On-line Insulation Monitoring Research Articles

Double-ring high-frequency common-mode switching oscillation current sensor for inverter-fed machine winding insulation monitoring

Double-ring high-frequency common-mode switching oscillation current sensor for inverter-fed machine winding insulation monitoring

A novel distributing–collecting on-line insulation monitoring system and line selection technology for the DC supply system

At present, the power supply system of 5G base stations is a micro smart grid, it generally uses 240 V DC power supply with multiple branches, and leakage accidents will threaten personal and property safety, so it is vital to identify the fault line accurately and remove the faults rapidly. In this paper, the leakage phenomenon of transmission lines in the HVDC power supply system of a 5G communication base station is studied. To address the issue of multi-branch line leakage diagnosis and line selection in the 240 V DC system, a new distributed DC insulation monitoring and fault line selection technology and system are proposed. The distributed DC insulation monitoring line selection technology is used to collect the leakage current of each branch by setting a unique single-core DC leakage transformer and process the signal primarily. In addition, a high-resistance bridge switchgear is added to the bus bar. According to different leakage currents caused by the imbalance of the bridge before and after the switch, the insulation resistance of electrodes to the ground is calculated accurately, which solves the problem that the current technology cannot judge the fault of the positive and negative electrodes to the ground at the same time. Through both simulation and prototype experiments, the feasibility of this technology and system device in line insulation monitoring and line selection of the HVDC communication base station power supply system is verified.

Accelerated Aging Procedure and Online Method for Stator Insulation Monitoring of Induction Motors

Online methods for stator insulation monitoring have been investigated with increasing interest in the last 15 years. These methods rely on the high-frequency behavior of the electric machine. In converter-fed machines, the high-frequency behavior is visible through the current ringings occurring during the switching commutations of the power electronics. As the lifetime of electric machines can last several decades, a faster way to evaluate insulation monitoring methods is through accelerated aging tests. This work aims to perform an accelerated aging procedure on an induction motor to test an online insulation monitoring method. The motor has a randomly-wound stator winding and it is aged by means of thermal cycles without the need for an oven. A custom converter is employed during the accelerated aging procedure to apply the thermal cycles and to record the current ringings. The proposed insulation monitoring method is based on a metric that quantifies the current ringing variations in a simple manner, following the quasi-linear variation of the parasitic capacitances during the motor aging.

A Comprehensive Operation Status Evaluation Method for Mining XLPE Cables.

At present, the online insulation monitoring and fault diagnosis of mining cables are extensively discussed, while their operation status assessment has not been deeply studied. Considering that mining cables are closely related to the safe and stable operation of coal mine power supply systems, a comprehensive evaluation method including the Analytic Hierarchy Process (AHP), the membership cloud theory, and the D-S evidence theory is proposed in this paper in order to accurately assess the operation status of the mining XLPE cable. Firstly, the membership cloud is introduced to solve the index membership degree and the weights are calculated by an improved weight vector calculation method. Secondly, the conversion from the base layer indicator membership degree to the target layer trust degree is realized based on the D-S evidence theory. Then, the cable operation status is judged via the trust degree maximum and the distribution of conflict coefficients is further analyzed to warn the indicators with a bad status in the base layer. Finally, the feasibility of the proposed evaluation method is verified by a sufficient and detailed case analysis.

Insulation Monitoring of Dynamic Wireless Charging Network Based on BP Neural Network

The transmission cable and power conversion device need to be buried underground for dynamic wireless charging of an expressway, so cable insulation deterioration caused by aging and corrosion may occur. This paper presents an on-line insulation monitoring method based on BP neural network for dynamic wireless charging network. The sampling signal expression of the injection signal is derived, and the feasibility of this method is verified by experiments, which effectively overcomes the problem of large calculation error of insulation resistance when the cable capacitance to ground is large. The experimental results indicate that the error of the proposed method is less than 9%, which can meet the needs of insulation monitoring.

Design of Insulation Online Monitoring and Anti-Condensation Control System for Distribution Switchgear

The partial discharge and condensation in distribution switchgear seriously affect the insulation state, which can cause insulation failure and lead to the shutdown of electrical equipment. This paper designs and develops a set of insulation online monitoring and anti-condensation control system for distribution switchgear. By comprehensive use of transient earth voltage (TEV) technology and ultrasonic technology for partial discharge detection, temperature and humidity detection, control technology and wireless communication technology, the system realizes the online monitoring of insulation, temperature and humidity in switchgear. In addition, the system can automatically control the heater, fan or other environmental adjustment equipment and reduce the occurrence of condensation in switchgear.

