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Tan Delta and Capacitance

December 23, 2010

We are discussing about the different tests done on Transformers and its other parts for healthy life. Tan Delta is another essential test carries out for measuring the insulating capacity of transformer oil. It has been done to determine the break down strength, flash point, its fire point, and also to identify the moisture content of the oil.

Tan Delta is also known as the ‘loss angle’ or ‘dissipation factor’. Regular measurement of electrical properties on periodical basis could help to know the operational unexpected breakdown. Tan Delta is one of the powerful tools to monitor the condition of solid insulation of various high voltage equipments. Tan Delta also applies on Transformer Bushing, Winding, CT, PT, CVT.

Importance of Tan Delta

  • It helps to predict the upcoming faults.
  • It helps to reduce the heavy cost on replacement of material.
  • Quality of insulation can be check out.
  • Its helps to plan the maintenance schedule.

Tan Delta & Capacitance should be done on regular basis. Testing period is depends upon the past history of failure, environmental condition. It is recommended once for every new transformer and then every 5 yrs.

Get more details at Transformer Testing Services



December 3, 2010

New Delhi Laboratories Pvt. Ltd has launched a new application on its website i.e . This is a “Live Chat Support“ Application which would help our website visitors and clients to get their queries solution. This application is Time as well as cost effective.

Our Executive will be online for whole working hour to serve the interested clients / visitors. This application not only will help the people for business purpose but it will also help those Students who are studying and interested in Electrical Field.

This Live Chat Support Application has been installed for convince of our visitors. We are always there to serve you our best.


November 9, 2010

Residual Life Assessment is carried out by two methods:

(1)   By Furan Analysis as per IEC: 1198.

(2)   By Measurement of Degree of Polymerization (DP Test) as per IEC: 450.

Insulation is an important entity in a transformer. Operation, loading and reliability of transformer is mainly dependent on the state of the insulation. Transformer insulation is subjected and thermal stresses during service. Life of transformer is mainly decided by the condition of insulation. The two major insulating materials in the Transformer are mineral insulating oil and paper.

The insulating paper degrades with time at rates which depend on factors like temperature, amount of air and moisture present. If the cellulose paper is heated to above 100’c, it begins to degrade more rapidly and the useful service life of the Transformer is reduced as a result.

Laboratory experiments and studies show a direct relationship between the DP Value and the amount of furanic concentration in the oil. The studies reveal the lower DP values indicate increased furfural content when paper samples were subjected to heating over a long period. Some reports suggest the end of life of cellulosic insulation would be reached when total furan content reaches 10 PPM for a corresponding DP value of 150-200.

I. It has been observed that the products of degradation of cellulosic materials   in Transformer appear in the oil in the form of furanic compounds commonly referred to as furans.

1.         2   – Furfural

2.         2   – Furfuralalcohal

3.         5   – Hydroxymethyl-2-furfural

4.         2   – Acetylfuran

5.         5   – Methyl-2-furfural

Oil sample of 250 ml is collected from the Transformer. Among the furanic compounds the most significant one related to paper decomposition is 2-furfural and this compound along with the above mentioned compounds are detected and monitored in furan analysis.

Generally a value of less than 1 PPM is considered normal and above than 10 PPM in oil assuming that End the life of transformer.

II. Depolymerisation of Paper (DP)

In this process paper sample is taken under proper shutdown after draining Transformer Oil.

The measurement of DP suffers from the following draw backs:

  1. Difficulty in collecting paper samples from in service transformer.
  2. Location specific nature for the test.

Complexity and accuracy factors involved in the test

Dehydration & Filtration of Transformer Oil

October 26, 2010

Dehydration: The process of removing the moisture (water content) from the body. Dehydration is one of the methods to improve the efficiency of Transformer. In Dehydration process Transformers is dried up so that the moisture and sludge could be removed out from winding.

