## 1 Introduction
### Motivation--Why BPL?
#### 1.1.2. BPL on Medium Voltage (MV)  
Distribution and transmission grids are being divided into two main groups based on the used topology--the radial grid topology and the mesh grid topology. The radial grid forms a tree where closed loops are being avoided. This topology is very simple and cheap, but when a line is being disconnected, power delivery to distant nodes is immediately interrupted. The mesh grid topology is based on closed loops where power might be delivered to nodes through different lines; thus,this topology performs with higher reliability through higher complexity and higher costs [15; 16; 17]. The issue of performance and availability of the whole communication system depending on network topology is being further discussed in [18; 19]. A BPL solution could be deployed in both segments of the power grid--LV (low voltage) and MV (medium voltage) [20; 21]. In comparison, MV has more suitable communication channels due to the lower attenuation, time-invariant behavior and simplified network configurations without any branches and with less significant sources of noise.  
On the other hand, in BPL networks on the LV, longer distances without repeaters are typical [22], but in MV topologies the positions of repeaters are fixed. Those repeaters are deployed in every distribution substation, and it is also necessary to implement repeaters on both sides of a transformer due to its physical disconnection and galvanic isolation of the powerline [23; 24]. For this reason, an absolute maximum communication distance cannot be achieved without a repeater, and it is necessary to count repeaters in every substation. BPL technology is being deployed mostly in the underground MV distribution substations, where it sometimes serves as the only possible way of communication. Based on the physical interconnections of MV distribution substations, managing the desired level of Quality of Service (QoS) and the impact of stream concurrence are important topics.  
The impact of repeaters on communication parameters (throughput, latency and reliability of communication) is a key question. Therefore, the knowledge of impact of repeaters on throughput helps with network architecture planning before the massive deployment (roll-out).  
The key parameters, indicating network performance of Smart Grids, are the communication availability and stability [25]. For ensuring an adequate level of cybersecurity, in terms of substation automation as a part of the critical infrastructure, methods such as tunneling, usage of Virtual Private Networks (VPN), Access Point Names (APN), IPSec and Transport Layer Security (TLS) are usually involved. It is also crucial to take into acount demands on protocols with regard to availability and sufficient network throughput of such networks; thus, knowledge of the PLC repeater's impact on network performance is vital.  
The contribution of this article is two-fold. Firstly, research on the exact influence of a repeater's operation on the network throughput is conducted, and values indicating throughput drop are discussed. Secondly, the topic of bottlenecks in linear topologies is a commonly discussed issue and is investigated through the usage of simulation. Simulations provide the times when multiple stream throughputs equalize over time with different influencing input values. Results obtained by measurements of real on-field topologies are used as input data for provided simulations. Outcomes of this paper should be helpful in further designs of complex Smart Grid networks based on powerline communication technology.