How to choose the transformer bushing insulation online monitoring system? Transformer bushing online monitoring comprehensive analysis

Transformer bushing is a core insulating component in the high-voltage transmission and distribution system that is subjected to both electrical and mechanical stresses. According to industry statistics, casing failure accounts for about 15% of the total number of power equipment failures, and is one of the important causes of unplanned transformer outages. Once the high-voltage casing insulation breakdown occurs, equipment losses and power outage losses are often incalculable, and in serious cases will also cause fire. Because of this, more and more substations, power plants and industrial users will casing insulation online monitoring system into the equipment condition maintenance system, in order to realize the casing health status of the continuous perception.

I. Why does transformer bushing insulation need online monitoring?

Casing long-term in high voltage, high current, hot and cold alternating severe operating conditions, the internal insulation material will occur moisture, aging, partial discharge and other progressive deterioration process. This type of failure is often in the offline inspection cycle between the quiet development, to appear obvious abnormality has jeopardized the safety of the equipment or even cause irreversible damage.

Traditional offline preventive testing is limited by overhaul intervals and fails to capture rapidly developing insulation defects. Studies have shown that some casing failures go from no warning to catastrophic breakdown in a matter of days to weeks, while about 50% of casing failures eventually lead to fire. The online monitoring system is able to continuously collect insulation characteristics under the transformer's energized operating condition, and discover early hidden defects through trend analysis, thus transforming passive "after-the-fact maintenance" into active "condition overhaul", and dramatically reducing the risk of unplanned shutdowns and the cost of overhauling.

Second, what are the main ways of online monitoring of transformer bushings?

Casing insulation online monitoring technology routes are diverse, different methods of monitoring dimensions and applicable scenarios have their own focus, understanding these methods is the correct selection of the prerequisite.

1. Dielectric loss and capacitance monitoring

Changes in dielectric loss factor and equivalent capacitance are continuously calculated by collecting the casing end screen current signal and the PT secondary voltage signal. Elevated dielectric loss usually means that the insulation is subjected to moisture, aging or filth intrusion; abnormal deviation of capacitance may indicate local defects in the internal insulation layer. This is currently the most widely used casing insulation monitoring means, mature technology, high coverage.

2. On-line monitoring of partial discharges

For the detection of charge discharges caused by defects such as air bubbles and impurities within the insulation, commonly used sensors include high-frequency current transformers, ultrasonic probes and ultra-high-frequency antennas. Complementary use of local discharge monitoring and dielectric loss monitoring can significantly improve the detection rate of early faults, and is suitable for key equipment with high requirements on insulation condition.

3. Temperature online monitoring

Casing connection point and body temperature is an important indicator of contact resistance and capacitive current abnormality. Fluorescent fiber optic temperature sensors have obvious advantages in high-voltage casing temperature measurement due to their complete electrical isolation and anti-electromagnetic interference characteristics, and can capture early local overheating signals that appear earlier than dielectric loss or capacitance changes.

4. Dissolved gas monitoring in oil

It is applicable to oil-immersed casing to determine the presence of internal overheating or discharge faults by detecting the content and trend of characteristic gases in the casing oil. The method is particularly suitable for in-depth insulation condition assessment of high-value oil-immersed casing.

5. Multi-parameter fusion diagnostics

The fusion and analysis of multi-dimensional data such as dielectric loss, capacitance, local discharge, temperature and so on through algorithmic modeling is the mainstream direction of current technology development. Multi-parameter fusion can significantly improve the detection accuracy of casing faults, and realize the insulation deterioration trend prediction, providing more powerful data support for maintenance decision-making.

Third, transformer bushing insulation online monitoring system consists of what parts?

A complete casing insulation online monitoring system usually consists of the following core units:

1. End screen current acquisition unit

According to the casing end screen structure customized matching connection, built-in voltage limiting protection and lightning impact protection circuit, with good electromagnetic shielding ability, effectively inhibit the mixing of on-site interference signals, to protect the purity of the collected signal.

2. Intelligent online monitoring IED (data measurement and control unit)

Installed at the transformer site, it integrates the functions of sensing signal acquisition, real-time calculation of characteristic quantity, harmonic interference suppression and local storage. Some advanced systems also attach temperature channels, real-time temperature correction of monitoring data, so that the measurement results more accurately reflect the real insulation state of the casing.

3. Local display unit

On-site configuration of high-definition LCD display, real-time display of casing capacity, dielectric loss value, end screen leakage current and other core parameters, convenient for operation and maintenance personnel to quickly grasp the status of the equipment on-site, the screen design usually takes into account the readability of the outdoor bright light.

4. network communication unit

Support RS485, fiber optic and other interface forms, compatible with Modbus RTU, IEC 61850 and other mainstream communication protocols, to meet the access requirements of different substation automation systems, to ensure the reliable transmission and reporting of monitoring data.

