Transformer online monitoring system introduction

Date: September 11, 2025 07:37:52

Voltage online monitoring system is a sensor, data acquisition, transmission and analysis module, the key status parameters of the operating transformer to carry outReal-time, continuous monitoringThe core role of the intelligent system is to discover latent faults within the equipment (such as insulation aging, partial discharge, overheating, etc.) in time to avoid sudden power outages, while prolonging the life of the equipment and reducing operation and maintenance costs. Its application covers all transformer-dependent power supply scenarios in power systems and industrial enterprises, and is the core component of modern power equipment condition-based maintenance (CBM) system.

I. Core monitoring parameters of the system and corresponding monitoring modules

The operational status of the transformer is determined by multiple dimensions, different monitoring modules are designed for different fault types, common core modules are as follows:

 

Monitoring module Core monitoring parameters Purpose of monitoring (associated fault types)
On-line monitoring of dissolved gases in oil H₂, CH₄, C₂H₂, C₂H₄, C₂H₆, CO, CO₂ Diagnosis of overheating of insulating oil/paper, partial discharges, arc discharges (e.g. winding short circuits, core multi-point grounding, poor tap changer contact)
On-line monitoring of partial discharges Discharge volume, number of discharges, phase of discharge Detection of partial discharges caused by internal defects in insulation (e.g., air bubbles, impurities, insulation breakage) to prevent insulation breakdowns.
Online oil condition monitoring Dielectric loss (tanδ), breakdown voltage, moisture Evaluate the degree of deterioration of the insulating properties of the insulating oil and determine whether the oil is damp, contaminated or oxidized.
Oil temperature and load monitoring Top oil temperature, winding hot spot temperature, load current Monitor equipment heating status to avoid accelerated insulation aging due to overloading and to assist in load scheduling.
Core ground current monitoring Core ground loop current Diagnosing core multi-point ground faults (which can lead to localized overheating of the core and burned insulation)
Casing insulation monitoring Casing dielectric loss, capacitance, leakage current Detection of casing insulation aging, moisture or internal breakdown, to avoid transformer damage caused by casing explosion

II. Overall system architecture

Transformer on-line monitoring systems typically utilize "tiered distributed architecture", which is divided into 3 layers from bottom to top to ensure the accuracy of data collection, stability of transmission and professionalism of analysis:

1. Perception layer (data acquisition layer)

  • core component: Various types of specialized sensors, data acquisition units (DAUs).
    • Examples: Dissolved gas sensors in oil (e.g. semiconductor type, infrared spectroscopy type), partial discharge sensors (e.g. high frequency current sensors HFCT, ultrasonic sensors), oil temperature sensors (platinum resistor PT100), earth current sensors (Roche coils).
  • functionality: In direct contact with or close to the transformer, "physical / chemical quantities" (e.g. gas concentration, temperature, current) are converted into "electrical signals" (analog or digital) and preliminary filtering, amplification and data pre-processing are carried out to reduce interference.

2. Transport layer (data communication layer)

  • core component: Communication modules (e.g., 4G/5G, LoRa, Ethernet, fiber), data gateways.
  • Transmission method selection::
    • Short distances within substations: Priority is given tofiber optics(high resistance to electromagnetic interference and high transmission rates) or Industrial Ethernet;
    • Remote area/decentralized transformers: with4G/5G or LoRa(Wireless transmission, no wiring required, wide coverage);
  • functionalityThe system is designed to transmit monitoring data from the sensory layer to the upper layer analysis platform "securely and in real time", while supporting reverse control (e.g., remote calibration of sensors, initiation of sampling).

3. Application layer (data processing and presentation layer)

  • core component: Monitoring mainframe, cloud platform, data analysis software, human-machine interface (HMI).
  • core functionality::
    1. data storage: Stores historical monitoring data (typically retained for 1-3 years) and supports querying, exporting, and traceability;
    2. data analysis: Automatic identification of anomalies through the "Threshold Judgment Method," "Trend Analysis Method," and "Troubleshooting Models" (e.g., IEC Triple Ratio Method, David's Triangle Method);
      • Example: If the C₂H₂ concentration in the oil suddenly rises (exceeding the threshold value of 1μL/L), the system determines that an arc discharge fault may exist;
    3. Alerts and warnings: Notify O&M personnel of abnormalities by "sound and light alarm (local), SMS / APP push (remote), monitoring center pop-up window", etc., distinguishing between "early warning" (abnormal trend) and "alarm " (parameter exceeding standard);
    4. Visualization: Visualize transformer health status through dashboards, curves (e.g. oil temperature change curve, gas concentration trend graph), and equipment status icons, and support remote viewing by operation and maintenance personnel.

III. Key points for system installation

Installation quality directly affects the monitoring accuracy, need to strictly follow the "power outage installation-oriented, safety first" principle, the core steps and precautions are as follows:

1. Pre-installation preparation

  • Reconciliation of equipment selection: Confirm that the specifications of the sensors and communication modules match the transformer (e.g., the gas-in-oil sensor needs to be compatible with the transformer oil type, and the temperature sensor range covers - 40~120℃);
  • on-site survey: Confirm the location of the transformer's terminals, oil pickup ports (oil sample collection points), and grounding terminals, avoid strong sources of electromagnetic interference (e.g., busbars, lightning arresters), and plan the direction of sensors and cables;
  • security measure: Handle the substation "work ticket", check the power after power outage, hang the grounding wire, and ensure that the installer is insulated and protected (insulated gloves, insulated shoes).

