Temperature sensors in energy systems

In the modern world, the increasing electricity consumption and high demand for energy lead to an increase in stress on the power cables that often reach their physical limits. This affects the safety of power lines and their efficiency. To combat these issues, real-time thermal ratings may be implemented to observe the thermal behavior of cables and calculate their operational limits. The knowledge of these parameters is key to control the safety and efficiency of power lines, as unforeseeable thermal conditions do, in fact, lead to system degradation and capacity reduction. Real-time thermal rating aid in saving maintenance time, optimization of resources, and improving the efficiency of power lines.

Real-time thermal ratings may not only assist in perfecting already existing energy systems but also to integrate alternative power sources, such as wind energy systems. To improve the wind energy infrastructure and to further integrate renewable energy sources into mainstream energy production, the reduction of restrictions placed on wind energy is necessary for elevating the efficiency of such systems. The following measurements are required in order to implement real-time thermal ratings into the network: wind speed, thermal state estimations, temperature, and voltage measurements. The combination of these variables creates real-time ratings for wind energy systems.

The evaluation of said measurements provides crucial information on the ways in which wind energy capacity may be increased. For example, an implementation of thermal ratings that was conducted in 2010 revealed that the cooling effect of wind significantly affects wind power lines and may potentially lead to an increase in their electrical capacity up to 30%.

These results proved to be significant to the field and provided valuable insight into the generation capacity and its potential increases. It is expected that real-time thermal readings will allow for increased integration of wind energy into the distribution network.

Fiber Bragg temperature sensors are insensitive to changes in the environment, which is important for wind energy generators, and have a long reliability period. If you would like to purchase Optromix FBG Temperature Sensors, please contact us: info@optromix.com or +1 617 558 98 58.

Distributed temperature sensors in experimental hydrology

Distributed temperature sensors are usually used in industrial applications, such as process control and infrastructure monitoring; however, in the past couple of years, fiber optic distributed sensors have been used in ecological monitoring. The ability to measure temperature in time and space simultaneously allows distributed temperature sensors to be used in groundwater detection, rainforest ambient temperature monitoring, stream temperature monitoring, and more.

Temperature sensing is one of the most significant methods of experimental hydrology as it provides valuable insight into the flow dynamics of different types of water bodies. The water temperature is determined by measuring the Stokes/anti-Stokes ratio of reflected light that was produced by sending a laser pulse through the cable. The cable is placed into the body of water to detect temperature fluctuations along the stream. The data density of distributed sensors allows to obtain high-resolution data and map temperature changes in the water with high accuracy, and the absence of electronic parts in monitoring zones makes distributed sensors safe to use underwater. High return speeds of such optic sensors are perfect for both fast-changing and subtle temperature changes that often occur in water. Moreover, distributed temperature sensors are extremely thin and are easy to use in shallow streams and wells, and resistance to corrosion determines their long life cycle even if used in harsh conditions.

The measurements obtained by utilizing distributed temperature sensors are then used to construct 3D temperature maps of water streams or to validate and refine existing models of water temperature fluctuations. This data assists in finding locations of groundwater sources and their contribution to the stream helps to better understand river ecosystems, determine the distribution of studied species and their migration paths.

Other fields that utilize distributed temperature sensors include healthcare and biomedicine fields, fire detection, oil and gas production, detection of leakages, pipelines integrity surveillance, and others.

Optromix company manufactures stainless-steel housed optic sensors that are tensile and impact resistant. If you would like to purchase Optromix FBG Temperature Sensors, please contact us: info@optromix.com or +1 617 558 98 58.

Fiber Optic Temperature Monitoring of Belt Conveyors

Major conveyor belt–related mining incidents are now relatively infrequent as a result of recent improvements in engineering standards and the use of fire-resistant materials. However, conveyor belts are still a potential cause of personal and structural damage. In addition, any unexpected breakdown of rolling components or failure of belts creates a significant interruption to production, which is a major concern for operators, who are responsible for achieving optimum mining production. This project aimed to develop a fiber optic-based distributed temperature sensing (DTS) system to monitor the temperature change of malfunction idlers for heavy-duty conveyor belts in underground coal mines.
Conveyor belts have been widely used for centuries to transport general goods, bulk materials, and passengers. Conveyor belts have attained a dominant position in the continuous conveying of bulk materials ranging from very fine, dusty chemicals to bulk materials, such as raw ore and coal, as well as for overburden, including stones, soil, and logs of wood. In comparison to other transportation methods for bulk solids, such as trains or trucks, conveyor belts are an extremely favorable choice in instances where suitable infrastructures for other modes of transport do not exist.
The main fire risks associated with belt type conveyors are as follows:
› Friction due to loss of belt traction and slipping on the drive roller;
› Welding activities can generate hot molten material;
› Overheated materials placed on the belt;
› Build up of materials that have fallen off the belt and dust cloud generation;
› Static electricity.Continue reading

