Technical Planning Method
This document describes the method used to calculate how much capacity can be offered at entry and exit points in the transmission network. It begins with a description of the network, then explains how transport capacity is offered to the market and what calculations are made to determine the volume of entry and exit capacities.
The transmission network
The transmission network operated by GTS consists of a series of pipelines and stations. The transmission network can be divided into different types of gas (with G-gas (Groningen gas) flowing through part of the network and H-gas (high calorific gas) flowing through the remainder). A distinction can also be made between pressure classes, the main transmission grid (HTL) and the regional transmission grid (RTL). The RTL is supplied by the HTL (through metering and pressure-regulating stations), and the distribution company networks are in turn supplied by the RTL (through custody transfer stations). The RTL is only used for the transport of G-gas; the HTL partly for G-gas and partly for H-gas. The diagram below shows the coverage for the HTL.
In the HTL, the two networks are interconnected via blender stations. H-gas can be added to the G-gas network via these stations. In addition to the pipelines, the HTL also contains a large number of compressor stations. These stations are used to increase the pressure of the gas to enable it to be transported further.
Gas is fed into the grid at entry points. These can be feeding points for gas from domestic production, border points where gas is fed in from other networks (or via an LNG terminal) and points that are connected to gas storage facilities.
Gas is delivered to exit points after transport. These can be the transhipment points for the distribution companies and domestic customers (the custody transfer stations), border points where gas is transferred to other networks or points connected to gas storage facilities.
Transport contracts at entry and exit points
Transport capacity is offered to shippers at entry and exit points. The capacity is set down in the form of a contract. Entry and exit capacity can be contracted independently from each other, so that upon entry a shipper does not have to indicate the corresponding exit capacity. This correspondence also does not need to be indicated by the shipper when the transport capacity is being used. The only condition is that the volume of gas (in terms of energy content) drawn from the grid must balance the volume of gas (in terms of energy content) supplied to it. Any imbalances will be corrected by means of balancing instruments.
Before transport capacity at entry and exit points can be agreed with shippers in the form of contracts, it is first established whether the transmission network has the necessary capacity.
In addition to contractual obligations with shippers at entry and exit points, the calculation is also based on the pressure, temperature and gas composition at these points and the configuration of the gas transmission network as a whole (including pipelines and stations).
The following algorithms are used for the calculation:
Drop in pressure in a pipeline (ref 2.127 Physical Properties of Natural Gases, 1980, N.V. Nederlandse Gasunie)
Capacity of a compressor station (ref 2.118 Physical Properties of Natural Gases, 1980, N.V. Nederlandse Gasunie)":
For the remainder of the underlying algorithms, see the reference works cited.
The process used to calculate the available capacity at entry and exit points is as follows. It is based at all times on existing commitments and on the network configuration for the current calculation year.
By incrementally increasing the capacity at entry and exit points, it is possible to determine at what level obstructions will not occur in the transmission network. This capacity can then be offered to the market. These calculations are performed for future years whose network configurations are known.
If a market survey indicates a likely need for additional capacity (over and above the capacity already available in the network), these requirements are set down in long-term contracts based on an Open Season process. Network calculations show what measures must be taken in the transmission network to expand the capacity in order to fulfil the new contracts. The contracts are finalised once an investment decision has been taken.