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Understanding the Basics of Power Distribution of Electrical Systems

When the topic of electricity enters your mind, it’s usually just a concern about whether you have one or not. You don’t really dive deeper into the technicals such as where electricity comes from and how it’s delivered to your homes.

Power distribution systems are an essential component of electrical systems because they are responsible for disseminating electricity for local use. Without it, electricity won’t be supplied to your homes from the transmission network or bulk power source. 

AC Distribution System

There are two types of power distribution systems according to the nature of current:

  • Alternating Current (AC) distribution system 
  • Direct Current (DC) distribution system. 

The AC distribution system is more mainstream nowadays because it allows high voltage to be greatly reduced through a transformer. This power distribution system encompasses everything that comes in between the transmission network and the consumer end, including circuit breakers and protective devices. 

AC distribution system can be classified into Primary and Secondary Power Distribution.

Primary Power Distribution

This part of the AC distribution system runs from the transmission system to the distribution transformer. It operates at higher voltages than those used in homes and offices and is carried out by a 3-phase, 3-wire system. Primary distribution can range from 4 kV to 35 kV but most countries use 11 kV, 6.6 kV and 3.3 kV. 

Because of the high voltage being transmitted, primary distribution supplies electricity to large consumers such as factories and industries. It can also provide current to small substations from where secondary distribution is carried out.

Secondary Power Distribution

Secondary distribution is the portion of the electric power distribution system that directly supplies to domestic consumers. It is carried out by 3-phase, 4-wire system.

These residential consumers are supplied with 1-phase current at 120 V or 230 V or 3-phase supply at 400 volts for big properties, commercial buildings, small factories etc. 

Components of AC Power Distribution System

  • Distribution substation
    Distribution substation is a station where power is generated locally by receiving electricity from a transmission network. This substation is placed near or inside the vicinity of cities, towns, or industrial areas to be supplied with electricity. 
  • Step-down Transformers
    Step-down transformers convert the high voltage from the transmission line to a medium voltage which ranges from 2.3 kV to 33 kV. This voltage transformation is crucial to meet the voltage level required for primary distribution.
  • Feeders 

Feeder conductors transmit the stepped-down voltage from the substation to distribution transformers. In this equipment, no tappings are taken in order to maintain the current level throughout the line. Distribution feeders are usually designed depending on their current carrying capacity.

  • Distribution Transformer

This transformer is located near the consumer end. It is the last voltage converter in the power distribution network which converts the primary power to secondary power. It’s a step-down 3-phase transformer that reduces the voltage to 400/230 V for domestic utilization.

  • Distributor conductors

Distributor conductors carry the stepped-down voltage from the 3-phase transformer. Distributors take tappings at multiple places throughout its length so that the current is not constant. They are designed by considering the voltage drop along its length.

  • Service mains conductors

Service mains conductors carry the power coming from the distributor conductors to the areas where electricity must be supplied such as homes, commercial establishments and industrial areas.


The distribution of electric power is as important as power generation. Without this distribution system, your lighting fixtures won’t be able to work since no electricity is supplied to your home. Moreover, the employment of transformers, circuit breakers, and protection equipment ensures that the voltage level your house receives is utilizable and safe.

If you’ve got any more questions regarding power distribution system, feel free to contact Sydney Eastern Suburbs Electrician at (02) 8378-2827.

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