Distributed Temperature Sensing (DTS) system resolution

DTS system resolutionThe main idea of the Distributed Temperature Sensing is Raman-based temperature measurement joined with Optical Time-domain Reflectometry (OTDR). A short pulse of light is enabled into the fiber. The propagating light creates Raman backscattered light at two wavelengths, from all points along with the fiber. The wavelengths of the Raman backscattered light are different from that of the forward propagating light and are named “Stokes” or “anti-Stokes”.The amplitude of the Stokes light is not very dependent on temperature, while the amplitude of the anti-Stokes light is strongly dependent on temperature.

A typically distributed sensing system is described by the spatial and temperature resolution. The spatial resolution is the minimum distance of the sensor to measure a step change in temperature along with the optical fiber. The temperature resolution is a measure of the precision to distinguish the absolute temperature. The temperature resolution depends on the measurement time and the launch pulse-recurrence rate. The laser pulse energy and duration are accurately controlled and optimized at the measurement maximum length to provide the best available temperature resolution within acceptable accuracy limits. As the sampling time is increased, the temperature resolution is improved and resolved temperatures become more accurate.

The report “Distributed Temperature Sensing (DTS) Market 2016 – 2023,” points out the key factors impacting the growth of this market and assesses its growth during the period between 2016 and 2023. Fiber optic sensing is challenging because the physical properties of light into the fiber are affected by strain, temperature, or sound. Several technologies enable local measurement – using sensors at chosen points along with the fiber (eg, fiber Bragg grating (FBG) technology for measuring localized pressure, strain, temperature, and flow) – or distributed sensing – with sensing occurring all along with the fiber.

Distributed sensing systems have been developed for the oil and gas industry to assist reservoir engineers in optimizing the well lifetime. Nowadays they find a wide variety of applications as integrity monitoring tools in process vessels, storage tanks, and piping systems offering the operator tools to schedule maintenance programs and maximize service life.

Optromix Company offers a Distributed fiber optic sensing system with high spatial and temporal profiling over large surfaces, long lengths, and at locations where conventional point sensing is not applicable or costs effective.

Pipeline Integrity, Safety, Structural health Monitoring and leak detection with the Fiber Optic Sensor system

Distributed fiber optic sensing is tested through practice technology for online monitoring of temperature, strain, vibration, and sound over long distances with the high local resolution that is apt to improve pipeline integrity, pipeline safety, and security considerations. Fiber optics distributed temperature sensing techniques have found applications in various domains such as civil engineering, oil, and gas, power plants, fire detection, etc.

Pipelines are the most modern, effective, and reliable global transport systems for oil, gas, and water. In order to guarantee the smooth transport of products the pipeline systems must be regularly maintained and monitoring. Optical sensing systems today facilitate pipeline monitoring and integrity as preventive means to continuously protect or monitor pipelines. The systems are based on interferometric sensing where ultra-stable, low noise lasers interrogate an optical fiber acting as one long continuous sensor embedded or attached to the pipeline. The monitoring of temperature profiles over long distances by means of optical fibers represents a highly efficient way to fiber optic leak detection along pipelines, in dams, dikes, or tanks. Different techniques have been developed taking advantage of the fiber geometry and of optical time-domain analysis for the localization of the information.

Distributed temperature sensing is used in all cases to improve the performance of computational monitoring systems. Although distributed temperature sensing is a well-proven technology that has shown to be able to detect very small leaks in a short time, it is very hard to calculate the minimum detectable leak size or to guarantee a maximum detection time which in many cases are necessary to receive pipeline operation licenses. Leak rates as low as 50 ml/min have been detected on a brine pipeline by temperature monitoring and identification of local temperature anomalies.

GeoHazards like earthquakes, landslides, and surface subsidence result in ground movement and thus put additional stress on the pipelines, tunnels, and other underground infrastructures. Structural health monitoring is a promising and challenging field of research in the 21st century. Civil structures are the most precious economic assets of any country, proper monitoring of these are necessary to prevent any hazardous situation and ensuring safety. Fiber Bragg Grating (FBG) sensors have emerged as a reliable, in situ, nondestructive device for monitoring, diagnostics, and control in civil structures. FBG sensors offer several key advantages over other technologies in the structural sensing field.

