*3.3. Electricity System*

The electricity market also consists of the electricity supply subsystem and the electricity demand subsystem, with the variable of the electricity satisfaction rate being the indicator of market efficiency. Infrastructural damages, electricity overload and extreme weather are the risk factors affecting the market, and a decline in the satisfaction rate induced by these risks may trigger response strategies such as electricity compression. As electricity cannot be stored, the additional supply under emergency circumstances was not considered to be a prominent risk response strategy in our experiments.

In the supply subsystem, multiple fuels can be adopted for generating electricity. We divided the sources into natural gas electricity generation and other fuels used for electricity generation, as natural gas was our main research focus. As defined in Equations (8) and (9), the natural gas electricity generation rate relies on the natural gas supply rate for electricity generation, which, in turn, depends on the actual natural gas supply rate from the natural gas market, as well as the proportion of electricity in natural gas consumption. According to the annual statistical data, the percentage of natural gas used for electricity generation was 16% of the total natural gas supply. However, during the transmission of electricity, damage to the infrastructure may also emerge and increase the rate of electricity transmission loss. Efforts would be made to repair the damaged infrastructure and recover the efficiency of electricity transmission to a normal level, as shown in Equations (10) and (11). China's Statistical Yearbook suggests a normal transmission loss rate of 5.26%.



Infrastructure damages = RANDOM NORMAL (0.3, 0.4, 0.3, 0.05, 0.3) × (STEP (1, 70) + STEP (−1, 120)), (10)

Electricity transmission efficiency = 1 − Infrastructure damages − Normal transmission loss rate, (11)

In the demand subsystem, the residential and nonresidential sectors, such as the industrial sector, were evaluated in Equation (12). The daily residential electricity demand rate was 32.17 hundred million kWh/d, while the daily normal industrial electricity demand rate equaled 195.52 hundred million kWh/d. Extreme weather in the winter may result in an electricity overload for heating or other purposes. Normally, when the temperature falls by 1 ◦C below 0, electricity consumption rises by 3%, as stated in Equation (13). The rise in demand may also produce dissatisfaction in the electricity market. Thus, a demand compression strategy might be utilized to close the gap. Since the residential sector always has the greatest supply priority, we also assumed that this compression would happen in other sectors. As illustrated in Equations (14) and (15), a high-level emergency generates demand compression, and these actions are delayed after the time when the market disruption occurred.

Overall electricity demand rate = Other sector electricity demand + Residential electricity demand rate, (12)

Electricity overload = IF THEN ELSE (Extreme weather ≥ 0, 0, 0.03 × (−Extreme weather)), (13)

Electricity demand compression rate= DELAY1 (IF THEN ELSE (Electricity market satisfaction rate ≥ 0.8, 0, 0.2), 10), (14)

Other sector electricity demand = Normal industrial electricity demand rate × (1 - Electricity demand compression rate), (15)
