I. National Natural Gas Transmission System
The National Natural Gas Transmission System (NNGTS) consists of:
- the main gas transmission pipeline and its branches,
- the Metering Stations of the Entry Points "SIDIROKASTRO", "KIPI", "NEA MESIMVRIA", "AGIA TRIADA" and "AMFITRITI" of the NNGTS,
- the Compressor Station in Nea Mesimvria, Thessaloniki,
- the Natural Gas Metering, Metering / Regulating, Regulating Stations throughout the country,
- the Natural Gas Control and Dispatching Centers in Patima Elefsina and Nea Mesimvria Thessaloniki,
- the Remote Control and Telecommunications system,
- the Operation and Maintenance Centers of Southern Greece, Central Greece, Northern Greece and Northeastern Greece.
I.1 Main Pipeline and branches of the National Natural Gas Transmission System
The main gas pipeline is 512 km long and diameter 36'' and 30'' while its branches have a total length of 954.16 km, including (a) the underwater pipeline with a diameter of 20" and a length of 14.20 km of the Aliveri branch and (b) the two (2) subsea pipelines, backup to each other, diameter 24" each and length 620 m and 630 m, connecting the LNG Station of Revithoussa with the mainland.
Along the main pipeline and branches are installed:
- Line Valve stations for the partial isolation of the National Natural Gas Transmission System in cases of emergency or scheduled maintenance,
- Scraper stations for sending and receiving cleaning devices (scrapers) or interior inspection devices for the pipeline; and
- Cathodic Protection System of the pipeline from corrosion phenomena.
National Natural Gas Transmission System (NNGTS)
I.2 Operation and Maintenance Centers
I.2.1. Southern Greece Operating System Center - Boundaries
The Operation & Maintenance Center of Southern Greece is located in the area of Patima, Elefsina. Its area of responsibility extends from the Mavroneri scraper station in Viotia to the metering station of PPC Megalopoli. The area of responsibility of the Center includes the branches of Antikyra, Aliveri, Lavrion, Keratsini, Oinofyta, HERON, Thisvi, ELPE Elefsina, MOTOROIL and Megara-Corinth-Megalopoli.
The operational facilities in the area of responsibility of the Operation & Maintenance Center include 280.23 km of 30" diameter high pressure natural gas pipeline, 169.16 km of 24" diameter high pressure natural gas pipeline, 128.98 km of 20" diameter high pressure natural gas pipeline, 0.75 km of 14" high pressure pipeline, 27.03 km of 10" diameter high-pressure natural gas pipeline and 0.73 km of 4" high pressure pipeline.
Twenty-nine (29) scraper stations, twenty-nine (29) line valve stations, and thirty-one (31) metering and/or regulating stations are installed along the above pipelines.
I.2.2. Central Greece O&M Centre - Boundaries
The Operation & Maintenance Center of Central Greece is located in the area of Ambelia, Farsala. Its area of responsibility extends from the exit of the scraper station of Platamonas in Pieria to the entrance of the scraper station of Mavroneri in Viotia. This area includes the branches of Volos and Trikala.
The operational facilities in the area of responsibility of the Operation & Maintenance Center include 205.7 km of 30" diameter high pressure natural gas pipeline, 40.42 km of 10" diameter high pressure natural gas pipeline of the Volos branch and 71.94 km of 10" diameter high pressure natural gas pipeline of the Trikala branch.
Along the above pipelines are installed six (6) scraper stations, thirteen (13) line valve stations, and nine (9) measuring and/or regulating stations.
I.2.3. O&M Center of Northern Greece - Boundaries
The Operation & Maintenance Center of Northern Greece is located in the area of Nea Mesimvria, Thessaloniki. Its area of responsibility extends from the scraper station of Promachonas on the border between Greece and Bulgaria to the scraper station of Platamonas, Pieria. The area of responsibility includes the branches of North Thessaloniki, East Thessaloniki, Platy and part of the Karperis - Halkero branch, from the Karperis scraper station to the Fotolivos line valve station.
The operational facilities in the area of responsibility of the Operation & Maintenance Center include 98 km of 36" diameter high pressure natural gas pipeline, 93 km of 30" diameter high pressure natural gas pipeline, 102.01 km of high pressure natural gas pipeline with a diameter of 24" and 13.08 km of 10" diameter high-pressure natural gas pipeline.
Fifteen (15) scraper stations, fifteen (15) line valve stations and nine (9) metering and/or regulating stations are installed along the above pipelines. Cyclone type filters are installed at Promachonas scraper station for the purification of natural gas.
The Center's responsibility also includes the operation and maintenance of the Sidirokastro Border Metering Station, the Interconnection Metering Station with the TAP Pipeline and the Nea Mesimvria Compressor Station.
I.2.4. Northeast Greece Coast Guard Center - Boundaries
The Operation and Maintenance Center of Northeastern Greece is 5 km away from the city of Xanthi, at the 2nd km of Diomedea – Lefki Road. Its area of responsibility extends from the Fotolivos line valve station to the Kipi Evros Border Metering Station, on the Greek-Turkish border.
The operational facilities in the area of responsibility of the Operation & Maintenance Center include 86.71 km of 36" diameter high pressure natural gas pipeline, 146.92 km of 24" diameter high-pressure natural gas pipeline, and 1.5 km of 12" diameter high-pressure natural gas pipeline.
Along the above pipelines, six (6) scraper stations, twelve (12) line valve stations, and nine (9) metering and/or regulating stations are installed, of which M/R Amfitriti station is an entry point to the NNGTS.
