Transformer Oil Test in Bangladesh

Last updated: 7 October 2026

A transformer oil test in Bangladesh checks a sample of insulating oil from a power or distribution transformer for breakdown strength, moisture, acidity, ageing and dissolved fault gases. The results show the condition of both oil and insulation inside the tank, so problems can be fixed before they cause an outage, fire or transformer failure.

Part of our Testing & Inspection Services.

Mineral insulating oil does two jobs in a transformer: it insulates the windings and it carries heat away from them. Over time heat, oxygen and moisture degrade the oil, and internal faults leave chemical traces in it. Because the oil circulates around every part of the active part, a small sample can reveal what is happening inside a sealed tank without opening it.

Veritas Technologies Ltd arranges transformer oil sampling and testing for factories, commercial buildings and sub-stations across Bangladesh. We sample correctly, arrange the required tests, interpret results against IEC 60422 and recommend clear actions. Oil testing is most useful when combined with thermography scanning of the transformer and its connections and with a wider electrical safety assessment.

What Does a Transformer Oil Test Reveal?

No single test tells the whole story. A routine set of tests describes the oil's insulating quality and ageing, while DGA and furan analysis look at the transformer itself. The table lists the main tests, what each one shows and the method commonly used.

IEC 60422 brings these results together. It explains how to evaluate mineral insulating oil in service, groups results by equipment category and voltage class, and recommends actions for each condition band.

Which Transformer Oil Tests Do You Need?

Routine oil quality tests

BDV, moisture, acidity, colour and appearance form the basic routine check for most distribution transformers in factories and buildings. Interfacial tension and dissipation factor add detail on ageing and contamination and are useful for larger or older units.

Dissolved gas analysis (DGA)

DGA is the main diagnostic tool for internal faults. Gases such as hydrogen, methane, ethane, ethylene, acetylene, carbon monoxide and carbon dioxide are measured. The pattern of gases points to the type of fault: thermal faults in oil or paper, partial discharge or arcing. Trends between samples are often more informative than a single result, so a baseline sample on a new or recently serviced transformer is valuable.

Furan analysis

Paper insulation cannot be replaced without rebuilding the transformer, and its condition largely sets the unit's remaining life. As paper ages it releases furanic compounds into the oil. Furan analysis estimates the degree of paper ageing and helps owners plan refurbishment or replacement of older transformers.

How Is a Transformer Oil Sample Taken? Step by Step

Bad sampling produces bad results. Moisture from the air, a dirty container or trapped air bubbles can make good oil look poor, or hide gases in a DGA sample. We follow a controlled procedure:

1. Review of the transformer data: rating, voltage, age, oil volume, previous results and any alarms.
2. Site safety check, permit-to-work and confirmation of safe access to the sampling valve.
3. Cleaning of the sampling valve and flushing of enough oil to clear stagnant oil from the valve and pipe.
4. Filling of clean, dry glass bottles for oil quality tests and gas-tight syringes or containers for DGA, following IEC 60567 practice.
5. Recording of oil temperature, ambient conditions, load and sample point on the label and site sheet.
6. Protection of samples from light, heat and air, and prompt delivery to the test facility.
7. Testing, review of results by an engineer and issue of the report with recommendations.

BDV can also be measured on site with a portable test set when a quick answer is needed, for example after oil filtration.

How Often Should Transformer Oil Be Tested?

Testing frequency is a risk decision. IEC 60422 gives recommended frequencies by equipment category, and the factors below decide where your transformer sits:

• Voltage class and rating of the transformer.
• Age and service history, including past faults and repairs.
• Loading pattern: heavily loaded units age faster.
• Importance to the business: a single transformer feeding a whole factory deserves closer monitoring.
• Previous results and trends, especially rising gases or moisture.
• Events such as a Buchholz alarm, protection trip, through-fault or overheating seen in thermography.

What Do the Results Mean and What Action Follows?

Results are interpreted together, not in isolation. Low BDV with high moisture usually means water ingress, often through a failed breather, gasket or a poorly sealed conservator. High acidity with low IFT and dark colour points to oxidation and possible sludge on the windings. Rising DGA gases call for the fault type to be identified and a shorter retest interval.

Typical actions include:

• No action: continue routine monitoring at the normal interval.
• Retest sooner to confirm a trend, especially for DGA.
• Filtration and vacuum dehydration to remove moisture, particles and dissolved gases.
• Oil reconditioning or reclamation where acidity and sludge are rising.
• Oil replacement when the oil is beyond economic treatment.
• Internal inspection, electrical testing or repair when DGA indicates an active fault.
• Correction of the root cause: breather silica gel, gaskets, cooling, loading or connections.

If the results suggest replacement of an ageing unit, our transformer supply and electrical sub-station solution services can help you plan the change.

Who Needs a Transformer Oil Test?

• Factories with their own HT/LT sub-station and one or more oil-filled transformers.
• Commercial buildings, hospitals and institutions with in-house distribution transformers.
• Owners preparing for a buyer audit, insurer survey or electrical safety assessment.
• Maintenance teams building a condition-based maintenance programme.
• Owners of transformers that have tripped, overheated or shown a gas relay alarm.
• Buyers of second-hand or relocated transformers wanting to know their condition before energisation.

What Do You Receive?

• Sampling record with transformer details, sample point and site conditions.
• Test results for each parameter, with the method used.
• Condition assessment against IEC 60422 bands for your equipment category.
• DGA interpretation and fault diagnosis where DGA is included.
• Estimate of paper insulation ageing where furan analysis is included.
• Clear, prioritised recommendations and a suggested retest date.

What Does a Transformer Oil Test Cost in Bangladesh?

The price depends on the test package (routine quality tests, DGA, furan), the number of transformers, site location and whether sampling is combined with thermography, earth testing or a full electrical safety audit. Share your transformer list with ratings and age, and we will propose a package and quotation.

Frequently Asked Questions