IEEE Std C57.12.40-2017 pdf free download – IEEE Standard for Network, Three-Phase Transformers, 2500 kVA and Smaller; High Voltage, 34 500 V and Below; Low Voltage, 600 V and Below; Subway and Vault Types (Liquid Immersed).
1.1 Scope
This standard covers certain electrical, dimensional, and mechanical characteristics and takes into consideration certain safety features of three-phase, 60-Hz, liquid-immersed, self-cooled, network transformers with a primary grounding switch. These transformers are rated 2500 kVA and below with high voltages of 34 500 volts and below and secondaries of 600 volts and below. These transformers are generally used for step-down purposes from underground primary cables and supply a secondary network system through network protectors. These transformers are typically installed below ground level.
1.2 Purpose
This standard is intended for use as a basis for establishing the performance, electrical and mechanical interchangeability, safety of the equipment covered, and to assist in the proper selection of such equipment.
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.
IEEE Std 386 ™ , IEEE Standard for Separable Insulated Connector Systems for Power Distribution Systems Above 600 V. 1,2
IEEE Std C57.12.00 ™ , IEEE Standard for General Requirements for Liquid-Immersed Distribution, Power,and Regulating Transformers.
IEEE Std C57.12.20 ™ , IEEE Standard for Overhead-Type Distribution Transformers, 500 kVA and Smaller; High Voltage, 34 500 V and Below; Low Voltage, 7970/13 800Y V and Below.
IEEE Std C57.12.32 ™ , IEEE Standard for Submersible Equipment—Enclosure Integrity.
IEEE Std C57.12.80 ™ , IEEE Standard Terminology for Power and Distribution Transformers.
IEEE Std C57.12.90 ™ , IEEE Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers.
3. Transformer performance requirements
3.1 Kilovolt-ampere ratings
Kilovolt-ampere ratings shall be as specified in Table 1.
The base rating as listed in Table 1 shall not exceed a 55 °C average winding temperature rise above standard ambient. The 65 °C rating is based on not exceeding a 65 °C average winding temperature rise or an 80 °C hot-spot temperature rise, as specified in IEEE Std C57.12.00.
The temperature rise of the insulating liquid shall not exceed 65 °C measured near the top of the tank. The dual-rated transformers as shown in Table 1 are based on utilizing an insulation system that allows continuous operation at a 65 °C rise and 112% of the 55 °C base rating. Dual-rated transformers shall also be capable of delivering the 55 °C base kilovolt-ampere rating when operated in a 40 °C average ambient temperature with a maximum ambient temperature not to exceed 50 °C. When required, a kilovolt-ampere base rating with a 65 °C average winding temperature rise can be specified. Nonsymmetrical unbalanced excitation or loading of wye-wye-connected units may cause heating of their tanks in excess of that which would be produced by balanced conditions. To reduce the probability of this tank heating, such a unit shall be provided with a core construction that will not saturate when 33-percent zero sequence voltage is applied.
3.2 Voltage rating and tap ratings
Preferred voltage ratings and taps shall be in accordance with Table 2. All taps shall be at rated kilovoltamperes.IEEE Std C57.12.40 pdf download