British technical columnist and journalist Tim Guest (Guardian) expresses his view on why TETRA is the most suitable standard for data collection in SCADA systems.
Talk about data transfer in the field of critical communications usually takes place against the backdrop of a growing demand for the transfer of photo-video materials from primary respondents using TETRA, TEDS and, possibly, LTE in the future. However, there are other areas where the requirements for reliable transmission of critical data are almost the same, and in some cases even stricter, in terms of public safety. For example, in the energy, oil, gas, and utility sectors, real-time monitoring, control, and data acquisition (SCADA) systems are very important for monitoring and transmitting data to the most complex engineering systems around the world, helping to keep them operational.
First introduced almost 50 years ago, SCADA systems allow both relatively simple temperature monitoring of the building and the operational management of extremely complex production processes in nuclear, hydro and power plants, in industry, as well as in oil and gas and chemical plants. If, for example, there was a break in the oil pipeline or radiation leak at a nuclear power plant, the SCADA system collects all the information about such an accident, transfers it to the control center, prioritizing the accidents, and also takes the necessary actions to eliminate them.
Some SCADA systems are used for telemetry (remote measurement), for telecontrol (control of remote equipment, such as power switches, valve and actuator controls), and often carry the function of transmitting reports on the current status of remote equipment. Other SCADA systems can be used to support smart energy systems - the competent interaction of all users connected to the network, including those who generate energy and consumers, ensures network stability, reliability, security and, ultimately, mutual economic benefit.
Typical SCADA systems include sensor systems in which the main control device is connected to a slave device or remote (CU) at infrastructure facilities. Asset groups, known as scan groups, are controlled by the host device. For example, in high voltage power distribution systems, CCs are installed at facilities that are potentially hazardous or require minimal response time in the event of a failure, such as, for example, a primary substation. Information about the state of such objects using the master device will be collected regularly and at high speed.
Another mode of operation of SCADA systems is the “report by exception” mode, in which reports from the control system will only arrive in the event of an accident. Such modes are usually used for less important and dangerous objects than those controlled by interrogation, including scenarios that are used to monitor oil and gas wells. But this involves regular checks to ensure that the control units that will be “silent” between alarms are operational. Nevertheless, “accidents” can often mean that many UUs suddenly “wake up” at the same time, and this “overload” should be provided for in any technological control system.
The importance of each application is displayed in the expected response time of the SCADA system devices. In the electric power industry, where high-voltage substations are involved, the typical polling time is 250 m / s, since it is not only a matter of supplying electricity, but also that the occurring failures and accidents can extremely negatively affect a huge number of end consumers, and the system should be “One step ahead” of the expected events. When it comes to high-pressure gas distribution, such a network (which already has automatic shut-off systems) should be analyzed only every two minutes in order to anticipate potential accidents. For an oil pipeline, where it takes time to detect a leak when the pressure of the oil flow changes, a survey usually occurs every 24 hours.
TETRA networks are well suited to support SCADA systems and control as very robust, secure, and powerful. Starting with the IP-based TETRA network providing the Short Data Service (SDS) - packet data transfer at 3 kbps on one slot in 1-2 seconds, and up to TETRA Enhanced Data Services (TEDS), where messages on several slots can transmitted even at higher speeds, the TETRA standard proves that it more than meets the requirements of SCADA systems - both for interrogation scenarios, and for “reporting exceptions”.
According to Nick Smaya, who co-chairs the TCCA Smart Grid and Telemetry (SST) Group, it’s difficult to directly relate data rates to SCADA system throughput per cell, as many factors play a role here. The required UE response time and the amount of traffic not related to SCADA TETRA in the network will be key factors, as well as the SCADA network architecture itself, for example, the number of UE in each cell. The complexity of the SU will also be a critical factor along with the number of measurements and controls on the network. This is also determined by the maximum and minimum size of the polling and scanning group. In the case of “exception reports”, the maximum number of UUs that try to transmit a message at the same time and the need for retransmission will also affect speed.
The advantage of using TETRA for SCADA systems in control, Nick Smy said that, along with its suitability for data transfer, there is also the possibility of voice communication. TETRA includes authentication, a radio interface and end-to-end encryption, which today is especially important for security when using SCADA systems. Smay also notes the speed and reliability of SDS, the ability to work in a group, which allows you to quickly work with multiple devices. Of the great capabilities of TEDS, in addition to its higher speeds, Smay noted the ability to process and transmit different types of data: real-time transmitted, telemetry information, background polls, data with various delays, data of medium and low importance and low predictability.
All this is a factor in favor of choosing TETRA for SCADA systems.
