Smart Grid Telecommunications. Ramon Ferrús
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install it and an appropriate power supply (in HV and MV networks, the existence of the typical LV AC or DC power is not readily available). The room aspect might become crucial, as there has been a historical trend to reduce the available space in grid assets. Even if this is something to be solved in future grid assets evolution, it is a constraint today with legacy infrastructure.
The HV segment of the electric power system do not usually has problems in terms of physical space available within premises. There are usually suitable shelters (e.g., substation control building) that have been pre‐conditioned to host electronics. The situation might be different when it applies to grid elements in the compound exterior area that may be close to grid component to be monitored, measured, or controlled. Providing power supply to these elements may require special transformers close to them or internal wiring through the substation. When it comes to cables, the situation is different, as if there is a need to incorporate some sort of monitoring along the power lines, the availability of power can be restricted to the inductive feeding possibilities.
The MV and LV grid segments are often less prepared to host electronic devices in general, and telecommunication equipment in particular. Power supply circumstances, however, are different in MV and LV, as in LV there is always AC power available by default. Thus, a combination of strategies is needed both to adapt physical spaces and telecommunication devices, where costs will be a matter of how repetitive the solutions will be and how many premises to adapt.
The variety of MV substation types is wide and any possible classification is non‐standard. A broad classification follows population density of the area where they are installed: urban areas usually present underground and in‐building type of substations (e.g., ground level and basement); suburban areas share the in‐building type with the urban areas and include the shelter‐type and the pad‐mounted transformers. In contrast, rural areas prevalently show pole‐mounted transformers. In terms of power lines, underground prevail in urban and suburban, where it gets mixed with on‐wall and overhead mounting, typical of rural.
In‐building and shelter‐type SSs are not so much a constraint in term of space as pad‐mounted constructions. Due to the lack of space in pad‐mounted and pole‐mounted SSs, there is usually the need of an outdoor enclosure. In all SSs cases, the access to LV AC power is readily available in the secondary winding of the transformer (DC power supply and battery solutions might be a concern).
However, the situation of the accessibility to LV power is more difficult in the parts of the MV grid where no SSs exist. In these places, the only standard possibility to feed electronic devices with a non‐negligible power need lays in the installation of a special transformer that increases the cost of the solution and may oblige the utility to adapt and reinforce the pole to which the element is attached. Inductive solutions may exist but are not suited for telecommunication devices needing to work in permanent operation.
The LV grid is still a challenge for telecommunications, as it has not been until very recent times when utilities have realized that, to improve the service quality, the LV grid must start to be monitored and controlled. With the likely exception of the meter locations construction, street‐cabinets and fuse boxes were never probably understood prone to host telecommunications. Meter rooms, as the result of the effort to avoid the installation of meters inside homes, are presented as built‐in wall enclosures or conditioned rooms for meters, depending on the house‐type. Thus, meter rooms and such spaces may have the capability (and the utilities the right) to host telecommunication equipment, as derived from the need to access meters for remote reading purposes. LV grid present a more amiable situation, as LV power supply is always available and there are easy and cheap ways to connect to the cables with piercing devices.
1.6.5 Telecommunication Services Control
The impact of telecommunication services on Smart Grid operations is a key aspect of the enablement of telecommunications for the grid. Telecommunications are not a simple add‐on over the grid, but a transformation vector. Whenever grid operations rely on telecommunications, telecommunications become as critical to the utility as any other resource.
Telecommunications private network design and/or third‐party TSP service selection must be performed to allow the provision of the Smart Grid needed services within the utility license conditions. When the utility operates a private network for this purpose, the performance responsibility is within its decision range. However, when third‐party TSP services are involved, Service‐Level Agreements (SLA) must be clearly defined to govern service delivery conditions.
ITU‐T E.860 provides a framework for SLAs, defined as “a formal agreement between two or more entities that is reached after a negotiating activity with the scope to assess service characteristics, responsibilities and priorities of every part. An SLA may include statements about performance, tariffing and billing, service delivery and compensations.” SLAs are based in some formal definitions that must be well known to both parties, especially when referred to the service characteristics that need to be expressed in telecommunication technical terms. However, they must also collate (see ITU‐T G.1000 and its reference to ETSI ETR 003) all different service functions (sales, service management, technical quality, billing processes, and network/service management by the customer) and quality criteria with each of them (speed, accuracy, availability, reliability, security, simplicity, and flexibility), to be consistent with the objective.
Smart Grid needs must be transformed into telecommunication technical parameter requirements that measure network performance. Network performance is defined as in ITU‐T Recommendation E.800, as “the ability of a network or network portion to provide the functions related to communications between users.” Performance is critical for applications to deliver their expected benefits and must be properly planned and controlled in networks that share resources among different users.
Two of the most important performance parameters in telecommunications are throughput and latency. These general parameters are included in the network performance objectives of different networks (e.g., ITU‐T I.350 and Y.1540 for digital and IP‐based networks):
Throughput is the maximum data rate where no packet is discarded by a network. Throughput is usually measured as an average quantity, with control over the peak limits.
Latency is the time it takes for a data packet to get from one point to another. Latency is usually defined as a requirement below a certain limit.
Service performance is assessed in terms of its Quality of Service (QoS). ISO 8402 defines QoS as “the totality of characteristics of an entity that bear on its ability to satisfy stated and implied needs.” ITU‐T E.800 defines it as “the collective effect of service performance which determine the degree of satisfaction of a user of the service.” Beyond QoS, QoE (Quality of Experience as in ITU‐T E.804) enters into the subjective domain of the service users' perception that cannot be neglected as it reflects previous experiences and expectations. Thus, SLA, QoS, and QoE go beyond the pure technical perspective.
Eventually, telecommunication systems must absorb all these service requirements and integrate them in their complex network structures. These networks will not only deliver them but also control and manage its performance in different circumstances. ITU‐T Study Group 12 “Performance, QoS and QoE” [60] is leading this work, as in ITU‐T E.804 “QoS aspects for popular services in mobile networks” and ITU‐T Y.3106 “Quality of service functional requirements for the IMT‐2020 network.”
1.6.6 Environmental Conditions
The harsh conditions of most grid sites are one of the most important aspect that need to be taken into account when designing a telecommunications network for Smart Grids or when using telecommunications services provided by a TSP. It needs to be born in mind that most electric grid premises are neither set up in the way a telecommunications site would be, nor service points are typical residential houses.
On the contrary, there are many aspects that need to be considered to design telecommunication products for Smart Grids. We will refer to them as non‐functional requirement (“functional”