IEEE C57.12.20-2005 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.
7.1.2 Terminals 220.127.116.11 High-voltage terminals Terminal details shall be as shown in Figure 5a. High-voltage bushings of transformers 200 kV BIL and below shall be equipped with tinned, copper alloy solderless connectors. High-voltage terminal sizes shall be as shown in Table 8. 18.104.22.168 Low-voltage terminals Terminal details shall be as shown in Figure 5a and Figure 5b. Low-voltage terminal sizes shall be as shown in Table 9. Terminals of low-voltage windings 600 V and below shall be arranged for vertical take-off. External spacing between low-voltage bushing terminals shall be such as to provide the maximum clearance between live metal parts in the working area. For low-voltage ratings above 600 V, the electrical characteristics of the bushings determine the spacing. For low-voltage ratings 600 V and below, spacing shall be within the limits of Table 10. 7.1.3 Neutral termination On single-phase transformers having one high-voltage bushing, the H2 end of the winding shall be securely connected internally to the grounded clamping structure or the tank. This connection shall be independent of all other eletrical connections. On all thee-phase transformers, a fully insulated low-voltage neutral bushing, Xo, shall be provided when the low-voltage w indings are wye-connected. On three-phase transformers, a fully insulated high-voltage neutral bushing, Ho, and a fully insulated low- voltage neutral bushing, Xo, shall be provided where wye-connected high-voltage windings are rated 8.32Y kV and below and low-voltage windings are rated 208Y/120 V or 480Y/277 V. On three-phase transformers, a common fully insulated low-voltage-type neutral bushing, HxXo, shall be provided where wye-connected high-voltage windings are rated above 8.32Y kV and low-voltage windings are rated 208Y/120 V or 480Y/277 V. The high-voltage and low-voltage neutrals shall be connected internally by a link that is accessible and capable of reconneetion. 7.1.4 Terminal boards On single-phase transformers with low-voltage ratings of 120/240 V or 240/48
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