To maintain the transformers to provide trouble free service, various schedules have been laid down by various national and international standards. Various safety equipments have also been in service since long so as to monitor the health of the transformers and its protection. But ironically, still the transformers do breakdown. The breakdown of a transformer can be due to many reasons such as Electric Fault, Thermal Fault, Internal Fault, Ageing Fault, Material Failure, Improper Loading, and Operating Environment etc. The existing techniques of monitoring the health of the transformer are such that by the time one comes to know about the transformer failure, sufficient damage has already been done to the transformer. Buchholz Relay, which has been installed from the transformers since years, does it the faults in the transformers, but at a very later stage. The Buchholz Relay required about 165cc of gas / air pressure to operate, by which time, too much damage is already done to the transformers.

Dissolved Gases Analysis (DGA) is a proven technique to know the type of defect in the transformers. But the limitation in this case is that DGA is a periodic process. Hence fault occurring in the transformer immediately after DGA shall not be know until next DGA.

So far we have not come across any instance where the transformers were undertaken for repairs only on the basis of report by any ON-LINE DGA that means detailed DGA by NABL APPROVED laboratories is the ultimate to decide the next action once any on-line system has given the warning.

It has been a long time desire of the transformer manufactures and operators that only if there could be such an equipment that would warn much before too much damage is done to the transformer, so that there would be minimum down period and maximum mean time between repairs (MTBR).

The next question is to identify one particular parameter that could form as an input to the required early warning system. The existing physical parameters i.e. WT1, OT1, Load, Voltage, Power Factor etc. would not solve this purpose. This leads us to direct our attention towards the Chemical properties of the Transformer Oil. It is a known fact the under thermal conditions, various liquids give out various gases depending upon its chemical composition. In the case of transformers, the oil is a hydrocarbon. Under different thermal condition, the transformer oil gives out different types of gases, out of which Hydrogen, Ethane, Methane, Ethylene, Acetylene are important as seen from the procedure followed in Dissolved Gas Analysis (popularly know by its short terms DGA). But to develop a system that would monitor all these gas is not only un-economic, but also undesirable as discussed below. If we concentration on Hydrogen, we find that of the all-key fault gases produced hydrogen is produced in 60% to 70%. However, while other gases get dissolved slowly back into the oil, the hydrogen gas remains undissolved to the extent of 95%. Hence to expedite the sensing of a fault, non-other gas is more important than hydrogen. Hence, we find that if we can keep track of hydrogen, we can keep track of any fault developing in the transformer.

Having identified the source that could work as an early warning system for transformers, the next major project is to develop such a system. ERDA (Electrical Research & Development Association) Vadodara had taken this challenge and come out with an efficient and economical solution.

The system developed by ERDA is a 24 hours online system that monitors the Transformers for any defect Internal Fault e.g. Electric Fault, Thermal Fault. The sensor is installed on the air vent of the Buchholz relay, which is the most likely place for the evolved gases to get collected. Out of all the gases, the sensor will sense Key fault gas i.e. hydrogen in PPM levels. The equivalent electrical signal from the sensor is passed on to a processing unit, installed locally near the transformer via a shielded cable. The output of the processing unit is used to drive a monitor unit (processing indicating and warning unit). The monitor unit is installed at any convenient place inside the Central Control Room or any other location. The figure given below shows the installation and working of the Sensofast.

 

The system provides for two warning levels. The two warning levels are user programmable using a hand held programmer. The lower warning (yellow-audio-visual) warns the user of the beginning of a fault in the transformer. The upper warning (Red-audio-visual) confirms the defect.

The system has field trial tested by ERDA on various capacities of transformers in different industries and utilities all over India such as BSES Ltd., KPCL, RSEB, and PGCIL etc. The figures given below give the data from some of the organization where field trials were carried out.

After successful field trials ERDA has handled the system on exclusive basis to M/s New Delhi Laboratories Pvt. Ltd. for manufacturing and marketing.

It is highly encouraging that Sensofast is the recipient of Best Product Award in ELECRAMA-2002 held in Mumbai in January 2002, where over 10,000 products were on display from over 1000 different national & international industries of the world.

As a conclusion, the On-line fault Monitoring System for Transformers based on Evolved Gas Principle is our intermediate step between the Buchholz and the DGA. While it is much faster in response than the Buchholz Relay, it is a continuous Monitoring System is contrast to DGA, which is an Off-Line Method.