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Hao M.,University of Southampton | Fazal A.,University of Southampton | Chen G.,University of Southampton | Vaughan A.S.,University of Southampton | And 2 more authors.
ICHVE 2016 - 2016 IEEE International Conference on High Voltage Engineering and Application | Year: 2016

HVDC cables play a vital role in the power transmission system for renewable energy and global power trade. Nowadays, the crosslinked polyethylene (XLPE) extruded cables have been widely applied in power industry due to the superior performance on the thermo-mechanical properties and dielectric properties. The low volume conductivity and the minimized space charge accumulation are the two key requirements for a reliable high voltage direct current (HVDC) cable insulation. This paper reports on the impact of temperature and electric field on the space charge behavior and DC conductivity in XLPE material for cable insulation. The samples were carefully prepared to simulate the real cable insulation structure. A layer of LDPE film mixed with DCP (dicumyl peroxide) was sandwiched between two layers of semicons (also contain crosslink agent) and then crosslinked at 200 °C to ensure the semicon layers were thermally bonded with the XLPE insulation. The crosslinked samples were then degassed in the vacuum oven with for 6 days at 80 °C. The space charge characteristics and the conductivity of the semicon-bonded XLPE samples were measured at room temperature and high temperature. The electric fields were kept at 20 kV/mm and 40 kV/mm and the influences of the electric field and the temperature on space charge dynamics and conductivity in the semicon-bonded XLPE samples are discussed. © 2016 IEEE.


Lan F.-T.,Smart Grid Research Institute | Cao Y.-W.,Dow Chemical Company | Wang Y.-N.,Shenyang power supply company | Chen X.,Smart Grid Research Institute | Zhang C.,Smart Grid Research Institute
Advanced Materials Research | Year: 2014

Hybrid composite rods, comprised of unidirectional reinforcing carbon/glass-fiber and adhesive epoxy matrix, are viewed as promising candidates to be used in high-voltage overhead conductors. However, before widespread application, their long-term durability needs to be clarified. In this study, accelerated creep testing for hybrid composite rods, is presented by taking dynamic mechanical analysis tests at different temperatures. Using the time-temperature superposition principle and thermal activation energy theory, the short-term creep data are combined to generate creep long-term compliance master curves. Through the master curve, predictions can be made concerning the creep levels that will occur during the design lifetime of hybrid composite rods (i.e., 30 years). It is found that after 30-year service at 120 °C, fully-cured hybrid composite rods only exhibit a slight increase in compliance (about 5%), indicating a satisfactory creep resistance at this temperature. © (2014) Trans Tech Publications, Switzerland.


Zhao G.,North China Electrical Power University | Li W.,North China Electrical Power University | Chen W.,State Grid Corporation of China | Cai B.,Smart Grid Research Institute | Qiao E.,Smart Grid Research Institute
Diangong Jishu Xuebao/Transactions of China Electrotechnical Society | Year: 2015

The paper focuses on the cascaded STATCOM (Static Synchronous Compensator) with energy gained from a transformer on the AC side. To study the DC voltage distribution of the converter and analyze the reason for its imbalance, an equivalent circuit that contains an energy-gaining unit is built for the converter during pre-charging. Based on it, a method for balancing DC voltages is proposed where the parameter differences in the energy-gaining unit are taken into account, which is also verified by LV physical experiment. ©, 2015, Chinese Machine Press. All right reserved.


