Electric Substations - Types and Functions

1. Electric Substations The Islamic University of GazaEngineering FacultyElectrical & Computer Department Prepared by: Ahmed Kulab Moh. Abed Foaad Al-Habeel 2003/0252 2003/0408 2003/0463 Presentation About: Supervisor: Dr.Basil Hamad

2. Contents: • What is a substation? • Substation Functions • Substation Types - Step-up Transmission Substation - Step-down Transmission Substation - Distribution Substation - Underground Distribution Substation • Substation Equipment • Conclusion • References

3. What is a Substation? A substation is a high-voltage electric system facility. It is used to switch generators, equipment, and circuits or lines in and out of a system. It also is used to change AC voltages from one level to another, and/or change alternating current to direct current or direct current to alternating current.

5. Substation Functions Substations are designed to accomplish the following functions, although not all substations have all these functions: • Change voltage from one level to another • Regulate voltage to compensate for system voltage changes • Switch transmission and distribution circuits into and out of the grid system • Measure electric power qualities flowing in the circuits

6. Eliminate lightning and other electrical surges from the system • Connect electric generation plants to the system  • Make interconnections between the electric systems of more than one utility • Control reactive kilovolt-amperes supplied to and the flow of reactive kilovolt-amperes in the circuits

7. Substation Types Step-up Transmission Substation It receives electric power from a nearby generating facility and uses a large power transformer to increase the voltage for transmission to distant locations. Step-down Transmission Substation The step-down substation can change the transmission voltage to a subtransmission voltage. The subtransmission voltage lines can then serve as a source to distribution substations.

8. Distribution Substation Distribution Substations are located near to the end-users. Distribution substation transformers change the transmission or subtransmission voltage to lower levels for use by end-users. Under Ground Distribution Substation The same of distribution substations but it is underground.

10. Substation Equipment Air Circuit Breakers: These are used to interrupt circuits while current flows through them. Compressed air is used to quench the arc when the connection is broken. Batteries: These are used in the substation control house as a backup to power the control systems in case of a power blackout.

11. Capacitor Bank: An array of capacitors connected into a circuit. Capacitors are used to control voltages supplied to the customer by eliminating the voltage drop in the system caused by inductive reactive loads. Bus Support Insulators: These are porcelain or fiberglass insulators that serve to isolate the bus bar switches and other support structures and to prevent leakage current from flowing through the structure.

13. Circuit Switchers: Circuit switchers a set of switches for redirecting current in a substation. Circuit switchers provide equipment protection for transformers, lines, cables, and capacitor banks. They also are used to energize and reenergize capacitor banks and other circuits. Disconnect Switches: Disconnect switches or circuit breakers are used to isolate equipment or to redirect current in a substation.

15. Distribution Bus: A distribution bus is a steel structure array of switches used to route power out of a substation. High Voltage Underground Cables: High voltage cables are designed to carry high voltage current and are constructed in many different ways, but are usually shielded cables.

16. Oil Circuit Breakers: Oil circuit breakers are used to switch circuits and equipment in and out of a system in a substation. They are oil filled to provide cooling and to prevent arcing when the switch is activated. Current Transformers: Current transformers can be used to supply information for measuring power flows and the electrical inputs for the operation of protective relays associated with the transmission and distribution circuits or for power transformers.

18. Power Transformers: Transformers raise or lower the voltage as needed to serve the transmission or distribution circuits. Relays: A relay is a low-powered device used to activate a high-powered device. Relays are used to trigger circuit breakers and other switches in substations and transmission and distribution systems.

19. Conclusion • The substation operates as regulator for the voltage. • The main function for the substations convert the AC voltage from level to another . • The converting operation pass many steps and many substation. • The substations are used many equipments, the important equipments the transformers, Capacitors and safety devices.

20. References www.atlaselectricinc.com/sub.html www.swelectric.com/substation_services.htm http://www.newkirk-electric.com/ http://www.transpower.co.nz/ http://www.turnerswitch.com http://www.electricsubstationsafety.com http://www.energetics.com/gridworks/substations.html

21. Thank You