IEEE C57.12.91-2020 pdf free download.IEEE Standard Test Code for Dry‐Type Distribution and Power Transformers.
1.3 Word usage The word shall indicates mandatory requirements to be strictly followed in order to conform to the standard and from which no deviation is permitted (shall equals is required to). 4,5 The word should indicates that among several possibilities one is recommended as particularly suitable, without mentioning or excluding others; or that a certain course of action is preferred but not necessarily required (should equals is recommended that). The word may is used to indicate a course of action permissible within the limits of the standard (may equals is permitted to). The word can is used for statements of possibility and capability, whether material, physical, or causal (can equals is able to). 2. Normative references The following referenced documents are indispensable for the application of this document (i.e., they must be understood and used, so each referenced document is cited in text and its relationship to this document is explained). For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments or corrigenda) applies. ANSI S1.4, American National Standard for Sound Level Meters. 6 ANSI S1.11, American National Standard for Octave-Band and Fractional-Octave-Band Analog and Digital Filters. IEEE Std 4™, IEEE Standard for High-Voltage Testing Techniques. 7,8 IEEE Std C57.12.01™, IEEE Standard for General Requirements for Dry-Type Distribution and Power Transformers. IEEE Std C57.12.80™, IEEE Standard Terminology for Power and Distribution Transformers. IEEE Std C57.96™, IEEE Guide for Loading Dry-Type Distribution and Power Transformers. IEEE Std C57.98™, IEEE Guide for Transformer Impulse Tests.
3. Definitions For the purposes of this document, the following terms and definitions apply. The IEEE Standards Dictionary Online should be consulted for terms not defined in this clause. 9 Standard transformer terminology available in IEEE Std C57.12.80 shall apply. ambient sound pressure level: The sound pressure level measured at the test facility or at the substation without the transformer energized. 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. C-weighted sound level: Loudness that is measured with a sound level meter using the C-weighted filter that is built into the meter circuitry. C-weighting has only little dependence on frequency over the greater part of the audible frequency range. guard: One or more conducting elements arranged and connected on an electrical instrument or measuring circuit to divert unwanted currents from the measuring means. semi-reverberant facility: A room with a solid floor and an undetermined amount of sound-absorbing materials on the walls and ceiling.
5.2 Measurements 5.2.1 Resistance Resistance measurements shall be taken on all phases of each primary and secondary winding at the transformer terminals and on the rated tap connection. If a temperature rise test is to be performed, cold- resistance measurements shall also be taken on all phases of each primary and secondary winding on the combination of connections and taps to be used for the temperature rise test. The cold-resistance measurements shall be made at the coils. When that is not feasible for a sealed or nonventilated transformer, the measurements may be made at the terminals. 5.2.2 Polarity The polarity of the core magnetization shall be kept constant during all resistance readings. A reversal in magnetization of the core can change the time constant and result in erroneous readings. The same relative polarity of the measuring leads and the transformer terminals should be maintained when transferring leads from one measurement to another. 5.2.3 Current The current used for measurement shall not exceed 15% of the rated current of the winding whose resistance is to be measured. Larger values can cause inaccuracy by heating the winding and thereby changing its temperature and resistance.