454 ELECTRICAL EQUIPMENT 



The coil should be examined whenever indications point to the 

 formation of a deposit. 



When water-cooled transformers are idle and exposed to cold, 

 the water must be drained or blown out of the cooling coils. In 

 addition to draining or blowing out the water, the cooling coil 

 should be dried by forcing heated air through it. If not con- 

 venient to force heated air through the coil, enough alcohol 

 should be poured into the coil to fill the two bottom turns of each 

 section. 



During the first month of service of transformers having a 

 potential of 40,000 volts or over, samples of oil should be drawn 

 each week from the bottom of the tank and tested. Samples from 

 all transformers should be drawn and tested once every six months. 



If at any time the oil should puncture below the safe voltage 

 the filter press may be used for treating it without taking the 

 transformer out of service. Oil should be drawn from valve in the 

 base, passed through the filter press and returned to the trans- 

 former through the cover, discharging into the tank diagonally 

 opposite the valve in the base and so directing the discharge that 

 it is not directly over the coils and insulation. Circulate until 

 the oil tests satisfactorily. 



The oil level in transformers should be kept up to the mark on 

 the oil gauge. On oil-cooled transformers with external cooling 

 pipes, the oil must be above the top pipes in the tanks or the oil 

 will not circulate and transformer will overheat. 



When chloride breathers are provided, only anhydrous chlor- 

 ide of calcium in half-inch lumps or larger should be used. The 

 frequency with which new chloride may be added will depend on 

 the changes in temperature and the humidity of the atmosphere. 



Oil-cooled transformers, occasionally, are operated under con- 

 ditions of poor ventilation, overload, or over-voltage. Any of 

 these conditions, or a combination of them may raise the tem- 

 perature of the oil abnormally high, causing the oil to throw down a 

 deposit which forms on the transformer surfaces. Should the 

 deposit on any surface, except the base, reach an average thick- 

 ness of about | inch, the oil should be renewed as soon as possible. 

 Before putting new oil into the tank the sediment should be 

 removed from all surfaces and the windings cleaned by forcing 

 dry, clean Transil oil through all ducts and against all surfaces 

 until all deposit is removed. 



