Project Name: Research on On-line Monitoring System for Transformer Insulating Oil Fault Gases Based on Semiconductor Laser Photoacoustic Spectroscopy Technology

Project Location: A 500kV Substation of a Power Supply Bureau under China Southern Power Grid

Equipment Name: PASL-3000 Laser Photoacoustic Spectroscopy On-line Monitoring System for Gases in Oil

△ PASL-3000 Laser Photoacoustic Spectroscopy On-line Monitoring System for Gases in Oil

Project Overview

The transformer is the heart of power grid load, and transformer insulating oil is an important medium for transformer insulation and cooling, which is directly related to the health of this "heart". During operation, when thermal faults, discharge faults or component aging occur inside the transformer, the insulating oil will crack and generate fault gases such as hydrogen, methane, carbon dioxide and acetylene. The content of fault gases is closely related to the type and severity of transformer faults. By monitoring the content of these fault gases on line, potential faults inside the transformer can be detected at an early stage.

In the past, a power supply bureau under China Southern Power Grid had a heavy workload of daily off-line oil chromatography detection for oil-immersed transformers in 500kV and above substations in accordance with the oil chromatography detection cycle requirements. In addition, many problems have been exposed in the application of on-line oil chromatography detection devices for tracking and monitoring operating equipment:

1. Low detection accuracy, with frequent false alarms or missing alarms;
2. High frequency of carrier gas replacement, leading to heavy maintenance workload and high use cost;
3. Failure to reflect the real health status of transformers in a timely manner, and instead increasing the maintenance and defect elimination work of maintenance personnel on the on-line oil chromatography detection devices themselves.

After extensive research, the power supply bureau adopted the on-line monitoring system for transformer insulating oil fault gases based on semiconductor laser photoacoustic spectroscopy technology to replace the traditional oil chromatography measurement and photoacoustic spectroscopy oil and gas measurement devices. As an upgraded technical product, the laser photoacoustic spectroscopy on-line monitoring system for gases in oil eliminates the need for carrier gas replacement, features high accuracy, good stability and low cross interference, and requires almost no daily maintenance. It can further improve the detection rate of initial defects of main transformers, reduce the failure rate of transformers, cut down operation and maintenance costs, and thus enhance the safe operation level of main equipment such as transformers.

△ Application Site

Technical Features

The laser photoacoustic spectroscopy oil and gas monitoring technology achieves accurate measurement of trace-level fault gases by customizing high-power, narrow-linewidth distributed feedback semiconductor lasers and independently designing a constant temperature resonant photoacoustic cell. It adopts a segmented calibration scheme to realize accurate measurement of wide-range components, and combines with the independently developed constant temperature vacuum degassing system to avoid oil sample contamination and ensure the safety of oil return.

Leading-edge technology: The semiconductor laser technology and photoacoustic spectroscopy technology are applied in a brand-new field, achieving remarkable results in detecting gases in transformer oil, improving the detection rate of initial faults of main transformers, and reducing the fault occurrence rate and operation and maintenance costs.

Full-component monitoring of fault gases in oil: The laser photoacoustic spectroscopy technology is used to analyze and detect the content of eight fault gas components including H₂, CO, CO₂, CH₄, C₂H₄, C₂H₆, C₂H₂ and micro water, and the measurement of N₂ and O₂ components in oil can be expanded.

No carrier gas required & installation without power outage: Oil samples are taken directly through the oil sampling port and returned to the oil tank after analysis, with no power outage needed during installation. No carrier gas or recalibration is required during operation, realizing true maintenance-free operation.

Narrow bandwidth accurate testing & anti-interference: Equipped with a laser light source without the need for optical filtering, it can accurately avoid cross interference when detecting mixed fault gases, with high measurement accuracy and good repeatability.

Constant temperature vacuum degassing & safe and reliable: Featuring high degassing efficiency, the degassed oil sample is not in contact with the outside air, realizing zero contamination and zero loss of the oil sample and ensuring the safety of transformer oil return.

Electronic modulation laser avoiding mechanical structure faults: The laser is driven by electrical signals to generate pulsed optical signals, replacing the modulation disc of the traditional infrared light source photoacoustic spectroscopy system, which reduces mechanical vibration and loss and lowers the equipment failure rate.

Remote terminal display: The equipment supports Modbus and IEC61850 protocols and can provide remote terminal display, including equipment operating status, real-time measurement data, data histogram analysis charts, trend charts, reports and early warning prompts.

Multi-channel data communication & remote centralized management: An advanced remote centralized management suite can collect and monitor the operating status and test data of multiple monitoring devices, and provide comprehensive trend analysis and diagnosis results. It supports communication methods such as RS485, wired Ethernet, GPRS and optical fiber.

The PASL-3000 Laser Photoacoustic Spectroscopy On-line Monitoring System for Gases in Oil innovatively uses laser light source technology to detect transformer insulating oil fault gases, providing true and reliable operating status information of transformers and a more accurate and timely early warning mechanism for power safety. It has positive significance for strengthening safety production management, reducing the labor intensity of operators and shortening fault delay time.

At present, the device has passed the testing of China Electric Power Research Institute Co., Ltd., China Southern Power Grid Research Institute Co., Ltd. and Hunan Xiangdian Test & Research Institute Co., Ltd., with its technical performance indicators meeting the requirements of DL/T1432.1 and DL/T1432.2 standards and the repeatability error as low as 1.42%. At the new product appraisal meeting organized by the China Electricity Council, the device was confirmed to have reached the international advanced level in comprehensive technical performance, with its photoacoustic cell technology and measurement accuracy reaching the international leading level, and it is recommended to be put into mass production and application.