Biggest reason for distribution transformer failures in gurantee period
Do you know that more than 70% of Distribution Transformer failures in the field is directly or indirectly related to failure of gaskets?
Gasket is one of those items which cannot be tested for long life performance at the time of transformer manufacturing, unlike components like conductors, CRGO core, radiators etc. It has been observed that in many developing countries where a transformer goes into overload due to excess current being draw from it beyond capacity, the active parts might survive the stress for a short period of time but the non-active parts like gaskets gives away. This leads to continuous seepage of oil from the transformer even when the overload condition is resolved, ultimately leading to transformer failure.
Selection of good quality and correct gasket is extremely important to make your transformers robust and free of such failures.
Some common reasons for leakage of oil in Transformers due to gaskets are:
- Wrong selection of gasket based on application: A gasket material should be selected based on the operating temperature and type of oil it will be exposed to. Generally for mineral oil filled transformer (inhibited or uninhibited), Nitrile rubber bonded cork gaskets is suggested. These gaskets adhering to IS or ASTM standards can work under operating temperatures of -30 deg Celsius to +120 deg Celsius and are highly resistant to mineral oils.
- Selection of incorrect gasket thickness: A gasket of lowest thickness based on the finish of the flange should be used. Generally most of the consumers believe that using a thicker gasket will prevent any leakage which is untrue. If your flange finish is good then ideally a 3mm or 4 mm thick gasket is sufficient. More undulation in the flange, thicker the gasket to be used, but thicker gasket also deteriorates faster due to more surface area exposure to ozone and UV rays.
- Gasket crushed due to over tightening: Any gasket when over tightened beyond its compressive strength will loose its integrity and get crushed. A rubber cork gasket should be tightened not more than 30% of its original thickness for best results. An automatic bolt tightening wrench which applies uniform torque should be used.
- Deterioration of gasket over time: Like any other material, a gasket also has its life. It get deteriorated gradually due to effect of oxidation by atmospheric ozone, effect of ultra-violet rays in sunlight and other weather elements. Change of gasket is advisable after around 10 years of its working for 100% leak-proof performance. This process of deterioration in gaskets over time is also known as aging of gaskets.
- Reuse of gasket: Many consumers have tendency to re-use gaskets when the transformer is opened for servicing or maintenance. Gaskets should never be re-used once opened after considerable time. This is because they loose substantial thickness over period of time and might lead to leakage of oil. Always use fresh gaskets every time a transformer is opened up for servicing and maintenance.
- Improper / incompatible joints in the gaskets: It has been observed that many a times, transformer manufacturers buy very good quality gasket but at the time of application they do not put proper joints. Sometimes the jointing method or compound is not compatible with mineral oil. Proper care should be taken while putting joints in the gasket or should be done by experts in the field.
Note: Reference for data has been taken based on our interaction with more than 700 distribution transformer manufacturers and their buyers.
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