Introduction

Introduction

For generation, transmission and distribution of electrical power, a.c. supply system is used. As the generating stations can not be erected in the midst of populated areas, the transmission network is inevitable. Thus power is delivered to the consumers through a network of transmission and distribution. It may be required at many points in the power system to change its characteristics such as voltage, a.c. to d.c. in case of high voltage d.c. transmission (HVDC), frequency, p.f. of the supply system. The substation accomplishes this task.

Now consider that voltage is generated at the generating station(typical value 6.6 or 11 kV). For gaining suitable advantages such as smaller conductor size, less loss and more efficiency of transmission, this voltage is stepped upto either 132 kV, 220 kV or 400 kV for transmission purposes. Now step up transformer along with other required equipments performing this task is called substation. At some points a.c. is required to convert into d.c. in cases of traction and electroplating. Again substation performs this task. The type of equipments as required by substation depends on service requirement. Based on this there are several types of substations.

Thus a substation may be defined as an assembly of apparatus which is used to change the characteristics of supply system such as voltage, frequency, a.c. to d.c. or p.f.

During distribution of electrical power also, substations are needed to step down the transmission voltage to suitable value. Thus substation is a link between generating stations and consumers of electricity. The main function of substation is to receive power transmitted at high voltage, reduce it to suitable value for distribution and provide facilities for switching.

Some substations act as switching stations where various connections between different transmission lines are made. These substations have additional functions of providing points where protective devices may be installed which can operate or disconnect the faulty circuit under abnormal conditions. They provide regulation of voltage on outgoing distribution feeders. The power factor improving devices may also be installed in a substation. Also overall monitoring of proper operation of a power system is possible with the help of substation. Hence its study is essential.

Review Question

1. What do you mean by substation ? What tasks are performed by substations.