Illustrated Glossary » Distribution Systems

A originates at a distribution substation and includes the lines, poles, transformers and other equipment needed to deliver electric power to the customer at the required voltages. Customers are classed as:

A distribution system consists of all the facilities and equipment connecting a transmission system to the customer's equipment.

A typical distribution system can consist of:

Figure 1. Energy flow through a typical substation

Figure 1. Energy flow through a typical substation

The following are examples of distribution systems components. Collectively they constitute a typical distribution system. These typically deliver voltages as high as 34,000 volts (34 kV) and as low as 120 volts.

Figure 2. Typical residential service drop

Figure 2. Typical residential service drop

Figure 3. Substation pull-off structure

Figure 3. Substation pull-off structure

Figure 4. Substation pull-off structure (connects substation busswork to overhead lines)

Figure 4. Substation pull-off structure (connects substation busswork to overhead lines)

Figure 5. Substation underground distribution bus

Figure 5. Substation underground distribution bus

Figure 6. Distribution primaries and secondaries on subtransmission pole

Figure 6. Distribution primaries and secondaries on subtransmission pole

Figure 7. Distribution underbuild

Figure 7. Distribution underbuild

Additional information:

  • The Lineman's and Cableman's Handbook, Shoemaker, T. M., Mack, J. E., Tenth Edition 2002, McGraw-Hill.

Most industries need 2,400 to 4,160 volts to run heavy machinery and usually their own substation or substations to reduce the voltage from the transmission line to the desired level for distribution throughout the plant area. They usually require 3-phase lines to power 3-phase motors.

Figure 8. Industrial facility distribution transformer

Figure 8. Industrial facility distribution transformer

Additional information:

  • The Lineman's and Cableman's Handbook, Shoemaker, T. M., Mack, J. E., Tenth Edition 2002, McGraw-Hill.

Commercial customers are usually served at distribution voltages, ranging from 14.4 kV to 7.2 kV through a service drop line which leads from a transformer on or near the distribution pole to the customer's end use structure. They may require 3-phase lines to power 3-phase motors.

Figure 9. Distribution transformer to 3-phase service - commercial facility

Figure 9. Distribution transformer to 3-phase service - commercial facility

Figure 10. Commercial service

Figure 10. Commercial service

The distribution electricity is reduced to the end use voltage (120/240 volts single phase) via a pole mounted or pad-mounted transformer. Power is delivered to the residential customer through a service drop line which leads from the distribution pole transformer to the customer's structure, for overhead lines, or underground.

Figure 11. Residential distribution transformer

Figure 11. Residential distribution transformer

Figure 12. Pad-mounted residential distribution transformer

Figure 12. Pad-mounted residential distribution transformer

Currently the only electric transportation systems are light rail and subway systems. A small distribution substation reduces the local distribution voltage to the transportation system requirements. The overhead lines supply electric power to the transportation system motors and the return current lines are connected to the train tracks.

Figure 13. Public transit train driven by overhead electric lines

Figure 13. Public transit train driven by overhead electric lines

Figure 14. Substation where electricity is conditioned for powering commuter trains

Figure 14. Substation where electricity is conditioned for powering commuter trains

Figure 15. Power runs from the substation underground to the poles where power is delivered to the power lines. The circuit is completed through the train tracks, with lines returning to the substation.

Figure 15. Power runs from the substation underground to the poles where power is delivered to the power lines. The circuit is completed through the train tracks, with lines returning to the substation.

Figure 16. Electric cables carry electricity to power the trains motors

Figure 16. Electric cables carry electricity to power the trains motors