Partial discharge (PD) testing of high-voltage (HV) cables and cable accessories has been implemented predominantly using high-frequency current transformers (HFCTs) as PD sensors. PD currents initiating at PD sources are coupled onto cable conductors. They travel away from the PD sources and are detected by HFCTs installed at cable terminations. In this paper, based on combining finite-difference time-domain (FDTD) modeling and transfer function theory, a hybrid modeling approach is proposed to investigate the processes of PD coupling and detection involved in HFCT-based PD testing of HV cables. This approach allows exciting a PD event anywhere in FDTD models of the cables and predicting output from HFCTs some distance away. Implementation of the method is illustrated using an 11 kV XLPE cable. Moreover, a “direct measurement” method of obtaining original PD pulses as the excitation source waveform is presented. The modeling approach introduced here will facilitate studies on the relationship between measured PD signals and those excited at PD sources, which can potentially give useful insight into the basic mechanisms behind PD detection in cables.

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Modeling of High-Frequency Current Transformer Based Partial Discharge Detection in High-Voltage Cables

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.

On-line monitoring method for long distance power cable insulation

High voltage power cables play a critical role in global electricity transmission and distribution. The currently used power cables cannot fulfil the green and sustainable requirement of modern society because of the thermoset nature of cable insulation and shields. This study is aimed at developing thermoplastic shields for high voltage power cable, which is one bottleneck restricting the development of environmental-friendly cables. Using carbon black (CB) as the main conductive component and a small amount of carbon nanotubes (CNTs) or graphene as the second filler, highly conductive polypropylene based composite materials were prepared for potential shield applications. It was found that, at a fixed conductive filler loading, the replacement of a small amount CB by CNTs can significantly enhance the electrical conductivity and suppress its temperature dependence. However, when CB was replaced by graphene, only limited enhancement of electrical conductivity could be achieved and the electrical conductivity is still highly dependent on temperature. Dissipative particle dynamics simulations demonstrated that the enhanced conduction property in the CNTs-containing composites could be understood by the shorter average distance between CB and CNTs. Finally, the coordination between the newly developed conductive composites and the environmental-friendly thermoplastic polypropylene insulation was evaluated via high voltage direct current measurements, and the results revealed that the CNTs-containing composites showed excellent suppression effect on the space charge injection and accumulation in the insulation. This research paved a new way for developing environmental-friendly high voltage power cable shields.

Highly conductive polymer nanocomposites for emerging high voltage power cable shields: experiment, simulation and applications

Increasing demand for renewable energy has led to a rapid growth of doubly fed induction generator (DFIG)-based wind farms around the world. As a critical component of the DFIG-based wind farms, online monitoring of the connected transmission cable is essential to maintain the reliability of the entire wind power plant. A novel online monitoring method for power cables in DFIG-based wind farms using high-frequency resonance (HFR) analysis is proposed in this paper. The HFR in wind farms due to the interaction between the DFIG unit and the connected cable is firstly modeled and the relationship between the HFR frequency and cable ageing severity is analyzed. An ageing severity estimation algorithm is then proposed based on adaptive hill climbing and particle swarm optimization (AHC&PSO). Simulations for wind farms with both the LCL and L filter are conducted to validate the proposed method. Effective online monitoring and accurate ageing severity estimation of the cables are achieved in the simulations under various operation conditions considering DFIG parameter deviations. Compared with existing approaches, the proposed method provides a superior online monitoring approach to accurately evaluate the ageing state of power cables in wind farms quantitatively with no need of extra monitoring sensors. 

