Training of Substation Design (Control, Protection and Facility Planning)
Overview
Substations are the key assets in any power system and serve as important nodes in a transmission and distribution network. Substations thus handle multiple voltages in a given location and link two or more systems of different voltages. In the first part of this two-part certificate series, the participants are given a thorough understanding of the basic principles of substation design, configuration of a substation, the specification/selection of equipment based on a selected configuration, conducting system studies to verify/correct the initial assumptions and to plan the layout of the substation.
In this part, the focus will be on the other subsystems that perform essential functions in substations. These include earthing/grounding, lightning protection of outdoor equipment and substation buildings, power system protection, control and interlocking equipment including the auxiliary power sources and various switch-yard facilities such as foundation, structures, cable routing, lighting, fire protection and surveillance equipment.
Earthing of a LV switch-yard requires careful design as it has a direct bearing on safety. The design approach to switch-yards will be discussed and the basic methods of calculation will be outlined. Lightning is a common occurrence which poses a threat to substation equipment and supply reliability by causing over voltage surges resulting in insulation failure or spark over. While lightning cannot be prevented, its effects can be minimized by proper lightning and surge protection measures.
Any electrical equipment is susceptible to insulation failures. Protection against such failures and the resulting short circuits is a vital need in power systems. The various protection options available to the designer and the protection of bus bars, transformers and substation feeders will be discussed in two parts. Another essential system is the control of switch-yard equipment and the auxiliary power supply required for control. Ac auxiliary power is generally used for operation of isolators/disconnectors, the operating mechanism of circuit breakers and for substation lighting. Essential functions are powered through dc supply backed with batteries for reliability. This includes control, annunciation and protection functions, breaker close and trip commands and in some cases emergency lightning.
A switch-yard has to be properly planned by preparing the site, measuring earth resistivity required for earthing design/optimization, earth work, foundations, cable trenches inside the switch-yard, draining arrangements etc. These aspects will be covered in detail in a separate module. The last module will discuss about gas insulated switch-gear as an alternative to outdoor open type switch-yards.