Transformers Single phase

If the GT is made of three, single-phase transformers, an interconnecting IPB will be required to form the delta as illustrated in Figure 31.2(b). 

The methods for determination of the electrical conductivity of solids are discussed in Section 2.1.7. For most materials, a change in electrical conductivity can be expected due to interaction of two solid phases. In a single phase transformation, the disorder in the solid must increase, causing an increase in conductivity which will be reversed when the new phase is formed. The change may be indicated by a change in temperature coefficient or by a sharp discontinuity. 

Currents now exist in both windings. Therefore a volt-drop must exist in each winding due to its leakage reactance (due to leakage flux) and its conductor resistance. The equivalent circuit of a single-phase transformer can be represented as in Figure 6.2. 

This formula applies to single-phase transformers, or to one phase of a three-phase transformer. 

The surface powerhouse, located at the confluence of Rothak Nala and Rangit River (Figs. 1 and 2) will accommodate three vertical axis Francis turbines to drive three generators of 40 MW capacity each. The powerhouse complex comprises machine area of size 56.7 m x 30.3 m with foundation level at El 333.3 m, and service bay of size 18.75 m x 20.2 m at El 355.0 m. The ten single phase transformers are placed on a 12 m wide platform at El 355.0 m. This platform is developed by filling behind the powerhouse from bottom elevation and forms part of the reinforced back slope in this reach. The powerhouse pit excavation goes down to about 16 m below the bed level of Rothak Nala. 

A three-phase transformer bank can be easily created by using three single-phase transformers. The two sides of these three transformers can be either connected as a wye or a delta, thus allowing four possible types of connections (1) wye-wye, (2) wye-delta, (3) delta-wye, and (4) delta-delta. These possibilities are shown in Fig. 10.108 to Fig. 10.112. As can be observed in the figures, the primary and secondary phase windings are drawn in parallel. 

Figure 3. Magnetization eurrent of single phase transformer with GIC equal to nominal magnetization current (red eurve) and three-phase thee-limb power transformer with GIC equal to 50 nominal magnetization currents (blue curve).

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