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Operational Reliability of Transmission and Substation Facilities


1.Reliability of Three Major Transmission and Substation Facilities
In 2016, reliability investigation shows that overhead lines with voltage levels of 220KV and above reached a total of 669,189.02km, and the number of transformers and circuit breakers was 14,464 and 41,259 respectively.

The availability factors of the three major facilities, overhead lines, transformers and circuit breakers were 99.570%, 99.867%, and 99.958% respectively. Compared with 2015, availability factors of transformers and overhead lines have decreased by 0.020 and 0.030 percentage points respectively, while the availability factor of circuit breakers increases by 0.005 percentage points.
Figure 1 shows the number of major transmission and substation facilities and their reliability indicators in 2016.


Figure 1  Number and Major Reliability Indicators of Major Transmission and Substation Facilities in 2016


2. Comparison of Reliability by Voltage Level
Figure 2 shows the availability factors of overhead lines of different voltage levels in 2016. Figure 3 describes the availability factors of transformers of different voltage levels. Availability factors of circuit breakers with different voltage levels is shown in Figure 4.

Figure 2  Availability Factors of Overhead Lines of Different Voltage Levels 2015 and 2016


Figure 3  Availability Factors of Transformers of Different Voltage Levels 2015 and 2016

Figure 4  Availability Factors of Circuit Breakers of Different Voltage Levels 2015 and 2016

3.Operational Reliability of DC Transmission Systems
23 DC transmission systems were incorporated into reliability statistics, which included 14 pointto-point EHV DC transmission systems, 6 point-topoint UHV DC transmission systems, and 3 back-toback DC transmission systems. Those systems have a rated transmission capacity of 82.42GW in total, and the total length of DC transmission lines stand at 24,894km.


Total energy availability and energy utilization rate of those systems are 94.67% and 54.17% respectively. The total forced outage is 40.5 times. Compared with the previous year, energy availability has a decrease of 0.55 percentage point, energy utilization rate has an increase of 3.57 percentage points, and forced outage has increased 12.5 times.


There are totally 40.5 times of forced outage around the year in operating DC transmission systems. Systems which do not have forced outage are Longzheng, Jiangcheng, Gaozhao, Debao, and Niucongjia.Figure 5 shows energy availability and forced outage of EHV and UHV DC transmission systems in the whole country. Forced outage events in DC transmission systems by cause is shown in Figure 6.

Figure 5  Energy Availability and Forced Outage of EHV and UHV DC Transmission Systems in China



Figure 6  Forced Outage Events in DC Transmission Systems by Cause

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