I.3. Metering/Regulating stations
Metering and/or Regulating stations shall reduce and control the pressure of the systems they supply, measure the amount of energy fed from the natural gas transmission system to medium pressure networks, or to consumers directly connected to the transmission system, and give the gas a characteristic odor (when required by international and national regulations) for the early detection of leaks.
For this reason, they are equipped with:
- pressure regulators, which continuously monitor and regulate the operating pressure of distribution networks,
- slum shut valves to protect the supplying downstream systems from any violation of their operating pressure limits (e.g. due to failure of the pressure regulator),
- modern metering systems for the continuous measurement of the flow and quality of natural gas channeled through the stations,
- modern automation, remote control and invoicing systems, and
- facilities for adding a characteristic odor.
I.4. Gas Control and Dispatching Centers
The operational parameters of the National Natural Gas Transmission System are checked on a continuous basis and determined by the Gas Control and Dispatching Center, located at the facilities of the Operation and Maintenance Center of Southern Greece (Patima Elefsina) and alternatively (in case of loss of the former) by the backup Gas Control and Dispatching Center located at the facilities of the Operation and Maintenance Center of Northern Greece (Nea Mesimvria, Thessaloniki).
The object of the Gas Control and Dispatching Center is, among others:
- the continuous monitoring of the operating parameters of the National Natural Gas Transmission System through a Supervisory Control and Data Acquisition (SCADA) system,
- the implementation of natural receipt and delivery schedules in accordance with the respective nominations of the Transmission Users,
- the determination of the operational parameters of the National Natural Gas Transmission System using modern network simulation software technology, aiming at the safe, smooth and efficient operation of the network,
- timely notification and guidance of maintenance personnel in cases of equipment malfunction, and
- support and coordination of maintenance personnel and authorities (Fire Brigade, Police) in emergency situations.
I.5. Remote Control and Telecommunications System
The Remote Control and Communications (RCC) system has as its primary objective "to ensure that the natural gas transmission system will supply the natural gas market with sufficient quantities under all foreseeable conditions, normal and extraordinary"
and as secondary objectives "the remote monitoring of natural gas stations, the management of alarms and the provision of technical and statistical data to DESFA's departments so that the transport of natural gas is constantly done in a safe, reliable and cost-effective way".
It consists of the following subsystems:
- Fiber optic cable, which is installed parallel to the high-pressure natural gas pipeline and is the main carrier of all kinds of internal communications (voice and data) of DESFA.
- Telecommunication system based on Ethernet and Internet protocols (Internet Protocol - IP) with routers and/or layer 3 switches installed at each station of the National Natural Gas Transmission System, which achieves the transmission of voice and data through the fiber optic cable as well as the connection to backup communication lines of telecommunications providers.
- Supervisory Control and Data Acquisition (SCADA) system, which achieves remote monitoring and remote control of all metering and/or regulating stations and valve stations of the National Transmission System from the Gas Control and Dispatching Centers.
- Cluster of three IP call centers installed at DESFA's headquarters, the Operation and Maintenance Center of Southern Greece (Patima Elefsina) and the Operation and Maintenance Center of Northern Greece (N. Mesimvria, Thessaloniki) for the management of all internal and external telephone calls of DESFA.
I.6. Geographical information system
DESFA, an innovator in technology and services, has developed an internal Geographic Information System in order to fully record its assets in digital form. GIS technology enables a faster and better understanding of the current state of the high-pressure natural gas network. The operation of the GIS-DESFA application is divided into the Desktop environment and the Web environment.
The information entered into the GIS relates to the entire NNGTS:
1. Pipeline networks
2. Facilities – Stations
3. Cathodic protection
4. Cadastral
5. Geological
l6. Environmental
I.7. Technical Systems for the Protection of NNGTS
I.7.1 Insulating coatings
The metal pipeline and its components are covered by special insulating coatings to provide protection against mechanical wear and corrosion.
I.7.2 Cathodic Protection System
An integrated Cathodic Protection System has been installed in the buried pipeline. The purpose of the system is generally the safe and economical transport of natural gas.
More specifically, it concerns:
- diagnosis of integrity problems of the metal pipeline and fittings,
- protection against electrochemical corrosion and corrosion from stray currents,
- the operation and inspection of the earthing electrodes of the pipeline and related protective equipment against adverse electrical interference,
- the operation and control of pipeline components that provide electrical isolation.
The basic equipment of the cathodic protection system is:
- Transformer/Rectifier Stations (T/R)
- Remote Monitoring and Control System of Cathodic Protection System
- Groundbed and Anode Cable
- Sacrificial (Galvanic) Anodes
- Earthing Electrodes and DC Decoupling Devices for AC mitigation
- Insulating Joints/Couplings
- Cathodic Protection Metering Stations - Test Posts
In total in the NNGTS, there are 37 T/R Stations, approximately 1700 Cathodic Protection Metering Stations, 200 monolithic insulating joints and 300 insulating flanges, 138 casings (i.e. reinforcing pipes surrounding the pipeline at certain intersections), 492 earthing electrodes in the pipeline and 93 earthing systems in fenced stations.
I.7.3 Surge/Lightning Protection, Explosion Proof and Intrinsic Safety Systems
A Surge/Lightning Protection System with Explosion Proof and Intrinsic Safety Systems has been installed. The Surge/Lightning Protection System is mainly divided into external and internal lightning protection. The external lightning protection system consists of:
- lightning arresters or rods
- down conductors
- grounding
- equipotential bonding.
Internal lightning and explosion protection concerns more specific protective devices of electrical and electronic equipment. Protection Systems are inspected according to procedures in accordance with international standards.
