Interruptions
Under current agreements with Shippers, Transporters can interrupt for three specific reasons
- Capacity Constraints
- Testing
- Emergency
Capacity Constraints
NTS
If National Grid expects that the gas demand in any part of the National Transmission System will exceed the available capacity, it will instruct shippers supplying gas to interrupt some, or all, of their customers with interruptible contracts to ensure there is sufficient capacity to deliver gas to consumers with firm contracts. National Transmission System interruption is generally invoked over a wide geographic area.
Distribution Networks
When a constraint occurs in a local distribution system, it may only affect a small number of consumers in that locality. As a result of this, some consumers may experience interruption more frequently than others, depending on their location within the gas transportation system and the severity of local system constraints.
Testing Interruption Capability
Transporters have the right to interrupt for up to three days per year to check the effectiveness of the interruption process. Such tests will be used when there are doubts that effective interruption can be achieved.
Emergency
Transporters also have the right to interrupt to avoid, or manage a gas supply emergency incident as defined by the Gas Safety (Management) Regulations 1996. This may be caused by unforeseen circumstances such as pipeline, plant or equipment failure, or where demand exceeds either total supply or planned firm capacity. The normal notice period for interruption is wavered for emergency interruption and sites should stop using gas as quickly as possible.
Non Transporter interruption
Depending on the contract with the consumer, gas suppliers or shippers may also interrupt the consumer for their own reasons. This could be for supply/demand matching or other commercial reasons.
Types of Interruptible Sites
There are two classifications of Interruptible Site. These sites form part of Northern Gas Networks' strategy for the safe and secure operation of the network under different circumstances.
Detailed below are the different classifications of Interruptible Sites.
Shipper Nominated Interruptible
Sites which are classified as 'Shipper Nominated Interruptible' (SNI) receive a reduction in the transportation charge which may be included in the price of gas. In return a Transporter can interrupt these supply points for up to 45 days in each Gas Year. SNI is a non-Network Code term and care must be taken in not confusing Transporter interruption at an SNI with a commercial interruption carried out by shippers, sometime referred to as "shipper interruption".
Northern Gas Networks Nominated Interruptible
Northern Gas Networks can designate a site 'Northern Gas Networks Nominated Interruptible' (TNI) by giving at least 12 months notice. This gives Northern Gas Networks the ability to interrupt these sites for more than the usual 45 days (for example, up to 60 days in a 1-in-50 cold winter). This number of interruptible days is determined by Capacity Management and Network Planning and is a specified number for each site.
In addition, sites which are located in a particularly vulnerable part of the network are described as Network Sensitive Loads. These can be either TNI or SNI.
Network Sensitive Loads
Sites which are designated as Network Sensitive Loads (NSL) are those which are on a part of the network that has limited transportation capacity. These sites are required to interrupt in order to maintain supply pressures to firm end users, at a level which avoids an actual or potential supply emergency, as defined by the Gas Safety (Management) Regulations 1996. As a result, an NSL may have a higher probability of being interrupted, particularly during mild weather conditions, than other sites.
Useful Links
 |
 |
 |