Online Monitoring for Power Cables in DFIG-Based Wind Farms Using High-Frequency Resonance Analysis

Insulation aging of underground power cables may lead to severe fault and system outages. Condition monitoring of cable insulation is essential to maintain power system reliability. However, most existing insulation monitoring methods can only work in offline mode and cannot describe cable aging severity quantitatively. In this article, a novel online monitoring scheme for underground power cable insulation based on common-mode (CM) leakage current measurement is proposed. An online neutral-point voltage injection approach is proposed, and CM leakage current distribution model for both the cables with and without metal sheath under the injected voltage is derived. The insulation capacitance can therefore be monitored online without disturbance to the system operation. Simulations and experiments are conducted to prove the effectiveness of the proposed method. With the aid of a designed CM leakage current sensor, CM leakage current smaller than 5 mA can be detected and the accurate evaluation of aging severity is achieved. The key feature of the proposed method lies in its nonintrusiveness and online fashion: the normal operation of the system will not be interrupted, and accurate quantitative monitoring of cable insulation can be achieved online.

A Novel Online Monitoring Scheme for Underground Power Cable Insulation Based on Common-Mode Leakage Current Measurement

Partial discharge (PD) detection and location is of great significance for the power cable insulation condition monitoring, where the high-frequency (HF) model is needed to analyze PD propagation. Considering the influences of conductor skin effects and semi-conducting layers (SCL), this paper presents the equivalent Γ-section lumped parameter model for single-core cross-linked polyethylene (XLPE) insulation cables. The longitudinal parameters per-unit-length in the model are obtained using available geometric data by vector fitting method. Unfortunately, the dielectric characteristics of SCL in XLPE cables, especially for an installed one, are usually unknown and hard to measure. To address this issue, based on the simulated annealing algorithm, an optimization approach for estimating the transversal parameters in the Γ-circuit model is developed. The proposed technique is then carried out on the XLPE cable with simulated and real SCL, respectively. Furthermore, the estimation results of the real case are validated on a 603 m cable with kinds of HF pulses responses.

Parameter estimation technique for the semi-conducting layers in single-core XLPE cable

The invention relates to a deep soil thermal parameter monitoring sensor and a detection method. The deep soil thermal parameter monitoring sensor mainly comprises a DC voltage-stabilizing voltage source, an insulated heating wire, a spherical probe, a temperature measurement module, a monitoring device, a balancing resistor, and a data collection unit. The DC voltage-stabilizing voltage source is used for supplying power to a heating circuit. The insulated heating wire is used for heating the probe. The probe is in the form of a hollow spherical shell made of copper-zinc alloy, and is embedded into the soil to measure the thermal parameters of the soil based on the heat transfer condition of the surrounding soil. The temperature measurement module comprises a thermal resistor as a temperature sensor and the thermal resistor is arranged on the inner surface of the spherical shell of the probe. The thermal resistor is used for measuring the temperature change on the surface of the probe. The monitoring device is composed of a resistance voltage divider and a sampling resistor and is used for monitoring the voltage and the current at the two ends of the insulated heating wire. The balancing resistor is used for stabilizing the output voltage and the temperature change before the measurement. The data collection unit is used for collecting the temperature on the surface of the probe, the voltage and the current at the two ends of the insulated heating wire. The deep soil thermal parameter monitoring sensor is convenient in measurement, rapid and portable. The deep soil thermal parameter monitoring sensor can be directly buried deep underground to monitor the thermal parameters of the soil surrounding a cable in real time.

Deep soil thermal parameter monitoring sensor and detection method

The utility model relates to a partial discharge's non -contact takes electric detection means in distribution cable annex, the device mainly include following unit: partial discharge detector receiving arrangement, signal cable and signal conditioning and display element. Wherein, partial discharge detector receiving arrangement adopts high band horn antenna to it is connected to pass through signal cable with signal conditioning and display element. The utility model discloses a check out test set has been developed, partial discharge's measurement in can connecting with the mode of non -contact to the distribution cable of soil with taking the electric detection means novelty. The utility model discloses the device has nimble, portable, efficient characteristics of using, and electrification that connects for distribution cable detects and provide capable instrument, is fit for electrification that electric power enterprise carries out joint state in service and patrols and examines and improve the diagnosis level that connects the insulation situation to distribution cable.

Partial discharge's non -contact takes electric detection means in distribution cable annex

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Parameter estimation technique for the semi-conducting layers in single-core XLPE cable

Deep soil thermal parameter monitoring sensor and detection method

Partial discharge's non -contact takes electric detection means in distribution cable annex