in commercial service operation, without any outage.

One of the serious problems that can occur in power XLPE cables is destruction of insulator. The best and conventional way to prevent this is ascertaining partial corona discharges occurring at small voids in organic insulators. However, there are some difficulties in detecting those partial discharges due to the existence of external noise in detected data, whose patterns are hardly identified at a glance. For this reason, there have been a number of researches into detecting partial discharges by employing a neural network (NN) system, which is widely known as a system for pattern recognition. We have been developing an NN system for auto-detection of partial discharges, and have input numerical data of the waveform itself and obtained appropriate performance. In this paper, we employed the discrete wavelet transform (DWT) to acquire more detailed transformed data in order to use them in the NN system. Employing the DWT, we were able to express the waveform data in time–frequency space, and achieved effective detection of partial discharges by the NN system. We present herein the results using DWT analysis for partial discharges and noise signals which we obtained. Moreover, we present results out of the NN system which dealt with those transformed data. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(1): 24–30, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10315

This paper describes a new method of measuring partial discharge (PD) via coaxial bonding wire for direct-buried power cable, with which partial discharge can be measured at the so-called link box usually installed beside the joint but on the ground. When cable joints are directly buried under ground, it is difficult to use the conventional measuring method to detect PD, since it is necessary to install a PD detection sensor directly at or on the joint. For direct-buried cable line, the formation of sheath bonding for each joint can be usually determined at a link box that is connected to joint via coaxial bonding wire. Five kinds of PD sensing circuits were proposed for PD measurement at link box and the methods have been verified through several experiments using sample cables in laboratory or being carried practically on a real cable line on-site. The paper summarizes the experimental results and gives a comparison of each method. The paper also shows the possibility of measuring PD for three phases instantaneously at one joint bay on-site. Some practical PD measurement for those kinds of direct-buried power cable conducted onsite will be also introduced with on-site photos.

This paper describes a new method of measuring partial discharge (PD) via coaxial bonding wire for direct-buried power cable of which the sheaths at an sheath-insulated joint can be bonded at a terminal box, so-called link box, usually installed beside the joint but on the ground. When cable joints are directly buried under ground, it is difficult to use the conventional measuring method to detect PD, since it is necessary to install a PD detection sensor directly at or on the joint. For direct-buried cable line, the formation of sheath bonding for each joint can be usually determined at a link box that is connected to joint via coaxial bonding wire. The terminals of coaxial bonding wire at a joint are connected with sheathes of both sides of the joint, and the terminals of the other end of the coaxial wire are fixed inside the link box. This paper deals with the possibilities of measuring PD from the terminals of the coaxial wire. Some problems have to be solved when connecting a detection circuit to terminals of the coaxial wire, a) how to detect the PD signals from the coaxial wires high sensitively and safely; b) how to evaluate of the propagation attenuation of coaxial wire; c) how to do the measuring calibration for PD measurement system before detection. Some results of experiments simulating the cable conditions on side will be discussed. A practical PD measurement for this kind of direct-buried power cable conducted on site will be also introduced.

This paper describes a new multiple means of discriminating partial discharge (PD) and noise for power cable lines, which is applied in some newly developed PD auto-measuring systems, not only for the PD measurement in laboratory, but also for the after-laying testing of power cable line on-site. Discrimination of PD and noise can be divided into two kinds of PD judgment. First, the judgment is executed automatically based on multiple logic gates: f-gate for frequency, n-gate for pulse count rate, q-gate for pulse magnitude, /spl phi/-gate for PD phase position, t-gate for continuous time, set logically in serial or in parallel. Second, the signals can be recognized by their pattern distributions: neural network recognition is based on the /spl phi/-q-n pattern; multiple frequency recognition is based on f-q-t pattern; and statistical source location pattern is based on x-q-t pattern. Satisfactory discrimination of high accuracy has been obtained through applying the measuring systems using the method in several PD measurements on-site.

For Partial Discharge (PD) measurement, not only detecting the signal magnitude of PD is enough for evaluating the insulating constructions of HV equipment such as GIS, GIL, power cable, and cable joint, but also localization of the PD position is important to them. PD localization can help to find out the defect point effectively and determine the cause of PD, improve the manufacturing process, and increase the insulating properties. This paper describes multiple new methods of PD localization including 1) use of metallic foil electrode sensors, 2) excitation of X-ray radiation, 3) application of acoustic emission sensor, applied to a EHV prefabricated joint in a length scale of about 2m long. Comparing with the conventional PD localization for long size of cable, it is more difficult to locate a PD for the short size of joint due to the pulse reflection, the pulse propagating route and the difference of propagating velocity, based on the materials and shape of the part units of the joint. Several successful PD localization shown that the method can locate PD with sufficient accuracy.

With an example of PD localization for EHV cable joint on site, multiple method of PD localization is studied in this paper, including (1) method of using metallic foil electrode sensors, (2) method of excitation by X-ray radiation and a foil electrode sensor, and (3) method of applying acoustic emission sensors and a foil electrode sensor. Compared with the conventional method of PD localization for long distance cables of more than hundreds of meters, it is more difficult to localize a PD for a pre-fabricated type of joint of only a short length of around 2 m, due to problems in measurement such as the disturbance of pulse reflection, the complicated route of pulse propagation and the difference of pulse propagation velocity. The results of the example also show that this multiple method can give a high accuracy of PD localization.

This paper describes a new developed automated partial discharge (PD) measuring system, which is not only for the small scale PD measurement of sample test in laboratory, but also for the large scale after-laying test of power cable line on site. The system comprises an 8-channel fast A/D transformer, a central signal processing unit and four computers, providing real time measuring for monitoring eight signals at the same time automatically. The judgment of PD or discrimination of PD and noise can be divided into three phases. In the first phase, PD judgment is executed automatically based on multiple signal gates: f-gate for frequency, n-gate for pulse count rate, q-gate for pulse magnitude, φ-gate for PD phase position, t-gate for continuous time, set logically in serial or in parallel. The alarm signal in this phase has three levels determined by the gate output. When an abnormal signal is detected the abnormal signal channel can be automatically fixed and connected to other sub-units, and the signal will be judged in the next phase. In the second phase, the abnormal signal will be recognized by three pattern discrimination units: a neural network based on the φ-q-n pattern, a multiple frequency pattern logic gate based on f-q-t pattern, and a statistical x pattern logic gate (x represented source position of the signal) based on x-q-t pattern. In the third phase, the operator can give a final judgment according to the summarized information including the original waveform displayed by oscilloscope, spectrum analyzer, and the signal processing results shown with more than six kinds of 3 D graphics by computer display. Furthermore, a helpful offline processing can give several kinds of serial graphics based on time history or voltage history to help observations and comparisons. The system has been put into practical uses for several PD measurements and all results have shown the system can perform with high sensitivity of PD detection and high accuracy of discrimination of PD and noise. In this paper, some examples of practical PD measurement on site are introduced.

In order to realize an anto-detection system of a single pulse of partial discharge in power cables, a neural network (NN) system with very fast computation (no more than I ms) are desired. In this paper, we present a trial manufactured auto-detection NN system using an analog parallel circuit. The feature of this system is adoption of a Random Weight Change learning algorithm, which is suitable for the analog processing without smooth sigmoid function. Experimental results of a manufactured circuit are also investigated.