Installation and use of transformer oil chromatography online monitoring device

I. Preparation before installation

1. Inspection of equipment and accessories

• Check whether the main body of the device (including oil and gas separation unit, chromatography detection unit, industrial control machine), oil accessories (valves, connecting tubes, seals), electrical fittings (power lines, communication lines, grounding cables) are complete, and the model is consistent with the design requirements.
• Check that there is no damage to the appearance of the device, no corrosion of the oil interface, no loosening of the electrical interface; open the shell of the device to make sure that there is no displacement or damage to the internal chromatographic column, sensors, circuit boards and other core components (need to be operated by professional and technical personnel).
• Verify that spare parts (e.g., spare seals, filters, columns) are available, and that the supporting software (troubleshooting system, data management software) is pre-installed or available as an installation package.

2. Site survey and confirmation of conditions

• Oil line connection location: Confirm the transformer body oil extraction valve (usually the bottom or side of the DN15/DN20 valve) and oil return valve (it is recommended to be higher than the oil extraction valve, to avoid air bubbles remain) position, to ensure that the oil extraction point and the oil return point distance to meet the requirements of the device oil circulation (generally no more than 5 meters, to reduce pipeline resistance).
• installation environmentThe device needs to be installed in the outdoor control cabinet or indoor room near the transformer, with ambient temperature - 30℃~+50℃, relative humidity ≤90% (no condensation), avoiding direct sunlight, strong vibration (such as directly under the transformer body) or corrosive gas areas; if it is installed outdoors, the control cabinet needs to have rainproof, dustproof and heat preservation functions.
• Electrical and communication conditionsConfirm that the site has 220V AC (±10%) power supply (need to be a separate circuit, to avoid sharing with strong electrical equipment to prevent voltage fluctuations), grounding resistance ≤ 4Ω (independent grounding, not shared with the transformer body grounding); communication interfaces (Ethernet, 485/232) need to be matched with the back-end monitoring system (such as substation SCADA system) interface protocols (common) Modbus, IEC 61850).

3. Preparation of tools and consumables

• Tools: Pipe pliers, wrenches (suitable for valves and piping interfaces), electric drills (for fixing devices or control cabinets), multimeters (to detect the power supply and grounding), insulation resistance testers (to detect the insulation of electrical circuits), nitrogen bottles (purity ≥ 99.999%, used for activation of the chromatographic columns and pipeline purging).
• Consumables: special transformer oil (the same type of oil as in the equipment, used for pipeline flushing), anhydrous ethanol (to clean the interface), raw material tape (only used for sealing the metal thread interface, prohibited to be used at the oil circuit sealing ring).

II. Installation process

1. Installation of the oil system (key link, leakage prevention is the core)

Step 1: Pipe Prefabrication and Cleaning

• According to the distance between the oil extraction point, oil return point and the device, cut special oil-resistant pipeline (usually stainless steel or PTFE pipe, pressure ≥ 10MPa, avoid using ordinary rubber hose), the length of the pipeline needs to leave a 10% balance to avoid overstretching or bending (bending radius of ≥ 5 times the diameter of the pipeline, to prevent clogging).
• Flush the inner wall of the pipeline with anhydrous ethanol, and then pass nitrogen (pressure 0.2~0.3MPa) to purge for 5~10 minutes to remove impurities and water to prevent contamination of the transformer oil or clogging of the chromatographic column.

Step 2: Connection of oil pickup and return lines

• pickup line: Close the transformer oil-taking valve, remove the original plug, install a tee at the valve outlet (one end is connected to the device oil-taking pipe, and one end is reserved for sampling valve for regular offline calibration), then connect the device oil-taking pipe, seal the interface with a special sealing ring (made of Viton material, oil-resistant and high-temperature-resistant), and tighten it uniformly with a wrench (with moderate strength, to avoid damaging the sealing ring or the screw threads).
• return lineConnect the oil return pipeline in the same way, and install a check valve (to prevent reverse oil flow) and a filter (precision ≤ 5μm, filtering impurities) at the oil return end to ensure that the oil return is smooth and no pollutants enter the transformer.
• outgassing: After the connection is completed, slowly open the oil pickup valve to let the oil slowly fill the pipeline, and at the same time open the exhaust valve of the device's oil system to discharge the air in the pipeline (the air will affect the accuracy of the gas detection), until the exhaust valve flows out pure oil and no air bubbles, then close the exhaust valve.

Step 3: Oil Line Sealing Test

• Close the device in and out of the oil valve, apply 0.3-0.5MPa pressure to the oil system (can be pressurized with nitrogen or transformer oil), keep it for 30 minutes, observe that there is no drop in pressure, and all the interfaces have no leakage (can be coated with soapy water in the interface, no bubbles), to confirm that the seal is qualified.

