both single-phase lighting and three-phase motor loads. The bank wiring is similar to that of the three-phase, 3-wire Delta banks shown in the prior examples. The exception is the center transformer in this diagram is grounded at its center tap and connected to the service neutral to form a 4-wire service. Voltage ratings for this type of bank may be 240∆/120 or 480∆/240 . As mentioned previously, 240∆/120 are very common where a mix of 120/240 3-wire single-phase loads are present along with 240∆ three -phase loads. 480∆/240 services are used for agricultural irrigation as well as oil-field and other industrial motor load. kVA Rating: The kVA ratings of each of the transformers in this bank may be conservatively derived from the following:
𝑇𝑇 𝑙𝑙𝑙𝑙𝑙𝑙ℎ 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 = 1 𝜙𝜙 𝑘𝑘𝑘𝑘𝑘𝑘 + 1 3 3 𝜙𝜙 𝑘𝑘𝑘𝑘 𝑘𝑘 𝑇𝑇 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 = 1 3 1 𝜙𝜙 𝑘𝑘𝑘𝑘 𝑘𝑘 + 1 3 3 𝜙𝜙 𝑘𝑘𝑘𝑘𝑘𝑘
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