Transformer oil chromatography online monitoring system how to choose? Dissolved gas in oil online analyzer comprehensive analysis

Transformer is the core equipment of the power system, and its insulation state is directly related to the safe operation of the whole power grid. Insulating oil, as the most important insulation and cooling medium for oil-immersed transformers, will decompose under the long-term action of thermal and electrical stresses, generating a variety of fault-characterized gases. By continuously analyzing the dissolved gases (DGA, Dissolved Gas Analysis) in the oil, accurate early warning can be realized at the early stage of the development of faults inside the transformer. Transformer oil chromatography online monitoring system is the core equipment to realize this goal, and it is also the key technical support for the power industry to shift from periodic maintenance to condition maintenance.

What is Dissolved Gas Analysis (DGA) in Transformer Oil? Why is it so important?

DGA, i.e. dissolved gas analysis in oil, is now internationally recognized as one of the most effective technical means to determine internal faults in oil-immersed power equipment. The principle is: when the transformer internal overheating, partial discharge or arc discharge and other faults, the insulating oil and solid insulating materials (such as insulating paper, cardboard) will be in the heat or the role of electrical energy cracking, generating hydrogen (H₂), carbon monoxide (CO), carbon dioxide (CO₂), methane (CH₄), ethane (C₂H₆), ethylene (C₂H₂), and so on. (C₂H₆), ethylene (C₂H₄), acetylene (C₂H₂) and other seven major fault characteristics of the gas, which are dissolved in the insulating oil, the type and concentration of these gases and the rate of growth is to determine the type of fault, the location and the severity of the important basis.

Traditional offline oil chromatography analysis requires manual sampling, sent to the laboratory for testing, the cycle is often calculated in months or even quarters. The insulation deterioration inside the transformer may develop dramatically within a few days, and the time blindness of offline detection is very easy to cause fault under-reporting. The online analyzer for dissolved gases in oil eliminates this risk by installing directly on the transformer body and realizing continuous automatic detection of characteristic gases.

What characteristic gases are produced by different fault types?

Low-energy partial discharge faults produce mainly hydrogen (H₂), and the presence of acetylene (C₂H₂) usually implies a high-energy arc discharge, which is the most dangerous early warning sign; oil overheating faults are characterized by methane (CH₄) and ethylene (C₂H₄); and the deterioration or overheating of solid insulating materials is typically marked by abnormally high levels of carbon monoxide (CO) and Carbon dioxide (CO₂) is typically characterized by an abnormal increase in carbon monoxide (CO₂) and carbon dioxide (CO₂). Based on this law, international and domestic standards such as IEC 60599 and GB/T 7252 have established mature fault diagnosis methods such as the three-ratio method and the David Triangle method, which provide a theoretical basis for automated diagnostic algorithms.

What is the difference between transformer oil chromatography online monitoring system and online analyzer for dissolved gases in oil?

In practical application, these two concepts are often mixed, but there is a certain distinction from the technical level. Dissolved gas in oil online analyzer (Online DGA Analyzer) usually refers to the completion of the oil and gas separation, gas component detection and concentration calculation of the core analytical instrumentation unit, emphasizing the detection capability of the analytical instrument itself; while the transformer oil chromatography online monitoring system is a more complete system concept, covering the front-end degassing and oil and gas separation device, chromatography unit, data acquisition and processing modules, communication interfaces, background monitoring software and troubleshooting expert system and a full set of sub-systems, is directly applicable to substations. The transformer oil chromatography online monitoring system is a more complete system concept, covering front-end degassing and oil/gas separation device, chromatography analyzing unit, data acquisition and processing module, communication interface, backend monitoring software and troubleshooting expert system, etc., which is a complete solution that can be directly applied to the substation field engineering.

When selecting a model, you need to specify whether you are purchasing a stand-alone analyzer or an integrated, complete monitoring system, which determines the subsequent installation, integration and operation and maintenance methods.

What is the working principle of transformer oil chromatography online monitoring system?

A typical transformer oil chromatography online monitoring system completes an automatic analysis cycle according to the following process:

Step 1: Oil sample circulation and collection

The system is driven by the built-in oil pump to circulate the insulating oil of the transformer body in the closed pipeline, to ensure that the collected oil samples can truly represent the oil state inside the transformer, and to eliminate the error brought by the dead zone oil samples.

Step 2: Oil and gas separation (degassing)

This is one of the most critical links in the entire analytical chain. The system adopts permeable membrane degassing, vacuum degassing or headspace equilibrium to separate the fault characteristic gas dissolved in the insulating oil, and get the mixed gas samples that can be analyzed by the chromatographic column. The performance of the degassing device directly affects the accuracy and repeatability of the test results, and is also one of the links where the performance of products from different manufacturers varies the most.