2. Installation of electrical systems (to ensure safety and signal stability)

Step 1: Grounding Installation

• The device shell should be separately connected to the grounding pole (grounding resistance ≤ 4Ω), the grounding cable adopts yellow and green two-color copper core wire (cross-sectional area ≥ 2.5mm ²), the terminal should be crimped with a copper nose and fastened, to avoid interference caused by false connection.
• The power supply ground and signal ground in the electrical control cabinet need to be connected separately and finally summarized to the total grounding pole to prevent signal interference (e.g., chromatographic detection signals are interfered by strong electricity).

Step 2: Power Wiring

• Lead the power line from the field dedicated power circuit, through the waterproof connector of the control cabinet to access the device power interface, the fire line, zero line, ground line should be corresponding (device marking L, N, PE), after wiring with a multimeter to detect the power supply voltage is normal, the insulation resistance is ≥ 10MΩ (tested by insulation resistance tester).
• An overload protection switch should be installed in the power supply circuit (the rated current is selected according to the power of the device, usually 10~16A) to avoid short-circuit or overload damage to the equipment.

Step 3: Communication Wiring

• Connect the communication cable according to the protocol type: Super Category 5 shielded cable for Ethernet communication (transmission distance ≤ 100 meters), shielded twisted-pair cable for 485 communication (transmission distance ≤ 1200 meters), and the shielding layer needs to be grounded at one end (only at the end of the device, to avoid loop current generated by the grounding at both ends).
• Mark the wires clearly after wiring (e.g., "Communication Wire - To Backstage A" "Communication Wire - To Backstage B"), and use a multimeter to test the communication wires through and through to make sure there are no breaks or shorts.

3. Installation and system commissioning

• Device fixing: Fix the main body of the device or the control cabinet to the cement foundation or wall with expansion bolts to ensure that it is firmly installed without shaking (vibration will affect the separation effect of the chromatographic column and the stability of the sensor).
• Initial power-up check: Turn on the power switch, the device industrial control computer start, enter the operating system, check whether the modules (oil and gas separation, chromatographic detection, temperature control) start normally, no alarm prompts (such as "chromatographic column temperature abnormality" "low carrier gas pressure").
• Carrier gas and column activation: Connect the nitrogen carrier gas (pressure adjusted to 0.4~0.6MPa), start the carrier gas control system, activate the column (set the temperature program according to the device manual, usually from 50℃ to 200℃, constant temperature for 4~8 hours), remove the residual impurities in the column to ensure the separation accuracy.
• Zero calibration and specimen calibration::
  1. Zero calibration: Pass pure nitrogen gas and let the device detect "zero gas" to calibrate the zero point of the sensor to ensure baseline stability (baseline drift ≤ 0.1mV/h).
  2. Standard calibration: inject a known concentration of standard gas (containing H₂, CH₄, C₂H₆, C₂H₄, C₂H₂, CO, etc., the concentration of which matches the concentration range of the transformer's common fault gases), and the error between the measured value of the detection device and the standard value, and the error needs to meet the industry standard (e.g. DL / T 1573-2016 requirements), if it exceeds the error needs to adjust the sensor sensitivity or column parameters. T 1573-2016 requirements, the error of each component ≤ 10%), if the difference needs to be adjusted sensor sensitivity or chromatographic column parameters.

III. Methods of use

1. Start-up and parameterization

• boot sequenceOpen the carrier gas valve (to confirm the pressure is normal), then turn on the device power supply, and finally start the industrial control computer and monitoring software; after powering on, the software will automatically complete the self-test (e.g., carrier gas pressure, column temperature, sensor status), and enter the "real-time monitoring" interface after the self-test is passed.
• parameterizationThe monitoring cycle (1~24 hours / time in general, 10~30 minutes / time in case of fault warning), gas concentration alarm threshold (refer to DL/T 722-2014, for example, H₂≥150μL/L, C₂H₂≥5μL/L (500kV transformer) trigger the alarm), and the data storage cycle (usually 1 hour / article, historical data storage ≥ 10 years) can be set up according to the needs of the site. (usually 1 hour / article, historical data storage ≥ 10 years).

2. Real-time monitoring and data viewing

• real time dataThe software interface displays the concentration of each component gas (H₂, CH₄, C₂H₆, C₂H₄, C₂H₂, CO, CO₂), the concentration of total hydrocarbons (TCG), the growth rate of the gas, as well as the device operating status (such as carrier gas pressure, column temperature, oil flow), and if a parameter exceeds the threshold value, the interface will pop up a red alarm prompt, accompanied by a sound and light alarm (can be manually turned off the sound and light alarm message can not be eliminated, need to be processed to reset). If a parameter exceeds the threshold value, the interface will pop up a red alarm prompt, accompanied by sound and light alarm (you can manually turn off the sound and light, the alarm message can not be eliminated, need to be processed and reset).
• Historical data and trend analysis: View historical concentration data (filtered by time and date) through the "Data Query" function, generate trend curves (e.g., C₂H₂ concentration change in 1 week, 1 month), and determine the development trend of the fault through the trend (e.g., a slow increase in concentration may be local overheating, and a rapid increase may be a serious discharge).

