Abstract
In recent years, the ultra-high voltage direct current (UHVDC) transmission system has been developed rapidly for its significant long-distance, high-capacity and low-loss properties. Equipment failures and overall outages of the UHVDC system have increasingly vital influence on the power supply of the receiving end grid. To improve the reliability level of UHVDC systems, a quantitative selection and configuration approach of redundant structures is proposed in this paper, which is based on multi-state reliability equivalence. Specifically, considering the symmetry characteristic of an UHVDC system, a state space model is established as a monopole rather than a bipole, which effectively reduces the state space dimensions to be considered by deducing the reliability merging operator of two poles. Considering the standby effect of AC filters and the recovery effect of converter units, the number of available converter units and corresponding probability are expressed with in universal generating function (UGF) form. Then, a sensitivity analysis is performed to quantify the impact of component reliability parameters on system reliability and determine the most specific devices that should be configured in the redundant structure. Finally, a cost-benefit analysis is utilized to help determine the optimal scheme of redundant devices. Case studies are conducted to demonstrate the effectiveness and accuracy of the proposed method. Based on the numerical results, configuring a set of redundant transformers is indicated to be of the greatest significance to improve the reliability level of UHVDC transmission systems.
Highlights
With the continuous improvement of electric power equipment manufacturing, direct current (DC) transmission technology has achieved a significant development from extra-high voltage (EHV)to ultra-high voltage (UHV) [1]
The probability of normal operation is much higher than the probability of de-rated operation and complete outage. It is a result of the characteristic that various components of the ultra-high voltage direct current (UHVDC) transmission system are provided with relatively low level of failure rate but high level of repair rate
A redundant structure configuration approach based on reliability equivalence of symmetrical UHVDC transmission systems is proposed
Summary
With the continuous improvement of electric power equipment manufacturing, direct current (DC) transmission technology has achieved a significant development from extra-high voltage (EHV). Reference [6] proposed that reliability is one of the most important challenges of UHVDC transmission systems. Reference [17] proposed a computer program to evaluate the state probability, frequency and other complicated indices of UHVDC transmission systems. Reference [18] introduced the fault tree analysis (FTA) method in UHVDC transmission system reliability evaluation, which considers the basic failure incidents, discusses the source of system outages, and goes deeply into the failure groups. Reference [19] considered the logical relationship among subsystems and proposed a UHVDC reliability evaluation model based on a state enumeration method. A novel UHVDC reliability model and evaluation method is proposed in this paper, which successfully reduces the dimension of the complex state space solution. Numerical results demonstrate that the proposed technique contributes to a better UHVDC structure design
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