What is the definition of a 'Smart Grid'?

A concept often causing confusion

The 'smart grid' is commonly presented as an indispensable part of the future power system. It is claimed that a true liberalised electricity market with a high penetration of distributed generation will only be able to supply a high degree of power reliability if grids are made smart.

But what exactly is a 'smart grid'? Reading through some literature on the subject, one quickly discovers that it can mean many different things to many different people, often leading discussions to end in confusion.

A smart grid is neither a clearly defined single concept nor a single technology. Rather it is like a basket containing various combinations of balls. The context and the interpretation depend upon the user. Carnegie Mellon University recently published an article describing all of the various balls typically found in this metaphorical basket. Some of them represent innovations that are still in the development phase, while others stand for technologies which have already been applied for years.

Some of the balls found in the smart grid basket include:

At customer level

• Meters that can be read automatically: this avoids sending out meter readers and can facilitate a fast and exact billing of consumption. It is already widely adopted by many power companies.
• Time-of-day and time-of-use meters: the former are meters that change the electricity price depending on the time of the day, the latter are meters that integrate the actual electricity price at any given moment in time.
• Meters that can communicate with the customers: a display shows the customers their current rate of electricity use, allowing them to adjust their consumption level in real time.
• Control of customer’s load: control systems that react to time-of-day or time-of-use meters to automatically switch certain circuits on or off.

At distribution grid level

• Distribution system automation: A first step is the operating of the distribution grid from a central control room, avoiding the need to send people into the field for switching actions. Such systems have already been installed in several places around the world. A second step is to change the tree layout of the grid into a meshed layout. By also adding sensors and remote control switches, incidents can be isolated and cut off, minimising problems for electricity consumers.
• Selective load control: selectively switching off customers to avoid a complete black out. A step further is the ability to turn individual loads on or off within customer’s premises.
• 'Islanding' of micro-grids supplied by distributed generation units. This concept can, in its turn, have several different meanings. The basic idea is that local DGs locally increase the reliability of supply.

At transmission grid level

• Phase measurements: the efficiency and stability of power system operation could be improved with the addition of phase measurement at various key locations on the transmission grid and combined with advanced communication and control systems.
• FACTS: Flexible AC Transmission Control Devices or FACTS are advanced systems that can change the flow of power in transmission lines. A phase shift transformer is an example of a FACT.
• Distributed and autonomous control: models demonstrate that advanced automatic control systems that cooperate with each other could in some cases do a better job than a centralised human operation of the system.