AM SGB SDN BHD

Grid transformers are used in similar situations to autotransformers but are used where the neutral point of both HV and LV system are required to be kept separately. They are physically larger than a correspondingly rated autotransformer as the windings are fully rated.

At higher voltages, large auto-transformers are used to interconnect the 400kV-500kV systems with either the 230kV-275kV systems or 120kV-145kV systems (the exact values depend on the country being considered). The HV and MV windings in an auto-transformer are connected together unlike in other transformers. The result is that the MV winding (common winding) is shared between the MV and HV systems. This results in a smaller and less expensive transformer than if the windings were separated as in a conventional fully rated two winding transformer.

The bulk transfer of power is mostly a passive affair, where the power flows to the load by the lowest impedance path. To influence this flow, the phase angle of the sending or receiving end must be modified – this may be done by the use of Phase Shifting Transformers. The phase shifting transformer introduces a circulating current into the system which acts to either reduce (when operating in buck mode) or increase (when operating in boost mode) the load current in the line where the phase shifting transformer is located.

A typical application of Shunt reactors is power factor compensation of a circuit, for example to compensate for the capacitance of long overhead transmission line or for much shorter lengths of HV cable. At low loads, the remote end of these lines may rise in voltage (the so called “Ferranti Effect”). This is especially prevalent in developing countries where the system may be only lightly loaded in the early years following installation

In a conventional power plant, thermal or potential energy is converted to mechanical energy, which in turn must be converted to electrical energy. A steam, gas or water turbine is used to drive a rotating shaft, which in turn drives a generator, producing electricity at a relatively low voltage (typically in the range 15kV-24kV). This low voltage must be transformed to a higher voltage using a generator step-up transformer, otherwise the transmission conductors would be too large in cross-section to be practical, and the voltage drop (typically 10kV on typical transmission line) would mean that little or no power could actually be transmitted.