Oil and gas sector requirements
When used in the oil and gas sector, the TETRA device must process data of various types and from any number of sources: from remote measurement of parameters in the well, including temperature, pressure, flow rate and alarms to monitoring voltage, current and accidents associated with Catholic corrosion and leakage. A reliable communication system is required to detect them by the dispatcher and take measures to eliminate them.
The purpose of using the SCADA system in managing an oil well is to maximize well productivity, manage its reserves and production. The system should also contribute to improving the well regeneration process, as well as to control a large area around each well for new drilling and subsequent complete restoration of the environment. And all this must be done in real time.
The SCADA system of an oil field, as a rule, launches and controls three aspects of the production process: 1) data collection and control over the field; 2) operation of the pipeline; 3) distribution of capacities and resources. Its main elements will include servers (control centers), control centers, well equipment components, and, of course, a communication system. For a communication system to be suitable for supporting SCADA, it must be an open standard, using reliable and proven technologies that can support the requirements of the SCADA system for it. Such a communication system should also be extremely reliable, as well as provide for the possible expansion of the network in the future. However, while meeting all these needs, such a system should also be cost-effective for the end user, easy to deploy and operate.
Given these requirements, Saudi Aramco, one of the world's largest oil and gas companies, uses a TETRA-based system to manage production facilities covering more than 330,000 km2 in the Middle East. Thanks to the world's largest proven oil reserves, the company’s network in this vast territory will ultimately contain more than 170 base stations, six TETRA switching and control nodes, at least 150 high-performance repeaters for providing radio coverage in buildings and equipment for more than 14,000 end users. Moreover, both on land and on most of the marine objects. Saudi Aramco’s TETRA end-users list covers everything from firefighters who need waterproof and explosion-proof equipment to refineries and tankers, vehicles, security groups and management personnel.
A company spokesman recently said that the main reasons for choosing TETRA for this project were its “technological efficiency, where each frequency can provide up to four time slots, which, he said, have reduced the cost of using radio frequencies by 75%.” The open TETRA platform, offering a wide selection of suppliers of end devices and infrastructure equipment, as well as its reliability and safety, also played a key role in convincing Saudi Aramco that TETRA is the right choice for its customers. Tey SCADA.
LS Telecom played an important role in the deployment of the network and did most of the RF planning work for this project. At the Berri offshore oil field in the north of the Persian Gulf, the system connects the SCADA ground node with UC scan teams located on offshore oil production platforms using a UHF narrowband station operating in the 330-350 MHz band. One of the most important goals of the project at the initial stage was to determine the number of necessary ground base stations and their locations to support and interact with all the necessary remote marine objects.
Today, it is obvious that TETRA is very well suited to provide reliable and fast data transfer in SCADA systems for all types of production activities. In the future, SCADA will require higher transmission rates, which are likely to be provided by TEDS.
Experience in detail
According to Funk-Electronic Piciorgros GmbH, a company with extensive experience in the oil and gas sector: “Typically, a full survey cycle in the oil and gas complex should not last more than five minutes.” Indeed, in a Saudi Aramco deployed network, the polling time varies from 30 seconds for some UEs to 300 seconds for the largest scan groups.
Assessing the suitability of a particular equipment for use on the network, Piciorgros leads an estimated one-second interrogation cycle using bus controllers under TETRA and SDS. This means that 60 UUs can be interrogated per minute and 300 UUs every five minutes on only one of the four TETRA time slots. The company claims that when using a TETRA data gateway, such as its own TGW-100, multiple nodes can use the same TETRA time slot in parallel without decreasing the polling rate. Using four polling nodes, the total number of UEs that could be polled over a five-minute period would be 1200 (300 (number of polling cycles in five minutes) x 4 (nodes used)). Using all time slots, the number of polling cycles that could be completed in five minutes would increase to 5000.
The importance of the oil and gas sector for TETRA
In the fall of 2012, TCCA and Smart Grid and Telemetry (SST) began promoting TETRA for traditional SCADA and telemetry applications, as well as for new capabilities in other areas, such as Smart City smart networks. David Taylor, lead consultant for Analysys Mason, has been named as co-chair of the SST with Nick Smay. Speaking about TETRA today, he said that: “The main tasks of the SST working group are to promote TETRA as a communication network in SCADA, telemetry and smart networks. To this end, we want to create a forum for users, manufacturers, system integrators and developers so that they can share their experiences and ideas. This, in turn, will help to stimulate the implementation of relevant activities among organizations involved in technological standards and will help in adapting the most important to the needs of the market in the future. ”