**6. Constraints in the natural gas system**

The present section has the aim to describe the technical constraints that may affect the natural gas system, highlighting the potential of demand response so as to overcome these limits and promote the development of a reliable natural gas system, able to quickly face sudden network failures.

Generally speaking, the physical/technical constraints of a gas network system are set by one or more of the following parameters:


Regarding the commercial constraints, they may be set by the following:


Interruptions of gas supply that could occur in the gas system determine a noncontinuity of the service. Traditionally, interruptions have been divided into short and long. Short interruptions are those whose duration is shorter than a standard value defined in regulation. For example, the Italian regulation defines an interruption as short when the duration is less than or equal to 120 min. However, interruptions are considered as long when exceeding such standard duration.

According to its nature, interruptions could be also classified as follows:

• Scheduled interruptions (also called interruptions with notice), which take place due to scheduled operations of maintenance of the system (transmission and distribution). Usually, operators notify the customers at least 24 h before

a planned interruption occurs, specifying the date, time, and duration for the scheduled activities. Generally, among the activities considered as scheduled interruptions, the more relevant are the following:


Depending on country-specific regulation, an emergency could be defined in different ways. For example, in Italy, and according to Article 27, paragraph 27.1, an emergency is considered an event that causes the interruption of the gas distribution without notice to at least a number of 250 end users and for the duration of 24 hours.
