在输电线和变电站组合联结网络中的非同调现象

Non-coherence Phenomenon in Combinative Transmission Line and Substation Configurations

非同调现象指的是:一个元件从系统中缺省反而产生一个更可靠的系统状态,或者甚至提供更高的系统可靠性水平。这个现象可能存在于输电系统中,但却没有得到电力工业界的充分认知。文中解释了输电系统可能存在非同调的概念,并提出一个输电线和变电站组合联结网络的实例。在该实例中,一个双回线并行结构通过分支点T接引入变电站,与一个单回线结构通过分段接入变电站相比,不仅多需要一条线路,而且可靠性也差。这与规划工程师通常的直觉判断相反。虽然这是加拿大某电力公司的例子,但却有一定普遍意义,因为许多电力公司大量采用类似的两端向中间负荷供电并通过分支点T接引入变电站的双回线并行结构。如果能够通过定量可靠性评估识别一个实际输电系统的非同调特性,就有可能避免多余的输电元件,从而既能节省投资又能改进系统可靠性。

Non-coherence in system reliability refers to the fact that absence of a component from the system creates a more reliable system state or provides a higher system reliability level. This phenomenon may exist in transmission systems. Unfortunately, it has not been sufficiently recognized in the power industry. This paper explains the basic concept of possible non-coherence in transmission systems and provides a case study where compared to a single transmission line structure with loop-in connection, a double transmission line structure with tap-connection not only requires one more line but also has a lower reliability level. This is contrary to intuition since transmission planning engineers normally make an opposite judgment. The example given in the paper is an actual application in a utility of Canada. It also has a general significance because the similar double-line arrangement with tap-connection is a popular choice of many utilities for power supply from two-end substations. If the non-coherence feature that could exist in transmission systems can be recognized and identified using quantified reliability evaluation, this will help improve system reliability while avoiding unnecessary transmission components and saving capital investment.