Products Transformers & Switchgear Preventing electrical transformer malfunction
Electricity transformers which are not monitored correctly and don’t get the right maintenance can quickly malfunc- tion and possibly catch fire. One of the ways this happens is when moisture inside the oil reservoirs contaminates and prevents the oil from cooling and insulating correctly. Brownell trans- former breathers have been developed with this in mind to prevent accidents like this happening. When the temperature of an electricity transformer changes an air displacement occurs. This air displacement can be caused by both diurnal cycling and the demand placed upon the transformer. This change in temperature causes the volume of air within the transformer/ conservator to vary. When the trans- former heats up the air in the airspace is pushed out of the transformer via the vent pipe. In this mode the duty on the transformer breather is negligible. However, the breather really starts to work when the transformer cools down. This cooling causes atmospheric air to be drawn into the transformer to restore the differential pressure. This incoming air will be moisture laden and the breather has the job of adsorbing the
incoming moisture. Once the desiccant has removed the moisture, the air will make its way into the air space above the oil. This in turn provides a dry air blanket above the oil. If the moisture was not removed then the low moisture concen- tration oil would act like a desiccant and take the moisture from the air. Once moisture has been adsorbed into the oil, it will in turn pass onto the windings of the transformer. Once the moisture gets into the windings it is very difficult and expensive to remove.
An electricity transformer which is on a constant load cycle will only have a very low breather duty cycle, a typical example of such a transformer is one installed at a hospital. A transformer which supplies a typical 40-50 hour working week factory estate will cycle daily and have reduced usage at week- ends. This scenario will create a much higher duty cycle and consequently a reduced service life. For the above rea- sons it is suggested that the breathers are periodically inspected to observe the condition of the desiccant. There are three main types of silica gel seen on transformers, orange to green (Envirogel), orange to clear and blue to
pink. The blue to pink desiccant is not that widely used these days within Europe owing to legislation regarding cobalt chloride and carcinogenic links. The desiccant will start off either orange or blue in its dry state and gradually the column will change colour to green, clear or pink as the bed saturates. Brownell uses Envirogel, the low dust- ing beaded adsorbent that is self indicat- ing. This has been developed by Brownell and allows the user to ascertain when the desiccant is fully saturated by the visual colour change from orange to green. To reactivate all you need to do is heat the Envirogel for three to four hours at 95°C and you will recover a capacity of 95%, which also saves you money on new material. The breathers are all constructed out of high performance plastic or metals in different sizes. The materials used have a high impact resistance that makes them vandal-proof and reduces the risk of accidental damage. Using a Brownell breather, you will be using product developed over many years with input from both users and trans- former manufacturers. Brownell also makes a Mark 7 version
which is even more robust and designed to meet the requirement of working under high mechanical stress. The Mark 7 is fabricated from welded steel, which is phosphate conversion coated before being powder coated. These are designed to withstand bumps, knocks, vibration and shocks that a breather might undergo in an electrical traction engine and other similar vehicles - the Mark 7 has been built for hard usage. Brownell
www.brownell.co.uk T: 0208 965 9281
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Enter 15 24 OCTOBER 2013 Electrical Engineering
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