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UL 1446-2020 pdf free download
UL 1446-2020 pdf free download.Systems of Insulating Materials General.
7.4.1 After exposure to moisture as described in 7.3.4, and while the samples are still in the humidity chamber or immediately after removal, the test samples are to be subjected to the following tests to detect winding-to-winding, winding-to-ground, and turn-to-turn breakdowns which is considered the end of test- life, Dielectric voltages specified are usable to detect a material’s end of test-life and shall not be used to establish a voltage rating for the system:
a) For a non-functional specimen representing an operating part, dielectric stresses of 600 V winding-to-winding and winding-to-ground, plus 120 V turn-to-turn are to be applied, each for 10 mm. End of test-life shall be identified when a 0.75 A circuit breaker opens during either dielectric stress test.
b) For a solenoid or relay type non-energized coil, either a shorted turns tester or input measurements are to be used to detect turn-to-turn breakdown. A 10% increase in input current of an aged coil as compared to an unaged coil is an indication of turn-to-turn breakdown. The check of ground insulation is to consist of a dielectric stress winding-to-ground at a voltage of twice that of the coils rated voltage plus 1000 V. To determine the condition of outer wrap intended to be used as ground insulation, coils are to be stressed winding-to-ground through the core and the outer wrap by means of immersion in lead shot, wrapping in metallic foil, or some equivalent means. Care is to be taken to avoid breakdowns at slots, end turns, and bare edges, or such results are to be discounted in evaluating the data. The test voltage is to be applied for 10 mm.
C) For operating part samples that are continuously energized at their intended voltage and as a result are self-heating, such as a solenoid, transformer, or motor, the testing to determine end of test-life shall be agreed upon prior to the start of testing. This testing is not prohibited from including, but not limited to, the opening of an overcurrent protective device, indiscriminate starting and stopping of the device, changes in the devices’ insulation resistance or dielectric dissipation measurements, or changes in the direction of a motor’s rotation. When end of test-life is detected. the time in hours to that point shall be taken as the accumulated thermal aging time.
7.4.2 To conduct the dielectric withstand test specified In 7.4.1(a) and L4j(b) above, a test transformer having a capacity of at least 500 VA is to be used so that leakage current through the Insulation system does not reduce the actual applied voltage below that indicated at the primary. However, a test transformer other than that specified is not prohibited from being used when the secondary potential of the test transformer is monitored during the test to determine that the required test voltages are not reduced clue to leakage current.
7.4.3 The end of test-life for each sample shall be verified by repeating the dielectric stress test after the sample has been subjected to one additional complete cycle. The first detected and confirmed dielectric breakdown is considered the end of test-life for that sample.
7.4.4 With the exception of samples aged by self-heating, when the end of test-life has been verified the time in hours is to be recorded as the accumulated thermal aging time for the first determination of end of test-life minus one-half the time of the last oven aging cycle.UL 1446-2020 pdf free download.
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