Hence it is not possible to operate this connection in parallel with star-star or delta-delta connected transformer. In this type of connection, the secondary voltage is not in phase with the primary. All the power required by the load is supplied by two phases of the ungrounded supply. Note that the grounding bank does not supply any real power to the load it is there merely to provide a ground path. With a load current equal to 3 times i, each phase of the grounded Y winding provides the same current i, with the -connected secondary winding of the grounding bank providing the ampere-turns required to cancel the ampere-turns of the primary winding.

Note that the connected winding is not connected to any external circuit in Figure 3. This system a grounding bank is connected to the system, as shown in Figure 3.If it is required to connect phase-to-ground loads to this system a grounding bank is connected to the system, as shown in Figure 3 below: Figure 3 – Y-D Grounding transformer Take, for example, a distribution system supplied by ∆ connected (i.e., ungrounded) power source. As Grounding Transformer: In Power System Mostly grounded Y- ∆ transformer is used for no other purpose than to provide a good ground source in ungrounded Delta system.But in practice the HV side is normally connected in delta so that the three phase loads like motors and single phase loads like lighting loads can be supplied by LV side using three phase four wire system. Some saving in cost of insulation is achieved if HV side is star connected. The delta connected winding carries third harmonic current due to which potential of neutral point is stabilized.It is also more stable to unbalanced loads since the D partially redistributes any imbalance that occurs. The Y-D connection has no problem with third harmonic components due to circulating currents inD.Large unbalanced loads can be handled satisfactory.The neutral point allows both types of loads (single phase or three phases) to be met.The neutral available on the primary can be earthed to avoid distortion.This makes the connection economical for large high voltage step down power transformers. Hence fewer numbers of turns are required. There is s +30 Degree or -30 Degree Phase Shift between Secondary Phase Voltage to Primary Phase Voltage.Secondary Phase Voltage = (K/√3 ) X Line voltage on Primary side.Secondary Phase Voltage = K X Primary Phase Voltage.

Line voltage on Secondary side = Phase voltage on Secondary side.

Now Transformation Ration (K) = Secondary Phase Voltage / Primary Phase Voltage.

Phase voltage on Primary side = Line voltage on Primary side / √3.

Line voltage on Primary side = √3 X Phase voltage on Primary side.

Star delta problem pdf