Filtration: Filtration is the process in which the oil being filtered with the help of High Vacuum Filtration Machine. Filtration helps out to eliminate the solid elements of oil.

Both of the above methods are being use to remove the Moisture, Sludge, Acidity and mainly to improve the BDV and Resistivity of Transformer’s oil. After Dehydration and Filtration of Oil the BDV of Oil should be around 60 KV.

New Delhi Laboratories (NDL) is carrying out this job with its 500 Gallon High Vacuum Filtration Machine to achieve optimum BDV of Oil. This method is included in Maintenance work, which should be carried out after every 1 year.

Dehydration Filtration Machine

How important is the Power Transformer Maintenance?

September 27, 2010

Every machine needs proper and regular maintenance service. It has been notice that less maintenance time may decrease your maintenance cost but on the other hand it increase your damage risk and this may cause a huge loss. Therefore it is better to go for proper servicing.

Every Power Transformer has a useful 30 yrs of life. That doesn’t mean that it cannot work beyond this limit. It is proved that a machine can work more than its life time if a proper servicing is given to it.

There is the list of techniques in Power Transformer Maintenance which should be carried out. These are:

  1. Dehydration / Filtration of Transformer oil
  2. Overhauling of Transformer
  3. Electrical Testing

Above all these Tests are included in Maintenance. These Tests not only help to keep your transformer healthy but it will also increase the age of Transformer and decrease the damage risk.

It is needed that the maintenance people should have the deep knowledge of these tests so that it could be perform in a better way. NDL has 15-20 yrs experience in this field and providing its client reliable and successful results.

Transformer overhauling

Oil Testing Laboratory

September 14, 2010

NDL has expertise in Oil Testing services. We mainly Test NABL logoTransformer Oil which is the first and most essential part of the Transformer Servicing. The Company was accredited by NABL (National Accreditation Board For Testing & Calibration Laboratories) in the field of Electrical Testing firstly on 29th October 1997, thereafter, NABL accreditation is being Maintained & Practiced.

The success of NDL reflects on its achieved various Certificates. High quality & Commitment of Excellence towards our clients have given us appreciation for various associations. Our Oil Testing Laboratory is situated at Bahadurgarh, Haryana. With highly qualified & Professional Testing team NDL has been successful to satisfy its clients.

oil testing labInstrumentation always play significant role in Laboratory. NDL is using latest Technology Testing instruments which help to get accurate results.  Whether it is Oil testing, Tan Delta or Dehydration Filtration job, all are being done by latest Technology instruments.

We are very particular about the Laboratory Hygiene. With Latest Technology Instruments we also take care of the cleanliness of Laboratory as it directly affect the health of Testing Team. We Believe:-
“A sound body and sound mind works well”

Transformer Overhauling

September 10, 2010

Transformer Overhauling – The basic meaning of Overhauling is to examine or go over carefully for needed repairs. In the process of Overhauling Engineers open the whole Transformer to do the needful cleaning, repair and replacement, in short the process includes overall inspection including lifting of core and coils.

Transformer Overhauling, Leakage Arresting & Elect. Testing

  • Dismantling of Transformer & Draining of Oil
  • Lifting, Cleaning and Tightening of Core & Coil Assemblytransformer maintenance
  • Gasket Replacement
  • Nitrogen Purging
  • IR Value Improvement by High Vacuum Oil Circulation
  • Winding Insulation Paper Measurement of DP for  RLA
  • Initial & Pre-Commissioning Testing
  • Winding Resistance
  • Turn Ratio Test
  • No Load/ Load Losses
  • Tan Delta & Capacitance Tests on Bushing & winding

Duration of Work:

  • After every 5 yrs for 1000 to 3000 KVA
  • After every 7-10 yrs for 3000 and above KVA


  • Increase IR Value
  • Increases 10 times age of your Transformer
  • Reduce maintenance expenses
  • Improve Transformer reliability
  • Reduce unnecessary repair/replacement costs