Benefits and Risks of Real Time Thermal Rating Systems

FBG sensors in real time thermal ratingA real-time thermal rating system has been developed initially for overhead transmission lines using actual meteorological data and real-time conductor temperatures and line loadings. Such a real-time thermal rating system provides much higher ampacity ratings than other conventional methods. A natural convective heat equation is developed for stranded conductors. The temperature of the conductor is solved directly without resorting to an iterative solution.

The temperature of an asset itself, such as a power cable, is a key for a real-time thermal rating system. This can be measured continuously if equipment utilizes a distributed temperature sensing (DTS) system. Distributed temperature sensing optical fibers are installed along with the fiber cable. The fiber cable can also be utilized for telecoms purposes as DTS systems typically utilize standard telecoms fiber optics.

Thermal headroom typically is determined using static ratings which are based upon probabilistic methods and are representative of worst-case scenarios. The “static” design calculation methods provide simple and conservative estimates of network capacity. In reality, networks can be complex and operational ratings can be influenced by multiple factors including weather conditions and loading. Soil condition, buried depth, burial configuration, cable size, and type must be considered for underground equipment.

The real-time thermal rating system works with such assets as:

 

  • Underground and subsea cables

 

Experience has shown that cable depth, soil type, and the shape of the load curve have a material impact on ratings. The real-time thermal rating system can determine actual thermal headroom indicating whether some unused network capacity can be released or locations where networks are constrained.

 

  • Overhead lines

 

  • Sag-based
  • Tension-based
  • Temperature-based
  • Current rating-based

 

  • Transformers

 

The real-time thermal rating systems for transformers utilize measurements including transformer load, ambient, and transformer temperatures based on the equations set out in IEC 6007. With the exception of emergency ratings, P15 recommends using an average ambient temperature and a weighted average that products the same aging if the temperature varies over a load cycle.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) products line: fiber Bragg grating sensors, FBG interrogators and multiplexers, distributed temperature sensing (DTS) systems. We create and supply a broad variety of top-notch fiber optic solutions for the monitoring of various facilities all over the world. Our main goal is to deliver the best quality fiber optic products to our clients. We produce a wide range of fiber optic devices, including our cutting-edge customized fiber optic Bragg grating product line and fiber Bragg grating sensor systems.

If you are interested in Optromix distributed temperature sensing systems, please contact us at info@optromix.com

Fiber optic well monitoring

The well integrity has become a critical concern after recent events in the oil industry, such as oil spills. The interaction of a salt layer with the cement and casting for Pre-salt wells is a concern for fiber optic well monitoring and the structural integrity of the well. The development of continuous monitoring tools for well structural integrity is an ongoing task for the oil industry.

Continuous fiber optic well monitoring has the advantage of allowing the quantification of the time needed for an event. Casting integrity logging operations may provide information regarding the damage location, however, the time in the life of the well when the damage happened or the process of the well degradation can not be determined. The logging operations can only provide information on the condition of the well at a particular time, not continuously. Continuous monitoring can help to correlate well damage and events that could be the cause of the damage, like outside intervention, allowing for corrective and preventive measures to take place.

The two main parameters that need to be measured are strain and temperature. The strain in fiber optic well monitoring can indicate the strain in the casting that is caused by the creep of the salt layer. Distributed temperature sensing may be used to indicate the positioning of the cement slurry, diagnose the curing process, and indicate the cementing failures.

The sensors need to be installed outside the production casing of the production liner. The size of the sensors, therefore, is required to be small. DTS sensors, in particular, are compact and are easy to install onto any surface. However, the mounting process of the sensors needs to be delicate as the casing properties may degrade. Fiber optic well monitoring solutions shouldn’t be intrusive as the sensors could potentially cause issues, like poor isolation.