2. Example of core module installation

module (in software) mounting position Key Considerations
Gas in Oil Sensor Transformer tank pickup valve / bottom of oil pillow 1. The oil pickup port needs to be located in the lower center of the tank (oil flow is stable and gas is less likely to accumulate);
2. Pipe connections need to be sealed (to prevent oil leakage and air intake), and valves should be installed to facilitate oil changes at a later stage;
3. Keep the sensor away from heat sources and direct sunlight.
Partial Discharge HFCT Sensor Transformer Neutral / Ground 1. The sensor is sleeved on a grounding wire, close to the cabinet, to reduce electromagnetic interference;
2. The cable shield is grounded at one end to avoid the introduction of interfering signals.
Oil Temperature Sensor Tank top layer (measuring top layer oil temperature), winding burial 1. The top oil temperature sensor is inserted at a depth of ≥100mm to ensure contact with the oil;
2. The winding sensor needs to be pre-installed in the transformer factory (built-in type), and only the signal line is connected on site.
communications gateway Substation Control Room / Outdoor Rainproof Cabinet 1. Keep away from high-voltage equipment (safety distance ≥ 1.5m);
2. Stable power supply access (UPS power supply is recommended to avoid power failure and disconnection).

3. Post-installation commissioning

  • Signal Calibration: Calibrate the sensor with a standard signal source (e.g., standard gas, standard current) to ensure that the error is within the allowable range (e.g., gas concentration error ≤ ±5%);
  • communications test: Simulate data transmission and check for packet loss and delay (delay ≤ 10s);
  • Linkage testing: Artificially set the "analog exceeding signal" to verify whether the alarm function is triggered normally (e.g. SMS push, sound and light alarm).

IV. Daily use and operation and maintenance of the system

Online monitoring system is not "installation that is no need to manage", need regular operation and maintenance to ensure long-term reliable operation, the core points are as follows:

1. Daily inspections (1 per week)

  • Local inspection: Look for oil leaks and loose sensors, normal gateway indicator lights (no fault lights on), and broken cables;
  • remote viewing: Check whether the real-time data is normal (e.g. oil temperature matches the ambient temperature, no abnormal alarms) and whether the historical data storage is complete through the platform.

2. Periodic maintenance (every 3-6 months)

  • Sensor Calibration: Gas sensors in oil need to be calibrated with "standard gas" (to avoid drift) and partial discharge sensors need to be recalibrated for sensitivity;
  • oil sample comparison: Compare the on-line gas concentration data with the off-line results in the laboratory. If the deviation is too large (e.g., more than 10%), the sensor or piping should be investigated;
  • Cleaning and fastening: Clean the sensor and gateway surfaces of dust and tighten the cable connectors (to prevent loosening that can cause signal interruption);
  • Software Maintenance: Upgrade the version of the analysis software to update the fault diagnostic model (e.g., add industry-standard algorithms).

3. Troubleshooting (immediately after alarm)

  • Step 1: Confirm the authenticity of the alarm: Troubleshoot for "false alarms" first (e.g., sensor failure, communication interruption), which can be verified by on-site inspection or restarting the device;
  • Step 2: Locate the fault: If it is a real alarm, combined with multi-parameter comprehensive judgment (e.g., "C₂H₂ elevated + local discharge increased", the probability is a short-circuit winding);
  • Step 3: Disposal and Recording: Notify maintenance personnel for on-site maintenance. After troubleshooting, record the disposal process in the system and update the equipment health file.

V. System application values and considerations

1. Core values

  • accident prevention: Early detection of latent faults (e.g., localized overheating) to avoid transformer burnout or explosion and reduce outage losses;
  • reduce costs and increase efficiency: Replaces traditional "periodic offline testing" (e.g., taking oil samples every 6 months to send to a lab), reducing labor costs and extending overhaul intervals;
  • Data support: Accumulate long-term operation data to provide a basis for transformer "state maintenance" (instead of fixed-cycle maintenance) and optimize operation and maintenance strategies.

2. Cautions

  • No substitute for offline testing: Online monitoring is a "real-time monitoring tool" that still requires offline testing (e.g., dielectric loss, voltage withstand tests) every 1-2 years, and the two complement each other;
  • anti-interference design: The electromagnetic environment of the substation is complex, the installation needs to do a good job of cable shielding, grounding (single-ended grounding), to avoid electromagnetic interference resulting in data distortion;
  • AdaptationSelect the appropriate sensor and protection class (e.g. IP65 or higher) according to the transformer capacity (e.g. 110kV, 220kV) and the operating environment (e.g. outdoors, humid areas).

Transformer integrated online monitoring system

In conclusion.Transformer online monitoring systemIt is an important embodiment of modern power system intelligence, the core of which is through "real-time perception - intelligent analysis - timely warning", to realize the transformer from "passive overhaul" to "active warning". The core is to realize the transformation of transformer from "passive maintenance" to "active warning" through "real-time perception - intelligent analysis - timely warning", to ensure the security and stability of power supply.