188 COMMERCIAL ELECTRICAL TESTING 



The tests on water-cooled transformers are the same 

 as for other types, but special instructions are neces- 

 sary for handling the water. The oil in the transformers 

 should completely cover the cooling coils. The cooling 

 coils are tested by the plumbers to several hundred 

 pounds per square inch, but they should also be tested by 

 the testing department at the water pressure available. 

 Allow water to flow through the coil until no air is left; 

 then close the overflow, allowing the pressure to rise. 

 Note whether there are any leaks, and if not, close the 

 inlet valve. If the pressure drops rapidly, a leak is pres- 

 ent. If the outside plumbing and valves are tight, test 

 the oil at the bottom of the tank for water by drawing 

 some off in a test tube. If water is present, it will settle 

 to the bottom of the tube. If water is found, the cooling 

 coil must be taken out and repaired. If, however, the 

 pressure does not fall, leave the transformer under pres- 

 sure for two hours. After all the tests are finished, the 

 oil should be tested for water. With wrought iron pipe 

 very little trouble is experienced. 



Make all tests except the heat run according to the 

 instructions already given for other types. At the start, 

 run at normal rating without water until a rise of 20 deg. 

 C. by resistance is reached. The oil should have a rise 

 of about 15 deg. C. The ingoing water should be heated 

 up to 20 deg. C. by using a steam heater; this is about 

 the average temperature found in practice. The water 

 should then be adjusted so as to have 10 deg. C. rise. 

 Temperature readings should be made every fifteen 

 minutes, in order that the quantity of water may be 

 properly adjusted without loss of time. As soon as the 

 transformers have nearly reached constant temperature, 

 the quantity of water should be noted and a record made 

 every half hour. The water may be weighed or measured. 



The amount of water required is estimated as follows : 

 One gallon of water will require about 2650 watts to 

 raise it 10 deg. C. in one minute, or one gallon of water 

 raised 10 deg. C. in one minute will carry away the heat 

 generated by 2650 watts loss. 



For a rough estimate, use one gallon of water for each 

 2500 watts loss a small portion of the heat will be 



