Tan Delta and Capacitance
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
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MONITORING PAPER INSULATION (Residual Life Assessment)
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:
- Difficulty in collecting paper samples from in service transformer.
- Location specific nature for the test.
Complexity and accuracy factors involved in the test
