# Reliability Assessment of Cyber-Physical Distribution Systems Considering Cyber Disturbances
## 5 Case Study
### Analysis of Results
#### 5.2.2 Impact of Cyberattacks on System Reliability  
In the distribution network CPS, the main potential points of attack are the servers in the control center and the IEDs connected through the switches. The various cyberattacks are shown below.  
1. The distribution network is operating normally, and the cyber attacker attacks the IED: * If the IED fails, the cyberattack will not affect the system's reliability; * If the IED is attacked during normal operation, the consequences are related to the number and location of the attacked IEDs.
2. The distribution network is operating normally, and the cyber attacker attacks the master server: * If the cyber system fails completely, the master server cannot be attacked; * If a part of the cyber system fails, the attacker can use the master to control the IEDs; * If the cyber system is normal, the attacked master server may cause the whole system to be paralyzed.  
To analyze the impact of different cyberattack objects on the system reliability, the calculation is divided into three cases below, and the results are shown in Figure 15.  
Figure 14: Trend of \(G_{\text{SAIDI}}\) under different fault rates.  
Case 3: The object of the attack is the master server.  
Case 4: The object of the attack is one IED.  
Case 5: The object of the attack is two IEDs.  
As shown in Figure 15, the impact of the cyberattack object on the system reliability is from one IED to two IEDs and the master server in order from large to small, indicating that for cyber systems, choosing the method with a higher success rate to carry out cyberattacks will cause greater economic losses to the system.  
To study the impact of specific IED attacks on system reliability, based on the situation of the normal operation of the physical system, various scenarios of cyberattacks on one IED and two IEDs are calculated separately. The types of scenes are shown in Table 4.  
The calculation results of the reliability indices for each scenario are shown in Figures 16-19.  
From Figures 16 and 17, it can be seen that the reliability indices of the system increase to different degrees when attacking one IED compared with the reliability indices without considering cyberattacks. This indicates that attacking one IED makes the system reliability decrease, and the fewer the number of switches on the bus where the IED control switch is located and the fewer the number of connected IEDs under the normal operation of the physical system, the smaller its impact on the reliability of the system.  
From Figures 18 and 19, it can be seen that the reliability indices of the system when attacking two IEDs increase to different degrees compared with the reliability indices  
Figure 19: Impact of attacking two IEDs on \(G_{\text{EENS}}\).  
Figure 17: Impact of attacking one IED on \(G_{\text{EENS}}\).  
Figure 18: Impact of attacking two IEDs on \(G_{\text{SAIDI}}\).  
without considering cyberattacks. This indicates that attacking two IEDs makes the system reliability decrease, and for cyberattacking two IEDs, the longer the distance between two IEDs in the attacked IED combination, the greater the impact on reliability. Accordingly, it can provide a reference for the investment of defense resources.