A Non-Contact Micro-Ampere DC Current Digital Sensor Based on the Open-Loop Structure

The non-contact accurate measurement of weak direct current (dc) is very important for various fields, such as the online insulation monitoring of power cables. Compared with other dc current sensors, the magnetic modulator is more suitable for dc measurement with its high sensitivity, low noise, and stable working. Most magnetic modulators adopt the closed-loop structure to achieve accurate measurement of large current. And the magnetic modulator only realized the accurate measurement of mA current in the filed of weak dc current, which is difficult to meet the $\mu \text{A}$ current measurement requirements of the online insulation monitoring. Therefore, this article proposes a new structure of open-loop digital magnetic modulator for precision measurement of $\mu \text{A}$ dc current. It adopts an annular shielding layer to weaken the zero offset and stray magnetic field. And a low-frequency excitation source, which can be adjusted with the ambient temperature, is used to improve the temperature stability. Instead of the traditional analog demodulation method, a digital demodulation algorithm is designed to reduce the measurement error caused by the zero offset and excitation source fluctuation. Measurement results show that the new sensor with the absolute error of 0.5 $\mu \text{A}$ can measure 5-1000 $\mu \text{A}$ dc current with a relative error of 0.05% in the full scale. And the sensor can effectively suppress the measurement error caused by the fluctuation of the excitation source and the ambient temperature to less than 0.5%.

A Novel Leakage-Current-Based Online Insulation Monitoring Strategy for Converter Transformers Using Common-Mode and Differential-Mode Harmonics in VSC System

Online insulation monitoring techniques for power transformers have been widely studied. However, challenges rise when they are applied to the converter-connected transformers which are operated under high electrical stress conditions. This article proposes a nonintrusive leakage-current-based insulation monitoring strategy for converter transformers, using inherent characteristic harmonics in voltage source converter system. Analytic relation between common-mode and differential-mode harmonics and insulation capacitances is first presented. Then, a combined strategy is proposed based on the differential measurement of leakage current, which enables online prognosis of not only overall ageing degree but also ageing localization of the phase-to-ground insulation. Experiments are conducted on a 15-kVA transformer driven by an industrial inverter. The proposed combined strategy shows robust performance over effective characteristic frequency spectrums. Several considerations for field implementation are further discussed. The major features of the proposed strategy are as follows: 1) easy implementation and nonintrusive measurement; 2) little impact on system operation and immunity to system interferences; and 3) lower requirements of data processing.

Analytical Analysis and Design of an Advanced Differential-Mode Current Sensor for Insulation Monitoring for Industrial Electrical Assets

Some industrial incidents are attributed to insulation degradation of electrical assets. The leakage current can be a crucial indicator for online insulation monitoring of asset. To realize per-phase monitoring, the measurement accuracy of milliampere-level leakage current is limited by the strong load current noises. This article proposes an advanced current sensor with a dual-core topology based on differential-mode (DM) measurement. An analytical model of magnetic field of the dual-core sensor is originally presented. It helps clarify the significances of the inner core in filtering noises and reducing the influence of system operation and cable positioning. Then, a comprehensive design procedure is fully investigated by selecting the optimal position and approach for magnetic field detection, and a high-speed and low-noise signal conditioning circuit is presented. The proposed current sensor is tested in the laboratory. Experimental results indicate that measurement errors can remain within 0.1mA in the testing scope, where the load current is up to 100A and the DM current varies from 0-7mA. The proposed sensor is further validated with superior performance compared with two commercial industrial sensors. The contribution of this article lies in providing the analytical analysis and design of a novel DM current sensor for leakage current measurement, which achieves online per-phase insulation monitoring for industrial electrical assets.

Partial Discharge Online Monitoring and Localization for Critical Air Gaps Among SiC-Based Medium-Voltage Converter Prototype

As a consequence of higher blocking voltage and power density by using SiC devices, detailed analysis and careful design of insulation are important for future medium-voltage power converters. Because of the insulation or mechanical coordination, air gaps inside the converters cannot be avoided. Moreover, some gaps are more critical than others, since much oversized design or electric shielding there cannot be acceptable. Admittedly, the final design should be partial discharge (PD) free under normal operation with a safety margin. However, due to possible change of air properties and insulation degradation, massive PD can be still initiated from high electric field regions along the gaps and may lead to the damage of devices, through the highly coupled power and driving circuitry. Therefore, with online PD monitoring and localization, insulation health condition of the critical gaps can be provided, which could have great values for converter operation, maintenance, and design. In this paper, after detailed acoustic signal propagation study, a fiber-optic acoustic sensor array has been implemented into a 6-kV H-bridge power electronics building block prototype, in order to realize online PD monitoring along the critical gaps. Finally, from experimental results, the proposed sensor array has good sensitivity, localization accuracy, and high immunity to the electromagnetic interference. It unveils a novel access to insulation online monitoring for future high voltage, high power density SiC-device-based converters.

