. Electric railway journal . ough the coils of the transformer, a box being providedabout the transformer so that the maximum cooling effectmay be obtained from the air circulation. While this air cooling is not necessary for regular testing work as nowcarried on, it would be found very advisable to cool thetransformer if current were to be passed through it forany long period of time. The transformer core is made of laminations cut fromNo. 26 gage stove iron clamped together by a through boltat each of the four corners. There are two windings madeup of No. 12 wire in the primary, 750 turns, a
. Electric railway journal . ough the coils of the transformer, a box being providedabout the transformer so that the maximum cooling effectmay be obtained from the air circulation. While this air cooling is not necessary for regular testing work as nowcarried on, it would be found very advisable to cool thetransformer if current were to be passed through it forany long period of time. The transformer core is made of laminations cut fromNo. 26 gage stove iron clamped together by a through boltat each of the four corners. There are two windings madeup of No. 12 wire in the primary, 750 turns, and No. 21wire in the secondary, 7050 turns; in all 100 lb. of wirewere used. The secondary leads of the transformer, whichcarry a maximum voltage of 3000 from side to side, termi-nate in spring brass connection boxes enclosed in woodsimilar to those used for the heating buses connecting thecars of an elevated train. This simple home-made converting and transforming setis made use of in the every-day work of the winding Alternating-Current Testing Set Alternating current at various voltages is used for testingair-compressor motors, small electrical devices and the fieldsand armatures of railway motors. All armatures that arerepaired are given an insulation test with alternating cur-rent by connecting one lead to the shaft and the other tothe commutator bars. In this testing work each piece undertest is first subjected to a low voltage and if this is satis-factorily withstood the voltage is increased to a predeter-mined maximum by the simple method of regulating throughthe medium of resistance cut in and out of the primarycircuit of the step-up transformer. Air-compressor coilsare subjected to a test of 1470 volts as obtained when thecontrol switch is on the fourth point. Contactor magnetsthat are rewound in the shop and field coils for railway 102 ELECTRIC RAILWAY JOURNAL. [Vol. XXXIII. No. 3. motors are tested up to the same voltage as that for air-compressor motors. The
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