Regulating Transformer

Definition: The transformer which changes the magnitude and phase angle at the certain point in the power system is known as the regulating transformer. It is mainly used for controlling the magnitude of bus voltage and for controlling the power flow, which is controlled by the phase angle of the transformer. They provide the small component of voltage between the line or phase voltage.

The main function of the regulating transformer is to control the magnitude of voltage and power flow of the transmission line.The regulating transformer is of two types. One is used for changing the magnitude of voltage which is called online tap changing transformer and the other is called phase shifting transformer. The regulating transformer compensates the fluctuation of voltage and current. The arrangement of the regulating transformer is shown in the figure below.

The main application of power system is to reduce the circulating current and minimise the losses in the power system. The regulating transformer reduces the losses in the power system network, and it also controls the unwanted exchange of the reactive power in the system.

Consider that, 

The primary winding of the transformer is connected in delta, and the secondary winding phase is connected in star. The voltage of the secondary phases is adjustable. From the phase shift property in delta-star transformer we have

The magnitude of V_m can be controlled in a small range. It is used for adjusting the three phase voltage V_a, V_b, and V_c. The voltage of the tertiary winding is given below.

The magnitude of V_Φ is adjustable and is used for control of the phase angle of the voltage V_a’, V_b’ and V_c’.

The voltage V_km, V_lk, V_ml is derived from the voltage V_ko, V_lo, V_mo as

The V_km, V_kl and V_ml are in phase with the system voltages V_an, V_bn, and V_cn The voltage V_rl, V_sm, and V_kl are 90º out of phase with the same voltage. The incremental voltage is given by

The phasor diagram of the voltage is shown in the figure above.