Optromix, Inc. is a U.S. manufacturer of innovative fiber optic products for the global market, based in Cambridge, MA. Our team always strives to provide the most technologically advanced fiber optic solutions for our clients. Our main goal is to deliver the best quality fiber optic products to our clients. We produce a wide range of fiber optic devices, including our cutting edge customized fiber optic Bragg grating product line and fiber Bragg grating sensor systems. Optromix, Inc. is a top choice among the manufacturers of fiber Bragg grating monitoring systems. If you have any questions, please contact us at info@optromix.com

Real Time Thermal Rating systems

RTTR, or Real-Time Thermal Rating, is a method of assessing real-time operational thermal rating of the equipment, or the amount of electrical current that a power line or an electrical facility can endure before suffering critical damage. Thermal rating devices can be used to measure the temperature of overhead power lines, transformers, underground and subsea cables.

Real-time thermal rating systems rely on real-time data from environmental conditions rather than theoretical assumptions and predictions. These systems are able to not only measure the thermal ratings in real-time but also to measure the stress levels of certain areas and determine their capacity. The calculation of the thermal ratings happen on the basis of: 1) weather conditions; 2) electrical current; 3) temperature of the equipment. However, other factors may need to be considered; this depends on the environment where real-time thermal rating needs to be performed. For example, soil condition, burial depth, and configuration must be considered for temperature measurement of underground cables, the mass of the transformer and type of the cooling mechanisms for temperature measurement of transformers, etc.

The key to the real-time thermal rating system, the temperature of the asset, should be continuously measured to avoid heating of the asset to dangerous levels. Distributed temperature sensing (DTS) systems should be used for this purpose, otherwise, only predictions about the temperature can be made.

The main advantage of real-time thermal rating systems is their ability to accurately measure the thermal behavior of assets, taking into consideration factors that static ratings do not. Static rating calculations are often overly conservative, therefore some power lines are often not used up to their full potential, while others are overloaded, which causes premature aging.

Thermal rating systems may be implemented into different types of power assets. Underground cable monitoring benefits greatly from introducing real-time thermal rating systems as they measure soil ambient temperature and soil thermal resistivity; these measurements help to determine actual thermal headroom to indicate unused network capacity.  

The thermal rating of the overhead power lines, depending on the actual system used, takes either the sag of the lines, the tension of the line conductor, the temperature of the line conductor, or environmental conditions into account during calculation.

Transformer load, ambient and transformer temperatures, oil temperature, and winding hot spot temperature are utilized by RTTR systems for transformers.

DTS optic sensing fibers are important for real-time thermal rating; they are installed along the length of the power cable and provide a continuous temperature profile.

If you would like to purchase DTS (Distributed Temperature System), please contact us: info@optromix.com or +1 617 558 98 58.

Dynamic Cable Rating

In recent years a lot of research has been done in order to increase the power flow of underground cables and to develop the equipment to effectively monitor the weather and thermal state of the cable by creating accurate thermal models. As a result of applying dynamic thermal rating technologies, the capacity is usually increased by 5 to 15%. Few factors determine the thermal rating of the underground, among them the soil temperature and thermal resistivity of the earth, and they change very slowly, don’t get affected much by weather and current loading.

The main challenge with underground installations is to accurately measure the maximum current value that can flow through the circuit breakers.

The current capacity carried in specific cable circuit breakers depends on certain aspects, such as cable construction, the soil, the temperature, and the sheath-bonding method. Only the soil properties are variable, and the others are constant.

The soil is affected by the weather change in different seasons and the cable heating, hence the current carrying capacity changes drastically. Dynamic current rating of a cable circuit is a crucial factor in order to utilize it in the full capacity all year round; because it is always the biggest challenge for power operators to choose the right power load for the underground cable.

That is why monitoring thermal conditions of the buried cable circuits and installed distributed temperature sensing (DTS) systems is crucial.

A real-time operating system is created to capture different load current parameters, cable surface, and soil temperatures to provide input to the real-time operating system. The data about current and temperature is passed to a computer through the fiber optic connection. The computer gathers load and temperature data and provides an updated ampacity rating.

Once the dynamic current rating data is received, it has to be analyzed within a set period of time. The results are usually used to develop risk management strategies. There are certain challenges when calculating line ampacity, such as conductor properties and atmospheric conditions, which have to be considered. Each of these factors increases the level of uncertainty when determining ampacity.

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.