Remote Transformer Monitoring Using DRYCORE Technology and DC-5M Systems
Remote transformer monitoring is an effective approach to addressing one of the most critical operational problems of oil-filled power transformers — increased moisture content inside the transformer tank. Elevated moisture levels lead to a significant reduction in operational reliability and a steady rise in operating and maintenance costs throughout the transformer lifecycle.
Excessive moisture inside a transformer tank can directly cause emergency failures. These failures are associated with a critical reduction in the dielectric strength of insulating oil, the appearance of short circuits in transformer windings, and damage to high-voltage bushings. Even when moisture concentration is not sufficient to cause immediate insulation breakdown, it inevitably degrades transformer performance, reduces permissible operating parameters, and increases the total cost of ownership of this high-responsibility equipment.
Moisture content in the solid insulation of a new oil-filled power transformer after manufacturing and installation typically does not exceed 1% by weight. During operation, moisture content in winding insulation continuously increases and may reach up to 3% after approximately 25 years, while the recommended limit is no more than 2%. This long-term trend makes continuous diagnostic supervision essential.
Sources and Accumulation of Moisture in Transformers
There are two main sources of moisture entering a transformer tank. The first is external moisture ingress caused by design imperfections or operating conditions that allow atmospheric moisture to penetrate the tank. In this case, the moisture content of solid insulation may increase by up to 0.05% per year.
The second source is internal moisture generation associated with aging and oxidation processes. Over a full cellulose aging cycle, up to 0.75% moisture can be generated within the solid insulation. Additionally, oil oxidation may contribute up to 1% moisture relative to the mass of insulation. As these processes develop, the need for drying transformer insulation becomes unavoidable.
Up to 98% of total moisture present in a transformer is concentrated in the cellulose insulation of the windings, while transformer oil contains, on average, only about 2% of the total water. This distribution significantly complicates condition monitoring, as there is no direct access to winding insulation during operation.
Forms of Moisture and Migration Processes
Moisture inside an oil-filled transformer exists in several forms, depending on its location and operating conditions. Free water may enter the tank as droplets or vapor and usually settles at the bottom due to higher density. Dissolved moisture in oil is a stable form and is always present. Moisture accumulated in solid insulation is also a stable form up to certain limits.
The most dangerous forms are non-stationary: dispersed microdroplets of water in oil and vapor bubbles inside windings. Dispersed moisture forms when temperature changes cause the oil’s water solubility to be exceeded. This condition is especially hazardous at low temperatures, where moisture may crystallize, significantly reducing oil dielectric strength.
Moisture continuously migrates between oil and solid insulation during transformer operation. Temperature changes caused by load variations or ambient conditions strongly influence this process. When oil temperature decreases rapidly, excess dissolved moisture is released throughout the oil volume in the form of fine droplets. Under electromagnetic fields, these droplets become polarized, align into chains, and may form conductive paths that reduce effective insulation gaps and lead to breakdown.
Influence of Moisture on Insulation Reliability
Regardless of how moisture enters the transformer, most of it eventually accumulates in the solid insulation of the windings. Moisture content in cellulose insulation can theoretically reach up to 17% by weight, although much lower values already have a severe negative impact.
Increased moisture accelerates cellulose aging, as water acts as a catalyst for insulation degradation. At moisture levels starting from 3–4%, and at elevated conductor temperatures, water may boil inside the insulation, forming vapor bubbles between winding layers. These bubbles reduce effective insulation thickness and may cause internal breakdowns, even though interturn insulation strength may still appear sufficient.
The temperature at which vapor bubbles form depends on multiple operational and design factors and may vary significantly across different winding zones due to competing moisture migration processes.
Remote Transformer Monitoring and Moisture Diagnostics
From the perspective of remote transformer monitoring, the most important task is determining the optimal timing for insulation drying procedures. This decision cannot rely solely on standard threshold values; it must consider individual transformer design features, oil properties, aging state, and operating conditions.
Several methodological approaches exist for estimating moisture content in solid insulation. Laboratory analysis offers high accuracy but is labor-intensive and unsuitable for continuous monitoring. Calculation-based methods using equilibrium distribution curves require real-time oil moisture sensors and are convenient for monitoring systems but have limited accuracy, especially as oil properties change with aging. Direct moisture sensors installed in solid insulation offer promising potential, though long-term operational experience with such sensors remains limited.
In practice, continuous monitoring systems typically rely on calculated moisture estimates supported by oil moisture sensors and analytical software.
Remote Transformer Monitoring DC-5M System
The DC-5M system is specifically designed for online transformer monitoring and moisture management using the DRYCORE analytical framework. It continuously evaluates insulating oil condition in power transformers, including traction, mining, marine, furnace, and wind turbine step-up units.
The remote transformer monitoring system forms a closed oil circulation loop, drawing oil from the transformer bottom and returning it to the top after passing through integrated sensors. Oil parameters are measured once per minute and transmitted to a cloud-based server, where DRYCORE algorithms calculate additional diagnostic indicators.
DC-5M also supports both transformer oil drying mode monitoring mode. The minimum oil flow capacity is 0.13 gpm (30 liters per hour). The adsorbers can absorb up to 2.4 gallons (9 liters) of water. The system operates without oil heating, reducing energy consumption and thermal stress on transformer components.