Step 3: Gas Chromatography Analysis

The separated gas mixture is fed into the gas chromatography column, carried by a carrier gas (usually high-purity nitrogen or a built-in carrier gas generator without cylinder design) to achieve precise separation of each component gas in the column, and the quantitative detection is completed by a thermal conductivity detector (TCD) or a hydrogen flame ionization detector (FID), outputting the numerical values of each component concentration.

Step 4: Data Processing and Troubleshooting

The collected gas concentration data is subjected to temperature correction, calibration calculation and trend analysis by the embedded processor, and the built-in fault diagnosis expert system is called to automatically evaluate the internal state of the transformer based on international standard algorithms such as the three-ratio method, the David's triangle method and the IEC 60599 guidelines, and output diagnostic conclusions and warning signals.

Step 5: Data Upload and Remote Monitoring

The analysis results are uploaded to the substation comprehensive automation platform or cloud operation and maintenance platform through RS-485, Ethernet, fiber optic and other interfaces and communication protocols such as IEC 61850 and Modbus RTU, which support historical trend query, overrun alarm remote transmission and remote parameter configuration, and realize centralized management of decentralized deployed equipments.

What are the main technical routes for on-line monitoring of transformer oil chromatography?

Currently on the market in the transformer oil dissolved gas on-line analyzer mainly adopts the following several technical routes, each with its own advantages and disadvantages:

Gas Chromatography (GC)

Gas chromatography is the mainstream method with the highest precision and the most comprehensive detection of gas components, which can simultaneously detect H₂, CO, CO₂, CH₄, C₂H₆, C₂H₄, C₂H₂ seven full-component characteristic gases and micro-water, and it is the recommended reference method of the standards such as IEC 60599 and DL/T 722. The main challenge is that the system structure is relatively complex. The main challenges are the relative complexity of the system, the long analysis period (typically 40 minutes to several hours), and the requirements for installation and maintenance.

Photoacoustic Spectroscopy (PAS)

Photoacoustic spectrometry is based on the absorption of gas molecules at specific wavelengths of infrared light to achieve detection, with fast response time, no need for carrier gas, compact structure and other advantages, suitable for high monitoring frequency requirements, the need for rapid early warning scenarios, part of the product can be covered by the full-component gas detection.

Single Hydrogen Sensor Method

Hydrogen (H₂) is the most critical early warning indication gas for partial discharges and early oil overheating failures. The use of palladium membrane sensors or catalytic combustion sensors for the dedicated detection of hydrogen in oil, combined with the detection of microwater, constitutes a simplified, low-cost DGA monitoring solution for applications with limited budgets or as a supplement to full-component monitoring.

Fourier Transform Infrared Spectroscopy (FTIR)

The FTIR method has the ability of fast broad-spectrum detection, can synchronize the detection of a variety of gas components, high measurement accuracy, in some high-end application scenarios have been used, but the machine cost is relatively high.

What should be focused on when selecting a transformer oil chromatography online monitoring system?

In the face of a wide variety of transformer oil chromatography online monitoring products on the market, the following dimensions are the most should not be ignored in the selection decision of the core considerations:

I. Detection of gas component coverage

The types of gases that can be detected by the selected system need to be specified. The coverage of seven characteristic gases (H₂, CO, CO₂, CH₄, C₂H₆, C₂H₄, C₂H₂) of the full component is the basis for a complete troubleshooting; some of the systems also support the simultaneous monitoring of the content of micro-water (H₂O), which allows for a further assessment of the aging and moisture content of insulating cardboard. Some systems also support simultaneous monitoring of micro-water (H₂O) content, which can further assess the aging and moisture status of the insulating cardboard, and are recommended to be prioritized.

II. Degassing methods and detection accuracy

The technical maturity of the degassing (oil/gas separation) device directly determines the reliability of the test data. The focus should be on understanding the technical principle of the manufacturer's degassing method, the stability of the degassing rate, and whether there is a risk of carrier gas contamination of the transformer's insulating oil. Cylinderless design and airtight degassing structure are more recognized solutions in current engineering applications.

III. Troubleshooting algorithm capabilities

Whether the fault diagnosis expert system built into the system supports mainstream international standard algorithms such as the three-ratio method and the David's Triangle method, and whether it has the functions of gas production rate analysis and trend prediction directly affects whether the monitoring data can be effectively transformed into the basis for maintenance decision-making, which is the embodiment of the core value of the system.

IV. Communication protocols and systems integration capabilities

Whether the system supports IEC 61850 standard communication protocols, and whether it can be smoothly interfaced with the substation automation platforms of the State Grid and the Southern Power Grid or the integrated online monitoring system is the key to the realization of the project. At the same time, it is necessary to pay attention to whether the system has the ability of remote operation and parameter configuration, in order to reduce the later operation and maintenance costs.

