PLAN No. 1078. TESTING
Nearly all electrical equipment is tested before it leaves the factory. That is to say, it is subjected to electrical and mechanical conditions similar to those under which it must operate in practice, so that its performance under such conditions may be predetermined. This is necessary to insure that the product which leaves the factory will not develop faults after it is in service. Where machines or devices are of large capacity, each is tested individually. Where the output comprises a large number of small, identical machines, as for example, automobile starting motors, or circuit-breakers, only one or a few out of each order which passes through the shop are subjected to test.
PLAN No. 1079. AS GENERAL APPRENTICESHIP TRAINING
Electrical testing is interesting work and affords a splendid opportunity for a man to acquire experience which will be valuable to him in almost any line of electrical work which he may subsequently elect to follow. Formerly, the larger electrical manufacturing companies would accept only university graduates in their testing departments. The testing work was usually offered in the form of an apprenticeship course, and as a stepping-stone to other more responsible positions. But of recent years, some of the companies have accepted in their testing departments men with only a high-school training or its equivalent. It has been found that this plan is satisfactory, both from the standpoint of the company and of the men themselves.
PLAN No. 1080. TESTING MOTORS
In testing a motor the machine is loaded by making it drive, usually through a belt, an electric generator. The energy which this generator develops is forced into the same circuit as that from which the driving motor takes its power. Hence, the net energy required to conduct the test is greatly minimized, being in fact equivalent only to the losses of energy in the generator and motor during the test. By increasing the load on the generator the load on the motor is increased correspondingly, until it is carrying its full-load horsepower output. Meanwhile, from properly connected voltmeters and ammeters, readings of the voltage impressed on the motor, and the current taken by it at different loads are observed. Simultaneously the temperature of different parts of the motor are taken by means of thermometers, which are bound to the machine with tapes or held with gobs of putty. The speed of the machine at different loads is noted. From the readings thus taken, the efficiency of the motor at different loads may be computed and its other characteristics determined. If the efficiency and other performance characteristics of the machine meet the specification, and its temperature does not become greater than the limit specified by the engineering department, the machine is painted and either shipped to the customer or put into stock to await a sale. If it does not “come up” to its specifications, the difficulty must be corrected.
PLAN No. 1081. TESTING GENERATORS AND OTHER DEVICES
The methods used for testing generators are somewhat similar to those used for the motors. Other devices, such as transformers, potential regulators, circuit breakers, switches, controllers, and one thousand and one others, involve test methods of their own.
In every test the object sought is the same, namely, to subject the device, before it leaves the shop, to practical working conditions. The testing department records readings from instruments during tests and “works these readings up” into the final test data. This working up involves considerable calculation. Hence, in all testing departments there are computers who spend practically all of their time figuring results. They use slide rules for many of the operations.