STANDARDIZATION RULES Ol- Till: ,!././ 



223 RATED TERMINAL VOLTAGE. DEFINITION. The rated terminal voltage 

 of circuit in the above table, means the voltage between the conductors 

 of the circuit to which the apparatus to be tested is to be connected, for 

 instance, in three-phase circuits the delta voltage should be taken. In 

 the following specific cases, the rated terminal voltage of the circuit is 

 to be determined as specified in ascertaining the testing voltage: 



224 (a) TRANSFORMERS. The test of the insulation between the primary and 

 secondary windings of transformers, is to be the same as that between 

 the high-voltage windings and core, and both tests should be made simul- 

 taneously by connecting the low-voltage winding and core together during 

 the test. If a voltage equal to the specified testing voltage be induced 

 in the high-voltage winding of a transformer it may DC used f>r insulation 



I instead of an independently induced voltage. These tests should IK- 

 made first with one ena and then with the other end of the high-tension 

 \\mdine connected to the low-tension winding and to the core. 

 226 (6) CONSTANT-CURRENT APPARATUS. The testing voltage is to be 

 based upon a rated terminal voltage equal to the maximum voltage which 

 may exist at open or closed circuit. 



226 (c) APPARAH - IN SERIES. For tests of machines or apparatus to be 

 operated in series, so as to employ the sum of their separate voltages the 

 testing voltage is to be based upon a rated terminal voltage equal to the 

 sum of the separate voltages except where the frames of the machines 

 are sepa: ulated, both from the ground and from each other, in 

 which case the test for insulation between machines should be based upon 

 the voltage of one machine, and the test between each machine and ground 

 to be based upon the total voltage of the series. 



(B) METHODS OF TESTING. 



227 CLASSES OF TESTS. Tests for dielectric strength cover such a wide 

 range in voltage that the apparatus, methods and precautions which are 

 essential in certain cases do not apply to others. For convenience, the 

 tests will be separated into two classes: 



228 CLASS 1. This class includes all apparatus for which the test voltage 

 does not exceed 10 kilo volts, unless the apparatus is of very large static 

 capacity, e.g., a large cable system. This class also includes all apparatus 

 of small static capacity, such as line insulators, switches and the like, for 

 all test voltages. 



229 METHOD OF TEST FOR CLASS 1. The test voltage is to be continuously 

 applied for the prescribed interval, (one minute unless otherwise speci- 

 fied). The test voltage may be taken from a constant-potential source 

 and applied directly to the apparatus to be tested, or it may be raised 

 gradually as specified for tests under Class 2. 



230 CLASS 2. This class includes all apparatus not included in Class 1. 



231 METHOD OF TEST FOR CLASS 2. The test voltage is to be raised to the 

 required value smoothly and without sudden large increments and is then 

 to be continuously applied for the prescribed interval, (one minute, 

 unless otherwise specified), and then gradually decreased. 



232 CONDITIONS AND PRECAUTIONS FOR CLASS 1 and CLASS 2. The follow- 

 ing apply to all tests: 



233 The WAVE SHAPE should be approximately sinusoidal and the apparatus 

 in the testing circuits should not materially distort this wave. 



234 The SUPPLY CIRCUIT should have ample current-supply capacity so that 

 the charging current which may be taken by the apparatus under test 

 will not materially alter the wave form nor materially affect the test volt- 

 age. The circuit should be free from accidental interruptions. 



236 RESISTANCE OR INDUCTANCE in series with the primary of a raising 

 transformer for the purpose of controlling its voltage is liable seriously to 

 affect the wave form, thereby causing the maximum value of the volt- 

 age to bear a different and unknown ratio to the root mean square value. 

 This method of voltage adjustment is, therefore, in general, undesirable. 

 It may be noted that if a resistance or inductance is employed to limit 

 the current when burning out a fault, such resistance or inductance should 

 be short circuited during the regular voltage test. 



