SMART GRID COMMUNICATION TECHNOLOGY – PART 1

A smart grid is automated electricity delivery and control system at which devices or “endpoints” located along the power line and on premise can interact with each other. Common interactions amidst these devices could be commands to check status, to connect, to disconnect, to turn on, to turn off and to read data. Communication technologies are used to relay information from the premises of electricity usage to utility and vice versa.

Most basic form of smart grid can be divided in two primary areas: Automatic Meter Reading (AMR) and SCADA (Supervisory Control and Data Acquisition)/ Distribution Automation (DA). AMR system collects consumption and diagnostic data from meters to bill accurately bill customer and analyze and/or troubleshoot Customer gained access to usage data as well.  SCADA/DA systems assist in efficient operations of a much wanted “reliable” power line. These systems can monitor larger area with electricity transmission and distribution level field equipments and allow utilities to measure voltage/current and control assets in its network through automated decision-making, effective fault detection and power restoration.

Though basic form of smart grid implementation is not obsolete today, between 1990s and 2005, the industry and technology moved from basic to more advanced functionalities. Two-way and real times are the key pillars in advancement. Utilities Advanced Metering Infrastructure (AMI) is a term denoting automated two-way communication between a smart meter and a utility data center.  AMR + two way communication + real time capability is AMI.  Similarly, in power line controls along with SCADA and DA, full smart grid application suites emerged: Voltage Management, Demand Response, direct Load Control, ingestion from Distributed Energy Resources (DER) etc.

AMI is a logical starting point to describe smart grid communication technology as other smart utility network components will be structurally covered with AMI technologies. AMI in a smart grid set up comprises of four tiers (see figure below):

  • Home network
  • Smart meter
  • Concentration point
  • Utility data center

AMI

Smart Grid : AMI – Communication Technology

Home Network and Smart Meter

Home network and smart meter access points are tightly coupled. The term home network is not confined within a home. It applies to a closely located territory. Home network is controlled by Home Area Network (HAN) that connects smart appliances, electric vehicles, storage and on premise electricity generators to an access point – smart meter. A smart meter is able to interface digitally. The devices working in concert allows load management at peak hours and overall energy control.  Peak load management is a critical consideration in electricity market due to high associated cost. Rest of the energy control, though nice to achieve in theory, would not incur same level of reliability requisite.  The amount of data transfer at a given point will likely consist only of a number representing the instantaneous electricity use of each device, expressed in watts. Hence the bandwidth requirement usually falls between 10kbps – 100 kbps per device. The required bandwidth could grow exponentially for large office buildings, so the chosen networking technology must scale.

Low-power, short-distance and cost effective technologies are well-suited for on-premises communications. There are number of choices: 2.4 GHz Wi-Fi, 802.11 wireless networking protocol, ZigBee (based on wireless IEEE 802.15.4 standard), IEEE 802.15.4g wireless Smart Utility Networks (SUN)  and HomePlug (a form of power line networking that carries data over the existing electrical wiring). Internet protocol (IP) based uniform standardization is widely shouted for communications on the premise.

Point to be noted that in-home applications can leverage smart grid. They can also exist independently without being part of a smart grid. For instance, any meter – smart or unsmarts (traditional) can be connected to HAN. E.g. a Wi-Fi enabled sensor can read traditional meter and send to a webserver to build many kinds of energy related consumer application. These kinds of applications, whether they use an existing meter or a smart meter, allow consumer-facing functions without the need for any communications technologies beyond those already installed in a usual internet-connected household.

Concentration Point

The collected information from a home network to an access point now needs to traverse to a concentration point as part of smart grid. Data traversal is indeed bi-directional. However, volume of data from concentration point to a device will be less compared to consumer side info flowing to the utility. A concentration point can be a substation, a utility pole-mounted device such as transformer, or a communications tower. Bandwidth requirements are in the 10-100 kbps range per device from the home or office. However if appliance-level data points as opposed to whole home data are transmitted to the concentration point then the bandwidth requirement will bump up.

Initial solution installations relied on Power Line Carrier (PLC). PLC transmitted data from device/meter or command to device/meter over existing power line. PLC is the most common conduit. It is cost effective for utilities especially in low-density areas, where deploying wireless technology is not viable yet power line is ubiquitous. Deploying wireless technology makes an appealing business case when expensive equipment installation can be shared. Deploying exclusive wireless technology across dispersed premises is cost prohibitive. But, at certain circumstances PLC is susceptible to interference and PLC offers extremely low bandwidth – less than ~20 kbps. Real time data intensive AMI requires bandwidth up to 100 kbps per device. In dense cities, AMI deployments use 900 MHz wireless mesh network for data transmission. In a wireless mesh network, connectivity between meters and collection endpoints is obtained via a dedicated network using unlicensed radio spectrum, run by the utility or a subcontractor. Stat network is another wireless alternative. It uses fixed point to multipoint RF network using licensed spectrum and communication towers. More bandwidth supportive broadband communications such as the IEEE 802.16e, mobile WiMAX, broadband PLC, and next-generation cellular technologies and satellite technologies are other possible choices. With growing data and big data buzz, bandwidth requirement tend to go up.

Utility Data Center

Information flow from concentration points to the utility typically functions over private network. A variety of technologies are available: fiber optic cable, T1 cable, microwave networks or star networks to conduit data from the hub to the utility. Sophisticated smart grid applications supporting two way and frequent communication, seek bandwidth in the range of at least 500 kbps to dispatch data from a concentration point to a utility. Currently many AMI networks support intermittent connectivity to the utility – data gets aggregated at a neighborhood node and only sent to the utility periodically. More bandwidth may be needed to support more functionalities or more real time connectivity.