The transformer is the key equipment in a power system, to ensure its safe and stable operation is important. Transformers either raise a voltage to decrease losses or decreases the voltage to a safe level. The failures of transformers in service are broadly due to temperature rise, low oil levels, overload, poor quality of LT cables, and improper installation and maintenance. Out of these factors temperature rise, low oil levels and overload, need continuous monitoring to save transformer life. A DTS system increases the reliability of the distribution network, by monitoring critical information such as oil temperature, and the oil level of the transformer. Data are collected continuously. Monitoring the transformers for problems before they occur can prevent faults that are costly to fix and result in a loss of service life. With modern technology, it is possible to monitor a large number of parameters of a transformer monitoring system at a relatively high cost. At the present day, the challenge is to balance the functions of the monitoring system and its cost and reliability. 

What is DTS?

A distributed temperature sensing system (DTS) is a device made to monitor power cable with fiber optic temperature sensors. DTS measures temperature on the large distances, greater than 30 km. It records the temperature along the cable as a continuous profile. DTS spatial resolution is 1 m with accuracy within ±1°C at a resolution of 0.01°C.

Adding RTTR to distributed temperature sensors allows achieving more precision when measuring high-temperature wire. DTS has some level of uncertainty when it detects the temperature, and its level increases when the conductor operates in an emergency situation. This happens because the conductor heating is detected with the time lag. Also, the temperature differs depending on the loading level. The higher the loading level is, the less precise are the measurements.

What is DTS measuring principle?

Certain factors, such as temperature or pressure, affect the optic cable and change the light transmission characteristics in the fiber. Optical fibers operate as linear temperature sensors when the light is projected in it through scattering to determine the location of the physical effect on the outside.

Optical fiber is made of doped quartz glass, silicon dioxide and has an amorphous solid structure. Its molecules interact with the photons when light falls on the thermally excited molecular oscillations. This process leads to light scattering, also called Raman scattering. The difference between the incident light and scattered light is that the later experiences a spectral shift that is equivalent to the lattice oscillation resonance frequency. The scattered light has three spectral shares, namely the Rayleigh (laser source wavelength scattering), the Stokes line components (lower frequency), and the anti-Stokes line components (higher frequency). Anti-stokes depend on the temperature, hence it is possible to calculate the fiber temperature as a ratio between anti-Stokes and Stokes line components.

What is DTS used for?

Distributed temperature sensing has multiple applications in different industrial segments to monitor power cables, tunnels, and industrial buildings, to detect leakages, and to control high-temperature wires. Recently DTS has been applied in monitoring ecological factors, such as groundwater, rainforests, river streams, etc.

RTTR – Real Time Thermal Rating System

A real-time thermal rating is a monitoring system. It helps to effectively use current-carrying capacity. Basically, it allows avoiding making assumptions about the current load, and instead to ensure that it is used in the most efficient way and the probability to exceed the acceptable temperature is low.

Smart grid technology, a real-time thermal rating system, has been created to rate the electrical conductors affected by the local weather conditions. It provides accurate real-time temperature measurements and current reading along the entire high-temperature wire. The RTTR is embedded in the cable and calculates the capacity of the current under specific conditions. It is a perfect solution to monitor power cable performing under abnormal conditions such as different emergencies, energy outages, etc.

RTTR is often used with the DTS system of temperature sensors because it gives more accurate data and allows monitoring operations in the real-time mode. For cables that have temperature sensors (DTS) embedded or touching it, the temperature is monitored continuously and the rating can be indicated accordingly. The cables without DTS have their operational temperature are calculated based on the real-time installation condition and loading. There are two types of RTTR to monitor power cable: self-contained and environmentally based.

Self-contained real-time temperature collects the data along with the entire circuits; the embedded fiber optic cable measures the internal temperature, and the attached one measures the sheath temperature.

Environmentally based RTTR measures soil temperature and its direct effect on the cable. It also measures soil thermal resistivity, which affects the heat exchange rate between the cable and the external environment.

RTTR usually uses the following parameters for the calculations:

  • The ground type (soil, clay, sand, gravel, thermal backfill)
  • Burial Depth
  • Cable Type
  • Cable Structure
  • Other cables laid in close proximity

Rating calculations of the high-temperature wire are based on the data derived from monitoring the underground cable. Standard static ratings are usually conservative and understate the real feeder capacity; hence the feeders are not loaded fully most of the time. The real-time thermal rating allows determining the times when the cable is not loaded fully and when certain actions need to be taken.