Gao H.,Smart Grid Research Institute | Bumiller G.,Ruhr West University of Applied Sciences | Liu W.,Smart Grid Research Institute | Lijianqi,Smart Grid Research Institute
2015 IEEE International Symposium on Power Line Communications and Its Applications, ISPLC 2015 | Year: 2015

Power line channel is hostile for communication. One concept we proposed for reliable communication in power line is to adjust the working band according to different channel conditions. In this paper, a new digital front end (DFE) structure, which combines equivalent complex baseband (ECB) structure and Nyquist windowing at both transmitter and receiver, is proposed to support this concept. By configuring parameters of ECB, it supports flexibly band selection. Besides, out-of-band interference is able to be attenuated to a large extent due to the cascaded low-pass filters in the ECB at receiver. Therefore, it is possible to apply much more simplified analogue front end. The Nyquist windowing at receiver makes side-lobe of narrowband disturbance fall down quickly and concentrates its energy on fewer subcarriers, which benefits the narrowband interference detection. Finally, system performance with the new DFE structure in the presence of in-band and out-of-band disturbance is simulated and compared with classic DFE and equivalent complex baseband (ECB)-based DFE. © 2015 IEEE.


Li W.,North China Electrical Power University | Luo Y.,North China Electrical Power University | Qiu Y.,Smart Grid Research Institute | Cui X.,North China Electrical Power University
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2013

The switching delay of high-voltage solid-state transfer switch (HV SSTS) is about half power cycle presently. The residual voltage at the time of transfer process is important because approximately 10 ms transfer time from main power to backup is objective existence. The profile, value, frequency and decay time constant of residual voltage have to be concluded in order to suppress inrush currents and to improve the success rate of switching. The residual voltage is related to the load character and SSTS valve design. Therefore, based on the mathematic model of the SSTS switching transformer with capacitor loads, induction motor loads and no load, the characteristic of residual voltages was deduced via an analytical analysis method in accordance with two switch approaches. First, the load current is transferred successfully from the vacuum breaker to the thyristor valve and is cut off at the crossing zero point. Secondly, the load current is transferred from the vacuum breaker to the thyristor valve unsuccessfully and is turned off by the vacuum breaker with chopping currents. The validity can be verified by MATLAB simulations and engineering tests. The paper provides a theoretical foundation for control parameter design of SSTS transferring different loads. © 2013 Chin. Soc. for Elec. Eng.


Zhao Y.,Smart Grid Research Institute | Liu D.,Smart Grid Research Institute | Wu X.,Smart Grid Research Institute | Lin C.,Smart Grid Research Institute
Proceedings of the IEEE Power Engineering Society Transmission and Distribution Conference | Year: 2014

This paper derives an electromagnetic transient mathematical model of the MMC based VSC-HVDC system. Based on the model, a coordinated control algorithm is presented for the MMC controllers design. A test system of the MMC VSC-HVDC is established in PSCAD/EMTDC to verify the correction of the algorithm. Simulation studies show the better dynamic responses of the MMC based VSC HVDC for the controllers with coordinated control algorithm than without. © 2014 IEEE.


Wang H.,Smart Grid Research Institute | Cao J.,Smart Grid Research Institute | He Z.,Smart Grid Research Institute | Yang J.,Smart Grid Research Institute | And 2 more authors.
IEEE Transactions on Power Delivery | Year: 2016

Due to the rapid development of the voltage-source converter (VSC), the demands for HVDC cables have increased significantly. Although more than ten VSC-HVDC projects are under construction and many more are in operations globally, the testing criteria for HVDC XLPE cables are mainly referenced to test guideline TB 496 recommended by CIGRE. Due to the large stray capacitance of the VSC-HVDC cables, the switching impulse overvoltage stress of the cables is the main electrical parameter concerned, a unified overvoltage factor of 2.1 p.u. being generally accepted. However, the switching impulse overvoltage stress of a VSC-HVDC cable system depends on not only the VSC topology but also the cable parameters and the volt-ampere characteristics of the dc cable surge arresters used. This paper studies the switching impulse overvoltage stresses for the dc cable system of a symmetrical monopole VSC-HVDC transmission system using the modular multilevel converter technology. The studies were performed according to the key technical parameters for a typical 1000-MW/320-kV VSC-HVDC transmission scheme, the XLPE dc cable links being assumed. The results show that a switching impulse overvoltage level of 2.3 p.u. should be applied during the type test of the overvoltage capability of the HVDC cables. © 2015 IEEE.