5. Back-office analytics management software

Aggregate monitoring data of all casing in the whole station and even the whole network, realize the functions of historical trend analysis, horizontal comparison, over-limit alarm, fault diagnosis report generation and centralized monitoring, etc., provide scientific basis for maintenance personnel to assess the status, and support the integration and deployment with the integrated on-line monitoring platform of the substation.

Fourth, the purchase of transformer bushing insulation online monitoring system should consider what factors?

When evaluating and selecting a model, it is recommended to consider the following dimensions in a comprehensive manner, rather than simply comparing a particular technical parameter:

1. Monitoring function coverage

Prioritize the core parameters to be monitored, including dielectric loss and capacitance, local discharge, temperature or gas in oil. For important main transformers or ultra-high voltage bushings, it is recommended to choose a system that supports multi-parameter fusion diagnostics to realize a more comprehensive insulation condition assessment.

2. System Integration Capabilities

Focus on whether the system supports seamless docking with existing substation integrated automation platforms, dispatching systems or cloud-based operation and maintenance platforms to avoid the formation of data silos, which affects the actual utilization value of monitoring data.

3. Field applicability

This includes whether the protection level of the equipment meets the requirements of the installation environment, whether the installation method of the sensor matches the end screen structure of the casing to be monitored, and whether outage construction is required or energized installation can be realized.

4. Anti-interference and reliability

Substation electromagnetic environment is complex, the system must have mature harmonic suppression and anti-jamming design, to ensure the stability and credibility of the measurement results under strong interference conditions, to prevent false alarms affecting normal operation and maintenance.

5. Manufacturer's qualification and service capability

Casing insulation online monitoring involves high-voltage safety, should be selected with power industry-related qualifications, mature engineering performance of professional manufacturers, focusing on after-sales service response speed, technical support capabilities and spare parts security capabilities.

6. Compliance and standards compliance

The system shall comply with the relevant technical standards of the domestic electric power industry and the requirements of the State Grid and the Southern Power Grid for grid access testing to ensure that the system has a basis for compliant use in the actual project.

V. Frequently Asked Questions (FAQ)

Q: Can on-line monitoring and periodic off-line testing of transformer bushings be substituted for each other?

A: The two cannot be completely replaced, but are complementary. The advantage of online monitoring lies in continuity and real-time, which can capture insulation degradation occurring between offline test cycles; while offline test has higher measurement accuracy and richer testing items, which can be used as an in-depth diagnostic means after abnormalities are found in online monitoring. It is recommended that the two be combined to form a casing insulation health management system.

Q: Will the installation of the bushing online monitoring system affect the normal operation of the transformer?

A: The professionally designed casing on-line monitoring system carries out signal acquisition by connecting the casing end screen lead wire, without directly interfering with the casing body structure. Part of the system supports electrified installation, which has almost no effect on the normal operation of the transformer. However, the installation process still needs to strictly comply with the high-voltage safety regulations, and it is recommended to be operated by qualified professionals.

Q: How do I handle false alarms on my system?

A: False alarms are usually related to grid harmonic interference, loose sensor wiring or improper system parameter settings. You should contact the manufacturer's technical staff to troubleshoot the signal quality, check the wiring status of the end screen, and verify whether the alarm threshold setting is reasonable. High-quality systems usually have perfect interference suppression algorithms, which can control the false alarm rate at a low level.

Q: Can the same monitoring system be used for casing of different voltage levels?

A: Usually, the same set of monitoring mainframe can be configured with different sensors and acquisition modules to meet the needs of casing monitoring from 110kV to 500kV or even higher voltage levels, but it is necessary to confirm the specific hardware configuration and signal compatibility with the manufacturer.

Q: How does the online monitoring data interface with the facility management system?

A: Mainstream casing online monitoring system supports standard communication protocols and can be integrated with PMS, EAM and other equipment management systems as well as substation integrated online monitoring platform. Specific docking methods and interface requirements are recommended to be confirmed with manufacturers and information technology departments at the early stage of the project.

Contact Inotera for professional program advice

If you need to know more about the technical solutions of transformer bushing insulation online monitoring system, welcome to contact INNOTD professional technical team. INNOTD specializes in the field of power equipment condition awareness and online monitoring, and can provide targeted technical consulting and solution proposals according to your equipment type, voltage level, station conditions and system integration needs.

Visit the official website for more product information: www.innotd.com

statement denying or limiting responsibility

The content of this article is only for industry reference and technical knowledge popularization, the technical description, application scenarios and selection recommendations are based on general industry knowledge collation, does not constitute the basis for the design of specific engineering solutions. The actual selection of different projects should be combined with the site conditions, equipment parameters and related standards, by qualified professionals to assess and confirm. This article is not responsible for any engineering decision-making consequences arising from reference to the content of this article. If you have any technical questions, please consult professional manufacturers or industry organizations.