Gas quality and metering
Through its national gas transmission system GTS is transporting, in separate transmission networks, two different qualities of gas: high-calorific gas (H-gas) and low-calorific gas (L-gas). A connected party (a final customer directly connected to the transmission network of GTS) receives gas of one of these two gasqualities. The specifications of these gases are laid down in annex 3 resp. 4 of the Regeling gaskwaliteit.
As a connected party, your equipment must be suited for natural gas with these specifications. In the annex 1B (exits) of the TSC, is noted to which ‘Gassysteem’ of the Regeling gaskwaliteit, your connection is attached. In this way, you can see which quality of gas is delivered to your connection.
Volume and quality measurements
The amount of energy that a connected party is withdrawing from the national gas transmission system is determined. At the gas delivery station, the connection between the transmission system and the installation of the connected party, the volume of gas withdrawn is measured. The gas composition is measured further upstream of the gas delivery station. From the volume withdrawn and the gas composition (more specific the calorific value of the gas) the amount of energy is calculated.
The program responsible party or parties (the shipper) and the supplier(s) that are registered for an exit point to a final customer are informed about the gas flows over that exit point. These parties as well as GTS will use this data for their invoicing. The amount of energy needs to be determined correctly and accurately. The process to measure gas flows and gas quality, including the accuracy of the measurements, is described in the Meetcode Gas LNB. Every year GTS publishes an evaluation of the performance of its gas quality and volume determination process. The fiscal metering process applied by GTS is ISO-9001 certified.
Metering data at exitpoints is also made available to the connected final customer. More information on this can be found on the webpage shippers/balancing-regime/documents/connected-party.
Two qualities of gas are transported in GTS’s transmission grid, i.e. H-gas (high-calorific gas) and G-gas (low-calorific or Groningen gas). An important measure for gas quality is the Wobbe index. The "Regeling gaskwaliteit" contains the Wobbe ranges for each type of gas including a summary of the gas composition. Please refer to www.agentschap.nl for more information about gas compositions.
You can indicate a preference for H-gas or G-gas on the "Application form new connection". Whether the preference indicated by a connected party can be honoured depends on the proximity of an H-gas or G-gas pipeline and the available capacity in the H- or G-gas system.
The connected party can state the desired pressure or pre-pressure at the connection point in bar (o). The gas transmission grid has two networks, the RTL (regional transmission line) and the HTL (high-pressure transmission line). The RTL has a maximum pressure of 40 bar(o) and the HTL a maximum pressure of 67 or 80 bar(o). The effective pressure at the connection point is dependent on the distance from a compressor station or a metering and pressure-regulating station. The RTL network has a minimum pressure of ca. 8 bar(o) and the HTL network a minimum pressure of ca. 40 bar(o). If possible, we will take account of the desired pressure put forward by a connected party.
Gas, which is odourless in its original state, has an odorant (THT) added to it at metering and pressure-regulating stations within the gas transmission grid. You can indicate a preference regarding whether it wants to receive odorised gas or not. In some cases, pipelines with non-odorised and odorised gas lie alongside each other and sometimes a choice has to be made. Ultimately we decide the network to which a connected party will be connected. In the event that we offer a connection point to the non-odorised gas network, you must take your own safety precautions in the form of gas detection or by fitting an odorant production unit in its gas receiving station.
In Gasport, under “Historical/Offline Metering /Quality per run”, connected parties can see which calorific value in a specified hour has been used for the energy determination for their exit point(s). The density, Wobbe, CO2 and N2 percentages are also shown here.
Please note; the energy determination requirements as set out in the Metering Conditions for Gas – NNO do not require the hourly calorific values determined by GTS at a delivery point to correspond exactly to the calorific value of the gas made available at that moment.
In Gasport, under “Dispatching/Near real-time metering/Quality per run” details of gas composition are shown for every fifteen minutes. The calculated parameters such as Wobbe, density and calorific value are also shown here.
These values are determined by GTS on the basis of the gas quality system as set out in the Metering Conditions for Gas - NNO. A description of the current gas quality system can be found on this website. The consequence is that the value shown does not need to correspond every hour with the value of the gas made available at that moment. And so, for those reasons, the measurements reported are not suitable to be used for, for example, process control. These data are suitable for invoice control, however, provided they are not shown as being ‘unreliable’.