In case a star-connected load is unbalanced and if there is *no neutral wire, *then its star point is isolated from the star-point of the generator. The potential of the load star-point is different from that of the generator star-point. The potential of the former is subject to variations according to the unbalance of the load and under certain conditions of loading, the potentials of the two star-points may differ considerably. Such an isolated load star-point or neutral point is called a *‘floating’ *neutral point *because its potential is always changing and not fixed. *All star-connected unbalanced load supplied from polyphase systems without a neutral wire, have floating neutral points. *Any unbalancing of the load causes variations not only of the potential of star-point but also of voltages across the different branches of the load. *Hence in that case, *phase voltage is not * *of the line voltage. *In general, the phase voltages are not only unequal in magnitude but also subtend angles other than 120^{o} with one another.

The following methods are used to tackle *unbalanced star-connected loads ha oing isolated *

*neutral points. *

- By Kirchhoffs laws.
- By star-delta conversion.
- By applying Milliman’s Theorem.
- By using Maxwell’s Mesh or Loop Current Method.

1. **Kirchhoff’s Laws. **By applying Kirchhoff’s laws, we get (Refer Fig. 47)

**2. Star-delta Conversion.** In case of unbalanced star-connected load it is somewhat more convenient to convert it into equivalent delta-connected load and solve it.

If Z_{R}, Z_{Y} and Z_{B} be the impedances of the given star-connected load and Z_{RY}, Z_{YB}, Z_{BR} be the impedances of the equivalent delta-connected load (Fig.48), then

Now the phase currents and line currents can be determined. (Refer worked examples).

**3. ****Milliman’s Theorem**. Refer Fig. 49. A number of linear bilateral admittances Y_{I}, Y_{2}, Y_{3},* *……. , Y* _{n} *are connected to a common point (or mode)

*O’.*The voltages of the free ends of these admittances with respect to another common point O are V

_{1O}

*,*V

_{2O}

*,*V

_{3O}

*,*….., V

_{nO}

*.*Then according to this theorem, the voltage of O’ with respect to

*A*is given by

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