Development of on-line monitoring system for insulation of high voltage electrical equipment

The development of on-line monitoring technology for high-voltage electrical equipment insulation, the working principle of online monitoring device, and the problems in operation were comprehensively expounded. The on-site verification technology of high-voltage electrical equipment insulation online monitoring system was studied, and online monitoring was analyzed. Management and technical issues with the device were found. On this basis, the on-site calibration device for the on-line monitoring system of high-voltage electrical equipment insulation was developed. The results of on-site non-power-off verification of high-voltage electrical equipment insulation online monitoring system produced by several manufacturers were introduced. Analysis and elaboration of its key technologies.

Simulation Research on On-line Multi-parameter Monitoring for Long Distance Three-phase Power Cable

Long distance three-phase power cable has the characteristics of the metal sheath cross-bonded and voltage drop and ground potential difference at both ends, which brings confusion to on-line insulation monitoring of long distance power cable. One parameter monitoring cable insulation will effect by voltage drop, load current change, frequency fluctuation and other factor. A method based on dielectric loss factor and resistive current to monitor cable insulation simultaneously has been put forward. The method named as a multi-parameter on-line cable insulation monitoring method. The method installs current transformers and voltage transformers on both side of three-phase cable and uses a high precision timing function of the GPS receiving module at both ends of the testing equipment respectively which can receives the pulse per second from the GPS satellite as time reference can realize the signal synchronous sampling. The principle and formula of the method are given. The metal sheath cross-bonded equivalent circuit of long distance three-phase cable is established by using MATLAB software and does dynamic simulation on the method. The results show that the method is not effect on load current, voltage drop and frequency fluctuation. The two parameters increase obviously when the cable operating temperature exceeds 80°C. The insulation condition of three-phase cable can be judged by the change of dielectric loss factor and resistive current under different insulation fault. The method was proved to be correctness and feasibility in the paper.

Assessing partial discharge intensity of electrical equipment based on UV detection and the ANFIS algorithm

UV detection has been generally used in external insulation detection of equipment. Currently used detection methods have many shortcomings, such as incomprehensive consideration of influencing factors, poor model adaption, and low accuracy. We propose a method that detects the ultraviolet pulse number (P), temperature (T), and humidity (H). Meanwhile, discharge intensity (J') was preliminarily estimated by UV detection using a fuzzy algorithm. Next, the ANFIS algorithm with a self‐study mechanism and an artificial neural network was introduced, which assessed that the discharge intensity is J. A UV detection circuit was established while carrying out a field test. The preliminary evaluation data of the fuzzy were used as training and testing data of ANFIS. The optimized model was obtained after ANFIS multiple trainings. Experimental results show that the relationships between P, T, H, and J in the optimized model are consistent with those of theoretical deduction. The assessment results remain highly stable with the occurrence of changes in external conditions, which indicates the feasibility of the ANFIS algorithm in UV detection of discharge intensity of electric equipment. This study can provide effective suggestions for online insulation monitoring and equipment maintenance. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Research on ON-LINE Insulation Monitoring Instrument of IT Power System in the Down Hole Mine

Base on The characteristics of IT power distribution system in metal mine downhole, on the basis of the analysis and comparison of existing insulation monitoring methods, with the low-frequency power injection method, the online insulation monitoring instrument of the IT power distribution system is designed in the metal mine down hole. By injecting the low-frequency power in the IT power distribution system, urge Low frequency signal source and insulation resistance and ground make up of circuit, Real-time detect voltage and current in the circuit. Sampling signals filtered By means of hardware and software filter, extracting low-frequency voltage and current in the circuit, implement ON-LINE insulation monitoring of IT power distribution system. Proved by experiment, the instrument is highly accurate and can complete the insulation performance monitoring of the whole IT power system.