Wang J.,China Electric Power Research Institute | Liu C.,Smart Grid Research Institute | Wu J.,Smart Grid Research Institute | Zhang X.,Smart Grid Research Institute | Yu H.,Smart Grid Research Institute
Dianwang Jishu/Power System Technology | Year: 2015

Rigid and close communication architecture of power WAN is hard to manage massive surging data traffic of power service. Traditional traffic engineering technology could improve resource utilization, but with the continually increasing requirements of power service end-to-end QoS, it has been unable to solve the problem fundamentally. This paper presents a service resource equitable allocation technology, a system that boosts the utilization of power WAN by centrally controlling when and how much traffic each service sends and frequently re-configuring the network's data plane to match current traffic demand. By designing resource allocation function, throughput maximization function, equitable allocation function and multiple flow function, the algorithm framework of resource equitable allocation is built in order to improve the network utilization in a software mode which realizes equitable allocation of electrical service resource in distributed centralized architecture. With experiments it is proved that the technique can protect QoS of power service in the context of equitable distribution of resources. ©, 2015, Power System Technology Press. All right reserved.


Fazal A.,University of Southampton | Hao M.,University of Southampton | Vaughan A.S.,University of Southampton | Chen G.,University of Southampton | And 2 more authors.
34th Electrical Insulation Conference, EIC 2016 | Year: 2016

Polyethylene exhibits many key characteristics including low dielectric loss, high breakdown strength and good processability. Most modern extruded high voltage cables employ cross-linked polyethylene (XLPE) as the insulation material. The main advantage of XLPE is its excellent thermo-mechanical properties; it is relatively cheap and has low dielectric loss and low conductivity making it an ideal material for this application. Crosslinking enhances a number of thermo-mechanical properties such as deformation resistance at higher temperatures, tensile strength and creep properties. In comparison with lov density polyethylene (LDPE), the heat deformation characteristics of XLPE are superior and, for this reason, XLPE is currently the most common insulation material for power cables ranging from low to high voltages. This paper reports on an investigation into the development of a new XLPE formulation for use in high voltage direct current (HVDC) cable applications. Specifically, the electrical performance of two novel LDPE resins are compared with an industrial standard (reference) LDPE material. For crosslinking, dicumyl peroxide (DCP) was selected, as the decomposition temperature is high enough to prevent pre-curing during processing and to allow an efficient and rapid crosslinking at moderate temperatures. Moreover, the behavior of various systems is compared in terms of electrical breakdown performance and the influence of material composition and processing on these parameters is described. © 2016 IEEE.


Wang H.,Smart Grid Research Institute | Tang G.,Smart Grid Research Institute | He Z.,Smart Grid Research Institute | Yang J.,Smart Grid Research Institute
IEEE Transactions on Power Delivery | Year: 2014

An unbalance voltage between a positive pole and negative pole will exist for a long time in an ungrounded modular multilevel converter (MMC) HVDC transmission system. A zig-zag transformer has been proposed to construct an artificial neutral point and keep voltage balance between the positive pole and the negative pole. An efficient grounding system consists of the zig-zag transformer and the neutral grounding resistor. In this paper, the different impedances, including positive-, negative-, zero-sequence impedance, and dc current impedance, have been analyzed, respectively. Then, the computer simulations have been performed to evaluate the characteristic of the zig-zag transformer under normal voltage, zero-sequence voltage and unbalanced dc voltage, respectively. The simulation results show that 1) the zig-zag transformer can effectively balance the unbalanced voltage in dc side of the MMC under different work conditions; 2) the zero-sequence impedance is low and zero-sequence current is convenient for the detection of a single-phase fault; 3) the power consumption of the neutral grounding resistor is of a light rating, and the cooling of the resistor is unnecessary. The method presented in this paper proves to be an efficient grounding method for the MMC-HVDC transmission system. © 1986-2012 IEEE.

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