You Are Here： Home > NEWS > Oil Purifier Technology

Oil Purifier Technology

How To Identify The Degree Of Transformer Oil Contamination By Color？

Writer： Kaiqian Oil Purifier Release time：2025-11-03 16:41 Clicks：

Color observation serves as a highly intuitive and commonly used field method for preliminary assessment of transformer oil contamination levels. The color of transformer oil is primarily influenced by its oxidation degree, solid impurities, moisture content, and carbonization. However, it must be emphasized that color observation should only be used as a preliminary, qualitative screening tool and absolutely cannot replace professional laboratory oil analysis.

20250925154644313

Transformer Oil Color and Contamination Level Correspondence Table

appearance	Contamination Assessment	Possible causes	Solution
Pale Yellow Clear Bright	New Oil / Excellent Condition	New oil or oil in excellent working condition with good insulation performance.	Continue with routine maintenance and conduct regular sampling for laboratory analysis.
Dark Yellow /Amber	Slight Oxidation / Normal Aging	Oxidation begins to occur, with small amounts of soluble aging products, but the oil is generally still safe to operate. This is the normal color of the oil after it has been in operation for a certain period.	Strengthen monitoring, consider oil purification treatment (such as vacuum oil filtration), and plan the next test time.
Orange-red Brown-red	Moderate to Severe Oxidation	As the degree of oxidation deepens, the acid value may increase, producing more sludge precursors.	Sampling must be conducted for laboratory analysis to test indicators such as acid value and dielectric loss factor. Purification or oil change should be arranged as soon as possible.
Dark Brown	Severe Oxidation / Contamination	The oil has been deeply oxidized, has a high acid value, and may have produced sludge. The electrical insulation performance has been severely degraded.	The insulation performance of the oil has deteriorated, posing a threat to the safe operation of the transformer. The oil should be changed as soon as possible and the interior of the transformer should be cleaned and inspected.
Turbid / Milky White	Contaminated by moisture	A large amount of water enters the oil, forming an emulsion, which causes a sharp drop in insulation strength.	The transformer must be shut down immediately (if conditions permit), vacuum-heated oil filtration and dehydration treatment must be performed, and the cause of water ingress must be investigated.
Black / Opaque	Critical Condition / Excessive Carbon	It is usually caused by overheating inside the transformer (such as tap changer failure) or arcing (such as coil short circuit) that produces a large amount of carbon particles.	The transformer should be shut down immediately for internal fault diagnosis and repair. The oil must be completely changed, and the interior must be thoroughly cleaned.

Precautions for Observing Color

Using Color Comparison Tubes: The professional method involves injecting the oil sample into a transparent glass color comparison tube and observing it against a white background to ensure consistent lighting and more accurate judgment.

Oil Comparison: Retain a small bottle of new oil of the same grade as a standard color reference. Compare it with the used oil sample-the color difference will be very noticeable.

Observing Sediment: After allowing the oil sample to settle, inspect the bottom for particulate sediment or suspended matter. Sediment (such as metal shavings, carbon powder, or sludge) provides crucial clues for identifying mechanical contamination and internal wear.

Color Is Not the Sole Indicator: Some severe contaminants (e.g., excessive trace moisture, abnormal dissolved gases) may not immediately cause significant color changes. Transformer oil that appears visually acceptable may harbor internal faults.

photobank 1

Essential Professional Laboratory Analysis

Color assessment is only the first step. Accurate evaluation relies on laboratory "Transformer Oil Chromatography Analysis" and "Physical and Chemical Analysis," with key indicators including:

Breakdown Voltage: Directly reflects the oil's insulation strength.

Dielectric Loss Factor: A critical indicator measuring oil degradation.

Acid value: Directly indicates the oil's oxidation level.

Moisture content: Water significantly reduces the oil's insulating properties.

Dissolved gas analysis: The most effective method for diagnosing latent faults within the transformer, such as overheating or electrical discharge.

photobank 4

Summary

"Observing the oil's appearance" is a simple yet crucial skill in routine transformer maintenance.

Last：Why Does New Transformer Oil Also Need To Be Filtered? Next：Causes Of Contamination in Excavator Hydraulic Oil

Related information

Main Causes Of Emulsification in Turbine Lubricati2025-11-03
Dehydration Principle Of Vacuum Transformer Oil Pu2025-11-03
The Practicality And Applications Of Diesel Filtra2025-11-03
Causes Of Contamination in Oil Purifiers And Treat2025-11-03
Why Transformer Oil Produces Acetylene2025-11-03

Navigation

Latest information

Main Causes Of Emulsification 2025-11-03
Dehydration Principle Of Vacuu2025-11-03
The Practicality And Applicati2025-11-03
Causes Of Contamination in Oil2025-11-03

Our Company

Address：No.66 Kecheng Road,Jiulongpo District, Chongqing, China

Phone:0086 13983031725

Whatsapp:0086 13983031725

Email:oilpurification@kaiqiancq.com