3. Troubleshooting and handling

• automatic diagnosis: The device has a built-in fault diagnostic system, which adopts the modified three-ratio method, David's Triangle method, etc. It automatically determines the type of fault (e.g., localized overheating, low-energy discharge, high-energy discharge) according to the ratio of the gas components (e.g., C₂H₂/C₂H₄, CH₄/H₂) and displays the diagnostic results on the software interface (e.g. "Suspected localized overheating, temperature about 300~700℃").
• Manual review and processing::
  1. If the alarm or diagnosis is abnormal, first review whether the device is normal (e.g., carrier gas pressure, column temperature, and rule out the device's own failure).
  2. Take transformer oil samples for offline chromatographic analysis (sampling through the sampling valve reserved in the device or the transformer body), compare the online data with the offline data, and confirm whether it is a real fault of the transformer (to avoid false alarms of the online device).
  3. If the fault is confirmed, depending on the type and severity of the fault, take downtime for maintenance (e.g., high-energy discharges need to be shut down urgently) or strengthen the monitoring (e.g., minor localized overheating can be operated for a short period of time to track the trend), and the device needs to be re-calibrated after the maintenance to ensure that the monitoring is back to normal.

4. Data transmission and remote monitoring

• The device transmits real-time data, alarm information and diagnostic results to the back-end monitoring system (e.g. substation control room) via communication lines, and the back-end can remotely view the data, modify the monitoring parameters (with permissions), and receive alarm pushes (e.g. SMS, pop-up windows).
• Some of the devices support access to the cloud platform, and operation and maintenance personnel can log in via mobile APP or webpage to remotely monitor the operation status of multiple devices without on-site guarding.

IV. Maintenance points

1. Monthly maintenance

• Check the oil system: Observe whether there is any leakage in the oil take-off valve, oil return valve, pipeline interface, and whether the oil flow is normal (according to the range of the manual, such as 50~100mL/min).
• Check the electrical system: measure the power supply voltage, grounding resistance, and confirm that communication is normal (no data interruption or delay).
• Software maintenance: backup historical data, clean software cache, check for software updates (e.g., troubleshooting algorithm optimization).

2. Quarterly maintenance

• Oil cleaning: replace the oil filter (precision ≤ 5μm) to prevent impurities from blocking the pipeline; if the transformer oil quality is poor (e.g. dielectric loss exceeds the standard), need to flush the oil pipeline (with the same type of transformer oil or anhydrous ethanol, after flushing with nitrogen gas blowing).
• Carrier gas check: Replace the nitrogen cylinder (replace it when the pressure is ≤0.1MPa), check the carrier gas line for leakage, and recalibrate the carrier gas flow (set according to the instruction manual, e.g. 20~30mL/min).
• Sensor calibration: Pass in the standard gas, calibrate the accuracy of each gas sensor, if the error is out of tolerance, adjust the sensor parameters or replace the sensor.

3. Annual maintenance

• Column maintenance: If the separation effect of the column decreases (e.g. overlapping of component peaks, prolongation of separation time), activation is required (according to the temperature procedure of the manual), and the column is replaced if the activation is not effective.
• Comprehensive testing: the device by professional and technical personnel to carry out comprehensive testing, including chromatography detection unit accuracy, temperature control system stability, fault diagnosis system accuracy, if necessary, dismantling and cleaning of oil and gas separation unit (to remove oil, impurities).
• System upgrades: Updating fault diagnosis software, upgrading communication protocols (e.g., adapting new back-office systems), and ensuring that device functions are synchronized with industry standards.

V. Precautions

1. Installation and maintenance must be operated by qualified professionals, non-professionals are strictly prohibited from disassembling the device and modifying the electrical wiring (to avoid electric shock or equipment damage).
2. The transformer pickup valve needs to be closed during oil line operation to avoid large oil leakage; if oil leakage occurs, operation needs to be stopped immediately to deal with the leakage and prevent environmental pollution or fire risk (transformer oil is flammable).
3. The sample gas is a dangerous gas and should be stored properly (away from fire source and high temperature), avoid leakage when using, and wear protective gloves and goggles when operating.
4. When the device malfunctions (e.g. column damage, sensor failure), it needs to be deactivated in time to avoid outputting incorrect data leading to misjudgment, and then put into use again after maintenance and calibration.