1 68 ELEMENTS OF ELECTRICAL ENGINEERING. 



e.m.f. should be a transformer of such size that the charging current of the apparatus 

 as a condenser does not exceed 25 per cent, of the rated output of the transformer. 



39. In alternating-current apparatus, the test should be made at the frequency for 

 which the apparatus is designed. 



40. The high-voltage test should not be applied when the insulation is low, owing 

 to dirt or moisture, and should be applied before the machine is put into commercial 

 service. 



The high potential test should be made at the temperature assumed under normal 

 operation, as specified, in Paragraph 2 under " Efficiency." 



41. It should be pointed out that tests at high-voltages considerably in excess of 

 the normal voltages, to determine whether specifications are fulfilled, are admissible 

 on new machines only. 



42. The test for dielectric strength should be made with the completely assembled 

 apparatus and not with its individual parts, and the voltage should be applied as 

 follows : 



1st. Between electric circuits and surrounding conducting material, and 

 2d. Between adjacent electric circuits, where such exist, as in transformers. 

 The tests should be made with a sine wave of e.m.f., or where this is not avail- 

 able, at a voltage giving the same striking distance between needle points in air, as a 

 sine wave of the specified e.m.f., except where expressly specified otherwise. As 

 needles, new sewing needles should be used. It is recommended to shunt the ap- 

 paratus during the test by spark gap of needle points set for a voltage exceeding the 

 required voltage by IO per cent. 



43. The following voltages are recommended for apparatus not including trans- 

 mission lines or switchboards. 



Rated Terminal Voltage. Rated Output. Testing Voltage. 



Not exceeding 400 volts Under 10 k. w 1,000 volts. 



" " " " 10 k. w. and over 1,500 " 



400 and over but less than 800 volts... Under 10 k. w 1,500 " 



" " " " " " 10 k.w. and over 2,000 " 



goo I)200 Any 3,500 " 



1,200" " " " 2,500"... Any 5,ooo. " 



2,500 " " " " " 10,000 " ... Any Double the normal rated vol- 

 tages. 



10,000" " " " " 2O,OOO" ... Any 10,000 volts above normal rated 



voltages. 



20,000 " " ... Any 50 per cent, above normal rated 



voltages. 



Except that transformers of 5,000 volts or less, directly feeding consumption cir- 

 cuits, should be tested at 10,000 volts. 



Synchronous motor fields and fields of converters started from the alter- 

 nating current side 5) v lts. 



