33 11kv distribution substation ppt

[anjali61]

Equipment in a substation can broadly be categorized as follows:

structures;

power transformers;

bus-bars;

circuit breakers (33 kV and 11 kV);

isolators or isolating switches (33 kV and 11 kV);

earthing switches;

insulators;

power and control cables;

control panel;

lightning protection surge arrestors;

instrument transformers (current and power transformers, i.e., CTs and PTs);

earthing arrangements;

reactive compensation;

DC supply arrangement;

auxiliary supply transformer; and

fire-fighting system.

The design of the substation equipment must comply with the requirement of relevant Indian Standards.We now briefly describe each one of these.

Structures

Structures are required to provide entry from the overhead line to the substation and to extend out required number of feeders. The numbers of structures should be kept to a minimum as large number of structures would not only be uneconomical but give an ugly look to the substation and may prove to be obstructions in extending bus-bar, lines, etc. The main structures required for 33/11 kV substations are:

incoming and outgoing gantries;

support structures for breaker, isolators, fuses, insulators, CTs and PTs; and

bus-bars.

Switchyard structures can be made of fabricated steel, RCC or PSCC,Rail or RS Joist.

Power Transformers

You have learnt about the underlying principle and design of a power transformer in previous unit. The general operation and maintenance practices of power transformers are similar to those of distribution transformers, which are discussed in detail in next Unit.

Bus-bars

A bus-bar in electrical power distribution refers to thick strips of copper or aluminum that conduct electricity within the substation (Fig. ). The size of the bus-bar is important in determining the maximum amount of current that can be safely carried. The bus-bar should be able to carry the expected maximum load current without exceeding the temperature limit.The capacity of bus should also be checked for maximum temperature under short circuit conditions.Different types of bus-bars, namely, single bus-bar, single bus-bar with bus sectionalizer, main and transfer bus, double bus-bar, double bus-bar with double breaker scheme and mesh scheme are used in a substation in accordance with the safety and reliability considerations.