V. Environmental adaptability and reliability

Substation site conditions are complex, and some projects are located in high cold, high temperature, high humidity or high altitude areas. Should examine the system's operating temperature range, protection level, anti-electromagnetic interference design and long-term trouble-free operation of the engineering verification, to avoid the selection of laboratory performance but the field reliability of the product is not enough.

VI. Ease of maintenance and operation and maintenance costs

The focus should be on understanding the system's daily maintenance workload, including carrier gas consumption and replacement cycles, column replacement frequency, and whether the calibration method supports remote auto-calibration. Cylinderless design has obvious advantages in terms of safety and operation and maintenance costs because it does not require regular replacement of high-pressure gas cylinders.

VII. Manufacturer's qualification and engineering experience

Professional manufacturers with relevant certification qualifications in the power industry and batch operation performance in mainstream power systems such as the State Grid or the Southern Power Grid should be selected, focusing on the number of actual engineering cases, the number of years of stable operation of the device and the ability to respond to after-sales technical services.

What equipment and scenarios are transformer oil chromatography online monitoring systems suitable for?

Transformer oil chromatography online monitoring system is mainly applicable to the following types of oil-immersed power equipment:

In the substation scenario, main transformers of 110kV and above, 500kV extra-high-voltage transformers, and important power plant step-up transformers are prioritized for deployment; main transformers with a long operating life, a history of anomalies, or those carrying critical power supply tasks are also the key application targets of the online monitoring system. In addition, oil-immersed reactors, transformers and other oil-filled equipment can also be included in the monitoring scope.

In industrial power scenarios, metallurgy, petrochemicals, data centers, and other industries that require high continuity of power supply, their key transformers also have a strong need for online monitoring to avoid major production losses due to unplanned transformer outages.

Frequently Asked Questions (FAQ)

Does the installation of transformer oil chromatography online monitoring system require power outage?

Most of the transformer oil chromatography online monitoring system through the transformer body oil valve position to install the oil interface to achieve online access, can be completed under the premise of non-power installation, does not affect the normal operation of the transformer. But the specific installation program due to the transformer structure and site conditions vary, it is recommended that before the project start by professional and technical personnel to confirm the site survey.

Why is there a discrepancy between online monitoring data and offline laboratory oil chromatography test data?

The differences between the two are mainly due to the different degassing methods, the different collection times of oil samples and the influence of ambient temperature changes on gas solubility. Online monitoring emphasizes real-time trend changes, while offline analysis in the laboratory is more accurate, and the two should focus on the growth trend of gas concentration rather than the absolute deviation of a single value when they are used in a complementary way. Relevant standards at home and abroad have also clearly defined the error ranges of the two methods.

Does the detection of acetylene in transformer oil mean immediate danger?

Acetylene (C₂H₂) is a characteristic gas of high-energy arc discharge, the appearance of itself is an important early warning signal, but whether it constitutes an immediate danger needs to be combined with the absolute value of its concentration, the growth rate, and the proportion of other characteristic gases to make a comprehensive judgment. Professionals should be organized at the first time to carry out comprehensive diagnosis according to DL/T 722 and other standards, instead of making conclusions only based on the value of a single gas.

Can the online monitoring system be interfaced with the PMS equipment management system?

Systems supporting IEC 61850 or open database interfaces can be integrated with PMS (production management system), EAM (asset management system) and substation integrated online monitoring platform. Specific docking scheme and interface specification are recommended to be confirmed with equipment manufacturers and informatization department at the project establishment stage to ensure the smooth landing of data process.

How often do I need to perform maintenance on my oil chromatography online monitoring system?

Maintenance intervals vary depending on the system design and frequency of use, and it is usually recommended to perform preventive maintenance every six months to one year, including oil circuit cleaning, degassing film status check, instrument zero calibration and system self-test. Cylinder-less design of the system can greatly reduce the daily maintenance workload and lower the cost of operation and maintenance labor.

For professional solutions, welcome to consult with Inotera!

INNOTD specializes in the field of power equipment condition awareness and online monitoring, providing complete products and solutions covering transformer oil chromatography online monitoring system, dissolved gas in oil online analyzer, bushing insulation online monitoring and multi-parameter integrated monitoring. If you need consulting or technical exchanges for specific transformer types, voltage levels and station integration requirements, please visit our website or contact our professional technical team for support.

Official website address: www.innotd.com

Disclaimer: The content of this article is only for the electric power industry reference and technical knowledge popularization, the text of the technical description, application scenarios and selection recommendations are based on the general industry awareness of the collation, does not constitute the basis for the design or procurement of specific engineering solutions. The actual project selection should be combined with the site conditions, equipment parameters and related technical standards, by qualified professionals to assess and confirm. The author and publisher of this article do not assume legal responsibility for any consequences of engineering decisions arising from reference to the content of this article.