Monitoreo de Descargas Parciales En-línea en Generadores Eléctricos de Alta Tensión

Rotating electric machines with operating voltage greater than 12 [kV] are an integral part of the installed base of electric generators in different countries. These voltages incorporate new challenges to be solved in maintenance practices. One of the most important challenges is the identification of the condition of the stator winding. For many years, the most commonly used monitoring techniques in electrical generators were off-line insulation measurements, especially in direct current. More recently, the use of on-line insulation monitoring techniques has enabled problems to be detected in advance, such as partial discharge measurement. This article presents the measurement of on-line partial discharges, as a condition monitoring technique for high voltage electric generators. It is also used for risk assessment and decision support for corrective actions. In the case study, it was evidenced that periodic monitoring is key during the operating time of the evaluated generator unit, which can be extended to other generators. The monitoring of on-line partial discharges allowed to know its condition and evolution through the trend in time.Keywords: Partial discharge, electric generator, failure mode, predictive maintenance, void.

Impact of SiC semiconductors switching transition speed on insulation health state monitoring of traction machines

In modern traction propulsion applications, voltage source inverter (VSI) fed traction motors today operate very close to borderline conditions. With new emerging semiconductor technologies, higher inverter switching frequencies will be possible and high inverter dv/dt-rates appear, resulting in transient overvoltages at the machine which increase the stress on the insulation system and lead to insulation degradation. Thus, insulation condition monitoring is getting more and more important to ensure a safe and reliable operation of traction motors in trains and locomotives, trams and so on. This study proposes an online insulation monitoring approach that is able to detect incipient insulation defects by evaluation of the motor transient current response on voltage pulses injected by standard inverter switching. Experimental results of this concept are obtained with tests on a 1.4 MW induction machine for railway application. Additionally, the influence of different dv/dt-rates up to 20 kV/µs on the monitoring performance is verified using a VSI-inverter equipped with SiC semiconductors.

On-line monitoring method for long distance power cable insulation

There are cross-linked metal sheath and voltage drop in the long distance power cable which make difference between the short and the long distance power cables on on-line insulation monitoring technology. In order to solve the problem, two terminal synchronous tanδ measurement as a new method of on-line insulation monitoring had been put forward in the paper. The working principle and theoretical basis of calculation were given. The feasibility of the method was demonstrated when there was synchronization error in the system. The Matlab software was used to simulate the circuit of three-phase cable and to calculate tanδ of cable insulation. The results show that the load current will not influence on tanδ measurement if choose the average of vector sum of voltage at the two ends of the cable. And the harmonic and frequency fluctuation had little influence on the methods. The methods were proved to be validity and feasibility in the paper. It can be obtained that the methods were suitable for all kinds of cable insulation monitoring whether the metal sheath of three-phase cable was cross-linked or not.

A Kind of Online Insulation and Error Online Monitoring Technique

A kind of online insulation and error monitoring technique had been introduced in this paper and this kind of technique had been applied on a dry-CT. This kind of technique takes the low-voltage capacitor which series with the end-screen integration into the insulating core of CTs. The technology ensure the connection point of high-voltage capacitors and low-voltage capacitor will never disconnected and the end-screen lead will grounded forever. In terms of error measurement, self-calibration and self-examination functions are achieved with adding standard and air coil next to the measuring coil. Independent power supply technique makes the device mounting more convenient.

Design of Cable Main Insulation and Outer Sheath Insulation Online Monitoring System

An online monitoring system of main insulation and outer sheath of power cable is designed in this paper. The system can monitor the insulation of the power cable without change the normal power cable wiring and grid structure. Changes of the main insulation and outer sheath of power cable can be monitor and recorded. Alarm of given when the insulation of the power cable is abnormal. System managers arrange outage maintenance depends on the status of the power cable.

Study on Measurement Error Test Method of On-Line Insulation Monitoring Device for Capacitive Equipment

The dielectric characteristic parameter, such as capacitance value, the dielectric loss tangent and leakage current values will change when insulation degradation occurs in capacitive equipment, thus the insulation on-line monitoring devices were used for the insulation state monitoring. At present, the monitoring mode, functional requirements, stability requirement, reliability requirement, and the access security impact has not been fully unified among different manufacturers. For the purpose of standardization of the design, production, testing and operation management of the device, studies were carried out in field of technical parameters and test methodology. Considering the structure and working principle of this kind device, key technical parameters of functional and technical requirements were put forward, and the measurement error performance testing method, as well as the detection circuit was also given under the laboratory conditions.