IEEE C57.12.90 -2006 IEEE Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers.
3. Definitions For the purposes of this document, the following terms and definitions apply. IEEE Std C57.12.80-2002 and The Authoritative Dictionary of IEEE Standards Terms [B5] 5 should be referenced for terms not defined in this clause. 3.1 actual time to crest: The time interval from the start of the transient to the time when the maximum amplitude is reached. 3.2 ambient sound pressure level: The sound pressure level measured at the test facility or at the substation without the transformer energized. 3.3 A-weighted sound level: Loudness that is measured with a sound level meter using the A-weighted response filter that is built into the meter circuitry. The A-weighting filter is commonly used to measure community noise, and it simulates the frequency response of the human ear. 3.4 C-weighted sound level: Loudness that is measured with a sound level meter using the C-weighted filter that is built into the sound level meter. The C-weighting has only little dependence on frequency over the greater part of the audible frequency range. 3.5 efficiency (of a transformer): The ratio of the useful power output of a transformer to the total power input. 3.6 guard: One or more conducting elements arranged and connected on an electrical instrument or measuring circuit so as to divert unwanted currents from the measuring means. 3.7 semi-reverberant facility: A room with a solid floor and an undetermined amount of sound-absorbing materials on the walls and ceiling.
4. General 4.1 Types of tests Various types of tests (routine, design, conformance, and other) are defined in IEEE Std C57.12.80-2002. 4.2 Test requirements A general summary of test requirements is included in Table 21 of IEEE Std C57.12.00-2006 and indicates which tests are normally considered routine, design, or other, by size. 4.3 Test sequence See for the sequence of dielectric tests when lightning impulse or switching impulse tests are specified. NOTE—To minimize potential damage to the transformer during testing, the resistance, polarity, phase relation, ratio, no-load loss and excitation current, impedance, and load loss tests (and temperature-rise tests, when applicable) should precede dielectric tests. Using this sequence, the beginning tests involve voltages and currents, which are usually reduced as compared with rated values, thus tending to minimize damaging effects to the transformer.
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