Installation commission and maintenance part 5

Topic includes

- Distribution system

- Layout
- Maintenance in installation commission part 2

• https://rahulsinghmar.blogspot.com/2020/04/installation-commission-and-maintenance_17.html?m=1

- Worldwide voltage and frequency
- Circuit breaker

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Distribution system

Distribution systems usually employ such equipment as transformers, circuit breakers, and protective devices. ... In general, the distribution system is the electrical system between the substation fed by the transmission system and the consumer end. It generally consists of feeders, distributors.

Electric power distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmission voltage to medium voltage ranging between 2 kV and 35 kV with the use of transformers. Primary distribution lines carry this medium voltage power to distribution transformers located near the customer's premises. Distribution transformers again lower the voltage to the utilization voltage used by lighting, industrial equipment or household appliances. Often several customers are supplied from one transformer through secondary distribution lines. Commercial and residential customers are connected to the secondary distribution lines through service drops.

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General layout of electricity networks. The voltages and loadings are typical of a European network.

The transition from transmission to distribution happens in a power substation, which has the following functions:

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Circuit breakers and switches enable the substation to be disconnected from the transmission grid or for distribution lines to be disconnected.

Transformers step down transmission voltages, 35 kV or more, down to primary distribution voltages. These are medium voltage circuits, usually 600–35000 V.[1]

From the transformer, power goes to the busbar that can split the distribution power off in multiple directions. The bus distributes power to distribution lines, which fan out to customers.

Urban distribution is mainly underground, sometimes in common utility ducts. Rural distribution is mostly above ground with utility poles, and suburban distribution is a mix.

World map of mains voltage and frequencies.

For maintenance visit installation commission part 2

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Circuit Breaker

A circuit breaker is a switching device that interrupts the abnormal or fault current. It is a mechanical device that disturbs the flow of high magnitude (fault) current and in additions performs the function of a switch. The circuit breaker is mainly designed for closing or opening of an electrical circuit, thus protects the electrical system from damage.

Working Principle of Circuit Breaker

Circuit breaker essentially consists of fixed and moving contacts. These contacts are touching each other and carrying the current under normal conditions when the circuit is closed. When the circuit breaker is closed, the current carrying contacts, called the electrodes, engaged each other under the pressure of a spring.

During the normal operating condition, the arms of the circuit breaker can be opened or closed for a switching and maintenance of the system. To open the circuit breaker, only a pressure is required to be applied to a trigger.

Whenever a fault occurs on any part of the system, the trip coil of the breaker gets energized and the moving contacts are getting apart from each other by some mechanism, thus opening the circuit.

Types of Circuit Breaker

Circuit breakers are mainly classified on the basis of rated voltages. Circuit breakers below rated voltage of 1000V are known as the low voltage circuit breakers and above 1000V are called the high voltage circuit breakers.

The most general way of the classification of the circuit breaker is on the basis of the medium of arc extinction. Such types of circuit breakers are as follows :-

Oil Circuit Breaker
Bulk Oil Circuit Breaker
Minimum Oil Circuit Breaker
Minimum Circuit Breaker
Air Blast Circuit Breaker
Sulphur Hexafluoride Circuit Breaker
Vacuum Circuit Breaker
Air Break Circuit Breaker
All high-voltage circuit breakers may be classified under two main categories i.e oil circuit breakers and oil-less circuit breaker.